Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous J. Hansen1, M. Sato1, P. Hearty2, R. Ruedy3,4, M. Kelley3,4, V. Masson-Delmotte5, G. Russell4, G. Tselioudis4, J. Cao6, E. Rignot7,8, I. Velicogna7,8, E. Kandiano9, K. von Schuckmann10, P. Kharecha1,4, A. N. Legrande4, M. Bauer11, and K.-W. Lo3,4 1Climate Science, Awareness and Solutions, Columbia University Earth Institute, New York, NY 10115, USA 2Department of Environmental Studies, University of North Carolina at Wilmington, North Carolina 28403, USA 3Trinnovium LLC, New York, NY 10025, USA 4NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA 5Institut Pierre Simon Laplace, Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS-UVSQ), Gif-sur-Yvette, France 6Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China 7Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109, USA 8Department of Earth System Science, University of California, Irvine, California, 92697, USA 9GEOMAR, Helmholtz Centre for Ocean Research, Wischhofstrasse 1–3, Kiel 24148, Germany 10Mediterranean Institute of Oceanography, University of Toulon, La Garde, France 11Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, 10027, USA
Abstract. There is evidence of ice melt, sea level rise to +5–9 m, and extreme storms in the prior interglacial period that was less
than 1 °C warmer than today. Human-made climate forcing is
stronger and more rapid than paleo forcings, but much can be learned by
combining insights from paleoclimate, climate modeling, and on-going
observations. We argue that ice sheets in contact with the ocean are
vulnerable to non-linear disintegration in response to ocean warming, and we
posit that ice sheet mass loss can be approximated by a doubling time up to
sea level rise of at least several meters. Doubling times of 10, 20 or 40
years yield sea level rise of several meters in 50, 100 or 200 years.
Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt
and ice sheet discharge. Our climate model exposes amplifying feedbacks in
the Southern Ocean that slow Antarctic bottom water formation and increase
ocean temperature near ice shelf grounding lines, while cooling the surface
ocean and increasing sea ice cover and water column stability. Ocean surface
cooling, in the North Atlantic as well as the Southern Ocean, increases
tropospheric horizontal temperature gradients, eddy kinetic energy and
baroclinicity, which drive more powerful storms. We focus attention on the
Southern Ocean's role in affecting atmospheric CO2 amount, which in
turn is a tight control knob on global climate. The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for
natural CO2 change, thus the time scale for paleo global climate, ice
sheet and sea level changes. This millennial carbon cycle time scale should
not be misinterpreted as the ice sheet time scale for response to a rapid
human-made climate forcing. Recent ice sheet melt rates have a doubling time
near the lower end of the 10–40 year range. We conclude that 2 °C
global warming above the preindustrial level, which would spur more ice
shelf melt, is highly dangerous. Earth's energy imbalance, which must be
eliminated to stabilize climate, provides a crucial metric.
Citation: Hansen, J., Sato, M., Hearty, P., Ruedy, R., Kelley, M., Masson-Delmotte, V., Russell, G., Tselioudis, G., Cao, J., Rignot, E., Velicogna, I., Kandiano, E., von Schuckmann, K., Kharecha, P., Legrande, A. N., Bauer, M., and Lo, K.-W.: Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous, Atmos. Chem. Phys. Discuss., 15, 20059-20179, doi:10.5194/acpd-15-20059-2015, 2015.
IF 5.053
SNIP 1.574
SJR 3.022
h5-index 92