Q: What are the five most difficult questions asked by smart climate-change skeptics at cocktail parties? And what are the best responses?
Asked by Gil Masters, PhD '66, Palo Alto, Calif.
Any concerned environmentalist should be able to answer questions about climate change. If you're asked a climate change question at a cocktail party, first pour yourself a cocktail and take a deep breath. If you manage to find a true skeptic, who is unconvinced but willing to listen, you may have an excellent discussion on your hands. From my experience, however, the average cocktail-party-climate-change-skeptic is more likely a "denier," than a skeptic. It's also worth remembering that climate change is a complex subject requiring more than a snappy response, so be armed with thought-out answers. With that in mind, I'll answer two questions here. The remaining three are waiting for you in the Nitty Gritty.
Global Climate Models (GCMs) can't really be validated unless we wait around 100 years, so why should we trust them?
It's true that we can't really validate a GCM in the strictest sense, but why should we wait to act given the potentially dire consequences? In the meantime, we can do two things: 1) examine how well a GCM reproduces observed climate; 2) test each component of that model. GCMs do an excellent job at modeling the last 150 years of observed climate. We may have built the models to match the observations, however, so while encouraging, this doesn't guarantee their ability to predict future events. We can validate the GCM components that represent systems governed by physical (e.g. conservation of energy) or empirical relationships (e.g. how quickly rain forms in clouds). Climatologists validate individual components. For example, does cloud formation occur in the same way in the tropics as in the Arctic? (The answer is no.) Climatologists then make new measurements, develop refined relationships, and then refine the model. A GCM is therefore validated piece by piece.
If the Earth is really warming, why is the stratosphere cooling?
The stratosphere is indeed cooling, but it does so because of global warming, not in spite of it. Earth's lower atmosphere is divided into two layers, the troposphere—where we live—and the stratosphere above it, which can be reached by powerful jet planes (~32,000 feet). Observations of the stratosphere by weather balloons indicate a cooling trend. This cooling was predicted by global warming scientists. Here's how it works: Incoming solar energy is trapped in Earth's atmosphere. Some of that energy is radiated back into space. When CO2 increases in the troposphere it traps a greater amount of heat in this layer, lowering the amount of energy radiated outwards into, and adsorbed by, the layers above it. (Extra energy trapped by CO2 in the upper reaches of the stratosphere also radiates heat, much of which goes back out into space.) Since we are now trapping greater amounts of heat in the troposphere, there is more energy leaving the stratosphere than entering it, which causes stratospheric cooling. Stratospheric cooling, predicted and observed by climatologists, is thus evidence for, not against, global warming.
Look to the Nitty Gritty for three more questions. You should keep in mind that there are numerous possible questions out there, and I've selected but a small subset of them. You may have read The Cocktail Conversation Guide to Global Warming, which has some overlap with the questions I address. I encourage you to read it ("Know thy enemy" —Sun Tzu). To help rebut the rest and more, check out the blog Skeptical Science. A second great site is the science blog A Few Things Ill Considered. The site is vetted by my favorite site for climate info, RealClimate. Real Climate is run by practicing climatologists, contains posts discussing climate science and has many links to excellent resources and original data sets. Happy reading, happy cocktail drinking and good luck answering questions!
Daniel Sinnett, MS '10, is a PhD student in geophysics.
