Geoengineering Could Slow—But Not Stop—Sea Level Rise

By Andrew Moseman | August 24, 2010 2:59 pm

Bay_of_bengalYou could plant huge new forests where none have been before. You could blast particles into the sky to block the sun’s radiation. You could put mirrors in space. These planetary hacks could slow global warming, but one thing that none of them could do, most likely, is to stop the rising sea levels that a warming planet will bring.

That’s the contention of John Moore, lead author of a study out in the Proceedings of the National Academy of Sciences. Moore’s team examined five different means that scientists have proposed to hack the planet and save ourselves from anthropogenic global warming. The geoengineering schemes—forestation, atmospheric aerosols, space mirrors, biochar, and the use of biofuels plus carbon sequestration—are focused either on reducing the amount of energy the Earth absorbs or pulling carbon out of the atmosphere. So Moore wanted to see what they could do about a side effect of the extra heat: melting ice raising the global average sea level.

The results weren’t terribly encouraging. Sea levels respond slowly to changes in the planet’s temperature, Moore told Nature News, so “you can’t just slam on the brakes.”

Injecting sulphate aerosols into the stratosphere – which reduces the amount of sunlight reaching the surface of the Earth – had little effect. If emissions are allowed to grow at current rates, the model showed sea levels rising by 1.1 metres by 2100. Aerosols could reduce that to 0.8 metres by 2100, but with the rate of rise showing no sign of slowing down at the end of the century, this would simply delay greater rises, not prevent them. [New Scientist].

Space mirrors began to reverse the rising sea level trend, but only at about the end of the 21st century. If people quickly developed biofuels and became adept at carbon sequestration, things were even a tad better—but in Moore’s model the sea level still rose by 30 centimeters, or about a foot, mostly because of effects that are already locked into the system. Says Moore:

“I think that sucking CO2 out of the atmosphere is the best way to stop sea-level rise before 2100.” That could be accomplished with the biomass power plants and new forests considered in the study, or by massively scaling up CO2 removal techniques currently deployed in spacecraft and submarines” [ScienceNOW].

Given the unintended consequences that could come with tinkering with the planet on such a massive scale, keeping intervention to a minimum would seem like the ideal choice. But Moore’s study reiterates that fear that it might be too late for little steps. It might be time to consider the “extreme geoengineering”—say, atmospheric aerosol injections every year and a half instead of every four years—that potentially could slow down rising temperatures and sea levels… at an unknown cost.

But once you start, you can’t stop.

Once started, geoengineering must be continued or temperatures will quickly rebound to what they would have been without intervention. An attendant surge in sea-level rise wouldn’t occur quite as quickly, but it would follow soon enough, at a rate of up to 1–2 centimetres per year, he says. “Those are speeds that were observed during the last deglaciation,” says Moore, “so we’re not forecasting anything that is out of the geological record” [Nature].

Related Content:
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80beats: Study: Climate Hacking Scheme Could Load the Ocean With Neurotoxins
80beats: If We Can’t Stop Emitting CO2, What’s Our Plan B?
DISCOVER: 5 Most Radical Ways to Squelch a Climate Crisis (photo gallery)

Image: Wikimedia Commons / Nafis Ahmed Kuntal

  • m

    um…sea levels are based on plate tectonics.

    not temperature.

    google any site that discusses the geology of Earth and how a warmer Earth had lower sea levels.

    Thanks for your attention to this matter.

    oh – incidentally – you might want to google Achimedes Principle while your at it (or some variation of that spelling)

  • Jason S

    Uh… no.

    The height of the continents and the corresponding depths of the seas have indeed changed due to plate tectonics over the billions of years since the planet was created. But that’s a small and constant change compared to the very large changes that occur to the ocean level when huge ice sheets form or melt.

    I have to wonder about denialists: ok, you guys think there is a global conspiracy amongst scientists who want more money for research. Ok, that’s dumb, but plausible. But what about the folks who want to do geoengineering? Do you think these people simply want to mess with the environment for fun? Or are they some cliched mad scientists who want to destroy the world?

  • Liz

    Geoengineering is scary – presuming we can get enough aerosols in the upper atmosphere to change the climate, there will most likely be unintended and undesirable changes in the weather somewhere. Imagine the US tries it and and inadvertently causes widespread and devastating flooding in China or Russia or India… it could start a war! But my guess is that we can’t change the climate that way anyway. After all, a typical hurricane releases some 600 trillion watts of heat energy, equivalent to 200 times the world’s total electrical generating capacity. And that’s just one storm!

  • Brian

    @m: I think you’re missing the point of the article. The calculations being done with regards to sea level are relevant to a tiny sliver of geologic time, namely from now up until around 2100. There’s no reason to suspect that plate tectonics will be relevant over this time period for any *change* in sea level. For that reason, there’s no point in discussing the role it plays in sea levels across geologic time, and so your point is irrelevant. The article instead focuses on how sea levels might rise if large quantities of ice, presently on land, melt into the oceans (something that does, actually, depend on temperature). Surely, since you are well versed in the Archimedes Principle, you are aware of the fact that when you drop ice cubes into a glass of water, the fluid level will rise. Global warming denial or not, the article is focused on that phenomenon only, and invoking arguments about plate tectonics either reveals that you did indeed miss the point of the article, or that you are purposefully offering up specious and irrelevant arguments against global warming. Skepticism of global warming can be a healthy and important thing, but you do a disservice to the cause by making straw man arguments like this one.

  • amphiox


    Sea levels are affected by both plate tectonics and temperature.

    The last time the earth was in a warm phase on geologic time scales was the Eocene. Kansas was under water. The time before that was the End Cretaceous (before the asteroid). Kansas was under water then too.

    And if you had bothered to google the Archimedes principle yourself you would have known that it presupposes a constant temperature in the fluid, and that it predicts that adding addition material to the fluid (say, like by melting a lot of ice) causes fluid levels to rise.

  • Tanya

    Not only does geoengineering pose the risks you mention, but there are also many toxicological dangers to both humans and the environment that must be considered. Can pumping innumerable megatonnes of heavy metal particulates into the atmosphere, which inevitably ends up in the air we breathe and in our water supply, be a good thing, regardless of how dire the “climate change” situation may appear (or be presented to appear)?


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