Scientific consensus on climate change
The human activities causing this warming include fossil fuel combustion, cement production, and land use changes such as deforestation,[3]: 10–11 with a significant supporting role from the other greenhouse gases such as methane and nitrous oxide.
The evidence for global warming due to human influence has been recognized by the national science academies of all the major industrialized countries.
[9] In the scientific literature, there is a very strong consensus that global surface temperatures have increased in recent decades and that the trend is caused by human-induced emissions of greenhouse gases.
The fourth NCA, released in 2017, involved the efforts of thirteen federal agencies, led by the National Oceanic and Atmospheric Administration (NOAA),[27] and around "1,000 people, including 300 leading scientists, roughly half from outside the government.
[31]In 2001, science academies from 17 countries (Australia, Belgium, Brazil, Canada, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, Trinidad, Turkey and the United Kingdom) made a joint statement endorsing the work of IPCC.
[33] In 2005, another joint statement from the science academies of major countries (Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, United Kingdom and the United States referred to the conclusions of the IPCC as "the international scientific consensus", and urged prompt action on both climate change mitigation and climate change adaptation.
[34] Elsewhere around the world, other organizations to have referred to the scientific consensus include Network of African Science Academies in 2007,[35] and the International Union for Quaternary Research in 2008.
[36] In 2013, a study which found that out of over 4,000 peer-reviewed papers on climate science published since 1990, 97% agree, explicitly or implicitly, that global warming is happening and is human-caused.
The California Governor's Office website lists nearly 200 worldwide scientific organizations who hold the position that climate change has been caused by human action.
The majority of respondents had expected some warming to occur between 1970 and 2000, and described human emissions of carbon dioxide as the primary cause, but there was a disagreement on the extent, and a few had thought that an increase in volcanic activity would offset carbon dioxide emissions by elevating atmospheric sulfate concentrations (which have a reflective effect, also associated with global dimming, and with some solar geoengineering proposals) and result in overall cooling.
The survey revealed widespread agreement that global warming is already happening, that it will result in negative impacts such as sea level rise, and that reducing carbon dioxide emissions and halting deforestation is an appropriate response to it.
[46][21] In 1991, the Center for Science, Technology, and Media sent a survey of 6 questions to around 4000 ocean and atmospheric scientists from 45 countries, and received 118 responses by January 1992, with 91% from North America.
Finally, when asked about the 1990 IPCC estimate of warming proceeding at 0.3 °F (0.17 °C) per decade throughout the 21st century under the business-as-usual climate change scenario, 13 (15%) expressed skepticism, 39 (44%) had emphasized uncertainty, and 37 (42%) had agreed.
This second survey received 530 responses from 27 different countries, but it has been strongly criticized on the grounds that it was performed on the web with no means to verify that the respondents were climate scientists or to prevent multiple submissions.
While the survey required entry of a username and password, its critics alleged that both were circulated to non-scientists, including to a climate change denial mailing list.
[49] Similarly, there was a 72% to 20% split in favour of describing the IPCC reports as accurate, and a 15% to 80% rejection of the thesis that "there is enough uncertainty about the phenomenon of global warming that there is no need for immediate policy decisions.
"[48] In 2004, the geologist and historian of science Naomi Oreskes analyzed the abstracts of 928 scientific papers on "global climate change" published between 1993 and 2003.
97% of the scientists surveyed agreed that global temperatures had increased during the past 100 years, and only 5% believed that human activity does not contribute to greenhouse warming.
At the same time, the respondents had strongly rejected the concept of intentionally presenting the most extreme possibilities in the hope of mobilizing the public, with around 73% disagreeing (1–3), 12.5% unsure and 14.5% agreeing in any way (5–7).
[55][56][57] Subsequent IPCC reports had been forced to regularly increase their estimates of future sea level rise, largely in response to newer research on the ice sheets of Greenland and Antarctica.
[58][59][60][61] In 2009, Peter Doran and Maggie Kendall Zimmerman at University of Illinois at Chicago polled 10,257 earth scientists from various specialities and received replies from 3,146.
79 respondents were climatologists who had published over half of their peer-reviewed research on the subject of climate change, and 76 of them agreed that mean global temperatures had risen compared to pre-1800s levels, with 75 describing human activity as a significant factor.
[67][68][69][70] This was a follow-up to an analysis looking at 2,258 peer-reviewed articles published between November 2012 and December 2013, which revealed that only one of the 9,136 authors rejected anthropogenic global warming.
[77] They included researchers on mitigation and adaptation in their surveys in addition to physical climate scientists, leading to a slightly lower level of consensus compared to previous studies.
They discovered that "replication reveals a number of methodological flaws, and a pattern of common mistakes emerges that is not visible when looking at single isolated cases".
[83] In 2017, James L. Powell analyzed five surveys of the peer-reviewed literature from 1991 to 2015, and found that they amounted to a combined 54,195 articles, few of which had outright rejected anthropogenic climate change, resulting in an average consensus of 99.94%.
