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Climate change affects ecosystems differently depending on the resilience and capacity of adaptation of the ecosystems. The book focuses on five specific ecosystems and how climate change is impacting them. This section will provide you with some basis information about how climate change already impacts those ecosystems.

To learn more, you can check the latest 2023 IPCC synthesis report or its 2021 report focusing on the Physical Science Basis and its FAQ 

Melting of ice caps and mountain glaciers

Retreat and disappearance of mountain glaciers and ice caps is one of the most dramatic pieces of evidence that our climate is warming. This assessment can be done all over the world: in nearly all high mountains, snow covers have shrunk. If no changes are made to our current trend of greenhouse gas emissions, the IPCC projects that “Regions with mostly smaller glaciers (e.g. Central Europe, Caucasus, North Asia, Scandinavia, tropical Andes, Mexico, eastern Africa and Indonesia), are projected to lose more than 80% of their current ice mass by 2100’. However, regardless of future emissions and because of the current warming, many glaciers are already projected to disappear.


Worse, the melting of ice caps and mountain glaciers can reach tipping points where their melting rates can dramatically increase, following the physical process described below.

The shrinking of mountain glaciers has immediate consequences for communities and natural ecosystems relying on snow and water-fed rivers. When glaciers seasonally retreat in the summer, they release fresh water into rivers supplying water to hundreds of millions of people in Western North America, South America, China and India, and to natural ecosystems. As mountain glaciers are melting earlier and at a fastest rate, without fully recovering in winter, their seasonal water runoff is getting smaller. A smaller flow can create hydrological droughts (i.e. water shortage due to smaller river flow) threatening the otherwise reliable water supply to those millions of people living downstream.

Another important impact of the melting of mountain glaciers (and of ice sheets) is to the rise of sea level. This topic is presented in the section below. 


FAQ 9.1, Figure 1 FROM the IPCC FAQ | Ice sheets growth and decay. (Top) Changes in ice-sheet volume modulate sea level variations. The grey line depicts data from a range of physical environmental sea level recorders such as coral reefs while the blue line is a smoothed version of it. (Bottom left) Example of destabilization mechanism in Antarctica. (Bottom right) Example of destabilization mechanism in Greenland.

Source: FAQ 9.1 Figure 1 in IPCC, 2021: Chapter 9. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Fox-Kemper, B., H.T. Hewitt, C. Xiao, G. Aðalgeirsdóttir, S.S. Drijfhout, T.L. Edwards, N.R. Golledge, M. Hemer, R.E. Kopp, G. Krinner, A. Mix, D. Notz, S. Nowicki, I.S. Nurhati, L. Ruiz, J.-B. Sallée, A.B.A. Slangen, and Y. Yu, 2021: Ocean, Cryosphere and Sea Level Change. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1211–1362,

Disappearance of the ice sheets and sea ice at the poles

Both the North pole (Arctic) and the South pole (Antarctica) are warming. The Arctic is warming two times faster than the rest of the globe. Warming in both regions has already triggered the melting of the poles ice sheets (ice resting on bedrocks below or above sea levels) and ice sea (part of the ocean which is frozen and whose size varies seasonally): 

  • Greenland and Antarctic ice sheets have melted respectively of 270 and 150 gigatons between 2006 and 2015. 

  • The Arctic sea ice is also steadily shrinking. In September 2020, the Arctic sea ice reached its smallest size in at least a millenia. At the same time, the composition of the ice itself is changing, becoming “younger”, fast: between 1979 and 2018, back-to-back periods of thinning have led to a 90% decline of areas made of ice at least 5 years old


This melting entails dramatic consequences both at the global and local level.

At the global level: first, melting of ice sheets and sea ice increase the global rate of warming (white surfaces such as ice sheets play a big role in reflecting back sunlight into space, thus reducing the amount of energy trapped) and second, it contributes to sea level rise (in theory if both ice sheets were to disappear in full sea level will rise by 65m / 213 ft). Contributions from the melting of the poles ice sheets to sea level rise have dramatically increased since 2016. They are now responsible respectively for 22% and 14% of the rise of sea level.

At the local level: shrinking of the Arctic sea ice tilts the equilibrium of the local ecosystems and how animals and plants had evolved to be fully adapted to this very specific environment. One iconic example is polar bears. With an ice sheet less stable, which breaks up earlier in Spring and forms later in Fall, it becomes harder for them to hunt seals, their main source of food. As a result, they exhaust themselves roaming and swimming many more miles, making them weaker, causing earlier death and threatening their reproduction rate. 


Oceans Warming and Acidification

Oceans play a crucial role in buffering the rise of global temperature through two trapping mechanisms: trapping of extra heat and extra CO2. Both have dire consequences on the oceanic ecosystem, sometimes compounding themselves.

First, oceans reduce the increase of temperatures in land by storing most of the excess energy trapped in the atmosphere. Since 1850, oceans have stored more than 90% of this excess energy. This in turn has started warming the oceans contributing for instance to doubling the frequency and intensity of marine heatwaves since the early 80’s. 

As the water warms, it takes more room (i.e: it expands). Warming of the ocean, triggering its expansion, is thus the main contributor to the increase of global sea level (up to 50% of the sea level increase since 1970). At 1.5°C/2.4°F of warming, sea level rise is projected to be 26 cm / 0.85 ft to 77 cm / 2.5 ft by 2100. For small islands, low-lying coastal areas and deltas (such as the New Orleans or the Gange Deltas), it means more tidal flooding, storms surges or waves inundations, damages to infrastructure and saltwater intrusion making lands improper to farming. In some regions, extreme sea level events that used to occur once every century will occur every year at 20 to 25% of locations by 2050. The rise of the sea level will continue over millenia even once emissions are down to net zero due to the inertia of the oceanic system. 

Second, oceans have also absorbed a significant portion of the excess CO2 emitted. In the last decade, oceans have taken in up to 30% of this excess emissions. In other words, oceans are contributing to reducing the size of the layer of our greenhouse gas “blanket” by preventing some of our emissions from reaching the atmosphere.

More CO2 in the oceans increases their level of acidity. Since 1850,  the PH level of the surface water of the ocean has fallen by 0.1 unit. Not much? Think twice. This means a 30% increase of acidity. Such change has direct negative impacts on the marine ecosystems. One of the more direct consequences is on shell builders, such as corals or pteropods (which are part of the plankton and a key element in the marine food chain). A more acidic ocean jeopardizes their growth and even their survival as it weakens and destroys their shells or skeletons.


Coral reefs, which are home to 25% of all marine life, are especially vulnerable both to a warmer and to more acidic ocean. In a 1.5°C/2.4°F warmer world, 70 to 90% of coral reefs would die. At 2°C/3.7°F, coral reefs would be almost extinct.

Rivers in regions affected by droughts

Hot extremes events, such as heatwaves, have already become more frequent and more intense across most regions since the 1950's, while cold extreme events being less frequent. As per the IPCC 5th assessment report “ at 2°C [3.6°F] of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health”. If emissions are not curtailed by 2100, a third of global lands are projected to suffer from some level of droughts, with droughts being more intense and occurring throughout the year. Regions most affected are the subtropical regions (Mediterranean, southern Africa, southwestern Australia, southwest South America) as well as tropical Central America, western Africa and the Amazon region. 

In contrast, this is also true that some areas could expect more rainfall due to an increase in cloud formation as a warmer atmosphere can hold up more water vapour (clouds). 7% more for each 1°C increase. The main areas which could be affected by heavier rainfalls are high-altitude (mountains) regions in North America and Asia, as well as the South Asian monsoon region. In many instances, those heavier rainfalls would exacerbate flooding.

Forests suffering from a dryer climate

A warmer climate impacts forests in different ways.


It increases tree mortality directly through droughts and wildfires. Those two phenomena also build on top of each other. Because of droughts, trees, made of dryer wood, are easier to burn. Deprived of enough water, they are also weaker, jeopardizing their chances of recovery after a fire.

Higher temperatures also threaten forests indirectly by making them more vulnerable to native and non-native insects outbreaks. Insects’ outbreaks are a main driver of tree mortality: they can stop the photosynthesis by eating up the leaves, they can bring disease inside the tree or weaken the tree’s structure itself. Those outbreaks are influenced in part by climate change as insects 1) are very sensitive to temperatures (with shorter or milder winters, more insects survive contributing to their subsequent outbreak) and 2) pests can easily migrate between regions that are becoming warmer (trees and plants are vulnerable to new bugs as they don’t have effective defenses against them).

Loss in forests coverage and forests health result in loss of carbon sinks. If forests cannot store as much carbon, this carbon is stored in the atmosphere, increasing the greenhouse gas effect, thus global temperatures. 

© 2023 Helene Costa de Beauregard and Anita Bagdi 

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