The scientific evidence on this question—does carbon dioxide, as emitted by human activity, cause climate change?—has been available for decades. Since the late 1970s, climate scientists have suggested that the accumulation of carbon dioxide in the atmosphere might cause global warming. In 1995, the Intergovernmental Panel on Climate Change, an international group of thousands of the world’s climate scientists, announced that the “balance of evidence” suggested that this had caused ongoing global warming.
This conclusion only strengthened throughout the 2000s. By 2013, the Intergovernmental Panel on Climate Change announced that there was at least a 95 percent chance that CO₂ was causing global warming.
Two branches of the U.S. government have also come to this conclusion. In 2007, the Supreme Court announced in a major decision that:
A well-documented rise in global temperatures has coincided with a significant increase in the concentration of carbon dioxide in the atmosphere. Respected scientists believe the two trends are related.
In 2009, the EPA formally agreed, announcing that carbon dioxide and five other greenhouse gases endangered public health and welfare by causing global warming.
Even the oil companies, who stand to be most harmed by the regulation of greenhouse gases, have come to accept the science. In its official statement on climate change, Exxon Mobil says: “The risk of climate change is clear and the risk warrants action. Increasing carbon emissions in the atmosphere are having a warming effect.”
In its own page on climate change, Shell says: “In order to prosper while tackling climate change, society needs to provide much more energy for a growing global population while finding ways to emit much less CO2.”
Pruitt has previously vacillated on some of these questions. Early last year, he cast doubt on the human origins of climate change, writing in the National Review that “scientists continue to disagree about the degree and extent of global warming and its connection to the actions of mankind.”
Speaking to Congress in January, he moderated those views—somewhat. “Science tells us that the climate is changing and human activity in some manner impacts that change,” he said. “The human ability to measure with precision the extent of that impact is subject to continuing debate and dialogue, as well they should be.”
As I noted at the time, this was a carefully crafted line: It seemed to recognize the reality of climate change while undermining the research methods that scientists used to discover it. It remained out of step with scientific consensus, though, because human activity doesn’t just “impact” contemporary global warming “in some manner.” It is the cause of this climate change. You could even call carbon dioxide and other greenhouse gases the “primary control knob” of the modern-day climate as Kernen did.