evidence: Scientists agree that global warming is caused mainly by human activity. Specifically, the evidence shows that certain heat-trapping gases, such as carbon dioxide, are warming the world—and that we release those gases when we burn fossil fuels like coal, oil, and gas. [...] Within the scientific community, there is essentially no disagreement on the causes of climate change. Multiple studies have shown that at least 97 percent of scientists agree that global warming is happening and that human activity is the primary cause. Major scientific assessments also agree. The 2018 US National Climate Assessment—whose authors include 300 leading scientists and thirteen federal government agencies—concludes that "it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence."