Somerville and Hassol reply: We appreciate the comments by all the writers but must take exception to several statements by Robert Adair, whose expertise famously ranges from particle physics to baseball but clearly does not include climate science. In examining the hoary claim by climate contrarians that global warming stopped in 1998, he may indeed have “looked at the data.” However, he obviously did not learn the research literature. The global mean surface temperature record displays both strong natural variability and a long-term warming trend, and decadal periods are demonstrably inadequate for evaluating long-term trends. Nineteen ninety-eight was a strong El Niño year, hence it was unusually warm, and using that year as a starting point for computing a meaningful trend is cherry picking.
Recent data are fully consistent with the expected warming trend of about 0.2 °C per decade. Every year since 2000 has been warmer than the 1990s average, every year of the 1990s was warmer than the 1980s average, and the 1980s were the warmest decade on record until then.1
Adair also inappropriately dismisses a warming of 0.8 °C as equivalent to moving 50 miles southward in the central US. Confusing local and global temperatures is nonsensical, and a global warming of about 8 °C is not at all like moving 500 miles. It is like the difference between an ice age and an interglacial period.
In another bizarre misrepresentation, Adair compares our list of terms to “sales jargon” that is “supposed to incite the populace.” In fact, our list of terms that mean different things to the public than they do to scientists has been widely cited and praised, because so many people have encountered the failure to communicate that can result from the different meanings. The only thing we’re selling is improved clarity of communication that can help bring science to its rightful place in decision making.
Adair consistently misrepresents our positions and those of the broader climate science community. The science we outline is entirely consistent with the 2007 Fourth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC). Adair says that “some very good scientists do not find the necessary feedbacks plausible and conclude that the increased [carbon dioxide] cannot be responsible for most of the perceived warming.” He fails to say that almost all those dissenting scientists are, like himself, neither credentialed experts nor active researchers in climate science. The IPCC report concludes that most of the warming is very likely (greater than 90% probability) due to human-caused increases in greenhouse gas concentrations. The evidence for carbon dioxide–induced warming amplified by feedbacks in the climate system, such as increased water vapor, is abundant and strong.
Adair also appears to misunderstand the physics of climate models when he claims that their projections of the future are based on the past 150 years of observational data. He also misreads the projections to suggest that atmospheric CO2 concentrations can climb to 1250 ppmv by 2100 and still result in temperature increases that would be “innocuous or even beneficial.” As the IPCC report on impacts2and many other assessments3 have shown, the 0.8 °C rise we’ve experienced to date is already causing impacts, most of which are not beneficial. Future impacts are projected to be more severe.
We do not, as Adair says, “argue” for a “radical” view. Rather, we simply explain that if governments decide on a certain limit for future temperature rise, as they have with the 2 °C target, then science can inform us of the emissions limits required to meet that goal. As we demonstrate in our article, Mother Nature herself thus imposes a time scale on when emissions need to peak and then begin to decline rapidly. The urgency is not ideological at all, but rather is due to the physics and biogeochemistry of the climate system. Advances in climate science have led to a profoundly deeper understanding of human-caused climate change. The impressive scientific story is certainly worth communicating well.
