Later today, President Barack Obama will tour the Exit Glacier at Kenai Fjords National Park with TV survivalist Bear Grylls. The president hopes that his made-for-TV moment will help persuade Americans and the rest of the world to endorse his climate change policies.
Yesterday, President Barack Obama addressed an international conference in Alaska at which representatives from many nations with interests in the Arctic region were meeting. In his remarks, President Obama mentioned his worries about how melting Alaskan glaciers are adding to sea level rise:
One new study estimates that Alaska's glaciers alone lose about 75 gigatons—that's 75 billion tons—of ice each year.
To put that in perspective, one scientist described a gigaton of ice as a block the size of the National Mall in Washington—from Congress all the way to the Lincoln Memorial, four times as tall as the Washington Monument. Now imagine 75 of those ice blocks. That's what Alaska's glaciers alone lose each year. The pace of melting is only getting faster. It's now twice what it was between 1950 and 2000—twice as fast as it was just a little over a decade ago. And it's one of the reasons why sea levels rose by about eight inches over the last century, and why they're projected to rise another one to four feet this century.
In January, 2015 Nature published a study that found that average sea level was rising between 1901 and 1990 at a rate of about 1.2 millimeter per year. After 1990, the rate increased to 3 millimeters per year.
In 2010, another Nature study reported that melting mountain glaciers from around the world were contributing about 0.5 millimeter annually to the increase in average sea level. Of that amount, the researchers calculated that Alaskan glaciers were adding 0.12 millimeter per year. The president was citing a newer study that found that runoff from melting Alaskan glaciers is more recently boosting sea level rise by 0.2 millimeter per year.
If this trend were to continue for the rest of the 21st century, how much higher would sea level be expected to rise? At a rate of 1.2 millimeters per year, average sea level would have gone up by 4.2 inches between 1901 and 1990. In 2013, the Intergovernmental Panel on Climate Change's Physical Science report estimated sea level rose from 1900 to 2010 at a rate of 1.7 millimeters per year which suggests a 7.4 inch increase over that period.
If Alaska's melting glaciers continued to contribute 0.2 millimeter per year to future sea level rise, that would amount to 0.7 inch by 2100. Overall, at a rate of 3 millimeters per year, sea level would rise by another 10.2 inches by 2100. If humanity managed to cope with an increase of 8 inches that president cited for the 20th century, it seems likely that much richer people living in 2100 will not be overly inconvenienced with 10 more inches.
On the other hand, climatologist James Hansen and 15 colleagues released an non-peer reviewed scenario in July warning that runaway climate feedbacks could boost average sea level by 5 meters (over 16 feet) in as few as 50 years. Interestingly, Hansen was worried about a 5 meter sea level increase more than 30 years ago.