Is it time to panic yet? Probably

Amid all the hoopla of the political season, which is worth panicking over on its own, a pair of recent articles turned up my climate panic meter (which was already pretty high).  First, the NY Times reports on a recent paper by leading climate scientists including James Hansen.   Hansen, a long time NASA researcher was one of the first to publicly state that climate change had started states bluntly that “we have a global emergency”

In the paper (full version, pdf –  abbreviated version, pdf) the researchers state that current models underestimate the impact that the rapidly melting polar ice cap and Greenland glaciers could have on the climate, and particularly on the magnitude of coming storms and degree to which the sea level will rise.

Our principal finding concerns the effect of meltwater on stratification of the high latitude ocean and resulting ocean heat sequestration that leads to melting of ice shelves and catastrophic ice sheet collapse. Stratification contrasts with homogenization. Winter conditions on parts of the North Atlantic Ocean and around the edges of Antarctica normally produce cold salty water that is dense enough to sink to the deep ocean, thus stirring and tending to homogenize the water column. Injection of fresh meltwater reduces the density of the upper ocean wind-stirred mixed layer, thus reducing the rate at which cold surface water sinks in winter at high latitudes. Vertical mixing normally brings warmer water to the surface, where heat is released to the atmosphere and space. Thus the increased stratification due to freshwater injection causes heat to be retained at ocean depth, where it is available to melt ice shelves

So, additional freshwater means that the cold water does not sink, the warmer water does not rise and release its heat, but rather stays at the ocean bottom, where it works to further increase the melt of the ice sheets, increasing the process.

deep water sea ice mixing-01

The result could be a significant slowdown, or possibly even a shut down of the global ocean circulation, altering or ending the modifying effect of this circulation on global climate.  The authors believe that in the event of a shutdown, sea levels could rise by as much as 9 meters (29 feet)  by the end of the century.  What would a 9 meter sea level rise look like?   Here’s New York:

sealevel

 

That’s not a pretty picture, and it is no better for San Francisco or Florida.  As the authors put it,   the rising sea levels would result in an “economic and social cost of losing functionality of all coastal cities (that) is practically incalculable.”   Along with the rising sea levels the authors also predict far more extreme storms.

So, what increase in temperature would cause this worldwide calamity?  Well, it could be as low as the 2 degree Celsius increase that the IPCC has deemed a “safe” level.

The modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level would 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 time scale of 50-150 years

.That’s where the other article really pushes my panic button.  FiveThirtyEight, my favorite statnerd site, asks the question “When Will The World Really Be 2 Degrees Hotter Than It Used To Be?”    The bottom line is that February 2016 might have already hit that point.  The reason we have to say *might* is that no one is 100% sure what worldwide temperatures were before 1850.  Estimates by Michael Mann suggest that the Earth may have warmed as much as 0.3 degrees C between 1850 and 1900.    Looking at this graph we can see the warming.

2015-12-23-1450832422-4386951-SchurerEtAlAnnotated

If you then take a look at how warm 2014, 2015, and now 2016 are, you see that we are perilously close to the 2 degree threshold, assuming we stop burning fossil fuels now.

holthaus-climate-1

 

But this assumes that the 2 degree threshold and a carbon level of 450 ppm  does provide safety, and Hansen argues that it does not.

  • First, our conclusions suggest that a target of limiting global warming to 2°C, which has sometimes been discussed, does not provide safety. We cannot be certain that multimeter sea level rise will occur if we allow global warming of 2°C. However, we know the warming would remain present for many centuries, if we allow it to occur (Solomon et al., 2010), a period exceeding the ice sheet response time implied by paleoclimate data. Sea level reached +6-9 m in the Eemian, a time that we have concluded was probably no more than a few tenths of a degree warmer than today.
  • Rapid phasedown of fossil fuel emissions is the crucial need, because of the millennial time scale of this carbon in the climate system
  • Third, we not only see evidence of changes beginning to happen in the climate system, as discussed above, we have associated these changes with amplifying feedback processes. We understand that in a system that is out of equilibrium, a system in which the equilibrium is difficult to restore rapidly, a system in which major components such as the ocean and ice sheets have great inertia but are beginning to change, the existence of such amplifying feedbacks presents a situation of great concern. There is a possibility, a real danger, that we will hand young people and future generations a climate system that is practically out of their control. We conclude that the message our climate science delivers to society, policymakers, and the public alike is this: we have a global emergency. Fossil fuel CO2 emissions should be reduced as rapidly as practical.

Here is Hansen explaining the paper:

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