The Status of the Greenland Melt Season

Although it is located in the Arctic Region, the Greenland ice sheet (GIS) is much different than the Arctic sea ice. For one thing, it is on land and not in water. But, it is also much thicker. The average thickness of the GIS is about 7000 ft (1.4 miles) and about 10,000 ft (1.9 miles) at the thickest. It covers an area of over 660,000 square miles (2.5 times the size of Texas) and is the second largest ice sheet in the world, after only the Antarctica ice sheet. There is enough ice stored in this ice sheet to raise the world’s ocean level by about 24 feet if it all melted.

Naturally, we are concerned with the conditions of the GIS. First, because it is a factor in the world’s weather and most North Atlantic icebergs originate here, but because it is a indicator of how the climate is going. Unfortunately, we see one more indicator of global warming going on here.

We would expect to see melting and freezing in the ice sheet due to the seasons, and that is what we see. Some of the ice melts in the summer and then snow is deposited in the winter. In addition to that, we also see that the amount of melt in the summer is greater than the amount of deposit in the winter. Take a look at this graph here:

https://i2.wp.com/polarportal.dk/fileadmin/polarportal/mass/Grace_curve_La_EN_20140100.png
Source: Polar Portal

This shows the mass of the GIS over a period of more than ten years and we can see that the mass has a seasonal change, just as we expected. It increases in the winter and decreases in the summer. No controversy there. We can also see that the total mass has been declining for the entire period. Before 2004, the total mass was over 1000 gigatons (billion tons) above the long-term average. By 2014, this total mass had dropped to about 1800 gigatons below the average. That is a change of over 2800 billion tons of ice in about 10 years. Not good.

By the way, this occurred during the period when deniers have insisted there is no global warming. Once again, we see facts put the lie to their claims.

So, how are things going this year? Again, not good. Take a look here:

https://i1.wp.com/nsidc.org/greenland-today/images/greenland_melt_area_plot.png
Source: NSIDC

This graph shows the percentage of the ice sheet that is melting at any given point of time compared to the long-term melt extent average (the dotted line). This shows us that the melt extent started out pretty close to average during the early part of the year. There was a spike in May, but that is not too alarming by itself. We expect to see the graph zig-zag back and forth as the weather changes. However, we are seeing much more than just a zig-zag starting with early June. The level of melt extent has shot up to the vicinity of 40%. That means about 40% of the ice sheet is melting right now. That percentage is already far in excess of the average maximum value which typically occurs in late July and reaches about 25%. 

And the forecast for additional melting? It is difficult to make a good forecast, but there is one thing that troubles me. Look at this plot.

https://i1.wp.com/polarportal.dk/fileadmin/polarportal/surface/Alb_SM_EN_20140613.png
Source: Polar Portal

This plot shows the albedo relative to the long-term average. Albedo is the measure of how well something reflects light. Something with an albedo of 1 (or 100) is a perfect reflector. An albedo of 0 means it reflects nothing at all – it would be perfectly black. Red areas on the above plot show where the current albedo is lower than the long-term average. Blue areas show where the current albedo is higher than the long-term average. The lower the albedo, the worse the surface reflects light and the more light it absorbs, leading to increased melting. Blue areas mean the albedo is higher and reflects light better, so melting would be reduced compared to the long-term average. The plot is not encouraging. There are some areas that are colored blue, but some shade of red dominates the plot area.

What could cause the lower albedo? There are two things that have been linked to this. One is soot from fires, the other is melt ponds. As we have more forest and wild fires due to climate change, the soot is carried on the winds and some of it is deposited on the GIS, lowering the albedo. Then, as the ice melts and forms ponds of water, the albedo drops even more because ice is a good reflector, but water is a good absorber.

Combining this data and the melting trend so far makes me think this will be a bad year for ice melt on Greenland. The summer of 2012 was the record bad year, hopefully we won’t get that bad.

Advertisements