Melting of the Greenland Ice Sheet: Short Term Event or Long Term Climate Change?
Science news has been buzzing lately about imagery from three satellites showing indications of melting snow and ice on Greenland. As we all learn in science classes, Greenland is basically a very large sheet of ice, so to see such melting as this is quite striking. Definitely newsworthy.
I was certainly interested in learning more. My master’s thesis 10 years ago was in remote sensing meteorology, meaning I was taking a measurement of one item and applying algorithms to translate it into another data point. In my case I was working with GPS error data that was converted into a surrogate measurement of water vapor in the atmosphere; that data could be used to estimate humidity.
In the case of this recent news, satellites are using the microwave portion of the electromagnetic spectrum to measure reflectivity of the earth’s surface and applying algorithms to translate it into melted ice. It’s pretty accurate, no argument there.
From 8 July to 12 July, Greenland’s surface transitioned from approximately 40% melted water to approximately 97%. That’s a lot of melting in not a lot of time. The first indications were seen while analyzing radar reflectivity data from the Indian Space Research Organisation’s (ISRO) Oceansat-2 satellite, then it was verified with temperature data from the American Moderate-resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites. Scientists at NASA Goddard Space Flight Center verified that the MODIS data indicated unusually high temperatures during the second week of July over the landmass; these conditions coincided with an upper air high pressure system, the same large-scale phenomena that has caused the recent heat waves in the eastern United States.
A third satellite verification was brought in, thanks to analyses from the Special Sensor Microwave Imager (SSM/I) on the U.S. Air Force’s Defense Meteorological Satellite Program (DMSP) satellites. Several of the channels on the SSM/I imager are tuned to sense data through the atmosphere all the way to the surface of the earth, detecting whether the surface is dry, flooded, forested, ocean water, iced-over or thawed.
Finally, on-site weather observations at research stations throughout Greenland have verified the warmer temperatures that correlate with the surface ice melting.
While this news is very significant in the climatology and glaciology community, some are going step further and are attempting to connect it with other indicators of climate change. The definitive answer to that question is not clear and many news outlets are doing a good job providing a balanced view of this news. Several points should be made about this news:
- The media is using the term “unprecedented”. In fact, the NASA press release about this is using the term “unprecedented”. What is “unprecedented” about this news is the ability for the satellites to see the warming, and the speed with which that data can be seen by the scientists. The warming itself certainly is not unprecedented. Conditions supporting this were last measured directly in 1889, and ice core samples, which have the ability offer evidence of climate conditions over 100,000 years old, have indicated that vast warming occurs approximately every 150 years. For this to happen in 2012 is not unreasonable.
- The satellites taking the measurements require some understanding regarding their capabilities and limitations. Greenland is unique in that there is very little else besides rock, ice, snow and water for measurement. So I’m more confident in Greenland’s data than I would be in many other locations. Sand, loam, clay, forests and urban areas can often make detection more difficult. The two satellites mentioned above that measure reflectivities of the land mass surface (Oceansat-2 and SSM/I) are only measuring a few centimeters deep. It essentially measures data that translates into water on the surface. So even if there’s a slight sheen of water for the satellites to sense, there could still be miles of ice directly underneath. As soon as the temperatures dip below freezing again, it will freeze again.
- Melting happens on Greenland every year at this time. The melting itself is not what’s unusual. It’s the amount of melting. Temperatures have been measured as high as 42F this July at locations that rarely exceed freezing temperatures year-round, according to NASA scientist Tom Wagner. Some media outlets are coming up with some pretty crazy headlines that might make readers believe Greenland has never experienced melting before.
- Because we have more data than ever before to assess this current melting period, it’s difficult to compare it to the very limited data — point data, if you will — of all the previous melting events. Ice cores and temperature measurements are many kilometers apart.
So I pose the question to the readers: Is this a short-term event, similar to the “derecho” that transited across the eastern Continental U.S. on June 29th, or is this a pointer to long-term climate change? My opinion: we don’t have enough data to make that connection. I’m not debunking the connection, nor am I proclaiming this a symptom of global warming.
What’s your opinion?