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SYFY WIRE Bad Astronomy

Our planet is melting at both ends: Arctic and Antarctica hit record low ice extents

By Phil Plait

[Art credit: Shutterstock / Barnaby Chambers]

Every year, the amount of ice floating in the Arctic Ocean around the Earth’s north pole melts in the summer and regrows in the winter. It generally reaches its maximum extent in early March, and it did so this year on March 7.

The problem: This was the lowest maximum ever seen since satellite records began 38 years ago.


By the numbers, on March 7 the Arctic sea ice extent* was 14.42 million square kilometers, which was about 100,000 square km below the previous record low maximum extents in 2015 and 2016 (those two years both had record low maxima, so close to each other they were in a statistical dead heat). That’s also nearly a half million square km less than the average maximum extent measured from 1981 – 2010 ... an area larger than the state of California.

This also makes it the third year in a row we’ve had a record low maximum extent.

This is extraordinarily troubling. Arctic sea ice has been declining so rapidly it’s been labeled a “death spiral,” and for good reason. Some computer models show we may get an ice-free summer Arctic Ocean as early as 2040.

So, why did the northern ice drop so low this year, and why is that bad?

The culprit is actually a combination of factors. For one, by September of last year —the time when the ice reaches its minimum extent after summer melting— the amount of ice in the Arctic was also lower than usual. That means it was already starting from a deficit.

Also, the temperatures in the Arctic were unusually high this past winter. And by “unusually” I mean “holy crap” high: Vast stretches of the Arctic reached temperatures a staggering 20°C (36°F) above normal. The waters were extremely warm, too, preventing ice from forming easily. On top of all that, a series of storms churned up the water, slowing ice growth.

Having said that, let me correct myself. I said there were a combination of factors contributing to this. But they, themselves, almost certainly have a common basis: global warming. While it’s hard to pin down any one factor to warming, taken together, it’s clear that this is the root cause of the ice melting. We see nearly the entire planet warming over time, and the Arctic is even more sensitive to this, with temperatures rising twice as fast as the planetary average.

This has caused a series of record lows, both in maxima and minima (2012, the actual record low minimum, also had other contributing factors). Not only that, but the volume of ice is dropping precipitously due to thinning; the ice isn’t as thick as it once was. This amplifies seasonal changes, since thin ice melts and grows faster, and it means that every year, very old ice is disappearing as well.

Arctic sea ice extent for March 2017

This comes on top of the Antarctic summer sea ice dropping to a record low at almost exactly the same time. Over the past few years, southern sea ice has increased a small amount — probably due to warmer air being able to hold more moisture, increasing snow fall in some areas. But this new loss over the past two years or so has been very dramatic. It’s unclear what the proximate cause of that is. It may just be a really large statistical deviation; it’ll take a couple of more years of measurements to know better.

With or without sea ice, the ice lost from the land of Antarctica is a staggering 130 billion tons per year, and that is very much due to global warming

This is all very bad. There exists a natural system on our planet that distributes heat around, called the Atlantic Meridional Overturning Circulation. In a nutshell, cold water from the Arctic flows south to the Equator, warms up, and flows back north, like a gigantic conveyor belt in the Atlantic Ocean. Weirdly, this flow depends on the salinity of water, or how salty it is. Fresh water is less dense than salty water, and floats on top of it. This acts like a lid on the circulation, blocking the warmer water from reaching the pole, disrupting the heat flow.

When the ice in the Arctic melts, it adds a lot of fresh water to the Atlantic. From just 2011 to 2014 Greenland alone lost a trillion tons of ice to warming. That’s why this is so concerning. This circulation is the cause of a lot of weather in the northern hemisphere. Screwing with it means screwing with our weather.

The warm Arctic waters also weaken the jet stream, the eastward flow of Arctic air, sometimes called the “polar vortex”. When the stream weakens, deep meanders can occur, dropping air farther south, blasting the US with frigid Arctic temperatures.

It’s weird to think global warming can cause such chilling weather in the US. A better way to think of it is that warming is causing the climate to destabilize. You get extreme weather, and in different places you get droughts, torrential rains, stronger cyclones, increased severe tornado outbreaks, and more.

It’s rare in science you can say something with anything near 100% certainty. And yet, here we are: Climate change due to global warming is real, and it’s because of us. We add 40 billion tons of carbon dioxide, a greenhouse gas, into the air every year. This upsets the Earth’s natural heat balance, allowing a small amount of warming sunlight to stick around rather than get radiated out into space.

Our planet is heating up, humans are the reason, and we know this to be a fact. Yet our politicians in charge deny this very simple and critical truth [the House Committee on Science, Space, and Technology just announced a hearing on climate science for next week, and invited four scientists to testify; one is realist Michael Mann (invited by the minority Committee members, of course) and the other three are well-known figures who downplay the effects of global warming on climate], even going so far as to deny the incredibly basic science about greenhouse effects we’ve known for over a century.

We’ll be seeing more statements and legislation coming from this science-denying Congressional majority as time goes by. When it happens, I urge you to contact your Senators and Representatives. Let them know that climate change is real, it’s now, and not only is it a threat national security, but denial of it is a national security as well, and we have to do what we can to stop it.

* Scientists use the term “extent” to measure the amount of sea ice. It’s defined as an area —say, a square kilometer of Arctic real estate, though the size of bin varies— where more than 15% is covered by ice.