This photo taken Aug. 4, 2012, shows tourists walking to Exit Glacier in Kenai Fjords National Park just outside Seward, Alaska.  (AP Photo/Mark Thiessen)

This story has been updated.

In Anchorage Monday, President Obama gave a rousing speech about just how dramatically global warming is transforming Alaska and the Arctic more broadly.

That included getting pretty nerdy when it comes to the science of Arctic change. For instance, the president used the phrase “negative feedback loop” to describe how wildfires can worsen the loss of permafrost, leading to more global warming and thus, more wildfires. It’s “a cycle — warming leading to more warming — that we do not want to be a part of,” the president said.

Granted, the climate science geekery was not without the occasional flub:

What Obama actually meant, of course, was a positive feedback loop with negative consequences.

And that’s just the beginning. Obama also explored the science of the gigaton — the huge unit that scientists often turn to to measure how we’re changing the planet, both when it comes to the loss of ice from Greenland, Antarctica, and the world’s mountain glaciers, but also when it comes to how much carbon dioxide we put in the atmosphere.

As the president put it:

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.

That scientist is Meredith Nettles of the Lamont-Doherty Earth Observatory at Columbia University, whom we quoted on the matter in June.

If you want another way of understanding the size of a gigaton, try this, from a visualization the Post designed to describe Antarctic ice loss (which is greater than Alaska’s, but not by all that much, at least for the moment):


Here’s why the president’s using of these admittedly alien scientific terms — and then explaining them clearly — really matters.

One of the key problems with a changing climate is that it is so big that humans have a very hard time comprehending it. The dynamics of ocean circulations, ice sheets, jet streams, boreal forests — what they all have in common is a scale that is hard to grasp.

Indeed, even Alaska isn’t all that big when it comes right down to it. At one point in his speech, Obama implicitly noted as much in remarking upon the state’s dramatic wildfire season this year:

More than 5 million acres in Alaska have already been scorched by fire this year — that’s an area about the size of Massachusetts.  If you add the fires across Canada and Siberia, we’re talking 300 [30] million acres -– an area about the size of New York.

Some people, facing problems at this scale, throw up their hands and insist that humans can’t affect systems this big — even though there are billions of us, too. These critics are wrong, but you can certainly understand the impulse — and also, perhaps, how such gigantic changes can trigger a response resembling denial.

But there is another, much harder route — actually striving to wrap your mind around what it all means, with the help of an analogy now and again, and a heck of a lot of conversations with scientists.

That’s what Obama is now doing, even as, at the same time, he grows more and more vocal. And maybe these two things aren’t unrelated. Once you start thinking in terms of gigatons and feedbacks — like scientists do — it is hard to go back.

Also in Energy & Environment:

Obama can rename Mount McKinley Denali — but he can’t stop its loss of ice

The surprising way that birds and wind turbines can coexist

NASA is very worried that Greenland’s melting could speed up

Alabama hunters are killing huge gators off the Gulf Coast. Is that a good thing?

For more, you can sign up for our weekly newsletter here, and follow us on Twitter here.