That's not the real problem--Venus, for example, shows that even heavy cloud cover can suport hot environments (heat is an energy budget issue, meaning that energy out is as important as energy in when doing the calculations). The real problem is that the majority of life on Earth functions within ecosystems based on photosynthesis. Solar radiation is the very foundation of the food web, and reductions in solar radiation will have profound impacts on the biosphere--and these impacts are demonstrable. I know it's demonstrable, because I've helped demonstrate some of it. Each trophic level has 10% the biomass of the lower ones, roughly (for oceans, remember that this is over a given period of time--phytoplancton are notorious for reproducing like mad, and getting eaten extremely fast, so there's the appearance of paucity in the oceans if you just take a grab sample). How many trophic levels can we support if we reduce solar radiation by 10%?r-j said:
The K/Pg boundary was hotter than any rational environmentalist proposes will happen with current warming (I'm not counting the completely bat-crap crazies, the ones that think we'll light the world on fire and whatnot). The impact actually had a net warming trend (though, before anyone jumps on this, the planet didn't get nearly as hot as it had been--thermohaline circulation was still functional, for example). It's not the temperature that caused one of the two most dramatic mass extinctions in history, but simply blocking the light.
Please read my entire comment. You'll find that I was talking about the fossil record--something that I think you'll agree counts as a qualification.macdoc said:
Have you done the comparison with OIS 11? If not, the statement is actually quite meaningless.
More generally, the Earth HAS warmed before. It's often been much, much hotter than today--and in fact is NORMALLY hotter (Zachos et al., 2001 is the data you'll need to argue against to convince me otherwise, by the way). Large temperature excursions both ways have occurred. Without an understanding of how life on Earth reacted to those temperature changes you can't state with any confidence what will happen. I can show you places in the fossil record where temperature increases caused a lot of problems, and others (such as the Eocene Climate Optimum) where it actually seemed to help the biosphere.
You want to attempt to fix a sitiuation you acknowledge is dangerous without even trying to learn the system? Ask a bomb squad guy what would happen if they acted in such a reckless manner. And it IS reckless--various attempts at altering climate have been attempted and, due to a lack of understanding of what's going on, they resulted in untold ecological devistation. Now people are proposing to muck about with the foundations of the majority of the biosphere. If you don't think that requires some serious and sober reflection, as well as intense analysis of what could happen, I frankly don't want you anywhere NEAR this thing. This is more dangerous than every nuclear bomb going off at the same time--and I can say this with absolute confidence, because the last time such a thing happened on the scales necessary to impact global temperature it WAS worse.
I probably don't know more in general. But I'd be very surprised if any of them knew as much about mass extinctions as me. They study modern oceans; I study mass extinctions.
Besides, who knows more is irrelevant--this is nothing more than an ad hom attack to dismiss my arguments without addressing them. Zachos et al. 2001 is fairly easy to track down. The K/Pg data is as well. Let's address the data, shall we? I've done far too much research to be intimidated by someone saying they're an expert--I've proven experts wrong on a number of occasions. Most commonly, they've stepped outside the limits of their field of expertise. And frankly, figuring out how the biosphere reacts to environmental perturbations is a question for paleontology--the science that actually studies exactly that. (Well, paleoecology if you want to get specific.)
Regional impacts can still be devistating. Which regions do you want to impact? What will the reaction to the biosphere be? Best-case scenario, in terms of impact to the biosphere, would be to put these at the poles, since they're already devoid of most photosynthetic life--but they're also shiny, so they're out. You can try to put it over the oceans, but then you've got to very carefully assess where the phytoplankton are, which is extremely tricky. You also run into the problems of how marine life will react. Land is right out; even over deserts there's simply nowhere you can cut solar radiation by enough to impact temperature without causes devistation. There's also farmland on land--and I'm frankly not brave enough to tell farmers I'm going to cut their sunlight.
The whole idea of reflecting sunlight is stupid, period. When something causes an event that leaves a record for 65,4000,000 years it's a bad idea to do it again.
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