Friday, June 1, 2012

Greenland record temperatures: How clue are we to the tipping point?

One of the few blogs I read consistently is Dr. Jeff Masters' WunderBlog. His focus is on hurricanes, but he also reports the latest in climatological and meteorological news. Yesterday, his key news was that record May temperatures have been experienced in Greenland.

Why is this so important? Because the future of civilization as we know it is potentially tied up in the Greenland ice sheet. People talking about climate change tend to focus on warmer summers, more droughts, extreme hurricanes etc. These are bad enough. However if Greenland melting accelerates, several drastic consequences could come to pass:
  • Sea level rises on the order of tens of meters, destroying the cities and agricultural lands of billions of people
  • Drastic shifts in climate, potentially freezing Europe by shutting down the North Atlantic Oscillation.
Two very interesting articles show that the Greenland situation is highly complex. There are huge volumes of information to absorb from the articles, but I would like to draw attention to two quotes:

To oversimplify somewhat, Greenland is unstable to increases in temperature, because it exists purely through its altitude maintaining low temperatures. If the Greenland Ice Sheet were somehow removed, it would not return.
Realistically, they mean it would not return until another ice age.

The net effect of these processes [melting ice removing gravitational attraction from surrounding seawater] is that sea-level rise occurs faster in areas further away from the source of the melting. For example, in the case of melting Greenland ice, there would be less sea- level rise than the global average in the North Atlantic, near to Greenland.
So if Greenland melts, who would be inundated the worst? This is complex and research is still ongoing: Density differences due to salinity and differing expansion of cold and warm water will be one influence; patterns of circulation (subject to rapid change) will have an effect, gravity mentioned above will have an effect and so will subsidence and rising of certain land areas due to geological action and rebound from the last ice age. It would seem, however, that areas of southern Asia with vast populations near sea level are going to be hit the worst. 

How far off is this? Again there I have read many estimates. A meter or two in the next century would be possible, and tens of meters in this millennium quite conceivable. But even if it takes two centuries to get to a meter that is still utterly unacceptable.

One thing is clear: Uncertainty will continue for multiple reasons: We don't know when the 'tipping points' will occur (e.g. shutdown of ocean circulation, feedback leading to accelerating melting), we can't run a controlled experiment, we can never get all the data we might like, and we can't know what socio-economic or technological impacts occur (e.g. reductions in fossil fuel use due to economic depression, technological advances etc., or the inverse). Conservative politicians and climate deniers feed on uncertainty, claiming the science is not settled. But what is not settled is the timing, not the certainty of drastic change if we don't take drastic action.

It is hard for politicians to think even ten years in the future. But we really must think hundreds and thousands of years into the future because we hope to have descendants around then. The further we get into the future, the more absolutely certain we are of devastation if we continue policies that will lead to climate change. 


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