IPCC Climate Change 2022: Six Themes for Freshwater Ecosystems
Human-induced climate change is causing significant disruption to global ecosystems and the lives of billions of people who depend on them, according to the latest Intergovernmental Panel on Climate Change (IPCC) Working Group Report, released this week.
“This report is a dire warning about the consequences of inaction,” says Hoesung Lee, Chair of the IPCC. “It shows that climate change is a grave and mounting threat to our wellbeing and a healthy planet. Our actions today will shape how people adapt and nature responds to increasing climate risks.”
Titled “Climate Change 2022: Impacts, Adaptation and Vulnerability“, the Working Group Report states that the world faces multiple unavoidable climate hazards in the coming two decades under projected global temperature rises of 1.5°C. It highlights the increasing frequency and magnitude of extreme weather events such as heatwaves, floods and droughts that are placing species at risk of extinction and exposing millions of people to water and food insecurity.
The report – the second installment of the IPCC’s Sixth Assessment Report (AR6), which will be completed this year – highlights the need for rapid, deep cuts in global greenhouse gas emissions, coupled with local adaptation and mitigation measures.
“This report recognises the interdependence of climate, biodiversity and people and integrates natural, social and economic sciences more strongly than earlier IPCC assessments,” says Hoesung Lee. “It emphasises the urgency of immediate and more ambitious action to address climate risks. Half measures are no longer an option.”
The Working Group Report suggests that assessments of climate change impacts on freshwater systems have been limited in previous reports. As a result, this report devotes significant space to assessing how freshwater systems are responding to ongoing climate change, and the potential opportunities for mitigation and adaptation. These assessments build on reviews of cutting-edge freshwater science and management, from which six key themes are highlighted here.
Climate change is already significantly altering global freshwater ecosystems
The report states that strong and consistent global trends show that ongoing changes to the health of freshwater ecosystems can be attributed to climate change. It outlines that trends in freshwater species populations are strongly related to changes in the physical environment. It states that water temperature has broadly increased in lakes and rivers globally in recent years, whilst ice cover extent has declined in polar regions. Moreover, changes to river flows have reduced connectivity of habitats across many catchments, with more than half of global rivers undergoing periodic drying. Further, decreases in dissolved oxygen concentrations and changes to water mixing in freshwaters have also been widely observed.
All of these climate-caused habitat changes are increasingly putting freshwater species at risk. The report states that climate-driven population extinctions have been higher in freshwater ecosystems than in their marine and terrestrial counterparts in recent years. Ongoing climate change increases the risk of such extinctions: the report suggests that extreme 5°C warming would likely put 60% of terrestrial and freshwater species at risk of extinction.
Floods and droughts: the impacts of extreme events
Climate change is causing increased extreme weather events, including storms, heavy rainfall, heat waves and droughts, the report states. Whilst the impacts of such events on freshwater ecosystems can be significant – such as heat wave fish kills – their consequences on ecological functioning are not always well understood. For example, whilst extreme floods cause massive habitat disturbances, moderate floods can help cycle nutrients and sediment through a river system. Given their increasing frequency and magnitude, the report states that understanding how the impacts of extreme floods and droughts cascade through freshwater ecosystems is a key area for future research.
Corridors and connectivity: species migrations and climate change
The report highlights how some freshwater species, particularly fish, are migrating in poleward directions due to warming climates across North America, Europe and Central Asia. This means that in some areas warm-water fish species are displacing cool-water species, which in turn seek cooler upstream habitats at higher altitudes. However, such cool-water species risk local extinction if migration to suitable refuge habitat is impossible. These processes highlight the importance of environmental management which prioritises connectivity across watersheds, creating freshwater corridors which allow species to move with climate shifts.
Climate change effects on humans and freshwaters
Freshwaters provide an array of benefits and services to human communities, which may be limited by climate change, the report suggests. In particular, it highlights the potential effects of floods, droughts and ice melt on the quality and quantity of drinking water. Floods can contaminate drinking water supplies with pollutants, whilst droughts can reduce its availability. The report also highlights the risks to freshwater fisheries posed by climate-induced processes of eutrophication and ice melt.
Feedback loops: freshwaters as a source of greenhouse gas emissions
The report highlights how in recent years freshwater ecosystems have been increasingly recognised as an important source of greenhouse gas emissions into the atmosphere. Emissions of carbon dioxide and methane can occur from warming, eutrophic lakes, and from exposed sediments during droughts. This flags the potential for climate change-altered freshwaters to become additional sources of atmospheric greenhouse gases, thus strengthening climate feedback loops.
Nature-based solutions for climate adaption and mitigation
The Working Group Report outlines the importance of management and policy interventions focused on climate change adaptation and mitigation. Beyond pressing goals of reducing global greenhouse gas emissions, one key area highlighted is the potential of nature-based solutions. As introduced here, nature-based solutions aim to harness the potential of natural processes to help tackle socio-environmental challenges such as climate change.
“Healthy ecosystems are more resilient to climate change and provide life-critical services such as food and clean water,” says IPCC Working Group II Co-Chair Hans-Otto Pörtner. “By restoring degraded ecosystems and effectively and equitably conserving 30 to 50 per cent of Earth’s land, freshwater and ocean habitats, society can benefit from nature’s capacity to absorb and store carbon, and we can accelerate progress towards sustainable development, but adequate finance and political support are essential.”
The report highlights the potential of peatland restoration and rewetting in boosting carbon storage and benefiting freshwater biodiversity. Similarly, it highlights the role of catchment restoration around urban areas as a means of improving natural water filtration and buffering floodwaters.
More broadly, the report states a clear urgency in limiting warming through concerted and equitable climate action. “The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet. Any further delay in concerted global action will miss a brief and rapidly closing window to secure a liveable future,” states Hans-Otto Pörtner.
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This article is supported by the MERLIN project.
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