Scientific consensus on climate change

• 1. Establishing The Consensus

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  In 1978, the National Defense University of the United States surveyed twenty-four experts about near-term climate change. Most respondents expected some warming between 1970 and 2000 but disagreed on the extent. A few scientists thought volcanic activity would offset carbon dioxide emissions by elevating atmospheric sulfate concentrations. This early uncertainty contrasts sharply with today's unified stance. By the 1990s, widespread agreement had emerged among researchers regarding human-caused global warming. Surveys conducted since then show that consensus levels have increased steadily over time. Individual scientists contribute through peer-reviewed publications while national bodies summarize collective agreement in synthesis reports.

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• 2. Quantifying Agreement Levels

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  A 2019 review of scientific papers found the consensus on the cause of climate change to be one hundred percent. Another study from 2021 concluded that over ninety-nine percent of scientific papers agree on the human cause of climate change. In 2013, John Cook examined eleven thousand nine hundred forty-four abstracts from peer-reviewed literature published between 1991 and 2011. He found that sixty-six point four percent expressed no position on anthropogenic global warming. Of those that did take a position, ninety-seven point one percent endorsed the consensus view. James L. Powell analyzed five surveys of peer-reviewed literature from 1991 to 2015. His combined analysis covered fifty-four thousand one hundred ninety-five articles resulting in an average consensus of ninety-nine point ninety-four percent.

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• 3. The Role Of Expertise

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  In 2009, Peter Doran and Maggie Kendall Zimmerman polled ten thousand two hundred fifty-seven earth scientists from various specialties. They received replies from three thousand one hundred forty-six respondents. Seventy-nine climatologists had published over half their research on climate change. Among these experts, seventy-six agreed mean global temperatures had risen compared to pre-1800 levels. Only eighty-two percent of all respondents believed humans significantly influence global temperature. Economic geologists were among the biggest doubters with only forty-seven percent believing in significant human involvement. Meteorologists showed slightly higher agreement at sixty-four percent. A 2014 survey by researchers from the Netherlands Environmental Assessment Agency confirmed this pattern. Ninety percent of those with more than ten peer-reviewed papers explicitly agreed greenhouse gases were the main cause.

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• 4. Major Institutional Endorsements

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  In 2001, science academies from seventeen countries made a joint statement endorsing the work of the Intergovernmental Panel on Climate Change. These nations included Australia, Belgium, Brazil, Canada, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, Trinidad, Turkey, and the United Kingdom. They concurred that temperatures are rising due to human activities. In 2005, another joint statement referred to IPCC conclusions as the international scientific consensus. The Network of African Science Academies issued a similar endorsement in 2007. The International Union for Quaternary Research followed suit in 2008. The California Governor's Office website lists nearly two hundred worldwide scientific organizations holding the position that climate change has been caused by human action. No scientific body of national or international standing disagrees with this view.

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• 5. Debunking Denial Arguments

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  A 2016 study titled Learning from mistakes in climate research examined the quality of three percent of peer-reviewed papers which had rejected the consensus view. Researchers discovered replication reveals methodological flaws common across these outlier studies. James L. Powell analyzed published research between 1991 and 2012 finding only twenty-four articles out of thirteen thousand nine hundred fifty rejected anthropogenic global warming. This represented less than zero point two percent of total publications. A follow-up analysis looking at nine thousand one hundred thirty-six authors revealed only one author rejected anthropogenic global warming. Economist Richard Tol criticized John Cook's methodology claiming it lacked controls. Cook and other researchers wrote results were consistent with other studies published before and since. Surveys show small percentages of dissent often contain errors or cannot be replicated.

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• 6. Evolution Of Scientific Opinion

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  Surveys of scientists' views on climate change have been undertaken since the 1970s. In March 1990, Cutter Information Corporation sent questionnaires to fifteen hundred researchers receiving three hundred thirty-one responses from forty-one countries. Only one point nine percent predicted overall cooling across the next one hundred years. By 2003, Bray and von Storch repeated their survey showing increased confidence. The mean response for global warming being underway shifted from 3.39 to 2.41 on a scale where lower numbers indicate stronger agreement. In 2016, seventy-five point eight percent said uncertainty in climate science had decreased since 1996. Seventy-five point seven percent stated risk associated with climate change had increased considerably. The decade of 2010 has been warmer than the late nineteenth century and the warmest since consistent instrumental records began. Warming over the past fifty years occurred faster than any other period in the last two thousand years.

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