“In the Spring of 2012, the Netherlands Environmental Assessment Agency PBL held a survey among 1868 scientists studying various aspects of climate change, including physical climate, climate impacts, and mitigation. The main results of the survey were published in an article in Environmental Science and Technology (ES&T) in August 2014: “Scientists’ views about attribution of global warming”. It showed that there is widespread agreement regarding a dominant influence of anthropogenic greenhouse gases on recent global warming. This agreement is stronger among respondents with more peer-reviewed publications.” That should not be surprising–there’s no question that most climate scientists feel that way. While I question the extent of dominance of AGW on overall warming, if it turned out to be 50% I would not be overly surprised.
However, there are other areas covered by the survey that are well worth exploring. A supplemental report detailing the findings has been recently released.
First, as a professional market researcher I would like to compliment the research team on their methodological choices and execution of the survey. As one who has been very sharply critical of other research on climate scientists (in particular Lewandowsky, Cook, Anderegg, Prall et al), it is refreshing to see someone taking care to get it right. In that respect, Verheggen, PBL et al is a return to good primary research as exemplified by von Storch, Bray et al in 2008. The results from the two surveys have a lot in common and should be considered mutually reinforcing.
On to the survey findings. Starting with the sexiest topic first, the question of attribution was explored in the survey. 66% of the respondents said that 50% or more of global warming since the mid-20th century can be attributed to human induced increases in greenhouse gases. As 19% responded ‘don’t know’ or ‘unknown’, it is clear that only a small minority has the opinion that GHGs caused less than 50% of recent warming. In fact, only 12% indicated that GHGs caused between zero and 50% of warming since the middle of the 20th century.
An interesting follow-up question was asked of those who felt AGW caused more than 50% of recent global warming. “What confidence level would you ascribe to the anthropogenic GHG contribution being more than 50%?” Similarly, those who ascribed less than half of recent warming to GHGs were asked about their level of confidence.
Those who think GHGs caused more than half of recent warming are far more confident in their perceptions than those who think GHGs caused less than half the warming.
Eighty-nine percent (89%) of those who attribute more than half of recent warming to GHGs said it was ‘virtually certain,’ ‘extremely likely’or ‘very likely’. In sharp contrast, only 45% of those who felt that GHGs had caused less than half of recent warming expressed similar levels of certainty.
I hope to continue with this analysis in subsequent posts. For now, I would suggest that it is fairly clear that there is a very real consensus among climate scientists about the role of human emissions of greenhouse gases in warming since 1945 and that those scientists who form the consensus are far more confident in their perceptions than those who doubt it.