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Results of climate change, past and present, have been documented and include species extinction, rising sea levels, and effects on organisms.
- Describe the effects of current and geological climate change
- Global warming has been associated with at least one planet-wide extinction event during the geological past; scientists estimate that during the Permian period, approximately 70 percent of the terrestrial plant and animal species along with 84 percent of marine species became extinct.
- Glacier recession and melting ice caps are direct effects of current global climate change, ultimately leading to higher global sea levels; as glaciers and polar ice caps melt, there is a significant contribution of liquid water that was previously frozen.
- Changes in temperature and precipitation are causing plants to flower earlier, before their insect pollinators have emerged; mismatched timing of plants and pollinators could result in injurious ecosystem effects.
- This mismatched timing of plants and pollinators could result in injurious ecosystem effects because, for continued survival, insect-pollinated plants must flower when their pollinators are present.
- phenology: the study of the effect of climate on periodic biological phenomena
- Permian: of a geologic period within the Paleozoic era; comprises the Cisuralian, Guadalupian, and Lopingian epochs from about 280 to 248 million years ago
Documented results of climate change: past and present
Scientists have geological evidence of the consequences of long-ago climate change. Modern-day phenomena, such as retreating glaciers and melting polar ice, cause a continual rise in sea level. Changes in climate can negatively affect organisms.
Geological climate change effects
Global warming has been associated with at least one planet-wide extinction event during the geological past. The Permian extinction event occurred about 251 million years ago toward the end of the roughly 50-million-year-long geological time span known as the Permian period. This geologic time period was one of the three warmest periods in earth’s geologic history. Scientists estimate that approximately 70 percent of the terrestrial plant and animal species and 84 percent of marine species became extinct, vanishing forever near the end of the Permian period. Organisms that had adapted to wet and warm climatic conditions, such as annual rainfall of 300–400 cm (118–157 in) and 20 °C–30 °C (68 °F–86 °F) in the tropical wet forest, may not have been able to survive the Permian climate change.
Present climate change effects
A number of global events have occurred that may be attributed to recent climate change during our lifetimes. Glacier National Park in Montana, among others, is undergoing the retreat of many of its glaciers, a phenomenon known as glacier recession. In 1850, the area contained approximately 150 glaciers. By 2010, however, the park contained only about 24 glaciers greater than 25 acres in size. One of these glaciers is the Grinnell Glacier at Mount Gould. Between 1966 and 2005, the size of Grinnell Glacier shrank by 40 percent. Similarly, the mass of the ice sheets in Greenland and the Antarctic is decreasing: Greenland lost 150–250 km3 of ice per year between 2002 and 2006. In addition, the size and thickness of the Arctic sea ice is decreasing.
This loss of ice is leading to rises in the global sea level. On average, the sea is rising at a rate of 1.8 mm per year. However, between 1993 and 2010, the rate of sea-level increase ranged between 2.9 and 3.4 mm per year. A variety of factors affect the volume of water in the ocean, including the temperature of the water (the density of water is related to its temperature) and the amount of water found in rivers, lakes, glaciers, polar ice caps, and sea ice. As glaciers and polar ice caps melt, there is a significant contribution of liquid water that was previously frozen.
In addition to some abiotic conditions changing in response to climate change, many organisms are also being affected by the changes in temperature. Temperature and precipitation play key roles in determining the geographic distribution and phenology of plants and animals. Phenology is the study of the effects of climatic conditions on the timing of periodic lifecycle events, such as flowering in plants or migration in birds. Researchers have shown that 385 plant species in Great Britain are flowering 4.5 days sooner than was recorded during the previous 40 years. In addition, insect-pollinated species were more likely to flower earlier than wind-pollinated species. The impact of changes in flowering date would be mitigated if the insect pollinators emerged earlier. This mismatched timing of plants and pollinators could result in injurious ecosystem effects because, for continued survival, insect-pollinated plants must flower when their pollinators are present.
Climate Impacts on Human Health
In 2016, the U.S. Global Change Research Program produced a report that analyzed the impacts of global climate change on human health in the United States. The report finds that:
- Climate change is a significant threat to the health of the American people.
- Climate change can affect human health in two main ways: first, by changing the severity or frequency of health problems that are already affected by climate or weather factors and second, by creating unprecedented or unanticipated health problems or health threats in places or times of the year where they have not previously occurred.
- Every American is vulnerable to the health impacts associated with climate change, but some populations will be especially affected. These groups include the poor, some communities of color, limited English-proficiency and immigrant groups, indigenous peoples, children and pregnant women, older adults, vulnerable occupational groups, people with disabilities, and people with medical conditions.
2. How do scientists know what they know?
When it comes to climate, there’s a lot that we know. The second warmest year on record was 2019, and it closed out the hottest recorded decade. Ocean temperatures are rising, too, hitting a high in 2019 as well, and increasing faster than previously estimated.
The changes over just the last few decades are stark, making plain that the planet’s climate is warming and that it’s human activity behind the temperature rise. But scientists can also look back even further to figure out temperatures on Earth before any humans were alive.
Understanding how scientists figure out what’s going on with the climate is an interesting part of being a climate reporter. My favorite piece of equipment is arguably a bathythermograph, essentially an open water thermometer, simply because it’s a fun word to say. Instruments like it, together with the GPS-connected devices in the global Argo floats network, are how researchers monitor ocean temperatures.
For annual temperature reports, scientists rely on a historical temperature record — someone or some machine taking daily temperatures. This is how we know, for example, that 2019 was hotter than 1942. But the temperature record only stretches back to the 1800s for much of the world, and has some gaps. To cover them, and to look back even further, researchers rely on proxy, or indirect, measures.
In much the same way that data on the daily consumption of chicken wings can help us suss out the dates of Super Bowl Sundays, things like ice core samples, tree rings, corals, pollen and cave deposits can help us understand how the climate behaved in the past, said Jacquelyn Gill, a paleoecologist and associate professor at the University of Maine.
“I like to think of it as environmental forensics,” Dr. Gill said. “Rather than directly observe the past, we use some of the same tools that forensic scientists use to reconstruct the environment through time.”
For example, some tree species can live for thousands of years. When cut into, their rings, which resemble a bull’s-eye on a tree stump, can clue researchers into not only past temperatures but also moisture levels from year to year.
“We’re not just guessing about how trees record climate in their rings because we have a century or more of actual measurements that we can then compare to tree rings,” Dr. Gill said.
In northern regions like the Arctic, researchers rely on another life form: tiny non-biting midges that spend years living in lakes as larvae before turning into winged insects. As they grow they shed parts of their exoskeletons, which are well preserved in lake sediments. If sediment samples transition from layers that contain species that prefer cooler temperatures into layers with species that prefer warmer ones, it’s a signal that temperatures increased.
Using multiple records means scientists can validate their findings, Dr. Gill said. With tree rings, lake sediments and ice cores from the same region, you can “look across those different proxies and see where you have good agreement and where you don’t.”
But to measure the levels of human caused climate emissions, researchers have other tools.
Since 1958, an observatory near the top of the Mauna Loa volcano in Hawaii has been recording the amount of carbon dioxide in the air and, more recently, observatories in Alaska, Samoa and the South Pole have also been recording measurements. Data is also collected from eight tall towers located across the United States, small aircraft, and volunteers at some 50 locations worldwide. Because carbon dioxide that comes from burning oil and coal is slightly different than the carbon that comes from living animals and plants, researchers know burning fossil fuels is behind the increase.
If you’re noticing a lot of redundancy in how researchers make sense of the climate, that’s the point. They aren’t using a single piece of data, but lots of pieces to stitch together a comprehensive picture that points in a single direction: the climate is warming and humans are causing it.
Global warming refers to the long-term rise in the average temperature of the Earth's climate system. It is a major aspect of climate change, and has been demonstrated by the instrumental temperature record which shows global warming of around 1 °C since the pre-industrial period,  although the bulk of this (0.9 °C) has occurred since 1970.  A wide variety of temperature proxies together prove that the 20th century was the hottest recorded in the last 2,000 years. Compared to climate variability in the past, current warming is also more globally coherent, affecting 98% of the planet.   The impact on the environment, ecosystems, the animal kingdom, society and humanity depends on how much more the Earth warms. 
The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded, "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."  This has been brought about primarily through the burning of fossil fuels which has led to a significant increase in the concentration of GHGs in the atmosphere. 
Individual consumers, corporate decision makers, the fossil fuel industries, government responses and the extent to which different countries agree to cooperate all have a profound impact on how much greenhouse gases the worlds emits. As the crisis and modelling techniques have evolved, the IPCC and other climate scientists have tried a number of different tools to estimate likely greenhouse gas emissions in the future.
Representative Concentration Pathways (RCPs) were based on possible differences in radiative forcing occurring in the next 100 years but do not include socioeconomic "narratives" to go alongside them.  Another group of climate scientists, economists and energy system modellers took a different approach known as Shared Socioeconomic Pathways (SSPs) this is based on how socioeconomic factors such as population, economic growth, education, urbanisation and the rate of technological development might change over the next century. The SSPs describe five different trajectories which describe future climactic developments in the absence of new environmental policies beyond those in place today. They also explore the implications of different climate change mitigation scenarios. 
The range in temperature projections partly reflects the choice of emissions scenario, and the degree of "climate sensitivity".  The projected magnitude of warming by 2100 is closely related to the level of cumulative emissions over the 21st century (i.e. total emissions between 2000 and 2100).  The higher the cumulative emissions over this time period, the greater the level of warming is projected to occur.  Climate sensitivity reflects uncertainty in the response of the climate system to past and future GHG emissions.  Higher estimates of climate sensitivity lead to greater projected warming, while lower estimates lead to less projected warming. 
The IPCC's Fifth Report, states that relative to the average from year 1850 to 1900, global surface temperature change by the end of the 21st century is likely to exceed 1.5 °C and may well exceed 2 °C for all RCP scenarios except RCP2.6. It is likely to exceed 2 °C for RCP6.0 and RCP8.5, and more likely than not to exceed 2 °C for RCP4.5. The pathway with the highest greenhouse gas emissions, RCP8.5, will lead to a temperature increase of about 4.3˚C by 2100.  Warming will continue beyond 2100 under all RCP scenarios except RCP2.6.  Even if emissions were drastically reduced overnight, the warming process is irreversible because CO
2 takes hundreds of years to break down, and global temperatures will remain close to their highest level for at least the next 1,000 years.  
Mitigation policies currently in place will result in about 2.9 °C warming above pre-industrial levels. If all unconditional pledges and targets already made by governments will be achieved the temperature will rise by 2.4 °C. If all the 131 countries that actually adopted or only consider to adopt net - zero target will achieve it the temperature will rise by 2.0 °C. However, if current plans are not actually implemented, global warming is expected to reach 4.1 °C to 4.8 °C by 2100. There is a substantial gap between national plans and commitments and actual actions so far taken by governments around the world. 
According to the World Meteorological Organization report from 2021, there is a 44% chance that the global temperature will temporarily pass the 1.5 limit already in the years 2021 - 2026. 
Warming in context of Earth's past
One of the methods scientists use to predict the effects of human-caused climate change, is to investigate past natural changes in climate.  Scientists have used various "proxy" data to assess changes in Earth's past climate or paleoclimate.  Sources of proxy data include historical records such as tree rings, ice cores, corals, and ocean and lake sediments.  The data shows that recent warming has surpassed anything in the last 2,000 years. 
By the end of the 21st century, temperatures may increase to a level not experienced since the mid-Pliocene, around 3 million years ago.  At that time, mean global temperatures were about 2–4 °C warmer than pre-industrial temperatures, and the global mean sea level was up to 25 meters higher than it is today. 
A broad range of evidence shows that the climate system has warmed.  Evidence of global warming is shown in the graphs (below right) from the US National Oceanic and Atmospheric Administration (NOAA). Some of the graphs show a positive trend, e.g., increasing temperature over land and the ocean, and sea level rise. Other graphs show a negative trend, such as decreased snow cover in the Northern Hemisphere, and declining Arctic sea ice, both of which are indicative of global warming. Evidence of warming is also apparent in living (biological) systems such as changes in distribution of flora and fauna towards the poles. 
Human-induced warming could lead to large-scale, abrupt and/or irreversible changes in physical systems.   An example of this is the melting of ice sheets, which contributes to sea level rise and will continue for thousands of years.  The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change. 
Effects on weather
Global warming leads to an increase in extreme weather events such as heat waves, droughts, cyclones, blizzards and rainstorms.  Such events will continue to occur more often and with greater intensity.  Scientists have not only determined that climate change is responsible for trends in weather patterns, some individual extreme weather events have also directly be attributed to climate change. 
Higher temperatures lead to increased evaporation and surface drying. As the air warms, its water-holding capacity also increases, particularly over the oceans. In general the air can hold about 7% more moisture for every 1 °C of temperature rise.  In the tropics, there's more than a 10% increase in precipitation for a 1 °C increase in temperature.  Changes have already been observed in the amount, intensity, frequency, and type of precipitation. Widespread increases in heavy precipitation have occurred even in places where total rain amounts have decreased. 
Projections of future changes in precipitation show overall increases in the global average, but with substantial shifts in where and how precipitation falls.  Projections suggest a reduction in rainfall in the subtropics, and an increase in precipitation in subpolar latitudes and some equatorial regions. In other words, regions which are dry at present will in general become even drier, while regions that are currently wet will in general become even wetter.  Although increased rainfall will not occur everywhere, models suggest most of the world will have a 16–24% increase in heavy precipitation intensity by 2100. 
As described in the first section, global temperatures have risen by 1 °C and are expected to rise further in the future.   Over most land areas since the 1950s, it is very likely that at all times of year both days and nights have become warmer due to human activities.  Night-time temperatures have increased a faster rate than daytime temperatures.  In the U.S. since 1999, two warm weather records have been set or broken for every cold one.  
Future climate change will include more very hot days and fewer very cold days.  The frequency, length and intensity of heat waves will very likely increase over most land areas.  Higher growth in anthropogenic GHG emissions would cause more frequent and severe temperature extremes. 
Global warming boosts the probability of extreme weather events such as heat waves   where the daily maximum temperature exceeds the average maximum temperature by 5 °C (9 °F) for more than five consecutive days. 
In the last 30–40 years, heat waves with high humidity have become more frequent and severe. Extremely hot nights have doubled in frequency. The area in which extremely hot summers are observed has increased 50–100 fold. These changes are not explained by natural variability, and are attributed by climate scientists to the influence of anthropogenic climate change. Heat waves with high humidity pose a big risk to human health while heat waves with low humidity lead to dry conditions that increase wildfires. The mortality from extreme heat is larger than the mortality from hurricanes, lightning, tornadoes, floods, and earthquakes together. 
Global warming not only causes changes in tropical cyclones, it may also make some impacts from them worse via sea level rise. The intensity of tropical cyclones (hurricanes, typhoons, etc.) is projected to increase globally, with the proportion of Category 4 and 5 tropical cyclones increasing. Furthermore, the rate of rainfall is projected to increase, but trends in the future frequency on a global scale are not yet clear.   Changes in tropical cyclones will probably vary by region. 
In the year 2019 the Intergovernmental Panel on Climate Change issued a Special Report on Climate Change and Land. The main statements of the report include:
- Humans affect 70% of the ice free land, that play a key role in supplying the needs of humans and in the climate system.
- The global food supply have raised what increased GHG emission, but 25% - 30% of the food is lost, 2 billion adults suffer from being overweight while 821 million people suffer from hunger.
- The rate of soil erosion is 10 - 20 times higher than the rate of soil accumulation in agricultural areas that use no-till farming. In areas with tilling it is 100 times higher. Climate Change increases land degradation and desertification.
- In the years 1960 - 2013 the area of drylands in drought, increased by 1% per year.
- In the year 2015 around 500 million people lived in areas that was impacted by desertification in the years 1980s - 2000s.
- People who live in the areas affected by land degradation and desertification are "increasingly negatively affected by climate change".
IPCC SRCCL 2019, pp. 7, 8 IPCC SRCCL Summary for Policymakers 2019, p. 7,8 harvnb error: no target: CITEREFIPCC_SRCCL_Summary_for_Policymakers2019 (help)
Climate change will also cause soils to warm. In turn, this could cause the soil microbe population size to dramatically increase 40–150%. Warmer conditions would favor growth of certain bacteria species, shifting the bacterial community composition. Elevated carbon dioxide would increase the growth rates of plants and soil microbes, slowing the soil carbon cycle and favoring oligotrophs, which are slower-growing and more resource efficient than copiotrophs. 
Warmer air holds more water vapor. When this turns to rain, it tends to come in heavy downpours potentially leading to more floods. A 2017 study found that peak precipitation is increasing between 5 and 10% for every one degree Celsius increase.  In the United States and many other parts of the world there has been a marked increase in intense rainfall events which have resulted in more severe flooding.  Estimates of the number of people at risk of coastal flooding from climate-driven sea-level rise varies from 190 million,  to 300 million or even 640 million in a worst-case scenario related to the instability of the Antarctic ice sheet.   the Greenland ice sheet is estimated to have reached a point of no return, continuing to melt even if warming stopped. Over time that would submerge many of the world's coastal cities including low-lying islands, especially combined with storm surges and high tides. 
Climate change affects multiple factors associated with droughts, such as how much rain falls and how fast the rain evaporates again. It is set to increase the severity and frequency of droughts around much of the world.  Due to limitations on how much data is available about drought in the past, it is often impossible to confidently attribute droughts to human-induced climate change. Some areas however, such as the Mediterranean and California, already show a clear human signature.  Their impacts are aggravated because of increased water demand, population growth, urban expansion, and environmental protection efforts in many areas. 
Prolonged periods of warmer temperatures typically cause soil and underbrush to be drier for longer periods, increasing the risk of wildfires. Hot, dry conditions increase the likelihood that wildfires will be more intense and burn for longer once they start.  In California, summer air temperature have increased by over 3.5 °F such that the fire season has lengthened by 75 days over previous decades. As a result, since the 1980s, both the size and ferocity of fires in California have increased. Since the 1970s, the size of the area burned has increased fivefold. 
In Australia, the annual number of hot days (above 35 °C) and very hot days (above 40 °C) has increased significantly in many areas of the country since 1950. The country has always had bushfires but in 2019, the extent and ferocity of these fires increased dramatically.  For the first time catastrophic bushfire conditions were declared for Greater Sydney. New South Wales and Queensland declared a state of emergency but fires were also burning in South Australia and Western Australia. 
The cryosphere is made up of those parts of the planet which are so cold, they are frozen and covered by snow or ice. This includes ice and snow on land such as the continental ice sheets in Greenland and Antarctica, as well as glaciers and areas of snow and permafrost and ice found on water including frozen parts of the ocean, such as the waters surrounding Antarctica and the Arctic.  The cryosphere, especially the polar regions, is extremely sensitive to changes in global climate. 
The Intergovernmental Panel on Climate Change issued a Special Report on the Ocean and Cryosphere in a Changing Climate. According to the report climate change caused a massive melting of glaciers, ice sheets, snow and permafrost with generally negative effects on ecosystems and humans. Indigenous knowledge helped to adapt to those effects. 
Arctic sea ice began to decline at the beginning of the twentieth century but the rate is accelerating. Since 1979, satellite records indicate the decline in summer sea ice coverage has been about 13% per decade.   The thickness of sea ice has also decreased by 66% or 2.0 m over the last six decades with a shift from permanent ice to largely seasonal ice cover.  While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur at least once every decade at a warming level of 2.0 °C. 
Since the beginning of the twentieth century, there has also been a widespread retreat of alpine glaciers,  and snow cover in the Northern Hemisphere.  During the 21st century, glaciers and snow cover are projected to continue their retreat in almost all regions.  The melting of the Greenland and West Antarctic ice sheets will continue to contribute to sea level rise over long time-scales. 
Global warming is projected to have a number of effects on the oceans. Ongoing effects include rising sea levels due to thermal expansion and melting of glaciers and ice sheets, and warming of the ocean surface, leading to increased temperature stratification.  Other possible effects include large-scale changes in ocean circulation. The oceans also serve as a sink for carbon dioxide, taking up much that would otherwise remain in the atmosphere, but increased levels of CO
2 have led to ocean acidification. Furthermore, as the temperature of the oceans increases, they become less able to absorb excess CO
2 . The oceans have also acted as a sink in absorbing extra heat from the atmosphere.  : 4
According to a Special Report on the Ocean and Cryosphere in a Changing Climate published by the Intergovernmental Panel on Climate Change, climate change has different impacts on the oceans, including an increase in marine heatwaves, shift in species distribution, ocean deoxygenation. 
The decline in mixing of the ocean layers piles up warm water near the surface while reducing cold, deep water circulation. The reduced up and down mixing enhanced global warming. Furthermore, energy available for tropical cyclones and other storms is expected to increase, nutrients for fish in the upper ocean layers are set to decrease, as well as the capacity of the oceans to store carbon. 
Sea ice reflects 50% to 70% of the incoming solar radiation, while 6% of the incoming solar engery is reflected by the ocean. With less solar energy, the sea ice absorbs and holds the surface colder, which can be a positive feedback toward climate change. 
Warmer water cannot contain as much oxygen as cold water, so heating is expected to lead to less oxygen in the ocean. Other processes also play a role: stratification may lead to increases in respiration rates of organic matter, further decreasing oxygen content. The ocean has already lost oxygen, throughout the entire water column and oxygen minimum zones are expanding worldwide.  This has adverse consequences for ocean life.  
Ocean heat uptake
Oceans have taken up over 90% of the excess heat accumulated on Earth due to global warming.  The warming rate varies with depth: at a depth of a thousand metres the warming occurs at a rate of almost 0.4 °C per century (data from 1981 to 2019), whereas the warming rate at two kilometres depth is only half.  The increase in ocean heat content is much larger than any other store of energy in the Earth's heat balance and accounts for more than 90% of the increase in heat content of the Earth system, and has accelerated in the 1993–2017 period compared to 1969–1993.  In 2019 a paper published in the journal Science found the oceans are heating 40% faster than the IPCC predicted just five years before.  
As well as having effects on ecosystems (e.g. by melting sea ice affecting algae that grow on its underside), warming reduces the ocean's ability to absorb CO
2 .  It is likely that the oceans warmed faster between 1993 and 2017 compared to the period starting in 1969. 
Sea level rise
The IPCC's Special Report on the Ocean and Cryosphere concluded that global mean sea level rose by 0.16 metres between 1901 and 2016.  The rate of sea level rise since the industrial revolution in the 19th century has been larger than the rate during the previous two thousand years. 
Global sea level rise is accelerating, rising 2.5 times faster between 2006 and 2016 than it did during the 20th century.   Two main factors contribute to the rise. The first is thermal expansion: as ocean water warms, it expands. The second is from the melting of land-based ice in glaciers and ice sheets due to global warming.  Prior to 2007, thermal expansion was the largest component in these projections, contributing 70–75% of sea level rise.  As the impact of global warming has accelerated, melting from glaciers and ice sheets has become the main contributor. 
Even if emission of greenhouse gases stops overnight, sea level rise will continue for centuries to come.  In 2015, a study by Professor James Hansen of Columbia University and 16 other climate scientists said a sea level rise of three metres could be a reality by the end of the century.  Another study by scientists at the Royal Netherlands Meteorological Institute in 2017 using updated projections of Antarctic mass loss and a revised statistical method also concluded that, although it was a low probability, a three-metre rise was possible.  Rising sea levels will put hundreds of millions of people at risk in low-lying coastal areas in countries such as China, Bangladesh, India and Vietnam. 
Recent warming has strongly affected natural biological systems.  Species worldwide are moving poleward to colder areas. On land, species move to higher elevations, whereas marine species find colder water at greater depths.  Of the drivers with the biggest global impact on nature, climate change ranks third over the five decades before 2020, with only change in land use and sea use, and direct exploitation of organisms having a greater impact. 
The impacts of climate change in nature and nature's contributions to humans are projected to become more pronounced in the next few decades.  Examples of climatic disruptions include fire, drought, pest infestation, invasion of species, storms, and coral bleaching events. The stresses caused by climate change, added to other stresses on ecological systems (e.g. land conversion, land degradation, harvesting, and pollution), threaten substantial damage to or complete loss of some unique ecosystems, and extinction of some critically endangered species.   Key interactions between species within ecosystems are often disrupted because species from one location do not move to colder habitats at the same rate, giving rise to rapid changes in the functioning of the ecosystem. 
Terrestrial and wetland systems
Climate change has been estimated to be a major driver of biodiversity loss in cool conifer forests, savannas, mediterranean-climate systems, tropical forests, and the Arctic tundra.  In other ecosystems, land-use change may be a stronger driver of biodiversity loss, at least in the near-term.  Beyond the year 2050, climate change may be the major driver for biodiversity loss globally.  Climate change interacts with other pressures such as habitat modification, pollution and invasive species. Interacting with these pressures, climate change increases extinction risk for a large fraction of terrestrial and freshwater species.  Between 1% and 50% of species in different groups were assessed to be at substantially higher risk of extinction due to climate change. 
Warm water coral reefs are very sensitive to global warming and ocean acidification. Coral reefs provide a habitat for thousands of species and ecosystem services such as coastal protection and food. The resilience of reefs can be improved by curbing local pollution and overfishing, but 70–90% of today's warm water coral reefs will disappear even if warming is kept to 1.5 °C.  Coral reefs are not the only framework organisms, organisms that build physical structures that form habitats for other sea creatures, affected by climate change: mangroves and seagrass are considered to be at moderate risk for lower levels of global warming according to a literature assessment in the Special Report on the Ocean and Cryosphere in a Changing Climate.  Marine heatwaves have seen an increased frequency and have widespread impacts on life in the oceans, such as mass dying events.  Harmful algae blooms have increased in response to warming waters, ocean deoxygenation and eutrophication.  Between one-quarter and one-third of our fossil fuel emissions are consumed by the earth's oceans and are now 30 percent more acidic than they were in pre-industrial times. This acidification poses a serious threat to aquatic life, particularly creatures such as oysters, clams, and coral with calcified shells or skeletons. 
Regional effects of global warming vary in nature. Some are the result of a generalised global change, such as rising temperature, resulting in local effects, such as melting ice. In other cases, a change may be related to a change in a particular ocean current or weather system. In such cases, the regional effect may be disproportionate and will not necessarily follow the global trend.
There are three major ways in which global warming will make changes to regional climate: melting or forming ice, changing the hydrological cycle (of evaporation and precipitation) and changing currents in the oceans and air flows in the atmosphere. The coast can also be considered a region, and will suffer severe impacts from sea level rise.
The Arctic, Africa, small islands, Asian megadeltas and the Middle East are regions that are likely to be especially affected by climate change.   Low-latitude, less-developed regions are at most risk of experiencing negative impacts due to climate change.  Developed countries are also vulnerable to climate change. For example, developed countries will be negatively affected by increases in the severity and frequency of some extreme weather events, such as heat waves. 
Projections of climate changes at the regional scale do not hold as high a level of scientific confidence as projections made at the global scale.  It is, however, expected that future warming will follow a similar geographical pattern to that seen already, with the greatest warming over land and high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic Ocean.  Land areas warm faster than ocean, and this feature is even stronger for extreme temperatures. For hot extremes, regions with the most warming include Central and Southern Europe and Western and Central Asia. 
The ten countries of the Association of Southeast Asian Nations (ASEAN) are among the most vulnerable in the world to the negative effects of climate change, however, ASEAN's climate mitigation efforts are not commensurate with the climate change threats the region faces. 
The effects of climate change, in combination with the sustained increases in greenhouse gas emissions, have led scientists to characterize it as a climate emergency.    Some climate researchers   and activists  have called it an existential threat to civilization. Some areas may become too hot for humans to live in   while people in some areas may experience displacement triggered by flooding and other climate change related disasters. 
The vulnerability and exposure of humans to climate change varies from one economic sector to another and will have different impacts in different countries. Wealthy industrialised countries, which have emitted the most CO2, have more resources and so are the least vulnerable to global warming.  Economic sectors that are likely to be affected include agriculture, human health, fisheries, forestry, energy, insurance, financial services, tourism, and recreation.  The quality and quantity of freshwater will likely be affected almost everywhere. Some people may be particularly at risk from climate change, such as the poor, young children and the elderly.   According to the World Health Organization, between 2030 and 2050, "climate change is expected to cause about 250,000 additional deaths per year."  As global temperatures increase, so does the number of heat stress, heatstroke, and cardiovascular and kidney disease deaths and illnesses.  Air pollution generated by fossil fuel combustion is both a major driver of global warming and – in parallel and for comparison – the cause of a large number of annual deaths with some estimates as high as 8.7 million [ dubious – discuss ] excess deaths during 2018.   It may be difficult to predict or attribute deaths to anthropogenic global warming or its particular drivers as many effects – such as possibly contributing to human conflict and socioeconomic disruptions – and their mortality impacts could be highly indirect or hard to evaluate.
Climate change will impact agriculture and food production around the world due to the effects of elevated CO2 in the atmosphere higher temperatures altered precipitation and transpiration regimes increased frequency of extreme events and modified weed, pest, and pathogen pressure.  Climate change is projected to negatively affect all four pillars of food security: not only how much food is available, but also how easy food is to access (prices), food quality and how stable the food system is. 
As of 2019, negative impacts have been observed for some crops in low-latitudes (maize and wheat), while positive impacts of climate change have been observed in some crops in high-latitudes (maize, wheat, and sugar beets).  Using different methods to project future crop yields, a consistent picture emerges of global decreases in yield. Maize and soybean decrease with any warming, whereas rice and wheat production might peak at 3 °C of warming. 
In many areas, fisheries have already seen their catch decrease because of global warming and changes in biochemical cycles. In combination with overfishing, warming waters decrease the maximum catch potential.  Global catch potential is projected to reduce further in 2050 by less than 4% if emissions are reduced strongly, and by about 8% for very high future emissions, with growth in the Arctic Ocean. 
Other aspects of food security
Climate change impacts depend strongly on projected future social and economic development. As of 2019 [update] , an estimated 831 million people are undernourished.  Under a high emission scenario (RCP6.0), cereals are projected to become 1-29% more expensive in 2050 depending on the socioeconomic pathway, particularly affecting low-income consumers.  Compared to a no climate change scenario, this would put between 1-181 million extra people at risk of hunger. 
2 is expected to be good for crop productivity at lower temperatures, it does reduce the nutritional values of crops, with for instance wheat having less protein and less of some minerals.  It is difficult to project the impact of climate change on utilization (protecting food against spoilage, being healthy enough to absorb nutrients, etc.) and on volatility of food prices. Most models projecting the future do indicate that prices will become more volatile. 
Droughts result in crop failures and the loss of pasture for livestock. 
A number of climate-related trends have been observed that affect water resources. These include changes in precipitation, the cryosphere and surface waters (e.g., changes in river flows).  Observed and projected impacts of climate change on freshwater systems and their management are mainly due to changes in temperature, sea level and precipitation variability.  Changes in temperature are correlated with variability in precipitation because the water cycle is reactive to temperature.  Temperature increases change precipitation patterns. Excessive precipitation leads to excessive sediment deposition, nutrient pollution, and concentration of minerals in aquifers.
The rising global temperature will cause sea level rise and will extend areas of salinization of groundwater and estuaries, resulting in a decrease in freshwater availability for humans and ecosystems in coastal areas. The rising sea level will push the salt gradient into freshwater deposits and will eventually pollute freshwater sources. The 2014 fifth IPCC assessment report concluded that:
- Water resources are projected to decrease in most dry subtropical regions and mid-latitudes, but increase in high latitudes. As streamflow becomes more variable, even regions with increased water resources can experience additional short-term shortages. 
- Per degree warming, a model [clarification needed] average of 7% of the world population is expected to have at least 20% less renewable water resource. 
- Climate change is projected to reduce water quality before treatment. Even after conventional treatments, risks remain. The quality reduction is a consequence of higher temperatures, more intense rainfall, droughts and disruption of treatment facilities during floods. 
- Droughts that stress water supply are expected to increase in southern Europe and the Mediterranean region, central Europe, central and southern North America, Central America, northeast Brazil, and southern Africa. 
Humans are exposed to climate change through changing weather patterns (temperature, precipitation, sea-level rise and more frequent extreme events) and indirectly through changes in water, air and food quality and changes in ecosystems, agriculture, industry and settlements and the economy.  Air pollution, wildfires, and heat waves caused by global warming have significantly affected human health,  and in 2007, the World Health Organization estimated 150,000 people were being killed by climate-change-related issues every year. 
A study by the World Health Organization  concluded that climate change was responsible for 3% of diarrhoea, 3% of malaria, and 3.8% of dengue fever deaths worldwide in 2004. Total attributable mortality was about 0.2% of deaths in 2004 of these, 85% were child deaths. The effects of more frequent and extreme storms were excluded from this study.
The human impacts include both the direct effects of extreme weather, leading to injury and loss of life,  as well as indirect effects, such as undernutrition brought on by crop failures. Various infectious diseases are more easily transmitted in a warmer climate, such as dengue fever, which affects children most severely, and malaria. Young children are the most vulnerable to food shortages, and together with older people, to extreme heat. 
According to a report from the United Nations Environment Programme and International Livestock Research Institute, climate change can facilitate outbreaks of Zoonosis, e.g. diseases that pass from animals to humans. One example of such outbreaks is the COVID-19 pandemic. 
A minor further effect are increases of pollen season lengths and concentrations in some regions of the world.   
A 2014 study by the World Health Organization  estimated the effect of climate change on human health, but not all of the effects of climate change were included in their estimates. For example, the effects of more frequent and extreme storms were excluded. The report further assumed continued progress in health and growth. Even so, climate change was projected to cause an additional 250,000 deaths per year between 2030 and 2050. 
The authors of the IPCC AR4 Synthesis report  : 48 projected with high confidence that climate change will bring some benefits in temperate areas, such as fewer deaths from cold exposure, and some mixed effects such as changes in range and transmission potential of malaria in Africa. Benefits were projected to be outweighed by negative health effects of rising temperatures, especially in developing countries.
Economic development is an important component of possible adaptation to climate change. Economic growth on its own, however, is not sufficient to insulate the world's population from disease and injury due to climate change.  Future vulnerability to climate change will depend not only on the extent of social and economic change, but also on how the benefits and costs of change are distributed in society.  For example, in the 19th century, rapid urbanization in western Europe led to health plummeting.  Other factors important in determining the health of populations include education, the availability of health services, and public-health infrastructure. 
Warming above 1.5 degrees can make tropical regions uninhabitable, because the threshold of 35 degrees of wet bulb temperature (the limit of human adaptation to heat and humidity), will be passed. 43% of the human population live in the tropics. 
On mental health
In 2018, the American Psychological Association issued a report about the impact of climate change on mental health. It said that "gradual, long-term changes in climate can also surface a number of different emotions, including fear, anger, feelings of powerlessness, or exhaustion".  Generally this is likely to have the greatest impact on young people. California social scientist, Renee Lertzman, likens the climate-related stress now affecting teenagers and those in their 20s to Cold War fears that gripped young baby boomers who came of age under the threat of nuclear annihilation.  Research has found that although there are heightened emotional experiences linked with acknowledgement and anticipation of climate change and its impact on society, these are inherently adaptive. Furthermore, engaging with these emotional experiences leads to increased resilience, agency, reflective functioning and collective action. Individuals are encouraged to find collective ways of processing their climate related emotional experiences in order to support mental health and well being.  A 2018 study found that unusually hot days have profound effects on mental health and that global warming could contribute to approximately 26,000 more suicides in the U.S. by 2050.  A study published in April 2020 found that by the end of the 21st century people could be exposed to avoidable indoor CO2 levels of up to 1400 ppm, which would be triple the amount commonly experienced outdoors today and, according to the authors, may cut humans' basic decision-making ability indoors by
25% and complex strategic thinking by
Gradual but pervasive environmental change and sudden natural disasters both influence the nature and extent of human migration but in different ways.
Slow-onset disasters and gradual environmental erosion such as desertification, reduction of soil fertility, coastal erosion and sea-level rise are likely to induce long term migration.  Migration related to desertification and reduced soil fertility is likely to be predominantly from rural areas in developing countries to towns and cities. 
Displacement and migration related to sea level rise will mostly affect those who live in cities near the coast. More than 90 US coastal cities are already experiencing chronic flooding and that number is expected to double by 2030.  Numerous cities in Europe will be affected by rising sea levels especially in the Netherlands, Spain and Italy.  Coastal cities in Africa are also under threat due to rapid urbanization and the growth of informal settlements along the coast.  Low lying Pacific island nations including Fiji, Kiribati, Nauru, Micronesia, the Marshall Islands, the Solomon Islands, Vanuatu, Timor Leste and Tonga are especially vulnerable to rising seas. In July 2019, they issued a declaration "affirming that climate change poses the single greatest threat to the human rights and security of present and future generations of Pacific Island peoples"  and stated their lands could become uninhabitable as early as 2030. 
The United Nations says there are already 64 million human migrants in the world fleeing wars, hunger, persecution and the effects of global warming.  In 2018, the World Bank estimated that climate change will cause internal migration of between 31 and 143 million people as they escape crop failures, water scarcity, and sea level rise. The study only included Sub-Saharan Africa, South Asia, and Latin America.  
A 2020 study projects that regions inhabited by a third of the human population could become as hot as the hottest parts of the Sahara within 50 years without a change in patterns of population growth and without migration, unless greenhouse gas emissions are reduced. The projected annual average temperature of above 29 °C for these regions would be outside the "human temperature niche" – a suggested range for climate biologically suitable for humans based on historical data of mean annual temperatures (MAT) – and the most affected regions have little adaptive capacity as of 2020.   The following matrix shows their projections for population-sizes outside the "human temperature niche" – and therefore potential emigrants of their regions – in different climate change scenarios and projections of population growth for 2070: 
Sudden-onset natural disasters tend to create mass displacement, which may only be short term. However, Hurricane Katrina demonstrated that displacement can last a long time. Estimates suggest that a quarter of the one million people  displaced in the Gulf Coast region by Hurricane Katrina had not returned to their homes five years after the disaster.  Mizutori, the U.N. secretary-general's special representative on disaster risk reduction, says millions of people are also displaced from their homes every year as result of sudden-onset disasters such as intense heatwaves, storms and flooding. She says 'climate crisis disasters' are happening at the rate of one a week. 
A 2013 study found that significant climatic changes were associated with a higher risk of conflict worldwide, and predicted that "amplified rates of human conflict could represent a large and critical social impact of anthropogenic climate change in both low- and high-income countries."  Similarly, a 2014 study found that higher temperatures were associated with a greater likelihood of violent crime, and predicted that global warming would cause millions of such crimes in the United States alone during the 21st century.  Climate change can worsen conflicts by exacerbating tensions over limited resources like drinking water. Climate change has the potential to cause large population dislocations, which can also lead to conflict. 
However, a 2018 study in the journal Nature Climate Change found that previous studies on the relationship between climate change and conflict suffered from sampling bias and other methodological problems.  Factors other than climate change are judged to be substantially more important in affecting conflict (based on expert elicitation). These factors include intergroup inequality and low socio-economic development. 
Despite these issues, military planners are concerned that global warming is a "threat multiplier". "Whether it is poverty, food and water scarcity, diseases, economic instability, or threat of natural disasters, the broad range of changing climatic conditions may be far reaching. These challenges may threaten stability in much of the world".  For example, the onset of the Arab Spring in 2010 was partly the result of a spike in wheat prices following crop losses from the 2010 Russian heat wave.  
Economic forecasts of the impact of global warming vary considerably. Researchers have warned that current economic modelling may seriously underestimate the impact of potentially catastrophic climate change, and point to the need for new models that give a more accurate picture of potential damages. Nevertheless, one recent study has found that potential global economic gains if countries implement mitigation strategies to comply with the 2 °C target set at the Paris Agreement are in the vicinity of US$17 trillion per year up to 2100 compared to a very high emission scenario. 
Global losses reveal rapidly rising costs due to extreme weather events since the 1970s.  Socio-economic factors have contributed to the observed trend of global losses, such as population growth and increased wealth.  Part of the growth is also related to regional climatic factors, e.g., changes in precipitation and flooding events. It is difficult to quantify the relative impact of socio-economic factors and climate change on the observed trend.  The trend does, however, suggest increasing vulnerability of social systems to climate change. 
A 2019 modelling study found that climate change had contributed towards global economic inequality. Wealthy countries in colder regions had either felt little overall economic impact from climate change, or possibly benefited, whereas poor hotter countries very likely grew less than if global warming had not occurred. 
The total economic impacts from climate change are difficult to estimate, but increase for higher temperature changes.  For instance, total damages are estimated to be 90% less if global warming is limited to 1.5 °C compared to 3.66 °C, a warming level chosen to represent no mitigation.  One study found a 3.5% reduction in global GDP by the end of the century if warming is limited to 3 °C, excluding the potential effect of tipping points. Another study noted that global economic impact is underestimated by a factor of two to eight when tipping points are excluded from consideration.  In the Oxford Economics high emission scenario, a temperature rise of 2 degrees by the year 2050 would reduce global GDP by 2.5% - 7.5%. By the year 2100 in this case, the temperature would rise by 4 degrees, which could reduce the global GDP by 30% in the worst case. 
Self-reinforcing feedbacks amplify and accelerate climate change.  The climate system exhibits threshold behaviour or tipping points when these feedbacks lead parts of the Earth system into a new state, such as the runaway loss of ice sheets or the destruction of too many forests.   Tipping points are studied using data from Earth's distant past and by physical modelling.  There is already moderate risk of global tipping points at 1 °C above pre-industrial temperatures, and that risk becomes high at 2.5 °C. 
Tipping points are "perhaps the most 'dangerous' aspect of future climate changes", leading to irreversible impacts on society.  Many tipping points are interlinked, so that triggering one may lead to a cascade of effects,  even well below 2 degrees of warming.  A 2018 study states that 45% of environmental problems, including those caused by climate change are interconnected and make the risk of a domino effect bigger.  
Amazon rain forest
Rainfall that falls on the Amazon rainforest is recycled when it evaporates back into the atmosphere instead of running off away from the rainforest. This water is essential for sustaining the rainforest. Due to deforestation the rainforest is losing this ability, exacerbated by climate change which brings more frequent droughts to the area. The higher frequency of droughts seen in the first two decades of the 21st century signal that a tipping point from rainforest to savanna might be close. 
Greenland and West Antarctic Ice sheets
Future melt of the West Antarctic ice sheet is potentially abrupt under a high emission scenario, as a consequence of a partial collapse.  Part of the ice sheet is grounded on bedrock below sea level, making it possibly vulnerable to the self-enhancing process of marine ice sheet instability. A further hypothesis is that marine ice cliff instability would also contribute to a partial collapse, but limited evidence is available for its importance.  A partial collapse of the ice sheet would lead to rapid sea level rise and a local decrease in ocean salinity. It would be irreversible on a timescale between decades and millennia. 
In contrast to the West Antarctic ice sheet, melt of the Greenland ice sheet is projected to be taking place more gradually over millennia.  Sustained warming between 1 °C (low confidence) and 4 °C (medium confidence) would lead to a complete loss of the ice sheet, contributing 7 m to sea levels globally.  The ice loss could become irreversible due to a further self-enhancing feedback: the elevation-surface mass balance feedback. When ice melts on top of the ice sheet, the elevation drops. As air temperature is higher at lower altitude, this promotes further melt. 
Atlantic Meridional Overturning Circulation
The Atlantic Meridional Overturning Circulation (AMOC), an important component of the Earth's climate system, is a northward flow of warm, salty water in the upper layers of the Atlantic and a southward flow of colder water in the deep Atlantic.  : 5 Potential impacts associated with AMOC changes include reduced warming or (in the case of abrupt change) absolute cooling of northern high-latitude areas near Greenland and north-western Europe, an increased warming of Southern Hemisphere high-latitudes, tropical drying, as well as changes to marine ecosystems, terrestrial vegetation, oceanic CO
2 uptake, oceanic oxygen concentrations, and shifts in fisheries. 
According to a 2019 assessment in the IPCC's Special Report on the Ocean and Cryosphere in a Changing Climate it is very likely (greater than 90% probability, based on expert judgement) that the strength of the AMOC will decrease further over the course of the 21st century.  Warming is still expected to occur over most of the European region downstream of the North Atlantic Current in response to increasing GHGs, as well as over North America. With medium confidence, the IPCC stated that it is very unlikely (less than 10% probability) that the AMOC will collapse in the 21st century.  The potential consequences of such a collapse could be severe.  : 5
Warming commitment to CO 2 concentrations.
If emissions of CO
2 were to be abruptly stopped and no negative emission technologies deployed, the Earth's climate would not start moving back to its pre-industrial state. Instead, temperatures would stay elevated at the same level for several centuries. After about a thousand years, 20% to 30% of human-emitted CO
2 will remain in the atmosphere, not taken up by the ocean or the land, committing the climate to warming long after emissions have stopped.  Pathways that keep global warming under 1.5 °C often rely on large-scale removal of CO
2 , which feasibility is uncertain and has clear risks. 
There are a number of examples of climate change impacts that may be irreversible, at least over the timescale of many human generations.  These include the large-scale singularities such as the melting of the Greenland and West Antarctic ice sheets, and changes to the AMOC.  In biological systems, the extinction of species would be an irreversible impact.  In social systems, unique cultures may be lost due to climate change.  For example, humans living on atoll islands face risks due to sea level rise, sea surface warming, and increased frequency and intensity of extreme weather events. 
Diego Cuevas / Getty Images
A tourist pier in Suesca, Colombia, gets little use, thanks to the extremely low water level, on March 12, 2021.
According to experts, the desiccation is due to climate change.
Snowfall in Yellowstone melts into rivers that span the continent from the Gulf of Mexico to the Pacific Ocean. Scientists are documenting significant changes in the amount of snow that falls here as well as the intensity and timing of spring runoff. These trends could affect everything you see when you come to the park, as well as everyone and everything living downstream.
Atmospheric concentrations of CO2 began a markedincrease that coincides with the Industrial Revolution. CO2 levels rose by more than 20% from 1958 to 2019.
Today, climate change is no longer a vague threat in our future it is the changing reality we live with, and it requires continuous planning and adaptation. Climate change presents significant risks to our nation’s natural and cultural resources. Though natural evolution and change are an integral part of our national parks, climate change jeopardizes their physical infrastructure, natural and cultural resources, visitor experience, and intrinsic values. Climate change is fundamentally transforming protected lands and will continue to do so for many years to come. Climate change will affect everyone’s experience of our national parks.
Some effects are already measurable. Warmer temperatures are accelerating the melting of mountain glaciers, reducing snowpack, and changing the timing, temperature, and amount of streamflow. These changes are expected to result in the loss or relocation of native species, altered vegetation patterns, and reduced water availability in some regions. Wildfire seasons have expanded, and fires have increased in severity, frequency, and size. More acres burned in the fire season of 2016 than in any year in the last century, except for 1988. Conditions that favor outbreaks of pests, pathogens, disease, and nonnative species invasion occur more frequently than in the recent past. In Alaska, melting sea ice threatens marine mammals as well as coastal communities, while thawing permafrost disrupts the structural basis of large regions, jeopardizing the physical stability of natural systems as well as buildings, roads, and facilities. Rising sea levels, ocean warming, and acidification affect wildlife habitat, cultural and historic features, coastal archeological sites, and park infrastructure, resulting in damage to and the loss of some coastal resources. Some studies suggest that extreme weather events such as thunderstorms, hurricanes,and windstorms that damage park infrastructure and habitat are increasing in frequency and intensity. Climate change will manifest itself not only as changes in average conditions, creating a “new normal,” but also as changes in particular climate events (e.g., more intense storms, floods, or drought). These extreme climate events may cause widespread and fundamental shifts in conditions of park resources.
A 2014 assessment of the magnitude and direction of ongoing climate changes in Yellowstone National Park showed that recent climatic conditions are already shifting beyond the historical range of variability. Ongoing and future climate change will likely affect all aspects of park management, including natural and cultural resource protection as well as park operations and visitor experience. In order to deal with the predicted impacts, effective planning and management must be grounded in concrete information about past dynamics, present conditions, and projected future change.
Impacts on Vulnerability and Equity
Projected climate change will affect certain groups of people more than others, depending on where they live and their ability to cope with different climate hazards. In some cases, the impacts of climate change are expected to worsen existing vulnerabilities.
Where people live influences their vulnerability to climate change.
- Over the past four decades, population has grown rapidly in coastal areas and in the southern and western regions of the United States. These areas are most sensitive to coastal storms, drought, air pollution, and heat waves. 
- Populations in the Mountain West will likely face water shortages and increased wildfires in the future. 
- Arctic residents will likely experience problems caused by thawing permafrost and reduced sea ice. 
- Along the coasts and across the western United States, both increasing population and changes in climate place growing demands on transportation, water, and energy infrastructure. 
The average temperature on the hottest days (i.e., those that occur only once in 20 years) are projected to increase by the end of the century relative to 1986-2005. Those days will be 10°F to 15°F hotter under the &rdquocontinued emissions increases&rdquo scenario by 2100. USGCRP (2014)
Thousands of New Orleans evacuees relocated to the Houston Astrodome after Hurricane Katrina in 2005. Source: FEMA (2005) Ability to Cope
Different groups have different abilities to cope with climate change impacts.
- People who live in poverty may have a difficult time coping with changes. These people have limited financial resources to cope with heat, relocate or evacuate, or respond to increases in the cost of food. 
- Older adults may be among the least able to cope with impacts of climate change.
- Elderly people are particularly prone to heat stress. Source: CDC (2009) Older residents make up a larger share of the population in warmer areas of the United States. These areas will likely experience higher temperatures, tropical storms, or extended droughts in the future.  The share of the U.S. population composed of adults over age 65 is also projected to grow from 13% in 2010 to 20% by 2050. 
- Young children are another sensitive age group, since their immune system and other bodily systems are still developing and they rely on others to care for them in disaster situations.
-  To find out more about climate change and health, please visit the Health Impacts & Adaptation page.
Indigenous communities and tribes are diverse and span the United States. While each community and tribe is unique, many share characteristics that can affect their ability to prepare for, respond to, and cope with the impacts of climate change. These include:
- living in rural areas or places most affected by climate change (like communities along the coast)
- relying on surrounding environment and natural resources for food, cultural practices, and income
- coping with higher levels of existing health risks when compared to other groups
- having high rates of uninsured individuals, who have difficulty accessing quality health care
- living in isolated or low income communities 
Climate change can impact the health and well-being of indigenous tribes in many ways. Climate change will make it harder for tribes to access safe and nutritious food, including traditional foods important to many tribes’ cultural practices. Many tribes already lack access to safe drinking water and wastewater treatment in their communities. Climate change is expected to increase health risks associated with water quality problems like contamination and may reduce availability of water, particularly during droughts.
By affecting the environment and natural resources of tribal communities, climate change also threatens the cultural identities of Indigenous people. As plants and animals used in traditional practices or sacred ceremonies become less available, tribal culture and ways of life can be greatly affected. Learn more about climate change and the health of indigenous populations.
City residents and urban infrastructure have distinct sensitivities to climate change impacts.  For example, heat waves may be amplified in cities because cities absorb more heat during the day than suburban and rural areas.
Cities are more densely populated than suburban or rural areas. In fact, about 80% of the U.S. population lives in urban areas. As a result, increases in heat waves, drought, or violent storms in cities would affect a larger number of people than in suburban or rural areas.  Higher temperatures and more extreme events will likely affect the cost of energy air and water quality, and human comfort and health in cities.
City dwellers may also be particularly susceptible to vulnerabilities in aging infrastructure. This includes drainage and sewer systems, flood and storm protection assets, transportation systems, and power supply during periods of peak demand, which typically occur during summer heat waves.
Changes in the Earth's orbit
The shape of the Earth's orbit around the sun naturally changes over time, and so does the way the Earth tilts toward the sun. Many of these changes happen in cycles that repeat over tens of thousands of years. These changes affect how much of the sun's energy the Earth absorbs, which in turn affects the Earth's temperature. Over at least the last few million years, these cycles likely caused the Earth to alternate between cold and warm periods. For the last few thousand years, we've been in a relatively warmer period.
About 20,000 years ago, ice sheets covered large parts of North America, where they extended as far south as where Chicago is now. In some places, this ice was a mile deep!
Source: Adapted from NASA (2011).
Five million years of climate change preserved in one place
IMAGE: Charlotte Prud'homme is abseiling to collect soil samples. The 80-meter-thick sedimentary sequence in Charyn Canyon, Kazakhstan, documents climate change over the past 5 million years. view more
Credit: Charlotte Prud'homme, MPI for Chemistry
Paleo researcher Charlotte Prud'homme, who until recently worked at the Max Planck Institute for Chemistry and is now a researcher at the Université Lausanne, explains: "The 80-meter-thick sedimentary sequence we found at Charyn Canyon in southeast Kazakhstan provides us with a virtually continuous record of five million years of climate change. This is a very rare occurrence on land!" The alternating dust and soil layers provide the first reliable evidence, in one place, of long-term interactions between major climate systems on the Eurasian continent. "Over the past five million years, the land surfaces of Eurasia appear to have more actively contributed to the land-atmosphere-ocean water-cycle than previously acknowledged. The sediments preserved at Charyn Canyon acted as a litmus test for the influx of freshwater into the Arctic Ocean, stimulating the transport of moist air masses from the North Atlantic back onto land via westerly air flows," corresponding author Prud'homme says. The results of the research have now been published in the scientific journal Communications Earth and Environment.
The researchers focused their investigation on the Pliocene and Pleistocene periods. The Pliocene, five to 2.6 million years ago, represents the best analogue for the climatic conditions of the Anthropocene: this geologic time period was the last time concentration of carbon dioxide in the atmosphere was comparable to today, around 400 parts per million (ppm). "That's why our insights from the Charyn Canyon sediments are so essential for understanding future climate," Prud'homme says.
Until now, little has been known about the role Central Asia plays in global climate evolution past and present. Earth's climate evolution over the past five million years has been understood mainly from the perspective of marine mechanisms. In contrast, the significance of climate feedbacks that originated on land - rather than in the oceans, lakes or ice cores - has remained largely unexplored. The international research team has filled this gap with their field research in Charyn Canyon.
Interactions between mid- and high-latitude climatic systems
The geographical location of the study site in the middle of Central Asia was of key importance to the team: "We needed to find a place that was inland and as far away from the ocean as possible," Kathryn Fitzsimmons, Group Leader of the Terrestrial Paleoclimate Reconstruction Research Group at the Max Planck Institute for Chemistry, explains. "We could hardly find a more continental situation than at Charyn Canyon in southeastern Kazakhstan." The semi-arid climate of the canyon, and its landscape, was shaped by the interaction between the mid-latitude westerlies and the high-latitude polar fronts, and by sediment transported from the nearby Tien Shan mountains. Charyn Canyon is ideal, according to Kathryn Fitzsimmons, for studying long-term land-climate feedback mechanisms.
The researchers examined the 80-meter-thick sedimentary succession and sampled by abseil to ensure continuous coverage of the record. By measuring the relative concentrations of isotopes within soil carbonates, they reconstructed the changing availability of moisture in the soil through time. A combination of paleomagnetic analyses and absolute uranium-lead dating of soil carbonates established the age and accumulation rates of the sediment record. The soil samples revealed a region characterized by ever-increasing aridity over the last five million years. In the early Pliocene, the soil was significantly wetter than in subsequent epochs or than today's climate. This process of aridification was not linear, however it was interrupted by short-term climate fluctuations which provide insights into the interaction between the mid-latitude westerly winds and the Siberian high-pressure system.
Interaction between the Siberian high and rain-bringing westerlies
The research at Charyn Canyon enabled the scientists to investigate the long-term interaction of the Siberian high with the rain-bringing westerlies. Kathryn Fitzsimmons says: "We're confident that the changes in soil moisture we found at our site can also be used as a proxy for Siberian river activity further north." The hydroclimate at Charyn Canyon reflects that of the steppe to the north, from where a number of large Siberian rivers, such as the Irtysh and Ob, flow, she says. These are similarly influenced by the dynamics of the Siberian high and westerly air masses. One particular phase where this link is important stands out: a sustained period of wet conditions at Charyn Canyon just prior to the first major global glaciation around 3.3 million years ago. It is likely that these wet conditions extended to the Siberian rivers to the north, whose outflow of fresh water to the Arctic ocean may have breached a tipping point for widespread increased sea ice formation.
The information from this most complete terrestrial climate archive for the past five million years provides a very valuable basis for future climate models. Charlotte Prud'homme literally says, "We have opened a door."
Information for editors:
- Max Planck Institute for Chemistry, Mainz
- Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, Rio Claro, Brazil.
- Université de Paris, Institut de Physique du Globe de Paris, Paris, France.
- Université Aix-Marseille, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France.
- Institute of Geological Sciences K. Satpaeva, Almaty, Kazakhstan
- Institute of Geosciences, Goethe University, Frankfurt, Germany
- Frankfurt Element and Isotope Research Center (FIERCE), Goethe University, Frankfurt, Germany
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.
What is Climate Change?
Climate change is a long-term change in the average weather patterns that have come to define Earth&rsquos local, regional and global climates. These changes have a broad range of observed effects that are synonymous with the term.
Changes observed in Earth&rsquos climate since the early 20th century are primarily driven by human activities, particularly fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth&rsquos atmosphere, raising Earth&rsquos average surface temperature. These human-produced temperature increases are commonly referred to as global warming. Natural processes can also contribute to climate change, including internal variability (e.g., cyclical ocean patterns like El Niño, La Niña and the Pacific Decadal Oscillation) and external forcings (e.g., volcanic activity, changes in the Sun&rsquos energy output, variations in Earth&rsquos orbit).
Scientists use observations from the ground, air and space, along with theoretical models, to monitor and study past, present and future climate change. Climate data records provide evidence of climate change key indicators, such as global land and ocean temperature increases rising sea levels ice loss at Earth&rsquos poles and in mountain glaciers frequency and severity changes in extreme weather such as hurricanes, heatwaves, wildfires, droughts, floods and precipitation and cloud and vegetation cover changes, to name but a few.
Find Out More: A Guide to NASA&rsquos Global Climate Change Website
This website provides a high-level overview of some of the known causes, effects and indications of global climate change:
Evidence. Brief descriptions of some of the key scientific observations that our planet is undergoing abrupt climate change.
Causes. A concise discussion of the primary climate change causes on our planet.
Effects. A look at some of the likely future effects of climate change, including U.S. regional effects.
Vital Signs. Graphs and animated time series showing real-time climate change data, including atmospheric carbon dioxide, global temperature, sea ice extent and ice sheet volume.
Earth Minute. This fun video series explains various Earth science topics, including some climate change topics.
Other NASA Resources
Goddard Scientific Visualization Studio. An extensive collection of animated climate change and Earth science visualizations.
Sea Level Change Portal. NASA's portal for an in-depth look at the science behind sea level change.
NASA&rsquos Earth Observatory. Satellite imagery, feature articles and scientific information about our home planet, with a focus on Earth&rsquos climate and environmental change.
Shutterstock credits: wandee007 (left), Amy Johansson (middle), Avatar_023 (right).