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http://www.livescience.com/environment/061130_ancient_tsunami.html
 
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'Space umbrella' could stop global warming

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Brandon
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« on: May 07, 2016, 10:43:05 pm »

Then there’s the sky itself. Even on a sunny day, the light-scattering particles could turn the blue sky white. With a sulphate sunshield, there would be more ‘diffuse radiation’, as opposed to direct sunlight. “You see it on a cloudy day. You can’t see the Sun, but it’s still light,” Watson says. However, this unnerving prospect comes with a silver lining.

Though volcanic eruptions can inject vast amounts of greenhouse gases into the atmosphere, the build-up of carbon dioxide actually slows down. No one knows why, but one possibility is that plants prefer whiter skies; they grow better because they don’t get so hot. “It’s actually quite a good argument against this form of intervention. It’s very difficult to predict the outcome because the system is really, really complicated,” he says.

With these uncertainties in mind, Dan Lunt of the University of Bristol, in the UK, and colleagues set up a climate-modelling study to predict the sunshade’s climatic effects.

    If you reduce the global temperature all the way back to pre-industrial, then you tend to over-dry the planet – Ben Kravitz, climate scientist

The model included three scenarios: the pre-industrial world, a ‘greenhouse world’ which has four times the current levels of atmospheric carbon dioxide and is 6C warmer, and ‘sunshade world’ with the same high CO2 but the strength of the sun reduced by 4%. That’s around 55 fewer watts per square metre, roughly the same amount as a light bulb.

They found that the sunshade could compensate for the warming in greenhouse world exactly – the geoengineering was a success. But it wasn’t all good news. Compared with pre-industrial times, the tropics were 1.5C cooler, while high latitudes were warmer by 1.5C. Even with a space sunshield, there’d be less sea ice. That’s because the planet would be shaded evenly. In the tropics, which receive substantially more sunlight than the poles, a 4% reduction amounts to more lost sunlight.

The 'sunshade world' was also drier, with 5% less rainfall on average. “If you reduce the global temperature all the way back to pre-industrial, then you tend to over-dry the planet. The only way to combat that is to have a little bit of left-over global warming,” says Ben Kravitz, a climate scientist who wasn’t involved in the study.

In the imperfectly engineered world, some countries would get a better deal than others. The sunshade could protect some areas from flooding, while inflicting droughts on others. “To get it up there there’d have to be a global effort, but in fact different countries would argue for a very different strength. There might be all sorts of political intrigue.” Lunt explained.
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