What’s the best way to respond to those who deny the reality or consequences of global warming?

In a culture where many people are shaky on science, my friend Jim Koplin always started with the basic physics: Life on Earth depends on energy from the sun. That heat warms the surface of the planet, and some of it goes back into the atmosphere. Certain gases, especially carbon dioxide, trap that heat, creating the greenhouse effect. There is an overwhelming scientific consensus that human activity, most notably the burning of fossil fuels, has produced anthropogenic global warming, a continuing rise in the average temperature of our climate system above what would be happening absent human activity.

The best place to find that scientific consensus: The Intergovernmental Panel on Climate Change (IPCC), created under the United Nations, is considered the authoritative source for that consensus on global warming and is typically cautious in its public presentations. The IPCC’s Fifth Assessment Report in 2014 concluded that warming of the climate system is unequivocal and unprecedented in human experience; that human activity is the clear cause; that substantial and sustained reductions of greenhouse gases are necessary to avoid catastrophe; and that even with such reductions, some effects of climate change can’t be reversed and will be felt for centuries.

Even more disconcerting is the widespread lack of awareness of the scope of consequences of this warming, which are worth summarizing. The American Association for the Advancement of Science’s 2014 report listed the key effects of this level of global climate destabilization: the accelerated melting of Arctic sea ice, and Greenland and Antarctica ice sheets; increase in sea levels that will threaten coastal areas; accelerating acidification of the ocean; and amplified threats, with less predictability, from wildfires, floods, droughts, and heat waves. All this will have wide-ranging, and generally negative, effects directly on human health and on agriculture, as well as on other species, including an increase in the extinction of species and the unpredictable consequences of a dramatic reduction in planetary biodiversity.

People also are often unaware of how collective action to deal with this climate crisis has lagged behind even the minimal steps necessary to avoid catastrophic consequences, which is not difficult to understand given the complications of constructing, securing agreement for, and then implementing and monitoring a plan with the governments of so many countries.

Harder to excuse is the level of denial in the U.S. public about the science itself. As the evidence for human-caused climate disruption has become more compelling, there has been no consistent increase in public awareness. Gallup polls have measured public concern about global warming since 1989, and the percentage of Americans expressing “a great deal of worry” has tracked with major global warming news (spikes in concern when an ecological catastrophe is in the news) but doesn’t reflect the steadily solidifying scientific consensus. The highest levels of worry occurred in April 2000 (40 percent) and March 2007 (41 percent) with the lowest points in October 1997 (24 percent), March 2004 (26 percent), and March 2011 (25 percent). The 2014 level of 34 percent worry is about the same as 1989.

Why would people who, in most every other aspect of life accept without question the results of peer-reviewed science, reject the overwhelming consensus of climate scientists in this case? One reason is the way in which the issue has been politicized, with the Gallup polls showing the most entrenched climate-change denial to be found in conservative spaces; distrust of the science is now seen by many as an important marker of conservative identity. Naomi Klein points out that many of those on the political right see climate change as merely a cover for an attack on capitalism. Others have theological reasons for ignoring the crisis, believing that whatever is happening is part of the plan of an omniscient God. For others perhaps it is simply easier to disbelieve than to face the implications, which is made easier by the well-funded media campaigns to create doubt.

Whatever the source of an individual’s climate denial, the question is how those of us who aren’t experts can engage in constructive dialogue with deniers. The first question I ask when talking to an audience or class about this issue is how many trained climate scientists there are in the room. The answer is usually none, which definitely includes me — I do not conduct original research on climate, nor am I competent to evaluate the scientific literature on the subject. Like everyone else in the room I have to make a decision about how to understand the consensus on the issue that emerges from modern science’s peer-review process, in which scientists submit their results to competent peers and over time build a consensus on how to understand the world.

That process does not produce a perfect understanding of the world, evidenced by the simple fact that scientists constantly modify theories and adapt their understanding as evidence changes. There is much debate about how to understand this process, and careerism and economic pressures connected to research funding can skew the results. But for a lay person, the key question is: On what basis would you challenge the overwhelming consensus of peer-reviewed science? I have no way of making an independent judgment about the validity of scientific conclusions that go beyond high-school chemistry, biology, and physics, and yet I don’t hesitate to act on the basis of those conclusions because my experience indicates to me that science does a reasonably good job of describing certain aspects of the world. When I turn on my computer — which is the product of a lot of science that I don’t have the expertise to understand — I don’t wonder whether the underlying conclusions of the scientists who conducted the research are correct.

The only other issue on which there is a significant challenge to the overwhelming consensus of peer-reviewed science is, of course, evolution, where the objection is clearly ideological. Most people who reject Darwinian evolution by natural selection do so out of religious convictions that, whatever one thinks of them, are outside the realm of science. It’s reasonable to assume that since most climate-change deniers lack the scientific basis for their assertions, they are likely also motivated by ideology.

Nothing in that analysis requires one to accept the recommendations of scientists on moral and political questions. Trusting scientists on scientific questions does not imply we should cede to them our ability to make independent judgments about what should be done in response to scientific conclusions. On questions of public policy, we are not bound to agree with scientists, who in my experience have no special status in questions about human values; accepting the power of the scientific method does not mean abandoning our role as human beings and citizens.

This is an excerpt from the new book Plain Radical: Living, Loving, and Learning to Leave the Planet Gracefully, published by Counterpoint/Soft Skull, which tells the story of Robert Jensen’s intellectual and political collaboration with teacher/activist Jim Koplin.