A new report from the United Nations and the International Cryosphere Climate Initiative warns of the risks of surpassing the 1.5 °C limit of global warming for regions covered by snow, ice, and permanently frozen soils. Some of the consequences could be irreversible on the timescale of human societies and exceed the capacity for adaptation.
Surpassing the 1.5 °C limit of global warming could trigger a large-scale loss in polar regions and in the cryosphere, with consequences that extend far beyond the directly affected areas. The warning is contained in the report Overshoot in the Cryosphere – Averting Global Meltdown, prepared by the United Nations in collaboration with the International Cryosphere Climate Initiative (ICCI).
The document analyzes the impacts of a scenario in which the global average temperature temporarily exceeds the 1.5 °C target, a situation known as overshoot. Among the risks identified are melting, thawing of frozen soils and the loss of ice in the polar oceans, processes with implications for the planet’s global climate balance.
The cryosphere encompasses the regions of the Earth where water is present in the form of snow, ice, or frozen soil. It includes glaciers, the ice sheets of Greenland and Antarctica, sea ice, and permafrost, whose stability plays an important role in the global climate system.
Some losses could be irreversible
One of the main conclusions of the report is that many of the impacts associated with overshooting 1.5 °C may not be reversible on timescales relevant to human societies. In certain cases, the effects may even exceed the limits of adaptive capacity.
The authors therefore question the notion that temporarily surpassing 2 °C, 2.5 °C, or even 3 °C of global warming is a manageable option or preferable to the costs of urgently reducing greenhouse gas emissions.
The report seeks to distinguish processes that may already be compromised from those whose evolution can still be slowed or delayed through climate mitigation measures.
The presentation of the conclusions was also the subject of a briefing session organized by the Science Media Centre in the United Kingdom, with participation from specialists in glaciology, oceanography, and ice-sheet modelling.
Among the participants were James Kirkham, the scientific lead of the International Cryosphere Climate Initiative; Chris Stokes, glaciologist at Durham University; Matthew England, Professor of Oceanography at the University of New South Wales; and Chen Zhao, senior researcher in ice-sheet modelling at the University of Tasmania.
The document reinforces the importance of limiting global warming and accelerating emission reductions, warning that some changes in the cryosphere may have lasting consequences, even if global temperatures later decrease.
