1.2 Tipping points in the cryosphere

Ricarda Winkelmann, Norman J. Steinert, David I. Armstrong McKay, Victor Brovkin, Andreas Kääb, Dirk Notz, Yevgeny Aksenov, Sandra Arndt, Sebastian Bathiany, Eleanor Burke, Julius Garbe, Ed Gasson, Heiko Goelzer, Gustaf Hugelius, Ann Kristin Klose, Petra Langebroek, Ben Marzeion, Fabien Maussion, Jan Nitzbon, Alex Robinson, Stefanie Rynders, Ivan Sudakow

Key Messages

  • Large-scale tipping points exist for the Greenland and Antarctic ice sheets, as inferred from multiple lines of evidence. Crossing these tipping points would lead to multi-metre sea level rise over hundreds to thousands of years.
  • There is evidence for localised and regional tipping points in glaciers and localised tipping points in permafrost, but evidence for large-scale tipping dynamics in sea ice, glaciers and permafrost is limited.
  • Some ice sheet tipping points could be close at current warming levels, with further warming increasing their likelihood. Localised tipping can already be observed for permafrost, and will worsen with further warming, along with non-tipping impacts.

Recommendations

  • Protect the cryosphere through urgent and ambitious phase-out of GHG emissions, as well as reducing co-drivers such as black carbon.
  • Reduce and/or better understand deep uncertainties, including: 1) instabilities in marine-based ice sheet dynamics; 2) the coupled dynamics of the Southern Ocean, sea ice, and ice shelf system; 3) integrating local glacier feedbacks into glacier modelling; and 4) the impact of abrupt permafrost thaw dynamics on the global permafrost-carbon feedback.
  • Invest in observations and improved modelling to constrain projected impacts for the next decades and beyond, and detect early warning signs of cryosphere tipping. Foster data sharing and international collaboration.
  • Co-design research, bringing together natural and social sciences and multiple knowledge systems, including Indigenous knowledge, to improve decision making under deep uncertainty, reduce risks and effectively adapt to unavoidable impacts.

Summary

Drastic changes in our planet’s frozen landscapes have occurred over recent decades, from Arctic sea ice decline and thawing of permafrost soils to polar amplification, the retreat of glaciers and ice loss from the ice sheets. In this chapter, we assess multiple lines of evidence for tipping points in the cryosphere – encompassing the ice sheets on Greenland and Antarctica, sea ice, mountain glaciers and permafrost – based on recent observations, palaeorecords, numerical modelling and theoretical understanding.

With about 1.2°C of global warming compared to pre-industrial levels, we are getting dangerously close to the temperature thresholds of some major tipping points for the ice sheets of Greenland and West Antarctica. Crossing these would lock in unavoidable long-term global sea level rise of up to 10 metres. There is evidence for localised and regional tipping points for glaciers and permafrost and, while evidence for global-scale tipping dynamics in sea ice, glaciers and permafrost is limited, their decline will continue with unabated global warming. 

Because of the long response times of these systems, some impacts of crossing potential tipping points will unfold over centuries to millennia. However, with the current trajectory of greenhouse gas (GHG) emissions and subsequent anthropogenic climate change, such largely irreversible changes might already have been triggered. These will cause far-reaching impacts for ecosystems and humans alike, threatening the livelihoods of millions of people, and will become more severe the further global warming progresses.

The scientific content of this chapter is based on the following manuscript in preparation: Winkelmann et al. (in prep.)

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