More evidence of a scientific consensus that global warming is real and caused by us

Since 1990, the scientific consensus on Global Climate Change has been documented in periodic assessment reports by the United Nations Intergovernmental Panel on Climate Change, the fifth and most recent of which was published in 2014. Below is a summary of the 2014 report’s conclusions as published on Wikipedia.

Figure B1. Summary of conclusions of the IPCC Fifth Assessment Report (taken from Wikipedia).

Doran and Zimmerman (2009) surveyed climate scientists about whether they believed (1) global mean temperatures had “risen,” “fallen,” or “remained relatively constant” since the pre-1800’s, and (2) human activity is a significant factor in changing mean global temperature. Among scientists the most active in publishing peer-reviewed articles on the subject of climate change, 96.2% answered “risen” to question (1) and 97.4% answered “yes” to question (2).

Anderegg et al. (2010) compiled a database of climate scientist who signed statements either endorsing or dissenting from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report conclusion that it is “very likely” that human-produced greenhouse gases have been responsible for “most” of the “unequivocal” warming of the Earth’s average global temperature in the second half of the 20th century. Of this group, 97-98% of the most actively publishing scientists endorsed the conclusion. Further, the authors determined that the endorsing scientists both published substantially more peer-reviewed articles and were cited by other scientists significantly more than the dissenting scientists, which the authors interpreted to indicate that the endorsing scientists were more active and published work deemed more useful by other scientists.

Bray (2010) examined the results of multiple opinion surveys administered to scientists between 1996 and 2009 on the subject of AGW (see graph below).

Figure B2. Graph from Figure 1 of Bray, Environmental Science & Policy 13 (2010) 340-350.

The results indicated a steady increase in the proportion of scientists expressing a high degree of confidence that global warming is really happening (referred to in the paper as “manifestation,” diamonds in graph above) and caused by humans (referred to as “attribution,” squares in graph above).  Both of these measures increased from about 60% to greater than 90% over the period between 1996 and 2009, coincident with the similar increase in the proportion of peer-reviewed journals endorsing AGW during the same period as reported by Cook (2013) (green data in my Figure A1 on previous page).

“Legitimization” (circles in the graph above) refers to the percentage of scientists expressing the opinion that reports by the IPCC accurately represented the scientific consensus related to the predicted effects of global warming.  This data set shows a lower level of agreement than “manifestation” and “attribution” because scientists could disagree on the basis that they thought the IPCC reports either underestimated or overestimated the expected effects.  In fact, as shown in the graph reproduced below, somewhat more of the scientists disagreeing with “legitimization” thought the IPCC reports underestimated the expected impacts compared with those who thought the IPCC reports overestimated the expected impacts.

Figure B3. Graphs from Figure 3 of Bray, Environmental Science & Policy 13 (2010) 240-250. Proportions of scientists either participating in IPCC or not participating in IPCC who responded that the IPCC reports tend to underestimate, accurately reflect (value of 4), or overestimate future changes in (a) temperature, (b) precipitation, (c) sea-level rise, and (d) extreme events.

Also, the responses were similar whether the scientists participated or did not participate in the IPCC process, indicating no evidence that politics associated with the IPCC process affected scientists’ opinions.