I've gotten a bunch of inquiries from reporters about how we know humans are causing climate change. So here goes.
We do know that the observed warming of the climate system is extremely likely to be caused by human emissions of carbon dioxide and other greenhouse gases. 1/
We do know that the observed warming of the climate system is extremely likely to be caused by human emissions of carbon dioxide and other greenhouse gases. 1/
The logic is as follows: we know theoretically that adding a greenhouse gas the atmosphere should warm the climate. 2/
We also know that we are adding greenhouse gases to the climate, so one should expect a warming trend. 3/
And the observed warming is about the magnitude that we would expect from warming induced by greenhouse gases — as evidenced by the fact that, if you put that much greenhouse gases into a climate model, you get about the observed warming. 4/
To be really confident, however, you also have to eliminate the other suspects. We have a pretty good idea of what other mechanisms could be causing warming (changes in the Sun, internal variability, etc.). 5/
We have investigated them all and find that none of them can explain the timing and magnitude of the warming nearly as well as greenhouse gases. 6/
The scientific community therefore concluded that humans are extremely likely to be responsible for most of the warming since the mid-20th century. 7/
This theory is extremely successful and predicted a lot of the things we now observe — i.e., cooling in the stratosphere, heating in the oceans, the overall pattern of surface warming. 8/
If you think you have a better theory of climate, then this is what you need to do.
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One thing I forgot to add: paleoclimate data also supports a key role for greenhouse gases in climate. They appear to play a key role in episodes like the PETM and ice ages. 9/9
