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Fossil Fuels Must Be Phased Out to Avoid Drowned Coastlines

New research suggests rising oceans could swamp the world’s coasts by the end of the century—sooner than previously anticipated

The world's ice is in trouble. Based on paleoclimate records, observations of the world today and computer models, a warming ocean is speeding the meltdown of massive ice sheets in Greenland and West Antarctica. This new finding, by climatologist James Hansen of Columbia University and colleagues, suggests that sea levels could rise at least five meters—and possibly as much as nine meters—within 50 to 100 years, a rate both faster than and six times as deep as previous estimates. And such dramatically rising seas and stronger storms followed during past periods when the global annual average temperature was only roughly 1 degree Celsius warmer than today, the team found. An outcome of that magnitude could doom most of the megalopolises lining today's coastlines, the team says. And the extent of current efforts to combat climate change are nowhere near what will be required to prevent the submersion of thousands of kilometers of coastline.

Already, freshwater flooding into the oceans from ice sheet meltdowns in Antarctica and Greenland has slowed the circulation of seawater—the upwelling and downwelling that draws both heat and CO2 out of the atmosphere. The cold freshwater flooding into the oceans has also cooled the surfaces of the North Atlantic and Southern oceans, allowing for sea ice near Antarctica to grow even as the overall climate warms. At the same time, warmer, deeper waters then further melt ice shelves, adding yet more freshwater and amplifying the climate effect.

Hansen hopes that this latest research will amplify the urgency that world leaders bring to their efforts to tackle climate change caused by fossil fuel pyromania. "It shows just how dangerous 2 degrees Celsius [of warming] would be," Hansen says, noting that concentrations of CO2 in the atmosphere should be reduced to 350 parts per million, down from 400 ppm or so today, in order to avoid this sea level rise and other ill effects of climate change. Current proposals to combat it will fail to accomplish the goal of making fossil fuels too expensive to burn, he adds, and the resulting air pollution will be dumped into the atmosphere. "The two degree target they came up with in Copenhagen [international negotiations to draw up a treaty to combat climate change in 2009] was pulled out of a hat rather than a scientific basis," he says. "The best diagnostics are the planet's energy imbalance. If more energy is coming in than going out, then the problem is getting worse even if melting ice is temporarily cooling the high latitudes." As it stands, excess atmospheric CO2 and other greenhouse gases trap an extra 0.6 watt per square meter—a number that needs to drop to zero.


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The distinguished scientist, who has been warning about the perils of global warming since at least 1988, held a press conference today to publicize the new findings, published in the open-access journal Atmospheric Chemistry and Physics and still awaiting peer review. Scientific Americangot to ask Hansen a few questions.

[An edited transcript of the interview follows.]

Haven't we already guaranteed unavoidable climate change and melt with emissions to date? And what kind of rate are you predicting for this sea level rise in the coming years, decades, centuries, millennia?

That's the $64 [-thousand] question. A nonlinear process when things collapse is very hard to predict. On the other hand, a nonlinear response means that it's sensitive to the forcing. So I think it's realistic to hope that if we could reduce emissions rapidly and move toward restoring the planet's energy balance, that the response would be modest and would not imply that many meters, which means all coastal cities are gone.

We are going to get some sea level rise. The rate has been increasing over the last several decades. It's now roughly 14 inches a century. That's still small compared to what it would be if we get collapse of the West Antarctic ice sheet.

So I can't really answer your question. Odds are that we could avoid a many-meter sea level rise if we begin to rapidly reduce emissions. That's the best advice that science is going to be able to provide.

What exactly do you mean by "rapidly" reducing emissions? Is zero by 2100, as is often talked about, enough?

What it needs to be in the near future is most important. The legal cases filed by Our Children's Trust asked me what was needed to do to restore the planet's energy balance and stop global warming by the end of the century. Other things being equal that means reducing emissions by 6 percent per year, which is pretty difficult if not implausible.

On the other hand, if you reduce emissions by 3 percent per year, which is readily plausible if you put a rising price on carbon emissions, then you are close enough that if you undertake other things, like getting more carbon stored in the soil and biosphere by means of improved agriculture [such as biochar] and forestry practices as well as special efforts for negative emissions [like enhanced weathering], it would be solvable.

If all you do is something by the middle of the century and in the meantime let emissions go up, then it creates a situation where the problem can't be solved.

Are there things, like what you've called "soft geoengineering," we might do to save the West Antarctic or Greenland ice sheets that might buy us some time?

The National Academy of Sciences says we better start talking about [geoengineering]. Maybe they're right in the sense that when people realize that in order to stop some of these things we're going to have to take some crazy actions, which most people would shudder to think. We're trying to take over as if we understand things well enough and there are no repercussions.

So you can think of things. The overturning circulation is slowing down because of all this freshwater. So let's dump some salt on the Southern Ocean [laughs].

It just makes so much more sense to simply reduce the human-made forcing. None of the actions that people talk about would solve the ocean acidification problem. The only way to do that is to stop putting so much carbon in the system.

Is it feasible that we're going to reduce CO2 pollution by 3 percent per year from here on out?

When we do decide to turn things around, it can happen very rapidly. If we get an agreement between China and the U.S., there are big incentives for moving to clean energies. Air pollution is so bad in China and India. They're coal burning, and coal burning is half of emissions at present. If we decided that we have to cut coal, it could be done quite rapidly, but it has to be treated as an emergency and we haven't reached that point yet.

The Chinese leadership does not deny the reality of this. I think there is a possibility we could get strong action in the fairly near future.