Seems like a good time to revisit anthropogenic global warming: what do we know, what can we assume, and what can we do it about it.
Anthropogenic global warming is a series of nested propositions:
1. The global temperature is rising. This is the heart of AGW, and until this week, it was the real consensus of informed scientists. After the CRU leaks, it turns out that we can't even be sure that the globe has been getting warmer over the last century. Other questions are, what is "global temperature" and is it even relevant. Maybe we should worry about peaks and not averages. Maybe we should worry more about temperatures at the poles or at the equator rather than global averages. Because it turns out that the only good temperature record we have lasting longer than decades is for particular spots in the US and Japan and some of those will have changed due to local urbanization (and in at least one case, because someone pointed an air conditioner dump vent at the thermometer). Of course, at some point we all agree that the globe's gotten warmer; we used to be in the little ice age, which ended about 1880, so the world has clearly gotten warmer since then. Of course, that's been a good thing, leading to the need for proposition 2.
2. Rising temperatures would be bad. In fact, the experience of mankind is to the contrary. Rising temperatures are good. We get more crops, we gain arable land, fewer seniors drop dead shoveling snow, etc. So AGWists need to posit large increases in temperature that push us past a tipping point at which civilization is devastated (or, at least, Bangladesh is under water). We can't get there through CO2 alone, though, even though AGWists put a lot of time into arguing proposition 3.
3. Carbon dioxide causes higher temperatures. This is probably true. Carbon dioxide is a greenhouse gas in that it absorbs sunlight and emits heat at levels higher than the atmosphere generally. But the direct effects of carbon dioxide on temperature are well understood and relatively mild; about one degree for every doubling of CO2 in the atmosphere. Since we're unlikely to double CO2 even twice from this point on -- even as India and China industrialize -- that really isn't going to get us over the tipping point, so
4. Carbon dioxide warming will be amplified by positive feedback mechanisms -- that we've never seen, can't describe and don't understand. The historical evidence seems pretty clear: temperature increases have been followed by atmospheric CO2 increases but never preceded by them. Even worse for the AGWists, we do understand at least two negative feedback mechanisms: more CO2 leads to more plant growth, which, by reducing the Earth's albedo, cools temperatures be reflecting more energy into space; and rising temperature leads to more cloud cover, which reduces Earth's albedo, etc. Basically, AGW's appeal to science just breaks down here, even though positive feedback is absolutely essential to the AGW as disaster scenarios.
5. Industrialization, which leads to release of CO2 into the atmosphere, causes AGW. This is actually more problematic than it appears, because industrialization also leads to the emission of particulate air pollution and other gases, like sulfur dioxide, that cause atmospheric cooling. Do the traces of CO2 we release into the atmosphere overpower the traces of SO2 we release into the atmosphere? Your guess is as good as the CRU's. At least one AGWist theorizes that the reason there hasn't been any warming over the last 10 years has been because of the increase in SO2 pumped into the atmosphere by India and China. That, of course, implies that the clean air act threatens to destroy the world.
6. Global warming is bad because it's anthropogenic. Lot's of AGWists seem to argue that we are obliged to do something about global warming because it's anthropogenic. But what difference does that make? If global warming were natural but disastrous, should we let it? If it were man-made but good (a real possibility, of course) should we stop it just because we're changing "nature?" This (and the continued opposition to nuclear power) is where it becomes clear that AGW isn't scientific at all for many proponents; rather it is political/religious/spiritual.