Forces behind Greenland melting —Edward Hanna on global warming—Radio Ecoshock 2019-09-04
Channel: Stop Fossil Fuels
Date: 2020-04-03

UK climate Professor Edward Hanna explains the forces behind the disastrous melting on Greenland. When billions of metric tonnes of Greenland ice melted into the sea in 2012, a team of scientists said it was more than global warming. A pattern of atmospheric pressure zones called the North Atlantic Oscillation, or NAO, was boosting the big melt.


Now that super-melt on Greenland has happened again this summer of 2019. Hundreds of billions of metric tonnes of ice just poured off Greenland into the sea. Sea levels will rise measurably from what happened there just in July.


Show by Radio Ecoshock, reposted under CC License. Episode details at https://www.ecoshock.org/2019/09/climate-disaster-greenland-is-melting-new-show.html

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SHOW DETAILS
The size and speed of the Greenland melt this summer just shocked me. I thought “this is a major climate event” which the public cannot see.

Scientists including Edward Hanna, Xavier Fettweis and others just published the paper “Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet“. If that sounds obscure, we delve into the importance of understanding atmospheric circulation in the Atlantic  when we want to grasp the main drivers of the big melt on Greenland this year.

Get ready to meet a new friend: the NAO  the North Atlantic Oscillation. You learned about El Nino and La Nina because it affects weather where you live. Those are changes in the ocean. But another back-and-forth pattern in the atmosphere over the North Atlantic can change weather in New England, the Canadian Maritimes, Ireland the United Kingdom  and especially Greenland. It’s worth knowing how it works.

Dr. Edward Hanna is a Professor of Climate Science and Meteorology at the University of Lincoln, UK. We last spoke on Radio Ecoshock in January 2018 about a cold pattern in North American or European winters  due to changes in the Arctic. I like talking with Edward because he has clear explanations on a wide range of topics.


THE JET STREAM CAN REVERSE, WHICH IS HOW THE EUROPEAN HEAT WAVE HIT GREENLAND

Edward was able to clear up the confusion of how the record-breaking heatwave in July, where North African heat flooded northern Europe, managed to reach Greenland. Normally weather goes from West to East, due to the direction of spin of this planet. But this heat wave had to go the opposite way, from East to West! Hanna tells us that the Jet Stream can reverse and flow East to West, and that is how this July heat wave traveled. I knew the Jet Stream could wobble and form into north/south waves, but did not know it could entirely reverse itself at times.

The reversal of the Jet Stream is really a function of the North Atlantic Oscillation. When the NAO is “negative”, as it has been for most of 2019, the Jet Stream changes direction. That also happened in 2012 when there was another massive melt on Greenland.

Hanna tells us the Jet Stream/NAO is so complex that we cannot make models or projections for how these will operate over the rest of the century. He did send along the chart mentioned in the interview  showing the state of the NAO over the last century. You may need to read up a little science to understand this one.

[Chart of state of North Atlantic Oscillation in past century, courtesy of Edward Hanna , University of Lincoln.]

Hanna says that using the American Grace satellites, scientists have measured the gravitational loss of ice over Greenland during the last 17 years. The average loss every year has been about 250 billion metric tonnes of ice  almost all of it pouring into the sea. I asked if some evaporated into the atmosphere, adding to humidity. But Hanna says that would be a small amount, partly due to dry atmospheric conditions over cold Greenland. Cold air holds less water vapor.

Aside from the Greenland melt, satellite photos reveal we have lost about three quarters of the volume of the sea ice cover in the Arctic in late summer (September) since the 1970s. Last year and this year, there is an open patch of ocean just North of Greenland, something we did not expect to see. When sea ice moves away from the Greenland glaciers, this may speed up ice loss due to greater wave action, the arrival of warmer seas, and possibly coastal erosion. Loss of sea ice does not affect sea levels, but loss of ice that was sequestered on land certainly does.

When we see frightening storm surges, like the 18 feet of seas that rolled over the Bahamas during Hurricane Dorian  remember that because we are heating the planet, Greenland is continually adding to sea level rise. That relentless water from Greenland will force us to re-draw the maps of coastlines and retreat from coastal cities toward higher ground.