Scientists warn that rising sea levels due to climate change may exceed high-end projections

Of the many threats posed by climate change, rising sea levels will undoubtedly be one of the most shocking, causing hundreds of thousands of square miles of coastline to live and displacing more than 100 million people. everyone at the turn of the century. This threat is a key concern for national security experts, as forced migration poses significant risks to international security and stability.

The magnitude of this threat depends largely on the elevation of the oceans in the coming decades. But due to the complex dynamics of massive ice sheets in Greenland and Antarctica, accurate estimates remain difficult to go, from just over a foot to a few feet above current levels. This disparity is the difference between tens of millions of people forced into their homes or hundreds of millions of much more unmanageable displaced people.

Now, a new paper released last week warns that if global warming continues at the current pace (reaching high-end warming projections for 2100), sea level rise is likely to surpass those projections.

Since the late 1800s, sea level has risen an average of about 10 centimeters globally, but the amount varies from region to region. In the last century, the main contributor to the rise of the oceans was thermal expansion; in short, the hottest water expands. But now the melting of the ice layers, mainly from Greenland and Antarctica, constitutes a larger proportion, and this fraction will only grow.

In fact, there is enough closed ice in Greenland and Antarctica so that if all the ice melted, it would cause a 210-foot rise in sea level, a little higher than the Leaning Tower of Pisa. No scientist expects anything, not even close to this century, but after the Earth exceeds a certain level of warming, the ice sheets become less stable and less predictable, with possible points of inversion coming into play.

In the latest report from the UN Intergovernmental Panel on Climate Change (IPCC AR5), median sea level rise projections at the end of the century range from 16 inches for a range warming scenario. low and 2 feet for high-end scenery (compared to the mid-sea level of 1986-2005). Estimates also include a high degree of uncertainty, which causes the upper limit of the likely sea level rise to exceed 2 and a half feet.

The new paper, titled “Rising Sea Level in the 21st Century Could Overcome IPCC Projections for Future Strong Warming,” questions this higher estimate, saying it is likely to be too low. The paper was published by who is who of the most expert and expert glaciologists at sea level rise, including Martin Siegert, Richard Alley, Eric Rignot, John Englander and Robert Corell.

John Englander is co-author of the paper and author of the books “High Tide on Main Street” and the upcoming release “Moving to Higher Ground: Rising Sea Level and the Path Forward.” He claims that this paper is a reaction to a “heart of concern of the scientific community that projections about sea level rise were underestimated.”

He said the research team hopes its work can inform the next major IPCC report, as it is the most cited document on climate change. “With the next report now being prepared for publication in 2021-22, our intention was to present the case to the IPCC management to better explain the reality of the melting Antarctic potential as it could increase significantly. sea ​​level rise this century. “

In a Zoom conversation with CBS News, Englander illustrated that the contribution to rising sea levels in Antarctica, the largest layer of ice on Earth, does not increase from a warming scenario of low-end to a high-end warming scenario in the latest IPCC report, but in the real world it should be. Although a footnote mentions the possibility of a significantly larger sea level rise due to Antarctica, it is by no means front and center.

The reason for this, Englander explains, is that the IPCC is very cautious with the data it uses in the report and only includes “numbers that meet its criteria of scientific accuracy with an acceptable degree of confidence.” The level of uncertainty in the scientific community stems from the fact that glaciers can be unstable and the computer models used to project fusion are not yet sophisticated enough.

In the paper, they write: “Existing ice sheet models are more likely to provide reliable projections if global warming remains below 2º Celsius [3.6º Fahrenheit], but a world in which warming exceeds 4º Celsius [7.2º Fahrenheit] presents a much more difficult situation. It is very possible that this extreme situation will lead to reactions and feedback in the atmosphere-ocean-ice systems that currently cannot be properly modeled … ”

In the following graph, compiled by Englander and based on the IPCC report, the various contributors to sea level rise (in inches) are projected to the end of the century. The contribution of Antarctica is shown in turquoise blue.

Englander explains that in a high-end warming scenario, obviously the melting of Antarctic ice should contribute more to sea level rise than in a low-end warming scenario, but this is not the case. reflects in the report. “The slight contribution shown of 2 inches in three scenarios, and after one inch in the highest stage, is clearly paradoxical,” says Englander.

This paradox is something that the authors of the paper intend to push the IPCC to clarify in the next report.

Another article published in Nature this week makes a similar case, focusing on Greenland testing. Using the latest models used to report the next IPCC report, the authors found that in a highly warming scenario, Greenland may contribute to rising sea levels by an additional 3 inches by the end of the century, compared to the previous version of the models used by the IPCC. This additional rise in sea level is due to an additional warming of 2 degrees Fahrenheit projected by the new climate models in the Arctic.

A major concern of Englander for our future is the nonlinear behavior of sea level rise. In recent years, the pace of sea level rise has been accelerating. In the 1990s, the oceans were rising to about 2 millimeters per year. From 2000 to 2015 the average was 3.2 millimeters per year. But in recent years the pace has accelerated to 4.8 millimeters a year.

At the current rate, we can expect at least another 15 centimeters of sea level rise for the year 2100. But, as has been the case over the last few decades, the rate of sea level rise is expected to continue. increasing over the foreseeable future. Therefore, 15 inches is not only a lower limit, but it is also extremely unlikely.

Adding confidence to the newspaper’s warning that IPCC projections for a strong warming scenario may be too low is evidence that sea level rise is running in the high range of projections of the IPCC for decades. In the image below, the 1990 and 2002 projections are shown in blue and green, compared to the actual observations in gold and red. It is clear that the actual measures are above previous expectations.

Because of this evidence and the possibility of a “turning point behavior,” the paper argues, “the results are superior to this. [IPCC] the scope is much more likely than below. “

For most of us, it is human nature to assume that the height of the oceans we have observed in our lives is constant, but Englander says this perception is misleading. “Sea level rise is easy to miss because it’s a slow effect, like a glass filling a bucket, as the ice sheets of Greenland and Antarctica melt,” he said.

For the past 8,000 years, much of modern human existence, this expectation of a constant height of the ocean has remained real. However, the height of the oceans has always changed, sometimes dramatically.

Since the last ice age, which reached its maximum extent about 20,000 years ago, global temperatures have warmed to about 18 degrees Fahrenheit and sea level has risen to 425 feet; this is greater than the length of the football field.

Historically, simple mathematics reveals that for every degree of Fahrenheit, the Earth heats up at sea level. finally rises to an astonishing 24 feet. However, there is a considerable lag time between warming, melting and the consequent rise in sea level.

Given that the Earth has already warmed 2 degrees Fahrenheit since the late 1800s, we know that the substantial rise in sea level is already occurring, regardless of whether we stop global warming. Scientists do not know exactly how long it will take to see the rise or how quickly it will occur. But using proxy records, glaciologists can see that as we emerged from the last ice age, sea level rose at a remarkable rate, even 15 feet per century.

That said, the fact that there is much less ice on Earth today than it was 20,000 years ago means that sea level rise by degree would probably be smaller now, and the maximum rate can also be moderated. But even a rate that is half the all-time high would still be catastrophic for an Earth with billions of people dependent on stability.

We must also remember that current warming, due to climate change caused by humans, is happening faster of what has to at least 2,000 years and possibly more than 100,000 years. Thus, scientists do not have a directly comparable situation with which to measure, once again highlighting our uncertain future.

While scientists and science newspapers tend to be conservative in their public projections of sea level rise, scientists will often remark that they are concerned that it could be much worse. When CBS News asked Englander what he believes is a “realistic range” of sea level rise in 2100, he said, “With the current global temperature level and the rate of temperature rise, I think we could reach 5 to 10 feet before the end of this century “.

While this is only the opinion of an expert, if sea level rise approaches these levels, the impacts would really be dangerous and destabilizing, dramatically reforming the coasts of nations and forcing hundreds of millions of people to do so leave their homes. Englander says that to reduce potential impacts, it is best to be prepared for a worse case.

“We need to start planning and designing this as long as there is time to adapt.”