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Over the past few years scientists have offered up some extreme measures — from carbon-capturing rocks to space nets — that could solve the crisis. Some focus on reducing or capturing carbon dioxide (CO2) emissions, which trap the heat on Earth, while other solutions are aimed at cooling the planet by preventing some of the sun's rays from hitting its surface.
We've rounded up eight of the most innovative — or at least the strangest — ideas that are currently getting attention.
1. Spray It Away
The Idea: Remember how we all had to stop spraying ozone-depleting aerosols into the atmosphere? Maybe it's time to re-think that.
A proposal known as stratospheric aerosol insertion suggests that chemicals — sulfur dioxide, in this case — sprayed into the Earth's nearest atmospheric levels could bind with other chemicals to reflect sunlight from the Earth. Helium balloons or high-flying planes could disperse the sulfur dioxide. The gas would oxidize and reflect back some (but not all) of the sunlight that would otherwise hit the planet's surface. Less sunlight hitting the surface means a cooler earth.
The sulfur would be cheap; it's a common industrial pollutant. According to the Council on Foreign Relations, one kilogram of the stuff could offset the effect of hundreds of thousands of kilograms of carbon dioxide.
Potential Problems: It could end up working too well, causing catastrophic weather changes in certain areas (such as sudden droughts). One scientist proposed trying it over the Arctic first, just in case things got a little too chilly.
The concept also involves using one pollutant to offset another — very tricky business indeed, especially when it's explained that stratospheric aerosol insertion creates sulfuric acid and would contribute to ozone depletion — the problem we licked a few years ago by banning CFCs.
2. Use Sunscreen
The Idea: We use sunscreen every day (or we should). Why not use the same principal on the Earth?
Like something out of 'Star Trek,' the concept is to build a giant screen made of criss-crossing aluminum strands and put it into space. The screen would act like a filter, preventing some infrared radiation from reaching the planet.
As wacky as the idea sounds, it's been promoted by scientists like Lowell Wood (one of the original Reagan-era Star Wars supporters) and "Whole Earth Catalog" founder Stewart Brand. Proponents claim the screen would appear as a tiny spot on the sun as viewed from the earth and that it wouldn't affect plant growth, which of course consumes CO2 themselves.
Potential Problems: A sunscreen is a last ditch effort. Building such a screen — an estimated 600,000 square miles in size — launching it into space and maneuvering it into a precise, gravity-neutral location between the sun and Earth may be beyond our current means. After all, we don't even have a working Space Shuttle replacement yet.
3. Scrub Like the Wind
The Idea: How about developing a giant air filter, like the HEPA filters used in homes and offices, to take the carbon dioxide out of the air?
The concept works, in theory. Like a huge radiator filled with chemicals instead of water, such filters could catch CO2 from the air and bind it with chemicals in the filter. Later, the carbon dioxide would be stripped from the chemicals and stored, hopefully nearby to avoid issues of transporting the compressed carbon.
Potential Problems: Testing the theory on a large scale is difficult. No one is sure how many filters you would need to make a significant impact (how many thousands of acres of land would need to covered with giant filters?). And there's the issue of separating the CO2 from the capturing chemicals: This would take a significant amount of energy, which in turn produces more CO2.
4. Plant Fake Trees
The Idea: Trees are superb at absorbing carbon dioxide, but what if we could build a better tree, at least one that could capture even more carbon dioxide?
A synthetic tree with plastic leaves could attract CO2 (much like smokestack filters or those wind scrubbers), then trap and compress the carbon dioxide to be stored in a harmless location. These fake trees wouldn't need direct sunlight, so they could be installed anywhere (not just in some forsaken place in the Midwest or desert). With the right design, fake trees could also work 1,000 times faster than the real thing.
Potential Problems: Fake trees wouldn't look like real trees (although they could be hidden indoors). Then there's that nagging problem of what to do with captured carbon dioxide. Several proposals to use it to enhance vegetable production or in jet fuel look too costly. The most difficult problem, however, is the same one that bedevils the idea of wind-scrubbing filters: it takes too much energy to separate the carbon from the filtering chemicals.
5. Needs More Salt
The Idea: Clouds protect the earth from overheating, so more clouds would be good, right?
The concept is reasonably sound. Clouds do help protect the Earth, so some scientists have proposed creating more clouds by blowing salt into the air. That would increase the chances of water vapor clinging to particles (the salt) and forming clouds. Salted clouds are also whiter and therefore would reflect more sunlight back into space, cooling the planet.
But how to get salt into the air? Some suggest computer-guided sailboats to create giant plumes of sea spray. The boats would use little energy, because they would be largely powered by the wind. And the idea wouldn't expose us to much climate risk: If extra clouds started creating hurricanes and tropical storms, for example, the process could be shut down simply by stopping the boats.
Potential Problems: No one knows how many boats it would take or if the idea would even work — cloud seeding has been notoriously unpredictable, after all. Plus the salt crystals from the evaporating sea water might be too small to form clouds.
6. Needs More Iron
The Idea: It has been demonstrated on a small scale that iron powder dumped into the ocean promotes the rapid growth of plankton. Plankton eats CO2, so the more the better.
Iron fertilization was tried in the Southern Ocean near the Antarctic, and based on those results it's estimated that we could at the very least offset 1,000 pounds of carbon emissions for as little as 10 cents. The low cost is what makes this idea so attractive.
Potential Problems: There just one problem, but it's a biggie: Large plankton blooms can destroy the underwater ecosystem, killing off other species as it consumes other nutrients. Without natural resources from the sea, we'd really be in a pickle.
7. Get Stoned
The idea: Limestone (aka calcium carbonate) actually contains trapped carbon dioxide. So why not turn carbon dioxide into stone?
It takes nature thousands of years to harden chemicals into stones, but scientists think they could do it in a very short time using a process called mineral carbonation. In this approach, carbon dioxide is compressed, heated and then mixed with a mineral such as serpentine or olivine and a chemical catalyst to form limestone-like rock. The end product would be harmless and might even be used as a building material.
Potential Problems: We would have to mine significant amounts of minerals to mix with the carbon dioxide for mineral carbonation to work, and mining has an environmental impact of its own. And heating the mixture to the high temperatures required would take — you guessed it — more CO2-producing energy. Ultimately, the cost may be prohibitive: an estimated $70 per 1 ton of carbon dioxide.
8. Push the CO2 Underground
The Idea: We have lots of cheap coal, but it's the biggest polluter of CO2. Why not filter it out and then pump it underground to store it? Better still, why not pump it into places where we're trying to push oil out of the ground?
This is the principal concept behind the so-called clean coal movement, and at least one such program is still being studied: the Weyburn Project in Saskatchewan, Canada. Researchers there have already shoved millions of tons of CO2 underground and say that if similar projects were initiated around the world, underground reservoirs could trap 200,000 gigatons of CO2; worldwide annual emissions are only 28 gigatons.
Potential Problems: Governments, researchers, and major companies around the world are racing to try to make such a system work. But so far the approach has proven too costly. The gas has to be captured, compressed, and then transported safely to the site of injection. And what if it escapes years from now? Trapped in cellars, carbon dioxide could be more lethal than radon.