photo: Julie G/Creative Commons
James Hansen may be as much as a celebrity as one can be in the world of climate change science, so when he and colleague Makiko Sato say that we're in for multi-meter sea level rise by 2100 you have to pay attention, even when that prediction falls well outside the range predicted by many other climate scientists. Climate Progress has its usually-thorough summary of Hansen and Sato's new work, but here is the gist of it:The new draft paper says, "[Business as usual] scenarios result in global warming on the order of 3-6°C. It is this scenario for which we assert that multi-meter sea level rise on the century time scale are not only possible, but almost dead certain."
Why? Based on observations from the Eemian and Holocene, we're approaching a tipping point after which ice sheet disintegration in the Arctic and Antarctica is inevitable, even though at the moment we're seeing more evidence of ice loss in the Arctic.
Arctic response to human-made climate forcing is more apparent than Antarctic change, because the response time is quicker due to the large proportion of land are and Greenland's temperature, which allows a large expansion of the area with summer melting.
If that ice melts (and without major reductions in emissions, in light of this research that that will happen) then you get the multi-meter sea level rise. Others have forecast such events, but not in such a quick time scale.
Why the quicker time scale? I'll just quote the same passage that Climate Progress does on the effect of an 'albedo flip':
Summer melting on lower reaches of the ice sheets and on ice shelves introduces the "albedo flip" mechanism (Hansen et al., 2007). This phase change of water causes a powerful local feedback, which, together with moderate global warming, can substantially increase the length of the melt season. Such increased summer melting has an immediate local temperature effect, and it also will affect sea level, on a time scale that is being debated, as discussed below.
We suggest that the warmest interglacials in the past 450,000 years were warm enough to bring the "albedo flip" phenomenon into play, while interglacials in the earlier part of the 800,000 year ice core record were too cool for surface melt on the Greenland and Antarctic ice sheets and ice shelves to be important. Increased surface melting, loss of ice shelves, and reduction of summer and autumn sea ice around the Antarctic and Greenland continents during the warmest interglacials would have a year-round effect on temperature, because the increased area of open water has its largest impact on surface air temperature in the cool seasons.
Further, we suggest that the stability of sea level during the Holocene is a consequence of the fact that global temperature remained just below the level required to initiate the "albedo flip" mechanism on Greenland and West Antarctica.
One implication of this interpretation is that the world today is on the verge of a level of global warming for which the equilibrium surface air temperature response on the ice sheets will exceed the global mean temperature increase by much more than a factor of two.
Here's the whole original paper: Paleoclimate Implications for Human-made Climate Change [PDF]
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More on Sea Level Rise:
Mainstream Media Has Accurately Portrayed Sea Level Rise Projections For Past 20 Years
Two Meter Sea Level Rise Now Inevitable - But How Fast Will It Happen?
Get Ready for 7 Foot Sea Level Rise by 2100 + Antarctic Glacier Past Tipping Point