Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Hansen, James, Sato, Makiko, Hearty, Paul, Ruedy, Reto, Kelley, Maxwell, Masson-Delmotte, Valerie, Russell, Gary, Tselioudis, George, Cao, Junji, Rignot, Eric, Velicogna, Isabella, Tormey, Blair, Donovan, Bailey, Kandiano, Evgeniya, von Schuckmann, Karina, Kharecha, Pushker, Legrande, Allegra N., Bauer, Michael, Lo, Kwok-Wai
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications (EGU) 2016
• Subjects: Greenland; Southern Ocean; Antarc*; Antarctica; Ice Sheet; Ice Shelf; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/31954/; https://oceanrep.geomar.de/id/eprint/31954/1/acp-16-3761-2016.pdf; https://oceanrep.geomar.de/id/eprint/31954/2/acp-16-3761-2016-supplement.pdf; https://doi.org/10.5194/acp-16-3761-2016

We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the ...