Steve Sherwood, in his article “Science controversies past and present” (PHYSICS TODAY, October 2011, page 39), finds similarities between the cautious reception of global warming and those of Copernicus’s heliocentric solar system and of Einstein’s general relativity; by the comparison, he implies that global warming is in very good company. But erroneous ideas met similar receptions. For examples, see the article “Pathological science” by Irving Langmuir and Robert N. Hall (PHYSICS TODAY, October 1989, page 36).
Then Sherwood complains that claims such as “global warming having stopped in 1998” can be trivially falsified by looking at the data. So I looked at the data. While I agree that the conclusion is overstated, I found no falsification. The mean global temperature has not increased much since 1998, but in view of the part that noise plays in global temperatures, the result is not yet significant. However, another decade without considerable further warming would require a serious reexamination of the present global warming models.
In the next article, “Communicating the science of climate change” (PHYSICS TODAY, October 2011, page 48), Richard Somerville and Susan Joy Hassol tell us how to sell their radical view of climate change to a dismissive populace. In a strange parallel to Madison Avenue sales jargon, they provide a list of terms and concepts that are supposed to incite the populace to buy their views. Also, they suggest that one should cultivate vivid comparisons. For example, in connection with the report that the Greenland icecap is now believed to be melting at the rate of 220 km3/year, they argue that the rate should be compared to the annual water use of “the entire city of Los Angeles . . . [of] about one cubic kilometer.” In that spirit, I can describe that melting rate by noting that a year’s melting raises the sea level a little less than 1/32 of an inch. And the global temperature increase of about 0.8 °C in the past century is about the same as one experiences by moving 50 miles southward anywhere in the central US from Minnesota to Louisiana.
In their radical position on the effects of warming, Somerville and Hassol argue that the world must shut down all processes that transfer carbon dioxide to the atmosphere so that the emissions (their figure 5) are “approaching zero by midcentury.” Since shutting down all fossil-fuel burning by 2050 would probably do as much damage to the economy as the warming and thus wreck the production and supply of food and shelter to the 8 billion humans who will be occupying our planet, I was concerned about the acceptance of that position. But my concern was muted by the public-opinion survey shown in their figure 1, which demonstrates that for good reasons or bad, the American people are not buying the position that one has to shut down civilization to save it.
The models used to predict future global climate means are molded to fit past climate. However, global climate is the average of local climates, which are known to be chaotic and are hence unpredictable in principle.
Thus the century and a half of good climate measurements on which the projections of the future are based are seriously affected by unpredictable but fundamental noise that limits the usefulness of those projections. The limitations to global warming prediction are clearly understood in the excellent 1000-page report Climate Change 2007: The Physical Science Basis,1 by the Intergovernmental Panel on Climate Change (IPCC), which reflects the contributions of about 500 authors—including Sherwood and Somerville—and another 500 reviewers.
In that bible we learn that the mean energy transfer from Earth’s surface is about 492 W/m2 (page 96), whereas the forcing from CO2 added by industrialization is only 1.6 W/m2 (page 32), with little uncertainty in either number. That small CO2 forcing leads directly to only a fraction of the 0.8 °C global temperature increase in the past century. The more general view is that positive feedbacks that amplify the direct CO2 contribution account for the temperature increase we perceive. Thus while most concerned scientists—perhaps 98%—believe that industrial CO2 has led to some warming, some very good scientists do not find the necessary feedbacks plausible and conclude that the increased CO2 cannot be responsible for most of the perceived warming.
I find the spectrum of informed scientific beliefs reflected sensibly in the projections described in the IPCC report. Assuming no effective CO2 control and an increase from about 390 ppm today to 1250 ppm by 2100, the IPCC scientists project (page 13) a likely temperature increase of 3.4 °C but with a one-in-six (one standard deviation) likelihood that the temperature increase will exceed 5.4 °C and cause serious harm and a one-in-six chance that it will be less than 2.0 °C and be innocuous or even beneficial.
In the face of uncertainty, the only broadly acceptable response is one that causes as little harm as necessary but does significant good if the dangers are as great as most of us fear. I suggest that a carbon or CO2 tax best fits that bill.2
