When he said "the earth is cooling this year," I probably should've cut and run. I'd just re-tweeted something on 2010 being tied for first place as the hottest-year-on-record, and I mistook an initial response for a genuine, thoughtful comment (albeit from a skeptical standpoint).
So I tried to engage, pointing him to the National Climatic Data Center (NOAA website) for the best available science. It didn't take long, however, before he launched into full-blown vitriol about green religion, how Al Gore is a liar, how the IPCC is not a scientific body and how the moon is made of green cheese. Okay, I made that last one up, but by then my eyes had glazed over and I was searching for the "block user" function to stop his cluster bombing of my twitter page.
How do you deal with people like that?
The first question is actually whether you should deal with them at all. Engaging in debate may simply serve to reinforce the misperception that the scientific fact base is, well, debatable. The more important discussion is what to do about it.
But if you do decide to go head-to-head, I would offer some advice.
First off, figure out who you're dealing with. Climate skepticism comes in many colors, with genuine science doubters at one end of the spectrum, and industry-funded denialists at the other. It's the people in the middle, who may be genuinely confused by what passes for "balanced reporting" of the subject in the media, who non-professionals can best engage.
Secondly, argue on the basis of what you know. You'll be far more convincing that way. If you're not a scientist, don't try to argue the fine details of climate science. It's complicated, and you run two risks: not being able to answer a point made by someone who knows more about the science than you; and discrediting the cause by making exaggerated or false claims.
If you want to argue the science, study the latest IPCC report or summaries from highly credible sources. Beware of using the shortcuts which can be found on the Internet (just google "how to talk to climate skeptics") because as good as some of these sites may be, they will never have the answer to every variation of the argument that may be thrown at you. Once you start down that path, it may be hard to retreat.
Here is a handy guide -- 5 things anyone can say about climate change with confidence:
1. According to the Intergovernmental Panel on Climate Change (IPCC), it is a fact that CO2 and other greenhouse gases are warming the atmosphere. The burning of fossil fuels is the primary source of increased CO2 in the atmosphere. The impacts of climate change could be catastrophic for life on earth.
2. The IPCC's latest assessment report (PDF) drew on the work of 3,750 scientists from all over the world who participate on a voluntary basis.
3. According to a recent analysis published by the US National Academy of Sciences, 97-98% of the most actively publishing climate researchers agree with the tenets of the IPCC, and the 2-3% who are unconvinced have substantially less climate expertise relative to the others (PDF).
4. Independent reviews of the body of climate science were undertaken in 2010 by notable academic bodies, including the Inter Academy Council -- a collection of the top science academies from around the world. While some of these inquiries highlighted areas where working practices and procedures of the IPCC could be strengthened, NONE of them found the underlying science to be inaccurate.
5. But hard science aside, you can always lead off with one simple question: When it comes to making decisions which will profoundly impact the lives of our children, grandchildren and generations to come, on whose advice should policy be based -- The US National Academy of Sciences, the UK Royal Academy, the Russian Academy of Sciences, the American Geophysical Union, the Royal Society of Canada, the Institute de France, the Japanese National Academy of Sciences (to name a few)... or a small handful of very noisy conspiracy theorists?
Take your pick.
Tell us your climate denier horror stories. What tips do you have from battling with anti-science rhetoric?