There is indeed a consensus that humankind is putting large quantities of greenhouse gases into the atmosphere; that some warming has resulted; and that some further warming can be expected. However, there is less of a consensus about whether most of the past half-century’s warming is anthropogenic, which is why, rightly, Oreskes is cautious enough to circumscribe her definition of the “consensus” about the anthropogenic contribution to warming over the past half-century with the qualifying adjective “likely”.
There is no scientific consensus on how much the world has warmed or will warm; how much of the warming is natural; how much impact greenhouse gases have had or will have on temperature; how sea level, storms, droughts, floods, flora, and fauna will respond to warmer temperature; what mitigative steps – if any – we should take; whether (if at all) such steps would have sufficient (or any) climatic effect; or even whether we should take any steps at all.
Campaigners for climate alarm state or imply that there is a scientific consensus on all of these things, when in fact there is none. They imply that Oreskes’ essay proves the consensus on all of these things. Al Gore, for instance, devoted a long segment of his film An Inconvenient Truth to predicting the imminent meltdown of the Greenland and West Antarctic ice-sheets, with a consequent global increase of 20 feet (6 m) in sea level that would flood Manhattan, Shanghai, Bangladesh, and other coastal settlements. He quoted Oreskes’ essay as proving that all credible climate scientists were agreed on the supposed threat from climate change. He did not point out, however, that Oreskes’ definition of the “consensus” on climate change did not encompass, still less justify, his alarmist notions.
Let us take just one example. The UN’s latest report on climate change, which is claimed as representing and summarizing the state of the scientific “consensus” insofar as there is one, says that the total contribution of ice-melt from Greenland and Antarctica to the rise in sea level over the whole of the coming century will not be the 20 feet luridly illustrated by Al Gore in his movie, but just 2 inches.
