Some effects of climate change
As we continue to increase greenhouse gases in the atmosphere, the planet continues to warm. Many changes happen as a result of this warming, and they are projected to worsen with each small increment in the temperature. This page explores the immediate effects of warming and of the accumulation of carbon dioxide in the air. Global warming is now about 1.2°C above the pre-industrial period (1850-1900), and the last decade was the warmest ever recorded.
Below are listed some of the major changes due to warming. The sections detail some of the impacts these changes have on people, other species and habitats. The section on extreme weather describes some of the impacts of weather events in 2019-2020.
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Sea levels are rising ▼
The rise in sea level is in part due to the higher temperatures melting ice sheets and glaciers, which drain into the oceans. It is also due to the ocean warming: as it warms the ocean expands and so the level of the sea rises. Worldwide the sea level is rising by around 3.3mm a year. It has risen by about 178mm (7 inches) since the beginning of the 20th century, and the rate at which it is rising has nearly doubled.wmo
- When combined with extreme winds, waves and rainfall, even a small rise in sea level increases hazards for coastal communities, and exposes low-lying islands to a greater risk of flooding (see extreme weather below). With continual melting of ice and expansion from heat, the sea will continue to rise. If the rise in global temperature is limited to 1.5°C, it is estimated that, by 2100, sea level will have risen by about half a metre (0.26-0.77m), relative to the period 1986-2005. This could affect about 600 million people living in low-lying coastal regions and small islands.wmo Many more people would be at risk if the temperature rose above 1.5°C.
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Arctic sea ice is shrinking ▼
Sea ice expands and thickens in the cooler months of winter, and shrinks and thins in the summer. This means that each year we get a maximum and a minimum expanse of sea ice. With the global rise in temperature, over the last four decades the extent of sea ice has decreased for every month of the year, but particularly when at its minimum extent in summer. The sea ice is also becoming thinner. But why does it matter?
- Loss of ice also causes further warming. When the ice melts, it exposes more of the ocean surface. The ocean is darker than the ice, so it reflects less solar energy (absorbing it instead), which increases the temperature even more.i This causes more ice to melt, more dark surface to be exposed, more energy to be absorbed by the ocean, more warming and so on. These effects are a key factor in the Arctic warming at a rate 2-3 times the global average.
- Changes in sea ice affect the habitat of many organisms, such as phytoplankton, polar bears, seabirds, walruses and seals. They can adapt to change but it can be dangerous for the young. For example, with less ice, or thinner ice, polar bears are forced to swim more and to travel longer distances for food, but the young bear cubs may not survive the long swim. Similarly young seals can become stranded and die in years when there is not much ice.
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Land ice is shrinking ▼
With higher temperatures, glaciers and the Greenland ice sheet have been shrinking over the last 40 years.wmo An ice sheet is a large version of a glacier. Both are formed from snow that has fallen over thousands of years and compressed into thick ice masses, and both move like a river, but slowly. The earth has two ice sheets: one covers most of Greenland, and the other covers Antarctica. Glaciers occur across the world, particularly in polar regions and mountainous areas.
The shrinking of ice sheets is expected to accelerate over the coming decades. It is also estimated that we will lose 36% of ice from glaciers if we allow warming to reach 2°C, which is double the estimated loss at 1.5°C. Some of the effects of losing land ice are identified below:
- Melting ice flows into the sea and contributes to sea level rise (see above).
- Glaciers provide freshwater to millions of people through runoff of water from the melting ice, mostly during warmer months. The water feeds into downstream river basins that cover vast areas of land. In the mountainous regions in Asia, for example, the glaciers provide water to 1.4 billion people through several river basins, such as the Indus and Ganges. However, with the shrinking glaciers, the meltwater runoff at some point starts to decline.i This can threaten the water supply to millions living in areas where the rainfall is low in summer. In the Indus basin alone 120 million people could be affected.a.g. This has already contributed to declines in agricultural yields in some high mountainous areas, such as parts of the Andes and the Himalayas. In the coming decades the decline in runoff is expected to have further impacts on irrigation and energy production (hydropower).
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Arctic permafrost is thawing ▼
Permafrost is ground that is continuously frozen, and much of it has been frozen for thousands of years. The ground contains soil, rock, sand, vegetation and ice. It covers about a quarter of the land in the northern hemisphere, including regions in Alaska, Siberia and Greenland. It is estimated that it contains about twice the carbon that is in the atmosphere. As with forests, it is a resource we need to protect to keep the carbon out of the air and prevent more warming.
However, with the hotter temperatures, the permafrost is thawing and, as it does so, it releases the greenhouse gases methane and CO2. (The gases are released because microbes in the soil start to decompose plant material as it thaws.)
It is estimated that by restricting our emissions and the temperature rise to 1.5°C, we would save about 2 million km2 of permafrost over several centuries, and avoid the release of the greenhouse gases.cb
A few more impacts of permafrost thaw are outlined below.
- When the temperature rises due to the permafrost thawing, it causes more permafrost to thaw, which releases more gases, increasing the temperature even more, and so on, in a positive feedback loop.
- The methane released from the permafrost as it thaws also contributes to extensive wildfires. These release even more greenhouse gases into the air to add to warming and also pollute the air thousands of miles away.a.i
- When the ice in permafrost melts, the ground becomes unstable, which can cause landslides and floods.e.i. Buildings, roads, power lines and other infrastructure are being damaged by the ground collapsing beneath them. Many people in Alaska and Russia are being forced to move from their homes.a.i
- In parts of Canada and Alaska the coastline is also becoming eroded and the sea is encroaching on coastal towns. This is happening because of the combined effect of softer thawed permafrost ground and the loss of sea ice. The sea ice used to protect the coasts from storms by acting as a wave-break, but now the soft ground is more exposed to the force of the storms. It is possible for one storm to erode 20 metres of the coastline.a.i Many coastal communities in Alaska have had to move from their homes, and many more are at risk of being displaced by coastal erosion.
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Oceans are becoming hotter and more acidic ▼
Ocean warming
Oceans absorb about 90% of the excess heat trapped by the increased concentrations of greenhouse gases. It is estimated that over the last 2 decades, the rate of ocean warming has more than doubled at all depths down to 2000m. As the heat is absorbed, the ocean temperature increases and the sea expands, contributing further to sea level rise (see above).
As well as heatwaves on land, we are experiencing marine heatwaves. These are periods of unusually high water temperatures in some parts of the ocean. Marine heatwaves have doubled in frequency since 1982, have become more intense and last longer. They are harmful to marine life that is not able to adapt to higher temperatures, such as the less mobile organisms that are unable to move to cooler waters.
Ocean acidification
Oceans have absorbed about a quarter of the carbon dioxide emissions that we have released into the atmosphere. However, when carbon dioxide dissolves in water, it reacts with the water and raises its acidity. It also has the effect of reducing the concentration of carbonate ions in the water, which, as we shall see, endangers sea organisms and indirectly has impacts on humans.
Loss of species ▼
About 1 million species face extinction from the effects of human activities, including pollution, global warming and overexploitation of resources. Of the climate-related changes, ocean warming and acidification are two changes that have major impacts on marine life. Coral reefs are particularly threatened, and already a large coral reef system has lost 50% of its coral.
Marine heatwaves can result in sudden death of coral, but where conditions are less severe, the reefs simply turn white (this is called coral bleaching).i Marine heatwaves are projected to increase in duration, intensity and frequency over the coming decades. As a result of this and other hazards, such as intense storms, it is estimated that we will have lost 70-90% of the coral by the time we reach 1.5°C, and 99% if it rises to 2°C.
The acidity of water is also a major threat to coral and many other sea organisms, including pteropods (a kind of sea snail), molluscs (e.g. oysters and mussels), some plankton, and some fish. They all depend on a supply of carbonate ions, which are needed to build and maintain their shells and skeletons. But we saw that carbonate ions are reduced when the water becomes acidic, which makes it hard for them to do this. This can affect their growth and development, and in highly acidic water, their shells can dissolve and threaten their survival.
Apart from the loss of some of the populations of these species, many other organisms that depend on them can be affected. For example, shallow water coral reefs provide food, shelter and habitats for thousands of species, such as fish, sea turtles and mammals. Some fish rear their young in amongst the reefs. Similarly, pteropods (also threatened by acidic waters) are an important link in the foodweb between phytoplankton and many more species, including fish, whales and birds.
Where organisms are unable to adapt, the decline in dependent species in the foodweb can ultimately affect humans. Coastal communities, in particular, may be affected where they depend on fish stocks for their food and for their livelihood.
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Extreme weather ▼
Globally the average temperature has risen by 1.2°C above pre-industrial levels, but this rise is not uniform across the world. Average temperatures over land are higher than over the ocean, and most land areas have experienced higher temperatures than the global average. The area that has warmed the fastest is the Arctic, where the annual average temperature is now 2-3°C above its pre-industrial temperature, and 1-2°C above the global average warming. Around one third of people (20-40%) live in regions where warming has already exceeded 1.5°C in at least one season.
As the earth warms the patterns of rainfall also change so that some areas have a lot more rain, and others receive much less. This can lead to floods in some regions of the world and droughts, heatwaves and fires in others. Global average rainfall is increasing since the warmer air can hold more water, but rainfall in some areas may be reduced by changes in wind patterns .
Heatwaves ▼
Heatwaves have been common during 2020. Average temperatures in Russia were 3.7°C above average, and some places in Siberia were 5°C above average. Record temperatures were set in many places including Mexico, Central America, Japan and Australia.wmo
With the rising global temperatures there have been more frequent and intense heatwaves in recent times. During the last 20 years there have been 3 times the number of heatwaves that resulted in significant loss of life by comparison with the previous 20 year period. A large proportion (88%) of deaths from the events occurred in Europe: in 2003 72000 people died during a heatwave across 15 countries, mostly in Italy and France. Another 55000 deaths occurred in Russia after a heatwave in 2010.undrr
Heatwaves have always been around, but the climate changes that have happened are exacerbating them. The greatest warming of hot extremes (the greatest increase in maximum temperature) is predicted to occur in central and eastern North America, central Europe and the Mediterranean.
The risks to health will be greater for those who live in areas that are already hot. So the risks are greater in cities where the temperature is several degrees warmer than surrounding rural areas.i Also the risks are higher in very hot countries, where people might be close to the limit of being able to regulate their temperatures.
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Forest fires ▼
Many extensive fires, including the largest wildfires on record, occurred in the U.S. states of California and Colorado in 2020. Major fires in Australia burnt from the latter part of 2019 through to early 2020. Many of these fires were exacerbated by high temperatures along with long periods of drought, making the vegetation very dry. Aside from the destruction of plant and animal species, these fires release massive quantities of greenhouse gases and particulate matter into the air. The air pollution is not only a threat to the health of the local population, but also to people living thousands of miles away.wmo
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Rainfall and flooding ▼
2020 saw intense rainfall and flooding over large areas of Africa and Asia. Sudan and Kenya were among the worst hit, with the loss of hundreds of lives from floods, and hundreds of thousands more people affected, some from subsequent disease. Many more deaths were reported across several countries in Asia, including some from a landslide and flash flooding. Severe flooding in Vietnam resulted from a succession of 8 cyclones, which exacerbated the usual heavy monsoon season.wmo
Heavier and more frequent rainfall is expected in some regions as we approach 1.5°C, including the Arctic, northern Europe, northern Asia, eastern North America and China, and this is predicted to worsen if the temperature rises above 1.5°C.
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Decreased rainfall and droughts ▲
By contrast droughts in 2020 affected many countries in South America and caused agricultural losses estimated at 3 billion US$.wmo
In many parts of the world water is already under stress or scarce as a result of increased consumption. Much of this is due to the demands of agriculture and a growing population. Some countries are using more than 80% of their available water,wri and the more frequent and intense droughts are exacerbating the situation. As the temperature rises, droughts are predicted to be worse in some regions, such as southern Europe, the Mediterranean and northern Africa, with a greater risk of water scarcity.
Reduced rainfall and drought also threaten food production where it relies on rainfall (as opposed to irrigation from rivers and lakes). This amounts to 70% of agriculture.undrr A farm can lose their crops and livestock (86% of livestock losses from disasters are due to droughts, and two-thirds of crop losses are due to floods).fao Where the farm is small and mainly provides food for one family with a small surplus to sell, the family may lose the income they might have had and there may be little left to feed themselves. This increases hunger, malnutrition and poverty. Families may have to move to another region for work, and may not be able to return if their land has become too degraded.
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Cyclones and storms ▼
One of the most intense cyclones ever to reach land hit the Philippines in 2020 with wind speeds of 220km/h. This was followed followed by another, a few days later, which caused extensive flooding. Vietnam was hit by 4 cyclones in 3 weeks which caused extensive flooding, and in Madagascar many lives were lost from flooding after a cyclone. A series of fast-moving severe thunderstorms across the U.S in 2020 resulted in severe agricultural losses, including an estimated 2 million hectares of corn and soya crops.wmo
Tropical cyclones are not projected to become more frequent as the temperature rises, but they are expected to become more intense and to be associated with heavier rainfall.
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Increased preparedness by disaster management agencies is helping to combat extreme weather events. Many lives are saved by evacuating people in advance. But the devastation and destruction to land and property can be such that people are unable to return to their homes afterwards. In 2019 almost 24 million more people were displaced by climate-related disasters, and a few million people were still displaced at the end of the year. The majority of displacements were in Africa and Asia, but more than 1.5 million were from the Americas and Europe.idmc
While additional preparation helps to save lives, there is a growing number of people affected in other ways. These include injuries, loss or disruption of livelihoods, particularly in agriculture, and the consequences of this, such as more poverty, malnutrition and hunger.undrr
Natural hazards such as these have always occurred, but the warming planet has increased either the frequency or intensity, or sometimes both. In the last 20 years, the number of climate-related disasters increased by about 80% compared to the previous 20 years.undrrr
References and resources: ▼
1. Centre for research on the epidemiology of disasters (CRED) UN office for disaster risk reduction (UNDRR) 2020 Human cost of disasters: an overview of the last 20 years (2000-2019) (pdf).
2. Internal displacement monitoring centre (IDMC) (2020) Global report on internal displacement. (pdf)
3.World Resources Institute (2019) 17 Countries, Home to One-Quarter of the World’s Population, Face Extremely High Water Stress Onine resource.
4.Renee Cho. (2018) Why thawing permafrost matters. Earth Institute, Colombia University
5.Bykova, A. 2020 Permafrost thaw in a warming word: the Arctic Institute’s permafrost series 2020
6.Davies,B. (2020) Glaciers as a water resource Antarctic Glaciers, Online resource.
7. i Lower reflectivity is also called lower albedo.
8. i Coral bleaching occurs when the coral expels the algae that normally live within their tissues, in a mutually beneficial relationship. They can recover but with the projection of more extreme temperatures, it becomes less likely that they will have time to recover.
9. i Urban heat islands are built-up regions that can be several degrees warmer than their rural surroundings. This is mainly due to there being a concentration of surfaces (e.g. buildings, roads) that absorb more of the sun’s energy and release it as heat. Unlike plants, these surfaces are unable to cool themselves.
10. i When glaciers shrink, the amount of meltwater, and runoff, changes. Initially there is more water than normal flowing downstream, which can lead to flooding. However, at some point the runoff reaches a maximum and runoff starts to decline, so less water flows into the river basin.
11. Food and Agriculture Organization of the United Nations (FAO) (2017) Figure 5, Different Disasters – different sector impacts. In: The Impacts of disasters and crises on agriculture and food security. (pdf)
12. Climate feedbacks are processes that increase an initial temperature rise (positive feedback) or decrease it (negative feedback). A negative feedback loop helps to maintain a balance and keep a system within a desirable range of states. Whereas a positive feedback loop tends to shift the system out of that range. So a positive feedback loop is not good for maintaining a stable system in spite of its name.
Background:
This is useful for weather events in 2020, as well as observed changes in previous years.
1. World Meteorological Organization (WMO) The state of the Global Climate 2020
These references are a useful summary of what the IPCC (see below) reported on observed changes to earth systems, as well as projections of change at 1.5˚C and 2˚C of warming
2. The Met Office Effects of climate change. Online resource.
3. NASA Buis, A (2019) A degree of concern. Why global temperatures matter: Selected findings of the IPCC special report on global warming. NASA’s global climate change website. Online resource
4. World Resources Institute. Levin, K. (2018) Half a Degree and a World Apart: The Difference in Climate Impacts Between 1.5˚C and 2˚C of Warming. World Resources Institute. Online resource.
5. Carbon Brief (2018) The impacts of climate change at 1.5C, 2C and beyond. Online resource.
Original sources:
The 2018 IPCC (the Intergovernmental Panel on Climate Change) special report provides the original source material for both observed and projected changes as a result of global warming. The 2019 special report focuses in detail for the first time on the oceans and frozen parts of the world (the cryosphere).
IPCC (2018) Chapter 3: Hoegh-Guldberg, O., D. Jacob, M. Taylor, M. Bindi, S. Brown, I. Camilloni, A. Diedhiou, R. Djalante, K.L. Ebi, F. Engelbrecht, J. Guiot, Y. Hijioka, S. Mehrotra, A. Payne, S.I. Seneviratne, A. Thomas, R. Warren, and G. Zhou, 2018: Impacts of 1.5°C Global Warming on Natural and Human Systems. (PDF).
IPCC, 2019: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.