Guest post by Indur M. Goklany
The latest Science magazine has an extended interview with Dr. Phil Jones. In this post, I’ll keep away from issues related to Climategate, whether this was a softball interview (given that, for example, there is no discussion of deletion of files, if any) or whether, by refusing to share data with skeptics, Professor Jones was undermining the scientific method (because the scientific method relies, among other things, on giving one’s skeptics the opportunity to disprove one’s conclusions). Instead I will focus on phenological arguments that have been advanced to argue that global warming indeed exists.
These arguments are the subject of the second question posed to Dr. Jones:
”Q: Let’s pretend for a second that we threw out the CRU dataset. What other data are available that corroborate your findings about temperature rise?
“P.J.: There’s the two other datasets produced in the U.S. [at NASA and NOAA]. But there’s also a lot of other evidence showing that the world’s warming, by just looking outside and seeing glaciers retreating, the reduction of sea ice … overall, the reduction of snow areas in the northern hemisphere, the earlier [annual] breakup of sea ice and some land ice and river ice around the world, and the fact that spring seems to be coming earlier in many parts of the world.”
I am very sympathetic to PJ’s argument, because, in the past, I have made the same argument. However, over time I have become more skeptical about the extent to which higher temperatures are the sole determinants of either (a) melting of glaciers and sea ice and (b) earlier springs. Accordingly, these phenological arguments have, in my opinion, become less compelling. I would, therefore, add caveats to PJ’s response.
Melting of glaciers and sea ice. It’s possible that higher levels of soot could have contributed to greater melting (see paper by James Hansen, also see here). On the other hand, ice core measurements in Greenland indicate that soot peaked around 1910 (with minor peaks occurring later), consistent with my claim that air pollution from combustion sources in industrialized countries was being reduced long before any Clean Air Act. In addition, a reduction in precipitation would also be manifested as a net reduction in glacier and ice extent, but it is hard to imagine that precipitation changes will only occur in one direction.
Earlier Springs. This suggests that temperatures might have increased, at least around springtime. This, however, is complicated by the fact that human activities have pumped out CO2, and various forms of sulfur and nitrogen into the atmosphere. Each of these acts as a plant fertilizer. This ought to affect the onset of spring. [If anyone has or knows of empirical information on fertilizers and earlier spring, I would appreciate getting details.] Moreover, while there are numerous studies (see, e.g. here) that indicate that spring has advanced, there is a recent satellite based study that indicates no consistent trends in the starat of spring in North America. This paper, Intercomparison, interpretation, and assessment of spring phenology in North America estimated from remote sensing for 1982–2006, notes in its abstract:
”We found no evidence for time trends in spring arrival from ground- or model-based data; using an ensemble estimate from two methods that were more closely related to ground observations than other methods, SOS [start of spring] trends could be detected for only 12% of North America and were divided between trends towards both earlier and later spring.”