IPCC Climate Change Report: Three Key Themes for Freshwaters

Humans are altering Earth’s climate in unprecedented and potentially irreversible ways, according to the latest Intergovernmental Panel on Climate Change (IPCC) Report, released today.

The report is the sixth assessment of global climate science published by the IPCC since 1988, and is based on the collaborative review of peer-reviewed science by hundreds of experts across the world. It states that global climate change is widespread, rapid and intensifying, and that many ongoing observed climate changes are unprecedented in thousands, if not hundreds of thousands of years.

“This report reflects extraordinary efforts under exceptional circumstances,” says Hoesung Lee, Chair of the IPCC. “The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making.”

“This report is a reality check,” says IPCC Working Group I Co-Chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”

The report states that climate change will increase globally in coming decades, bringing multiple potential impacts such as heat waves, droughts and flooding to different regions. “It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” says Masson-Delmotte.

The complex impacts of multiple climate change pressures on aquatic systems are increasingly well-documented. In this context, the IPCC report highlights three overarching impacts on freshwater ecosystems arising from its assessment.

Intensification of the water cycle

The report states that ongoing climate change will cause the global water cycle to continue to intensify as global temperatures rise over coming decades. This means that some regions will experience more intense rainfall, and associated flooding, whilst others will experience intensified droughts. Overall, the impacts of such extreme events on freshwater systems are likely to increase in the future.

Increased variation in rainfall patterns

Precipitation patterns are also expected to alter globally over coming decades. The report suggests that precipitation will increase over high latitudes, the equatorial Pacific and parts of the monsoon regions, but decrease over large parts of the subtropics. Average annual global land precipitation is projected to increase under each scenario of future greenhouse gas emissions by 2100. Additionally, regional changes to monsoon rainfall patterns are predicted.

Impacts of warming on snow and ice melt

The report suggests that ongoing increases in air temperatures will amplify permafrost thawing, the loss of seasonal snow cover and the melting of glaciers and ice sheets. This has the potential to significantly affect water flows and habitat quality in freshwater ecosystem at high latitudes and altitudes, and potentially cause flooding issues downstream.

The message from the report is clear: act now to restrict global carbon emissions to minimise the harmful effects of future climate change. “Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” says IPCC Working Group I Co-Chair Panmao Zhai. “Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” Zhai states.

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Read the IPCC Sixth Assessment Report, Climate Change 2021: The Physical Science Basis