Is Antarctica melting?
This may be the most important scientific question facing humanity. If (when) the southern ice cap melts, it’s pretty much all over for human civilization.
So, there is a lot of attention to measuring and modelling Antarctica these days.
One of the outstanding questions is the effects of warmer climate. Warmer oceans and air generally mean more precipitation, which means more snow in Antarctica. At the same time, warmer water and air melts sea ice and glaciers along coasts, which means less ice in Antarctica. In addition, there are relatively short term changes, such as the El Nino cycles, which warm and cool in different years.
In short, there are plusses and minuses to the snow and ice every year, and Antarctica is a big place, where more than one thing happens. What is the overall trend of the ice cover?
There is only one way to find out, and that is to actually measure the ice and snow. And the only reasonable way to measure a whole continent is with Earth observing satellites.
This winter a team of scientists working at NASA’s Jet Propulsion Lab and other institutions report on a study that combined data from four ESA satellites to create a record of the ice depth in West Antarctica for the last 23 years. These measurements are from radar on the orbital satellite, which, in combination with careful measurement of the satellite position, gives a measure of the top of the ice.
The research team further adjusts the measurements for atmospheric pressure and buoyancy, to derive as accurate a measure as possible for 30 x 30 km patches over the period 1994 – 2017. These measures are correlated with other data representing the wind, ocean, and other weather.
The research finds that, over the period of the study, the ice has been steadily thinning, likely due to incursions of warmer ocean water under the ice shelf. Accounting for the general trend, the study examined the effects of the El Nino and Southern Oscillation. These periodic events intensify surface snow accumulation and ocean-driven basal melting. The combined result is “an overall height increase, but net mass loss”, because the basal ice lost is denser than the fresh snow.
In El Nino years, this effect adds to the long term trend, and in El Nina years, there is a slowing of ice loss. If such oscillations become more frequent, intense, or longer, there could be profound effects on the West Antarctic Ice.
The researchers note that these multi year trends can only be observed by continuous satellite coverage, i.e., a series of missions lasting decades. Unfortunately, the US has dropped its coverage, and ESA’s Cryosat-2 will end in a couple of years. We are going blind to what is happening in this crucial part of the world.
- Jonathan Amos, El Nino’s long reach to Antarctic ice, in BBC News – Science. 2018. http://www.bbc.com/news/science-environment-42614412
- F. S. Paolo., L. Padman, H. A. Fricker, S. Adusumilli, S. Howard, and M. R. Siegfried, Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation. Nature Geoscience, 2018/01/08 2018. https://doi.org/10.1038/s41561-017-0033-0