Q. What can we say for sure about anthropogenic climate change?
A. First, we know that carbon dioxide is a greenhouse gas. We know what its molecular structure looks like, and we know that this structure means that it absorbs infrared radiation. If we’re wrong about this, we’re wrong about the very basics of physics and chemistry.
Second, we know that burning fossil fuels increases carbon dioxide in the atmosphere. The chemical reactions that produce energy when we burn oil, gas, or coal inevitably produce CO2 as a byproduct. And that CO2 goes into the atmosphere. We have excellent measurements of atmospheric CO2, and they clearly show a dramatic increase since the industrial revolution.
Third, we know the climate has been changing. Multiple independent datasets show the global temperature rising. But that’s not all that’s been happening. There is more water vapour in the atmosphere. Spring is coming earlier. Rainfall patterns are shifting. Glaciers and sea ice are melting. There are more and deadlier heat waves.
Fourth, we know that these changes are very, very likely to be due to human activities. We know that the climate changes due to natural factors, but we also have a fairly good understanding of what the climate would look like without us. We can model this natural variability using powerful supercomputers, and we can also study the climate of the past using things like tree rings and ice cores. The changes we’ve observed are too large and too rapid to be attributable to any known natural factors. And they’re very consistent with what we expect increased carbon dioxide to do to the planet. An alternate explanation would have to come up with a plausible natural mechanism for these changes and explain why CO2 doesn’t act the way we think it should – and that’s a very tall order.
Here is Kate talking about climate modelling and clouds in a TED talk:
Also, from her website, a lesson in how to write succinct research summaries:
“My postdoctoral work identified a “fingerprint” of human influence on global precipitation patterns and showed that we are already changing rain and snowfall. This is both reassuring, because it suggests climate model projections are credible, and terrifying, because it suggests climate model projections are credible.”
Ha ha! thank you Dr Marvel.