n Gallup’s 2016 environment poll, 64 percent of U.S. adults are now worried a “great deal” or “fair amount” about global warming, with a record 65 percent attributing warming primarily to human activities (1). These poll results come several months after the pivotal Paris Agreement taking place at COP 21, the 21st Conference of Parties of the United Nations Framework Convention on Climate Change (UNFCCC). In an unprecedented consensus of the participating 195 countries, on December 12, 2015, the Paris Agreement set global standards to reduce greenhouse gas emissions and limit global temperature rise to well below 2 ˚C.
Global warming has been recognized as a significant issue for decades, with annual meetings of the UNFCCC beginning in the mid-1990s. There is a broad consensus within the scientific community, supported by agencies such as the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA) and the National Research Council, that climate change is occurring and that humans are contributing to it (2). First, in 1998, the same year the IPCC was established, NASA scientist Dr. James E. Hansen testified before Congress that there was a 99 percent certainty that unnatural warming trends were caused by a buildup of carbon dioxide in the atmosphere (3). In 2004, Naomi Oreskes published one of the first studies of scientific literature on climate change. Upon analysis of 928 abstracts of scientific papers from peer-reviewed journals published between 1993 and 2003, she concluded that there is a scientific consensus on the reality of climate change (4). This sparked several subsequent studies by Harris Interactive (2007), Dennis Bray and Hans von Storch (2008), Peter Doran and Maggie Zimmerman (2009), among others, all of which arrived at similar conclusions (5, 6, 7). In more recent years, publications in the Proceedings of the National Academy of Sciences of the United States (PNAS) and in Environmental Research Letters found 97-98 percent endorsed the significant human causes of climate change.
Furthermore, in its Fifth Assessment Report, published in 2014, the IPCC reported that carbon dioxide is 40 percent higher than in pre-industrial times. Between 1880 and 2012, the Earth’s surface warmed 0.85 ˚C and human activity caused most of the warming between 1951 and 2010. Due to warming, heatwaves and heavy rains have also become more frequent since the 1950s and Arctic sea ice has declined on average 3.8% per decade since 1979, leading to an expected global sea level rise between 26 and 82 cm by 2100. In conclusion, the IPCC found that only an aggressive mitigation scenario could keep temperature rise below 2 ˚C (8).