Catch-22: Scientific communication failures linked to faster-rising seas

Scientists failed for decades to communicate the coming risks of rapid sea-level rise to policymakers and the public, a new study has found.

That has created a climate catch-22 in which scientists have soft-pedaled the kinds of catastrophic risks most easily headed off by cutting emissions.

While scientific communication has improved in the 2020s, this trajectory led policymakers to make decisions based on risks that are better understood, easier to quantify — and also easier to write off as an acceptable long-term risk. 

The findings published Monday in Nature Climate Change suggest a fundamental weakness in the past 30 years of communication by climate scientists: a profound difficulty in assessing the possible impacts of breakdowns in the Earth’s biggest and most complex systems.

The Nature paper focused on sea-level rise — a hallmark of planetary heating that is influenced by a wide range of processes both well and poorly understood.

For some of these processes, “we understand the physics quite well – for example, how the ocean takes up heat and expands in response to that,” said lead author Robert Kopp, a climate scientist at Rutgers University.

This kind of process is marked by “quantifiable uncertainty” — the sort that scientists know how to factor it in. 

But other processes — like those that keep ice sheets whole, or drive their sudden collapse — “involve factors we don’t understand that well … but might nonetheless be able to cause rapid sea-level rise,” Kopp said.

That, he added, is the realm of “ambiguity,” which he defined as “a form of deep uncertainty that cannot be well represented quantitatively.”

For decades, scientists writing public-facing documents — like the annual “assessment” reports put out by the United Nations’s Intergovernmental Panel on Climate Change (IPCC) — have had to juggle both forms of uncertainty. 

While the complexity of the underlying physics makes that a tough proposition on its own, the political dimension makes it even harder. Over the short term, Kopp noted, ambiguity around sea-level rise is relatively minimal. The past century of burning fossil fuels has locked in a fixed amount of heating, and the impacts of our current energy policy debate have not had time to take effect — for good or ill.

But for the second half of the century, the prediction game gets far more plagued by ambiguity — and is much more influenced by changes to how much society is able to restrict burning and the accompanying release of greenhouse gasses, over the near term. 

For example, if we significantly reduce emissions, Washington, D.C., can expect about 1.5 feet of sea-level rise by 2060 and 2.5 feet by 2100, according to a tool from the National Oceanographic and Atmospheric Administration.

If emissions stay high, then those numbers look more like 2.4 feet of rise by 2060 — and 6.6 feet by the end of the century. 

That’s enough sea-level rise to convert the National Mall into a national salt marsh — but this easily quantified risk is only part of the story. 

In practical terms, the authors write, that ambiguity means future projections are haunted by unlikely scenarios that would nonetheless be disastrous if they happened. (These are what statisticians call “tail risks.”)

Those tail-risk scenarios become a lot more likely if we don’t stop burning fossil fuels — which policymakers are drawn to do in part by communications from scientists about these kinds of ambiguities.

A breakdown in the ice sheets, for example, could “contribute more than one additional meter of sea level rise by 2100,” the authors wrote.

In D.C., that would be enough to swallow much of the lowlands around Capitol Hill, leaving water lapping at the base of Congress itself. It would also wipe out most of Charleston, S.C., and Miami and tear holes in the fabric of the metro areas of San Francisco, New York and Philadelphia.

Sea-level rise here is a useful stand-in for the potential impacts of a sudden change in other complex, poorly understood and climate-bolstering earth phenomena — like the stabilizing gyre in the mid-Atlantic, the atmospheric gulf stream or the intact equatorial rain forests.

In these “tipping point” systems, a significant, rapid breakdown would lead to knock-on effects across global society — effects that rising emissions would have made more likely, but that scientists would have struggled to quantify ahead of time.

Over the past decades, scientists have gotten better at communicating the many different shades of scientific uncertainty in lay terms.

For example, the first IPCC report, which was released in 1990, described the prospects for the rapid disintegration of the West Antarctic Ice Sheet as “unlikely in the next century.”

That sentence remains technically true: Such a scenario, which could lead to 12 feet of global sea level rise by itself, is probably not “likely,” at least based on our current understanding of the physics.  

But it also does little to communicate the underlying systems — or risks — that human-caused planetary heating is destabilizing.

By contrast, the sixth IPCC report — released more than 30 years later in 2021 — took a more precise approach.

In that document, scientists added a qualitative note to their quantitative estimates. They wrote that rates higher than those they had predicted could be caused by “earlier-than-projected disintegration of marine ice shelves, the abrupt, widespread onset of marine ice sheet instability and marine ice cliff instability around Antarctica.”

Then, the report gives a lay-friendly explanation of the “deep uncertainty” at work here. “Under high emissions such processes could in combination contribute more than one additional meter of sea level rise by 2100,” they wrote.

This, Kopp argued, is the right approach. A proper picture of the role of ambiguity “can affect how planners make decisions, and thus is important to communicate clearly and effectively,” he said.