Leonardo DiCaprio made waves at the 2016 Toronto International Film Festival with the world premiere of Before the Flood, a documentary highlighting the increasing scale and severity of climate change impacts around the world.

The Oscar-winning actor, producer, and United Nations Ambassador of Peace also used the film to provide a platform for climate scientists to debunk some of the pervasive myths advanced by climate change deniers.

The film is a stark reminder that, despite decades of increasingly alarming warnings from the scientific community regarding the projected effects of climate change, climate change skepticism is still a problem.

Indeed, the Republican Party in the United States has nominated a presidential candidate who has publicly attacked the veracity of anthropogenic climate change on several occasions. What is arguably more disturbing is that a significant portion of the populations of the US and Canada continue to deny the effects of climate change.

This is despite the fact that, concerning the link between human activity and the rapidly changing climate, the science is clear, and it has been for some time now.

A paper published in 2009 surveyed climatologists who are active publishers on climate change and found that 97.4 per cent of these experts supported the claim that human activity is causing changing global temperatures.

Similarly, a 2013 paper examined close to 12,000 abstracts from papers published between 1991–2011 on the topics of “global warming” or “global climate change.” Of those abstracts that stated a position on anthropogenic global warming, 97.1 per cent supported the consensus position that human activity is linked to climate change.

Further, beyond overwhelming agreement on the part of climate scientists, the body of climate change science itself offers multiple independent, converging lines of evidence to support the claim that there is a causal link between human activity and climate change.

Examples of this converging evidence include: the observed sea level rise; melting sea ice; increasing moisture in the air; more fossil fuel carbon in oceans, trees, and air; satellites recording less heat escaping to space; a cooling upper atmosphere as a result of greenhouse gases trapping heat in the lower atmosphere; and many more.

In the past, climate change deniers have tried to dispute this scientific literature by taking issue with the interpretation of the data offered by climate science. Most often, this has been in the form of an argument positing that the changes and trends identified by climate scientists are, in reality, components of the earth’s natural temperature variation. Thus, the argument goes, the current global warming trend is part of the planet’s natural warming and cooling cycle, which has in the past yielded ice ages and other significant deviations from the norm.

Professor W. Richard Peltier of U of T’s Department of Physics and Director of the Centre for Global Climate Change Science states, “All of these excuses for denial have now been entirely debunked. The planet continues to warm and the expected impacts of the warming are being felt, for example, in the increasing frequency and severity of extreme meteorological events.”

Given the absence of any remaining scientific basis for climate denial, explaining the stubborn persistence of this position requires looking to economic, ideological, and psychological factors.

The ongoing controversy engulfing multinational oil and gas giant ExxonMobil regarding its alleged climate science cover-up is a reminder that actors endorsing climate science skepticism can be fueled by powerful economic incentives to maintain the status quo.

Evidence has come to light suggesting that Exxon has long had scientific evidence supporting the causal connection between burning fossil fuels and dangerous climate change but chose to mislead the public and its shareholders by promoting climate change skepticism instead.

This dynamic parallels earlier attempts by tobacco companies to discredit scientific findings that suggested a causal link between smoking cigarettes and lung cancer throughout the mid-to-late twentieth century.

The similarities are not superficial — in fact, some of the individuals and organizations involved in Exxon’s climate change skepticism strategy were also involved in manufacturing scientific skepticism for the tobacco industry.

Beyond economic incentives, people may harbour psychological and ideological incentives that encourage climate change denial.

Researchers have found that individualists in the United States are more likely to accept the scientific consensus on anthropogenic climate change, if it is compatible with their ideological beliefs. In the study, individualists and hierarchs who read an article on climate science that recommended deregulation and increased nuclear energy capacity were more likely to accept the scientific claims compared to a second group who read a nearly identical article that instead recommended increased regulations.

In another example of motivated cognition and ideological leanings, Peltier also notes that the persistence of climate denial can be partially traced back to a “deep distrust” of expert opinion, along with a “high degree of anti-intellectualism and disrespect for, and misunderstanding of, the scientific method whereby we seek understanding of the natural world.”

To understand the impacts of climate denial, it is important to clarify what is meant by ‘scientific consensus’ with respect to climate change. This phrase signals that the relevant scientific community has overwhelmingly accepted the evidence that there are significant, long-term changes in the earth’s climate, and that these changes are causally linked to human activity.

This phrase does not indicate, however, that there is also universal agreement within the scientific community with respect to the extent of climate changes, the most likely future trajectories that the changes signal, or what action should be taken by governments, institutions, or individuals in response to climate change.

Thus, while climate change denial remains problematic, tackling it is only part of the challenge of addressing the types of damage highlighted in DiCaprio’s film.

Even in settings where there is universal agreement that anthropogenic climate change is real and requires action, translating the climate science into effective policy instruments and then successfully implementing those instruments is immensely challenging. It is especially difficult to accomplish this in a manner that addresses the simultaneous, often competing concerns of the global South, Indigenous peoples, business groups, governments, environmentalists, and countless other stakeholders.

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