Ask the weather guys: How is the Arctic ice pack going? | Local weather

Q: How is the Arctic ice pack going?

A: The extent of sea ice in the Arctic is one of the diagnostic signs of global warming, particularly its minimal annual extent that often occurs around the autumnal equinox.

The extent of sea ice is directly measured by satellite data and is available via the National Snow and Ice Data Center, supported by NASA, at the University of Colorado-Boulder.

This year's low took place on September 19 and September 23, when the sea ice extent shrank to 1.77 million square miles, the sixth record-breaking summer minimum. 40 years old.

The 2018 minimum was 629,000 square miles below the 1981-2010 average, continuing a trend that a portion of Maryland and New Jersey-sized ice has been lost each year over the last four decades.

The 12 smallest summer minimums have all occurred in the last 12 years.

This is another unequivocal signal of progressive warming happening around the world.

Sea ice is a very important aspect of a positive feedback that can accelerate this warming.

As the ice cover decreases each year at the end of the summer, the amount of free water increases. Free water absorbs solar radiation much better than highly reflective ice covered with snow.

Therefore, the freezing of water in the pack ice in winter is delayed by the increased absorption of the sun. This leads to finer ice at the edge of the ice cap at the end of the winter, which facilitates melting in the summer to expose even more free water at the end of each successive hot season.

Ongoing research is examining the influence of this systematic reduction of Arctic sea ice on changes in atmospheric circulation fall / winter in the northern hemisphere.

Steve Ackerman and Jonathan Martin, professors in UW-Madison's Department of Atmospheric and Oceanic Sciences, are invited to WHA radio (970 AM) at 11:45 am on the last Monday of each month.