- A survey among more than 1800 climate scientists confirms that there is widespread agreement that global warming is predominantly caused by human greenhouse gases.
- This consensus strengthens with increased expertise, as defined by the number of self-reported articles in the peer-reviewed literature.
- The main attribution statement in IPCC AR4 may lead to an underestimate of the greenhouse gas contribution to warming, because it implicitly includes the lesser known masking effect of cooling aerosols.
- Self-reported media exposure is higher for those who are skeptical of a significant human influence on climate.
In 2012, while temporarily based at the Netherlands Environmental Assessment Agency (PBL), my colleagues and I conducted a detailed survey about climate science. More than 1800 international scientists studying various aspects of climate change, including e.g. climate physics, climate impacts and mitigation, responded to the questionnaire. The main results of the survey have now been published in Environmental Science and Technology (doi: 10.1021/es501998e).
Level of consensus regarding attribution
The answers to the survey showed a wide variety of opinions, but it was clear that a large majority of climate scientists agree that anthropogenic greenhouse gases are the dominant cause of global warming. Consistent with other research, we found that the consensus is strongest for scientists with more relevant expertise and for scientists with more peer-reviewed publications. 90% of respondents with more than 10 climate-related peer-reviewed publications (about half of all respondents), agreed that anthropogenic greenhouse gases (GHG) are the dominant driver of recent global warming. This is based on two different questions, of which one was phrased in similar terms as the quintessential attribution statement in IPCC AR4 (stating that more than half of the observed warming since the 1950s is very likely caused by GHG).
Literature analyses (e.g. Cook et al., 2013; Oreskes et al., 2004) generally find a stronger consensus than opinion surveys such as ours. This is related to the stronger consensus among highly published – and arguably the most expert – climate scientists. The strength of literature surveys lies in the fact that they sample the prime locus of scientific evidence and thus they provide the most direct measure of the consilience of evidence. On the other hand, opinion surveys such as ours can achieve much more specificity about what exactly is agreed upon and where the disagreement lies. As such, these two methods for quantifying scientific consensus are complementary. Our questions possibly set a higher bar for what’s considered the consensus position than some other studies. Furthermore, contrarian viewpoints were likely overrepresented in our study compared with others.
No matter how you slice it, scientists overwhelmingly agree that recent global warming is to a great extent human caused.