The party line of climate change skeptics these days is that global warming has paused, or even reversed, in the last 15 years. According to the Nongovernmental Panel on Climate Change, “Global temperatures stopped rising 15 years ago despite rising levels of carbon dioxide, the invisible gas the IPCC claims is responsible for causing global warming.” Typical denialist refusal to accept the facts, right? Perhaps not! A recent paper in Geophysical Research Letters explains, “Although the Mount Pinatubo eruption in 1991 caused a short-term reduction in TOA radiation, increasing greenhouse gases should have led to increasing warming. However, sea surface temperature (SST) increases stalled in the 2000s and this is also reflected in upper ocean heat content (OHC) for the top 700 m in several analyses.”1 Despite this apparent anomaly, however, climate scientists have not been jumping ship from their consensus position that anthropogenic global warming is occurring.
Skeptics see this lack of response as evidence of liberal bias or even conspiracy, but I think there is a much more compelling explanation: anthropogenic warming is part of the hard core of climate science. That is, the AGW claim is not subject to revision, and so when anomalies occur—when observations fail to meet predictions—other components of climate science must be revised to preserve it.
“Hard core” is a term from philosopher of science Imre Lakatos’s account of scientific change. According to Lakatos, scientific research programs consist of a hard core of propositions that are not subject to revision surrounded by a “protective belt” of propositions that are subject to revision. These revisable propositions are also known as “auxiliary hypotheses”. When observations conflict with the research program’s predictions, it is the auxiliary hypotheses that are altered in response. In Lakatos’s account, research programs are judged “progressive” if alterations to the auxiliary hypotheses generate novel predictions and “degenerative” if they are not. Research programs that are continually degenerative ought to be, he claims, abandoned.
Faced with temperature readings that did not match model predictions, climate scientists did not abandon the AGW proposition, because it is part of climate science’s hard core. Rather, they searched for where the “missing energy” might have gone. Recently, two papers have offered possible solutions. First, the above-quoted paper from Balmaseda, Trenberth, and Kälén argues that this missing energy has been located in the deep ocean, below 700 m. Based on model reanalysis and measurements, they conclude that there is “a long-term ocean warming trend, while heating continues during the recent upper-ocean-warming hiatus, but the heat is absorbed in the deeper ocean. In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend” (1754). Starting around 1998, they tell us, changes in wind patterns have caused stirring of the ocean in a way previously unaccounted for by climate models. It is this part of the climate science research program—propositions concerning deep ocean circulation—that should be revised.
Second, a forthcoming article by climate scientists Kevin Cowtan and Robert G. Way concludes that the missing heat is not missing at all, but is instead underestimated by surface measurement networks. They report, “Microwave sounding data from satellites, reanalysis data from weather models, and observations from isolated weather stations all confirm that the unobserved regions of the planet, and in particular the Arctic, have been warming faster than the globe as a whole since the late 1990s.”2 It is no simple task to measure global temperatures, partly because not all parts of the planet are equally covered by measuring stations. Cowtan and Way argue that there is a correlation between poorly-covered locations, such as the Arctic, and locations where there has been significant surface heating. Therefore, surface temperatures have been rising all along; our measurements have just failed to record this warming.
Because it was not an option for climate scientists to revise their belief that anthropogenic global warming is occurring, they were forced to search for other explanations for the apparent failure of climate model predictions to match observations over the last decade. Such explanations have now been found. Skeptics see these recent reports as ad hoc attempts to preserve an untenable hypothesis, but the work of Lakatos councils us to judge them differently: as corroborated novel predictions resulting from the alteration of auxiliary hypotheses. It is conceivable that, in the future, the current consensus climate science research program will degenerate and need to be abandoned, but there is no sign of that yet. This is just science as usual.
- Magdalena A. Balmaseda, Keven E. Trenberth, and Erland Kälén, “Distinctive climate signals in reanalysis of global ocean heat content,” Geophysical Research Letters, Vol. 40 (2013), 1754. ↩
- Cowtan, Kevin, and Robert G Way. 2013. “Coverage Bias in the HadCRUT4 Temperature Series and Its Impact on Recent Temperature Trends.” Quarterly Journal of the Royal Meteorological Society (November). ↩