Imagine if the amount of lake ice in Minnesota and Wisconsin declined so much over several generations that some lakes didn't ice over at all.

Something similar is happening in the Arctic when it comes to ocean ice. The National Snow and Ice Data Center (NSIDC) just announced that this winter they observed the second-lowest amount of Arctic sea ice on record. The four lowest seasonal maxima have all occurred during the last four years.

"It's the North Pole -- who cares?" is a reasonable question to ask.  The answer is that what happens at the North Pole doesn't stay at the North Pole.

First, it's helpful to understand the term albedo. Albedo is a fancy word for a concept you are already familiar with: snow and ice reflect a lot more sunlight than grass or bare ground do.  The albedo of ice and snow is why winter-sports enthusiasts sometimes get sunburns in the winter.

When reflective arctic sea ice isn't as expansive as it once was less sunlight is bounced back into space; that can lead to darker land and water absorbing more of the sun's energy, which leads to warming in turn.

These long-term temperature differences can change the Earth's large-scale winds - or jet stream - resulting in a change in weather patterns in the Midwest and across the globe.

Recent research shows that average temperatures at the North Pole are warming twice as fast as the rest of the globe, a phenomenon that NASA calls "Arctic Amplification."

If you're wondering, during Southern Hemisphere summer on February 20 and 21, Antarctic sea ice also reached the second-lowest extent on record.  In tracking sea-ice extent in both hemispheres the NSIDC says:

"Ice in the Antarctic is highly variable from year to year—much more so than in the Arctic. Low 2011 values were followed by record or near-record highs in 2013, 2014, and 2015. This was then followed by record or near-record lows in 2017 and this year."

Climate is changing faster in the Northern Hemisphere than it is in the Southern Hemisphere because there is more land area in the Northern Hemisphere.  Middle-school physics tells us that it takes more energy to warm water than it does to warm land, and so average temperatures have been going up more slowly in the Southern Hemisphere. 

The bottom line is that disappearing sea ice is a symptom of climate change, which is happening now, is human caused, is having economic impacts today, and can be fixed if we work together.

This blog was inspired by a March 2018 article by my partners at Climate Central, and draws on information from NOAA, NASA, and the National Snow Ice Data Center at Colorado University.