Pictures of climate change

Weart replies: Jonathan Katz worries about the validity of computer studies of projected impacts of climate change. And John Curran notes that illustrations to my article show particular events, which computer studies indeed have difficulty attributing individually to climate change. I apologize if any reader jumped to the conclusion that a specific attribution was intended. I wanted only to illustrate the subject of the article—namely, impacts in general. Still, part of the sea-level rise of the past century is reliably attributed to global warming, and the rise did extend the area of Sandy’s inundation. And a peer-reviewed study has reported that global warming did contribute to the Texas drought that was illustrated.

For reasons of length I had to leave out the interesting story of attribution studies of particular impacts; for a sketch and references see http://www.aip.org/history/climate/impacts.htm . Researchers have labored for decades to test computer models against observations, and the matches have been good although imperfect. Anyway, it is not computers but simply the thermal expansion of water and the visible decay of ice sheets that support expectations of further sea-level rise if greenhouse gas emissions continue. Other serious impacts have already been observed in weather statistics, including global intensification of heat waves and of extreme precipitation events.

Finally, Curran misunderstands a phrase he took out of context. I wrote that “in this short article” I could not present a convincing scientific case for impact projections. A convincing case can certainly be made, but only, alas, to those who will undertake a thorough study of the technical literature. Therefore officials and the public have little choice but to heed the consensus of committees of expert scientists—unless (like some people) they dismiss the entire scientific process.