Wednesday, December 17, 2014

Greenland Mass Loss is Bad and Getting Worse

Greenland is melting, which is not good. Recent studies indicate it is even getting worse, too. Take a look at the mass of the Greenland Ice Sheet (GIS) and see what has been going on. This is plot of the GIS mass and comes from the Danish Polar Portal site:

Source: Polar Portal

This graph is of data obtained by the GRACE satellite and shows the change in mass due to the small change in the gravity field. It is easy to see the total mass of the the GIS is declining. The upticks in the graph show the mass is growing in the winter and the down ticks show the mass is declining in the summer. Hopefully, that is not a surprise nor should there be any controversy with that. But, what we see is that over a period of time the mass is decreasing more during the summer melt season than it is growing during the winter freeze season. As a result, the overall mass is decreasing on an annual basis.

But, there is something even more significant. Take a trend line for the period of about 2003 - 2009. Then, take another trend line for the period of 2010 - 2014. The second trend line is much steeper than the first. That means the rate of decline was much greater in the second period than in the first. Is the rate of decline accelerating? The data suggests it is and is something we will need to monitor. But, it gets worse.

A recent study used NASA laser altimeter data to study the entire surface of the ice sheet. That study found the estimate of mass loss was actually low and the amount lost during the 2003 - 2009 period amounted to 243 metric gigatons per year. This mass loss was enough that it contributed .68 millimeters of sea rise per year. During that one, seven-year period, Greenland melt water raised the oceans by about 5 millimeters (about .2 inches) all by itself. Projections are that melt water from the GIS will add about 9 inches (22 centimeters) to the sea level by the year 2100. That figure does not include melt water from Antarctica and glaciers.

Meanwhile, another study has been released that also indicates the melt rate is not going in our favor. The second study has to do with the melt ponds on the surface of the ice. As the ice melts in the summer, not all of it can flow away and it forms lakes on top of the ice. Sometimes, these lakes will refreeze when winter returns. Sometimes, the ice will crack and the water can flow into the interior of the ice sheet in a matter of a few hours. Either way, melt ponds are not good. Ponds are darker than ice and absorb more sunlight than the bright ice. The more ponds you have, the more heat gets absorbed, leading to more melting. If the water flows into the interior then it transports that heat into regions that would otherwise be insulated. That heat then gets trapped inside instead of being able to radiate into space. One scenario leads to more melting. The second scenario leads to a lot more melting.

The study released some interesting data. The melt ponds normally do not form outside of a band along the edge of the ice sheet. Away from the coast, it remains cold enough through most summers to prevent melt ponds from forming. But, that melt pond band has grown by 35 miles (56 kilometers) since the 1970s and is expected to have doubled by the middle of this century. Meaning, the melt rate will accelerate.

This changing nature of the melt ponds has not been included in projections, so the authors of this study believe the projections are low and we can expect to see even larger amounts of ice melt than we previously thought we would.

All in all, the data is not looking good for anyone in low-lying coastal areas. That's only a few billion people.

Once again, tell me how global warming is good for us.

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