Calamitous communications failure

When it comes to the dramatic changes in sea level rise coming just a handful of decades from now, UN scientists have gotten in their own way

Today, a thousand scientists sent an open letter urging the public to act to reduce emissions. They're trying this direct route out of frustration that collective action by governments has been so slow.

One of the signatories, Minal Pathak, told the Guardian she was angry: "'At one point we would think that writing impactful papers in high quality journals or publishing UN reports [is] the thing, to lay down evidence,' she said. 'But apparently that’s not working, right? Or not working as it should.'"

That "should" is a cultural cry for help. "Surely," Pathak is saying, "policymakers will act rationally to ensure humans can continue to live on this earth, once they've seen the UN-sanctioned evidence that we have collectively wrapped the globe in an ever-warming electric blanket."

The trouble is, some of these "UN reports" have been so careful, conservative, and scientific that it has been relatively easy for policy actors to ignore them and claim that the entire predictive enterprise is completely uncertain. This is particularly true when it comes to predictions about sea level rise over the coming decades, where cultural scientific caution and unclear communication is actively putting coastal residents at risk.

Here's a vivid example. A recent report from the International Cryosphere Climate Initiative did its level best to explain clearly why today's unbelievably rapid, human-caused warming of the atmosphere will result in nearly 10 feet of sea level rise in about 75 years. Here’s a summary of the Cryosphere Initiative report:

Translated: Three meters of sea level rise (9.84 feet) is already probably inevitable eventually, given how much warming has already happened. But the scientists' point is that things are moving so quickly right now that the globe will experience those three meters around 2100, and a meter of rise (3.28 feet) by 2070. That's the global average. The East Coast of the US will see more than that. 

The group of scientists who make up the Cryosphere Climate Initiative have a communications problem: In 2021, the IPCC put out a presumably human-readable and (relatively) brief "Summary for Policymakers" that included a picture of what it thought was going to happen:

See that dotted line? It's labeled "low-likelihood," and it shows a swift zoom up to much, much higher amounts of sea level rise, starting right about now. It's a dotted line, though. It looks... dodgy and uncertain. With that label ("low-likelihood") most normal people would assume, reasonably, that it wasn't depicting something real. Or, in other words, that whatever it was predicting wasn't likely to happen.

But that line wasn't labeled "low-likelihood" because it was clearly unlikely. It was labeled "low-likelihood" because at the time the window closed for scientific contributions to the 2021 Summary for Policymakers there were only two studies that were well-enough done and significant enough that the IPCC authors thought the line was worth showing. The scientists involved in that report wanted to communicate that they couldn't rule out that staggering rate of sea level rise, given the two studies that were already out. One of those two studies showed that if you included ice-sheet modeling evidence, Antarctic ice melt could contribute much more sea level rise than what the UN was assuming. I wonder how many policymakers took these subtle meanings from the words "low-likelihood." 

Since then, much more work has been done on the instability of ice sheets in Western Antarctica. Several new studies confirm that Antarctic ice sheets are highly "sensitive to warming," meaning that the structures holding them in place are being undermined by the warming Southern Ocean. (Here's a 2023 study by Park et al.) "That dotted line is, you could say, becoming more and more solid," says Pam Pearson, the Executive Director of the ICCI. "Low-likelihood," meaning, again, based on only two studies at the time the 2021 report came out, no longer seems the case.

How quickly will things change?

To tell this story, the ICCI scientists say to "remember forward"—remember how things used to be, and we can make pretty confident predictions about the future. Paleo-climate scientists have a ton of data running all the way back to the Pliocene. They can document that the last time the world was 2-3Cº warmer and CO2 levels were where they are now (420ppm), sea levels were at least 16-18 meters (52-50 feet) higher than they are now.

We're already at 1.1º above pre-industrial temperatures, the time my grandfather's grandfather was young and was living without matches, already. We're likely to hit 1.5ºC by the mid-2030s and 2 to 3ºC by the end of the century.  

The news from the ICCI is that if we keep doing what we're doing, and stay on a path to hit say 2.8º C above pre-industrial temperatures (which is going to happen as things stand now), sea level rise continues to accelerate very very quickly, with a huge contribution from Antarctica. That’s why we’ll reach 3 meters by the end of the century.

Any small change in the Antarctic's glacier system can cause dramatic effects around the globe, because 58 meters (or 190 feet) of global sea level rise is frozen there.  

Scientists know from what they've observed in Greenland that ice shelves keeping the Antarctic glaciers in place can fracture ("calve") under high-stress conditions, and they're now able to model (predict) the fracturing of Antarctic ice shelves given what they've learned about these processes—something only one or two studies had been able to show before the 2021 UN report came out. 

Rob DeConto is a leading ice scientist and member of the ICCI. DeConto says that what scientists are seeing from this modeling is that if emissions keep going as planned by the countries of the world in their promises under the Paris Agreement, which will take us on a path rising to around 3º above pre-industrial averages by 2100, the following will happen: 

Once we get to around 2060, 2070 essentially all hell breaks loose where we're beginning to lose some of those critical buttressing ice shelves.

DeConto says ice from the interior of Antarctica will flow toward the ocean, icebergs will break off (or calve) from the buttressing ice shelves, and there will be a "massive acceleration in the pace of sea level contribution from Antarctica." This will be an irreversible process at that point.

At three meters, Miami and Fort Lauderdale are under water.

So is Newark, the outer rim of Manhattan, and a big chunk of Long Island:

So is Dhaka.

So is Shanghai.

"All hell breaks loose by 2060, 2070" because seas will suddenly start rising at rates that can't be adapted to is a good, strong message. But it hasn't been communicated to the general public, and the scientists of the IPCC have played a role in this failure.