I covered Antarctica's melt for a decade. How I think about the risk
We don't know exactly what's going to happen. We definitely don't know that it's no big deal.
My last post contained a graphic showing some 20 years of land-based ice losses from Antarctic and Greenland, based on NASA data. It didn’t really ruffle feathers here, but it drew nearly 800 comments on Facebook. And yes, many were skeptical that the losses are a big deal.
This is that graphic:
I covered the ongoing changes to Antarctica and Greenland at the Washington Post beginning in 2014. I’ve spoken over the years with many dozens of experts who study these ice sheets. So, I decided to share a bit more perspective on how to interpret these data. (I will post an abbreviated version of all of this to Facebook.)
It is straightforward to translate ice losses into sea level rise, as every 360 gigatons (or billion tons) of grounded ice (not sea ice!) entering the ocean raises the global sea level by 1 millimeter. So this chart shows the same data as the last, converted into this new unit.
You’ll see that the two ice sheets, combined, have raised sea levels by a little over 20 millimeters since 2002.
How big of a deal is that? Well, it’s still a little less than an inch of sea level rise. For now, there are other drivers of sea level rise that are actually larger than the contributions of either ice sheet on its own. Namely, the melting of mountain glaciers around the world and the heating of the oceans, which causes them to expand.
It would be hard to call these 20 or so millimeters of sea level rise, alone, a crisis. Anybody who is worried about Antarctic or Greenland ice losses must therefore be more worried about the future than the present.
Is such a worry justified?
Well, let’s begin with Antarctica. Most of the ice losses are from West Antarctica, and we know West Antarctica is a marine-based ice sheet. In other words, the ice sits on the seafloor well below sea level, and is so thick that it rises up through the ocean water column, above the surface, and then up high into the air. We are talking about ice that is over a mile thick in places and much of that thickness is underwater.
This beautiful graphic, from a recent Scientific Data paper by Antarctic experts, pretty much tells you everything I just wrote above in sentences. But here, you can see it. The image shows what is beneath Antarctica’s ice, and you can see that if not for that ice, much of West Antarctica would be open ocean. The deepest blues show the areas where the bedrock beneath the ice is farthest below sea level:
And now the ocean is eating into West Antarctica in the Amundsen Sea region, the bumpy but ultimately very deep area on the central left side in the map above. This is where the famous Thwaites glacier, shown at the top of this story, is located. This is just the start of a process, but the problem is that this is the pathway into the center of West Antarctica, which contains the ice equivalent of several meters worth of potential sea level rise. Moreover, the ocean floor slopes downward the further in you go along this path. So the ice gets thicker further in, and ocean can eat into more ice as the process advances.
This concern is further heightened because of evidence that West Antarctica has seen major ice loss events in the past. In the past when it was warm. In a prior post I listed some of this evidence; the foregoing links do the same here. What we’re seeing now, the ocean eating into Thwaites, is presumably how this process begins. There are real concerns that once it begins, there is little (maybe nothing) to stop it.
There are also some areas in the larger East Antarctic ice sheet that are marine based, showing signs of ocean influence, and could start to lose ice faster.
Turning to Greenland: Well, this is a place I’ve actually visited. I’ve seen the major melting atop the ice itself due to warm temperatures. I’ve stood there as rain fell on a floating ice shelf. Greenland is losing ice through the Antarctica route, which is ocean melting, but it also has lots of simple runoff due to atmospheric heat and yes, nonfrozen precipitation.
Here’s a picture I took nearly a decade ago, on an August day above the grounding line of Petermann glacier, one of the big ones in Greenland. It shows the meltwater, which was then beginning to freeze back over:
In Greenland there is no one equivalent of Thwaites glacier, no single Achilles Heel. The closest is maybe Greenland’s northeast. There and in a few other places, there are really large outlet glaciers like Petermann, pretty much all of which are seeing significant changes already and contributing to sea level rise. There is also the worry that the ice sheet itself will slump lower in altitude as it continues to melt, which exposes it to warmer temperatures in the lower atmosphere…a feedback that runs in the wrong direction.
Higher seas are already contributing to worsening flooding and other damages around the world. And the forecasts suggest it gets worse from here. But there is plenty of ground to debate how fast all of this could play out, and how far it may go.
Models give different answers. Reports give ranges. There’s still lots of debate about a concept, marine ice cliff instability, that could potentially make the retreat process in West Antarctica go a lot faster. And there are other factors that remain inadequately understood or poorly quantified. The most important unknown variable, of course, remains us: How many fossil fuels we burn, how rapidly we decrease emissions.
This all matters because it is not only the magnitude of potential sea level rise, but also the speed at which it could occur, that counts when you are trying to adapt. Even if the eventual loss of Thwaites has already been set in motion, that still doesn’t tell us how rapidly this will happen.
In my view, it’s not so wise to try to guess what will happen in the future.
Rather, all of the above constitutes a reason for serious concern about what will happen to the ice in Antarctica and Greenland going forward. And you should continually update your level of concern based on new evidence. For instance, there has been some modest good news (but only quite modest) in the form of recent major snowfalls that have put a bit of ice back onto the Antarctica continent. The problem though is that while this could slow near term losses, it doesn’t do anything to stabilize Thwaites.
Conversely, there are a range of viewpoints that strike me as hard to justify. One is to assume that we’ll see sudden, rapid sea level rise in the very near future due to some sort of West Antarctic collapse. Experts right now are predicting increasing rates of sea level rise from the ice sheets going forward, but that is different from a sudden spike. As one sober assessment of what’s been learned about Thwaites Glacier, following a major $ 50 million U.S.-UK research program, puts it:
Results from the collaboration so far indicate that some potential scenarios for runaway glacier change, which suggested an abrupt increase in the rate of ice loss could occur within even the next couple of decades, are less likely than previously feared. However, our latest results and computer models indicate that rapid ice loss from the gigantic retreating glacier, which was initiated by climate and ocean changes, will continue and the rate of loss will accelerate.
So, one hard to justify view involves being overly alarmist, or at least more alarmist than the above statement (which is bad enough). But another unjustified view assumes change will be on the low end, or that there is nothing to worry about. How could you know? What if you’re wrong?
A very warm October for the globe
Switching gears briefly, the data are now coming in about October 2025 and I’ve updated my charts. October’s global warmth is quite striking, at least for those of us who figured that after 2023 and 2024, 2025 might cool down significantly once again as the influence of El Niño faded.
It’s looking less like that now, with yet another month above the 1.5 degrees C threshold, according to the Copernicus Climate Change Service.
We are now living in what will be either the 2nd or 3rd hottest year on record, according to Copernicus. And if the warmth of 2023-2024 is going to persist, this will deepen debate over why we seem to have jumped upward several rungs on the ladder, and how much this may have to do with clearing air pollution, among other factors.
And just to add one more chart: Arctic sea ice in October came in at the 8th lowest extent in a record dating back to the late 1970s.
For more of my charts, check out the ReportEarth chart archive!
