Friday, August 7, 2015

But, What About Antarctica?

Finishing out the big three ice reservoirs, let's talk about what is happening in Antarctica.

Now, first a word about the difference in the Greenland Ice Sheet (GIS) and the Antarctic land ice. The Arctic sea ice is just what it says, it is frozen ocean floating on top of the water. There are all sorts of important things about the sea ice, but one thing it does not affect is the sea level. The sea ice is already in the water and it will not affect the sea level when it melts. The GIS and the Antarctic ice sheets are not in the water - they are on land. As they melt, the water runs off into the oceans and is partly responsible for the rising sea level observed worldwide (heating the water also causes the sea level to rise). The more they melt in the future, the more the sea level will rise. We saw yesterday the GIS is melting at an alarming rate and that rate is continuously increasing. Now, let's turn our attention to Antarctica.

Unlike Greenland, Antarctica has two major ice sheets - the West Antarctic Ice Sheet (WAIS) and the East Antarctic Ice Sheet (EAIS). These two ice sheets combined are unbelievably large. The GIS, the second largest ice sheet in the world, is about 2.8 million cubic kilometers and covers an area three times the size of Texas. If all of that ice were to melt it would raise the world's sea level by about 7.2 meters. In comparison, the EAIS and WAIS combined have about 30 million cubic kilometers, more than ten times the volume of the GIS. The Antarctic ice covers an area greater than the continental U.S. and Mexico combined. If all of that ice was to melt it would raise the sea level by about 70 m. Together, these ice sheets contain 99% of all of the fresh water ice on the planet.

Now, I give those statistics to provide an idea of the mass of these ice sheets. I am in no way suggesting any of these three ice sheets are at risk of completely melting within the next few hundred years. But, what if only 10% were to melt? That would result in a rise in the sea level of about 7.7 meters (25.26 feet) and that would be enough to inundate every coastal area of the world. What if only 5% were to melt within the foreseeable future? That is still enough to drown all coastal areas with about 3.9 meters (12.8 feet) of sea level rise. The point is, we don't need a catastrophic failure of the ice sheets to have a catastrophe. For this reason, it is extremely important for us to pay attention to the ice sheets. There is no turning back at this point. The sheets will melt and we will have to pay many trillions of dollars as a result as the coasts are drowned. The question is, just when are we going to have to pay? Of course, Southern Florida is already being drowned.

So, we understand the state of the ice in Antarctica is important, but just what is the state of those ice sheets?

People skeptical of climate change frequently claim the total ice mass is increasing. This is a false claim. The total ice mass around the world is decreasing and decreasing at an alarming rate. However, they are correct if they limit their claim to Antarctic sea ice. This is a plot of the southern sea ice trend for September, the month of maximum extent in the south:

Source: NSIDC

This would be reassuring, if that were all there was to the story. Unfortunately, most of that ice melts in the southern summer, reaching a minimum of about 4.4 million square kilometers in March every year. Also, this plot is for only the sea ice and does not include the land ice. Here is a comparison plot of the mass for the both the GIS and the Antarctic ice:

Source: Penn State University Department of Geosciences

Comparison of these two plots shows bad news, good news, and more bad news.

The first bad news is obvious. The ice sheets in both Greenland and Antarctica are losing mass, i.e., they're melting. This is not good due to the data I provided above. Melting land ice raises sea levels and the two largest reservoirs of ice on land are both melting.

The good news is that Antarctica is not melting at fast as Greenland. Draw a tangent line and you can see the line for the Greenland data has a steeper slope than the line for the Antarctica data.

But, that brings up the second batch of bad news - the slope on both is increasing. This means the rate of melting for both land masses is increasing. That is really bad news.

The EAIS is gaining mass due to an increase in snow fall. Unfortunately, at the same time, the melting of the WAIS is accelerating. The melt increase in the west is more than enough to offset the snowfall gain in the east. The result is a net mass loss, and one that is increasing in rate. In fact, the loss rate in the west has doubled in the last six years.

So, while the winter sea ice extent has been increasing in recent years, the land is losing about 90 Gtons of ice per year. The complete picture is that the southern continent is losing ice - and it is losing it at an increasing rate.

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