Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous
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...
| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf |
| Summary: | 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 CO<sub>2</sub>, 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 CO<sub>2</sub> 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 North Atlantic and Southern oceans increases
atmospheric temperature gradients, eddy kinetic energy and baroclinicity,
thus driving more powerful storms. The modeling, paleoclimate evidence, and
ongoing observations together imply that 2 °C global warming above
the preindustrial level could be dangerous. Continued high fossil fuel
emissions this century are predicted to yield (1) cooling of the Southern
Ocean, especially in the Western Hemisphere; (2) slowing of the Southern
Ocean overturning circulation, warming of the ice shelves, and growing ice
sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic
overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise,
reaching several meters over a timescale of 50–150 years. These
predictions, especially the cooling in the Southern Ocean and North Atlantic
with markedly reduced warming or even cooling in Europe, differ
fundamentally from existing climate change assessments. We discuss
observations and modeling studies needed to refute or clarify these
assertions. |
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| ISSN: | 1680-7316 1680-7324 |