Climate Change and Rising Seas: Rising by 69 Feet?
August 12, 2013
Ben Strauss / Climate Central & Chris Mooney / Mother Jones
Global average sea level is currently rising by about 1 inch per decade. But in an invisible shadow process, our long-term sea level rise commitment or "lock-in" -- the sea level rise we don't see now, but which carbon emissions and warming have locked in for later years -- is growing 10 times faster, and this growth rate is accelerating. Meanwhile, the unprecedented melting of Greenland could foreshadow a massively destructive global sea-level rise of 69 feet.
(August 7, 2013) -- Despite the fact that 97 percent of scientists agree that climate change is real, Rep. Steve King (R-IA) and other "climate deniers" in Congress, insist that climate change is "not science" and that environmentalists are missing the potential upsides.
At an event sponsored by the climate-denying, Koch-funded Americans For Prosperity, King reportedly told the audience that climate change "is not proven, it's not science. It's more of a religion than a science." And he argued that an increase in carbon in the atmosphere might actually be a good thing:
Sea Level Rise 'Locking In' Quickly, Cities Threatened
Ben Strauss / Climate Central
(July 29th, 2013) -- Measurements tell us that global average sea level is currently rising by about 1 inch per decade. But in an invisible shadow process, our long-term sea level rise commitment or "lock-in" -- the sea level rise we don't see now, but which carbon emissions and warming have locked in for later years -- is growing 10 times faster, and this growth rate is accelerating.
An international team of scientists led by Anders Levermann recently published a study that found for every degree Fahrenheit of global warming due to carbon pollution, global average sea level will rise by about 4.2 feet in the long run.
When multiplied by the current rate of carbon emissions, and the best estimate of global temperature sensitivity to pollution, this translates to a long-term sea level rise commitment that is now growing at about 1 foot per decade.
We have two sea levels: the sea level of today, and the far higher sea level that is already being locked in for some distant tomorrow.
In a new paper published Monday in the Proceedings of the National Academy of Sciences (PNAS), I analyze the growth of the locked-in amount of sea level rise and other implications of Levermann and colleagues' work. This article and its interactive map are based on this new PNAS paper, and they include extended results.
To begin with, it appears that the amount of carbon pollution to date has already locked in more than 4 feet of sea level rise past today's levels. That is enough, at high tide, to submerge more than half of today's population in 316 coastal cities and towns (home to 3.6 million) in the lower 48 states.
By the end of this century, if global climate emissions continue to increase, that may lock in 23 feet of sea level rise, and threaten 1,429 municipalities that would be mostly submerged at high tide. Those cities have a total population of 18 million. But under a very low emissions scenario, our sea level rise commitment might be limited to about 7.5 feet, which would threaten 555 coastal municipalities: some 900 fewer communities than in the higher-emissions scenario.
To develop such figures, I combined my sea level debt findings with analysis from Climate Central's Surging Seas project, which is a national assessment and mapping of coastal vulnerability in the US based primarily on elevation and census data.
A quick tour of the interactive map on this page shows that Florida is by far the most vulnerable state under any emissions scenario. Louisiana, New Jersey and North Carolina would also face enormous difficulties.
If we call a place "threatened" when at least half of today's population lives below the locked-in future high tide line, then by 2100, under the current emissions trend, more than 100 cities and towns would be threatened in each of these states.
Nationally, the largest threatened cities at this level are Miami, Virginia Beach, Va., Sacramento, Calif., and Jacksonville, Fla.
If we choose 25 percent instead of 50 percent as the threat threshold, the lists all increase, and would include major cities like Boston, Long Beach, Calif., and New York City. The lists shrink if we choose 100 percent as the threshold for calling a community "threatened."
But each fraction is arbitrary, and true critical levels will depend on geography and economics. Some places when partly or wholly below sea level may be defensible, at least to some degree -- like New Orleans with its network of levees and flood barriers. Other places may be indefensible with well under 25 percent of exposure. For example, South Florida will be very difficult to protect, due in large part to the porous bedrock underlying it.
Overall, this analysis does not account for potential engineering solutions; it is based simply on elevations.
The low-emissions scenario could reduce impacts substantially -- by almost threefold -- but is profoundly ambitious compared to current trends and policy discussions. It includes a halt to global emissions growth by 2020, followed by rapid global emissions reductions, and a massive program to remove carbon from the atmosphere, resulting in net negative emissions -- atmospheric clean-up -- by late in the century.
The big question hanging over this analysis is how quickly sea levels will rise to the committed levels. Neither Levermann and colleagues' analysis, nor my new paper, address this question.
In a loose analogy, it is much easier to know that a pile of ice in a warm room will melt, than to know exactly how fast it will melt.
Levermann and company do put an upper limit of 2,000 years on how long it will take the sea level commitments described here to play out. Recent research indicates that warming from carbon emitted today is essentially irreversible on the relevant timescales (in the absence of its massive-scale engineered removal from the atmosphere), and will endure for hundreds or thousands of years, driving this long run unstoppable sea level rise.
On the other hand, our sea level rise commitment may be realized well before two millennia from now. The average rate of global sea level rise during the 20th century was about half a foot per century. The current rate is 1 foot, or twice that. And middle-of-the-road projections point to rates in the vicinity of 5 feet per century by 2100.
Such rates, if sustained, would realize the highest levels of sea level rise contemplated here in hundreds, not thousands of years -- fast enough to apply continual pressure, as well as threaten the heritage, and very existence, of coastal communities everywhere.
* Surging Seas: Sea Level Rise Analysis by Climate Central
* Cutting Short-Lived Pollutants Can Slow Sea Level Rise
* US Airports Face Increasing Threat From Rising Seas
* Rising Sea Level May Trigger Groundwater Floods
* Report: Can US Carbon Emissions Keep Falling?
Global Emissions Hit Record High, Report Finds
* Stabilization Targets and Irreversible Climate Change
* Two Key Climate Change Topics are 'Misunderstood'
Humans Have Already Set in Motion 69 Feet of Sea Level Rise
Glaciologist Jason Box describes a post-warming world that you won't even be able to recognize
Chris Mooney / Mother Jones
(January 31, 2013) -- Last week, a much-discussed new paper in the journal Nature seemed to suggest to some that we needn't worry too much about the melting of Greenland, the mile-thick mass of ice at the top of the globe.
The research found that the Greenland ice sheet seems to have survived a previous warm period in Earth's history -- the Eemian period, some 126,000 years ago -- without vanishing (although it did melt considerably).
But Ohio State University glaciologist Jason Box isn't buying it.
At Monday's Climate Desk Live briefing in Washington, DC, Box, who has visited Greenland 23 times to track its changing climate, explained that we've already pushed atmospheric carbon dioxide 40 percent beyond Eemian levels. What's more, levels of atmospheric methane are a dramatic 240 percent higher -- both with no signs of stopping. "There is no analogue for that in the ice record," Box said.
And that's not all. The present mass scale human burning of trees and vegetation for clearing land and building fires, plus our pumping of aerosols into the atmosphere from human pollution, weren't happening during the Eemian.
These human activities are darkening Greenland's icy surface, and weakening its ability to bounce incoming sunlight back away from the planet. Instead, more light is absorbed, leading to more melting, in a classic feedback process that is hard to slow down.
"These giants are awake," said Box of Greenland's rumbling glaciers, "and they seem to have a bit of a hangover."
To make matters worse, there's also Antarctica, the other great planetary ice sheet, which contains 10 times as much total water as Greenland -- much of which could also someday be translated into rising sea level.
While Greenland is currently contributing twice as much water to sea level rise as Antarctica, that situation could change in the future. It's kind of as though we're in a situation of "ice sheet roulette" right now, wondering which one of the big ones will go first.
Box also provided a large-scale perspective on how much sea level rise humanity has already probably set in motion from the burning of fossil fuels. The answer is staggering: 69 feet, including water from both Greenland and Antarctica, as well as other glaciers based on land from around the world.
Scientists like Box aren't sure precisely when, or how fast, all that water will flow into the seas. They only know that in past periods of Earth's history, levels of atmospheric greenhouse gases and sea levels have followed one another closely, allowing an inference about where sea level is headed as it, in effect, catches up with the greenhouse gases we've unleashed.
To be sure, the process will play out over vast time periods -- but it has already begun, and sea level is starting to show a curve upward that looks a lot like…well, the semi-notorious "hockey stick."
So what can we do? For Box, any bit of policy helps. "The more we can cool climate, the slower Greenland's loss will be," he explained. Cutting greenhouse gases slows the planet's heating, and with it, the pace of ice sheet losses.
In the meantime, to better understand where we're headed, Box has launched a scientific project called "Dark Snow," which seeks to crowdfund a Greenland expedition to help determine just how much our darkening of the great ice sheet in this unprecedented "Anthropocene" era will push us well beyond Eemian territory.
The video for that project is below. If the remote, dangerous science of ice sheets intrigues you enough (or scares you enough), then you definitely will want this research to succeed.
Posted in accordance with Title 17, Section 107, US Code, for noncommercial, educational purposes.