Is James Hansen part of the consensus on anthropogenic global warming?

Hansen, James, Lacis, Andrew, Ruedy, Reto, & Sato, Makiko. (1992). Potential climate impact of Mount Pinatubo eruption. Geophys. Res. Lett., 19(2), 215-218.


Cook et al. rating: Level 4: "No Position" = not part of the consensus because the abstract did not “address or mention the cause of global warming."

Abstract: We use the GISS global climate model to make a preliminary estimate of Mount Pinatubo's climate impact. Assuming the aerosol optical depth is nearly twice as great as for the 1982 El Chichon eruption, the model forecasts a dramatic but temporary break in recent global warming trends. The simulations indicate that Pinatubo occurred too late in the year to prevent 1991 from becoming one of the warmest years in instrumental records, but intense aerosol cooling is predicted to begin late in 1991 and to maximize late in 1992. The predicted cooling is sufficiently large that by mid 1992 it should even overwhelm global warming associated with an El Nino that appears to be developing, but the El Nino could shift the time of minimum global temperature into 1993. The model predicts a return to record warm levels in the later 1990s. We estimate the effect of the predicted global cooling on such practical matters as the severity of the coming Soviet winter and the dates of cherry blossoming next spring, and discuss caveats which must accompany these preliminary simulations.

Hansen, J, Russell, G, Rind, D, & Stone, P. A. Lacis, R. Ruedy, M. Sato, and H. Wilson, 1993: How sensitive is the world’s climate. Nat. Geogr. Res. Explor, 9, 142-158.


Cook et al. rating: Level 1: “Explicit endorsement with quantification” = part of the consensus.


Abstract: We estimate climate sensitivity from observed climate change on time scales ranging from the 100000-year periods of major ice ages to brief periods of cooling after major volcanic eruptions. The real-world data indicate that climate is very sensitive, equivalent to a warming of 3±1°C for doubled atmospheric CO2. Observed global warming of ~0.5°C in the past 140 years is consistent with But interpretation of current climate change is extraordinarily complex, because of lack of observations of several climate forcings as well as an unpredictable chaotic aspect of climate change. Climate change during the next decade may help confirm knowledge of climate sensitivity, if global climate forcings are accurately observed.

In the article on the left, Hansen and colleagues were writing about the role of a natural event: the eruption of Mount Pinatubo and the effect on temperature of the aerosols it injected into the atmosphere. There was no reason for them to "express a position" in their abstract on the role of human activities and they did not. The article on the right was about climate sensitivity: the effect of doubled CO2 on global temperatures, so of course they stated their conclusion: that anthropogenic greenhouse gases were the dominant climate-forcing agent.

That Cook et al. placed these articles in two different levels of endorsement demonstrates that their rating system is not about what scientist-authors accept or agree with, the true measure of consensus, but about the subject of their articles and the language they chose. Jim Hansen, of all people, cannot be both in the consensus and out of it. (If Cook et al. did not measure the true consensus on AGW--what did they measure? See here.