Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of study (In this context, it is Anthropogenic Greenhouse Gases). Consensus implies general agreement, though not necessarily unanimity. Consensus is normally achieved through communication at conferences, the publication process, replication (reproducible results by others) and peer review. People attached to a particular study can often recognize such a consensus where it exists, but communicating to outsiders that consensus has been reached can be difficult, because the arguments through which science progresses may seem to outsiders as contestation. “Of note is the large proportion of abstracts that state no position on AGW. This result is expected in consensus situations where scientists '...generally focus their discussions on questions that are still disputed or unanswered rather than on matters about which everyone agrees' (Oreskes 2007, p 72).”
Two studies on this topic are: (1) “Quantifying the consensus on anthropogenic global warming in the scientific literature” by John Cook and others in and (2) The Scientific Consensus on Climate Change by Naomi Oreskes.
The first study conducted by John Cook and others tries to quantify the consensus on anthropogenic global warming in the scientific literature and have extended the analysis of peer-reviewed climate papers and examined a large sample(12465 papers) of the scientific literature on global CC, published over a 21 year period, collected from the ISI search, in order to determine the level of scientific consensus that human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW). They examined four metrics to quantify the level of endorsement:
(1) The percentage of endorsements/rejections/undecideds among all abstracts.
(2) The percentage of endorsements/rejections/undecideds among only those abstracts expressing a position on AGW.
(3) The percentage of scientists authoring endorsement/ rejection abstracts among all scientists.
(4) The same percentage among only those scientists who expressed a position on AGW.
They classified each abstract according to the type of research (category) and degree of endorsement. Written criteria were provided to raters for category and level of endorsement of AGW. Explicit endorsements were divided into non-quantified (e.g., humans are contributing to global warming without quantifying the contribution) and quantified.
Abstracts were randomly distributed via a web-based system to raters with only the title and abstract visible. All other information such as author names and affiliations, journal and publishing date were hidden. To complement the abstract analysis, email addresses for 8547 authors were collected, typically from the corresponding author and/or first author
In the 2nd study conducted by Naomi Oreskes, is mainly a report on scientific consensus on AGW. The author viewed that the scientific consensus is clearly expressed in the reports of the Intergovernmental Panel on Climate Change (IPCC). IPCC's purpose is to evaluate the state of climate science as a basis for informed policy action, primarily on the basis of peer-reviewed and published scientific literature. In its most recent assessment, IPCC states unequivocally that the consensus of scientific opinion is that Earth's climate is being affected by human activities. The author also states that IPCC is not alone in its conclusions. In recent years, all major scientific bodies in the United States whose members' expertise bears directly on the matter have issued similar statements. The National Academy of Sciences report, “Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise”. It also states that “The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue”. The American Meteorological Society , the American Geophysical Union , and the American Association for the Advancement of Science (AAAS) all have issued statements in recent years concluding that the evidence for human modification of climate is compelling. The author then states that the hypothesis was tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003, and listed in the ISI database with the keywords “climate change”.The 928 papers were divided into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position.
· The results reported in each paper
The 1st study reported the result in through analyses of their study. They conducted Time series Analysis of each level of endorsement of the consensus on AGW in terms of the number of abstracts and the percentage of abstracts.
A direct comparison of abstract rating versus self-rating endorsement levels for the 2142 papers that received a self-rating is observed.
Each abstract was categorized by two independent, anonymized raters. Raters were then allowed to compare and justify or update their rating through the web system, while maintaining anonymity.
The 2nd study reported the result in more generalised manner. It reported the findings that of all the papers, 75% fell into the first three categories, either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position on current anthropogenic climate change. Remarkably, none of the papers disagreed with the consensus position. The authors states that this analysis shows that scientists publishing in the peer-reviewed literature agree with IPCC, the National Academy of Sciences, and the public statements of their professional societies.
· The conclusions from each study
The authors of the 1st study concluded that there is a significant gap between public perception and reality, with 57% of the US public either disagreeing or unaware that scientists overwhelmingly agree that the earth is warming due to human activity. Contributing to this 'consensus gap' are campaigns designed to confuse the public about the level of agreement among climate scientists. A key strategy involved constructing the impression of active scientific debate using dissenting scientists as spokesmen (Oreskes 2010). The situation is exacerbated by media treatment of the climate issue, where the normative practice of providing opposing sides with equal attention has allowed a vocal minority to have their views amplified (Boykoff and Boykoff 2004). They states that a systematic, comprehensive review of the literature provides quantitative evidence countering this assertion. The number of papers rejecting AGW is a miniscule proportion of the published research, with the percentage slightly decreasing over time. Among papers expressing a position on AGW, an overwhelming percentage (97.2% based on self-ratings, 97.1% based on abstract ratings) endorses the scientific consensus on AGW.
In the 2nd study Naomi Oreskes stated that the scientific consensus might, of course, be wrong. If the history of science teaches anything, it is humility, and no one can be faulted for failing to act on what is not known. But our grandchildren will surely blame us if they find that we understood the reality of anthropogenic climate change and failed to do anything about it. Politicians, economists, journalists, and others may have the impression of confusion, disagreement, or discord among climate scientists, but that impression is incorrect.
The author also states that many details about climate interactions are not well understood, and there are ample grounds for continued research to provide a better basis for understanding climate dynamics. The question of what to do about climate change is also still open. But there is a scientific consensus on the reality of anthropogenic climate change. Climate scientists have repeatedly tried to make this clear. It is time for the rest of us to listen.