World - COMMENTARY COP28: Earth’s frozen zones are in trouble – we’re already seeing the consequences
As this year’s UN climate summit (COP28) gets under way in Dubai, scientists studying Earth’s frozen regions have been delivering an urgent call for action to policy makers. But is anyone listening?
Throughout 2023, we have been warning of an impending series of crises occurring in the cryosphere – polar ice sheets, ice shelves, sea ice, mountain glaciers and permafrost.
The Scientific Committee on Antarctic Research (SCAR) released its decadal synopsis on the state of Antarctic climate change and ecosystems. It led the recent Antarctic Treaty meeting to issue the Helsinki Declaration to highlight that significant observed changes in Antarctica influence climate impacts globally.
And this month, a State of the Cryosphere 2023 report assessing the most recent science warned that even 2°C of warming would trigger irreversible loss of ice sheets, glaciers, snow, sea ice and permafrost, with disastrous consequences for society and nature.
I have contributed to all three documents. Some of the most dramatic changes are occurring in Antarctica and the Southern Ocean, including extreme heatwaves, record lows in sea ice and the emergence of an amplified warming pattern across the entire Antarctic continent.
These changes are melting Antarctica’s ice sheet and delivering vast quantities of freshwater to the ocean. This in turn drives an accelerating rise in shorelines around the world.
Polar warming is also contributing to drought and wildfires in Australia, floods in New Zealand and extreme weather at every latitude.
Breaching planetary thresholds
In July this year, average monthly global temperatures breached 1.5°C above pre-industrial levels for the first time. With a large El Niño event underway in the Pacific, 2023 is virtually certain to be the hottest year on record.
The World Meteorological Organisation predicts the world is on track to exceed the Paris target to keep warming below 2°C within the next five years, on an annual basis.
Scientific evidence is clear that due to the current trajectory of human-derived greenhouse gas emissions, the polar regions will continue to warm at rates of up to four times the global average.
This is because of self-reinforcing feedbacks, such as those related to retreating sea ice. The more sea ice melts, the more energy the darker ocean surface absorbs, in turn leading to more land ice melting and the potential crossing of tipping points linked to temperature thresholds close to 1.5-2°C of global warming.
There are two key planetary thresholds in the polar regions. Firstly, thawing permafrost in the Arctic has the potential for widespread release of methane and carbon dioxide into the atmosphere, further enhancing global heating.
Secondly, meltdown of up to two-thirds of Antarctica’s ice sheet may become irreversible, locking in multi-metre sea-level rise for generations to come even if the warming were to stop or reverse after peaking before 2100.
Dramatic consequences at all latitudes
The Southern Ocean has taken up most of the heat from global warming (70%). This excess energy will remain in the ocean for centuries and continue melting parts of the coastal fringes of Antarctica from underneath.
The amplified polar warming is accelerating the melting of ice sheets. They are now the largest contributors to rising global sea levels. But they respond slowly, trapping heat and releasing it over long timescales. Sea-level rise will therefore continue for centuries to come, even with net zero emissions.
Projections show substantial differences between low- and high-emissions scenarios, especially after 2050. A high-emissions scenario could result in multi-metre sea-level rise for coming centuries. This includes a “low likelihood, high impact” scenario in which two metres by 2100 cannot be ruled out due to rapid loss of Antarctica’s fringing ice shelves and consequent melting of the ice sheet.