Our multi-trillion ton impact on the Earth

Welcome to the era of tera -- the teratonne, a unit equivalent to 1 trillion metric tons.

Margerie Glacier, Alaska. Photo by the National Parks Service.

The story of climate change is the story of humans realizing their planetary power. We can shake the whole system.

And when it comes to measuring that impact, it’s time we shift to the next unit on the scale. For the global melting of ice, at least, figures in the billions of tons are becoming, amazingly, too small. We need to start thinking about trillions.

That’s a key implication of a recent study in Nature on the amount of ice now being lost from the more than 200,000 glaciers found in mountain ranges, fjords and other icy environments across the globe. Their yearly losses have increased rapidly and in the most recent year available in the new data, 2023, exceeded 500 billion metric tons — or gigatonnes. Each of these is the equivalent of an ice cube whose sides are each a little bit over a kilometer long.

That’s an enormous volume, but it’s frankly still too small to capture what’s happening.

When the glacial loss figures are tallied over time, then you’re dealing instead with trillions of metric tons. To make that a little more formal, we’re talking about tonnes (metric lingo) with the prefix “tera” attached, according to the International System of Units.

Aka terabytes, terawatts — and, teratonnes.

First, just consider the cumulative loss of global glacial ice in the new study (by the GlaMBIE team). These are the losses from all the glaciers that aren’t part of the great ice sheets — glaciers from Alaska to Patagonia, from the Alps to the mountains of New Zealand. They have poured over 6 teratonnes of ice into the oceans from the year 2000 through 2023, the new research finds.

“We didn’t have a reason to use teratonnes 10 years ago,” said William Colgan, a glaciologist with the Geological Survey of Denmark and Greenland, and one of dozens of scientists behind the latest work.

“We’ve entered the age of the teratonne.”

Now, add in two ice sheets

That statement is true for ice and also, actually, for greenhouse gas emissions. According to the Intergovernmental Panel on Climate Change, total human-caused emissions between 1850 and 2019 amount to 2.4 teratonnes of carbon dioxide. (For more on the scale of these emissions, see here from The Climate Brink.)

These emissions, of course, are warming the Earth and melting all this ice. And when you combine the glacial losses above with what has been happening with other types of ice, the figures get even larger.

In 2020, a group of scientist led by Tom Slater, who is currently at Northumbria University in the UK, added together the losses from all ice that adds to sea level rise — glaciers, the Greenland and Antarctic ice sheets — and ice that largely doesn’t (floating sea ice, floating ice shelves at the ends of ocean-terminating glaciers). They considered these over the period from 1994 through 2017, and, when all sources were put together, found losses that exceeded 1.2 teratonnes per year in the 2010s.

In a few places in their paper, these researcher do use the abbreviation “Tt” — teratonne. When their work came out, there was an early round of discussion about the trillion-ton scale ice of global losses.

Inspired by the new research on glaciers, I attempted to do something similar with data that extends a bit further into the present.

The glacier team, made up of dozens of scientists from around the globe who joined forces to hash out common methods and create a shared record, calls themselves GlaMBIE (Glacier Mass Balance Intercomparison Exercise). They’re preceded by something called IMBIE (the Ice Sheet Mass Balance Intercomparison Exercise), which has released a series of reports, most recently this one, charting losses in Greenland and Antarctica based on multiple methods.

In the following chart, I combined together the losses in GlaMBIE and IMBIE for the two decade period where they currently overlap, which is from the beginning of 2000 through the end of 2020. I conferred with a number of scientists who are experts on global ice, and who contributed to the research above, about how to do this, and will credit all of their names further below. (They were an enormous help!)

So here it is, showing that over this shared period alone — there are more losses before it, and many more after — the world saw more than 12 trillion metric tons of ice losses.

Notably, in the final years in the data, the losses get close to (or even slightly exceed) 1 trillion tons in a single year. And remember that these figures, unlike the work by Slater and colleagues discussed above, do not include the very large losses from sea ice or floating ice shelves.

So will we all soon live on a planet that’s sending an additional teratonne of ice into the seas annually?

“We’ll get there for sure,” said Colgan.

But Ted Scambos, an Antarctic expert with the University of Colorado Boulder, issued a note of caution. Scambos noted that in several recent years, beyond those shown in the last figure, massive snowfalls in Antarctica actually caused the continent to regain some ice mass.

“I would caution against sounding the ‘trillion ton alarm’ too soon,” Scambos said.

“In the long run, warming causes ice loss,” he continued, but there could be plenty of years in the near term future in which warmer oceans actually trigger large snow events, which grow interior ice in the Antarctic. This growth would partially offset losses elsewhere.

What perhaps stands out most here is that the largest losses today are still from the one ice category — the global glaciers — that is the smallest in terms of total ice mass, and therefore, sea level rise potential. The ice sheets are capable of losing vastly more ice than these glaciers, and are expected to overtake them over time.

Finally, there’s one small caveat here to note. While the global glaciers and ice sheets are mostly distinct categories, Colgan said it is possible there is a small overlap in their measurement due to one method, a gravity-based one, that the IMBIE project uses to measure Greenland and Antarctic ice loss. This method may pick up some of the losses that are also within GlaMBIE’s categories for glaciers peripheral to Greenland and Antarctica. However, the overlap should be small, according to Colgan.

Analogize

Aerial view of the National Mall, Dec. 18 2014. By Mariordo (Mario Roberto Durán Ortiz) - Own work, via Wikimedia Commons. CC BY-SA 4.0

In 2015, my first full year at the Washington Post, I wrote an explainer about a unit that has appeared several times in this article — the gigatonne, equivalent to one billion metric tons. It was full of all kinds of analogies to help explain this massive unit of change, including the sci-comm winner (at least for U.S. audiences) by Columbia’s Meredith Nettles, who explained the size of a gigatonne as follows:

If you took the whole National Mall, and covered it up with ice, to a height about four times as high as the [Washington] monument. All the way down from the Capitol steps to the Lincoln Memorial.

So ten years later, consider this my follow up. How do we explain a teratonne, besides that it’s a thousand of these?

Slater and colleagues had some visuals of ice blocks towering over major cities when their work came out. One can be seen at the end of the video here. It’s a powerful start.

Another tried and true analogy for very big water volumes: The Great Lakes. According to the EPA, they range in volume from Lake Erie, which holds about half a teratonne of water (at the baseline low water level), to Lake Superior, which holds about 12.

Thus, the world’s ice losses are easily adding a Lake Erie to the ocean every year, and in 20 years, more or less added a Lake Superior.

I had lots of help with this article. I’d like to thank Livia Jakob from Earthwave, Ltd, for looking at the analysis and advising me on the best way to do it. I also got additional helpful feedback from William Colgan, Tom Slater and Andrew Shepherd (of Northumbria University), and Lauren Miller (University of Virginia).