A legal challenge to the EPA’s finding on greenhouse gases will test whether the science behind climate change can stand up in court

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The debate over carbon emissions and climate policy is no longer confined to academic journals or political speeches. It is moving into the courts, where the stakes are far higher.

Last month, the U.S. Environmental Protection Agency (EPA) rescinded its 2009 “endangerment finding,” which concluded that greenhouse gases threaten public health and welfare. That finding underpinned the United States government’s authority to regulate carbon emissions under the Clean Air Act. Its removal strips away the legal foundation for much of U.S. climate policy and sets up a legal fight that could put the underlying science itself on trial.

The challenge to the prevailing view of climate science did not begin with this case. Environmentalist and author Lawrence Solomon documented dissenting scientific perspectives in his 2008 book, The Deniers. He pointed to researchers who questioned whether the available evidence supported dominant climate models.

That debate, once confined to academic circles, is now being drawn directly into a legal forum.

At the centre of the case is the CO2 Coalition, a U.S.-based nonprofit group of more than 200 scientists and researchers. The organization focuses on carbon dioxide’s role in plant growth, agriculture and ecosystems. It argues that higher CO2 levels contribute to increased plant productivity and that carbon emissions produce global greening far more than global warming. That position is now at the centre of the case.

On March 20, the coalition applied for intervenor status, which would allow it to present evidence directly to the court. Executive director Gregory Wrightstone said the scientific basis for the endangerment finding is “weaker than previously believed and contradicted by empirical data, peer-reviewed studies and research.” He argues carbon dioxide is not a toxin and that rising CO2 levels have produced measurable environmental benefits.

The coalition also challenges how climate science is interpreted. It argues some climate crisis claims have been driven by what it calls “not science,” including government opinion and funding streams that reinforce it, climate models that it says overestimate warming effects, a “consensus” idea it calls antithetical to science, one-sided peer review, and research that it says cherry-picks, fabricates, falsifies, or omits contradictory data.

To support that argument, the coalition points to several lines of evidence.

It begins with the role of greenhouse gases themselves. Water vapour accounts for about 90 per cent of the atmosphere’s heat retention, while carbon dioxide contributes much of the rest, with a diminishing effect at higher concentrations. The EPA’s own modelling, it argues, suggests that if net zero emissions were achieved now instead of 2050, the difference in global temperature by 2100 would be only 0.17 degrees Celsius.

It also points to historical patterns. CO2 levels have varied widely over time, often exceeding current levels, while temperature trends have not always moved in step. Periods such as the medieval warming era saw higher temperatures without industrial emissions. The Earth has also been warming since emerging from the Little Ice Age, and the exponential growth in greenhouse gas emissions since 1850 has had what it describes as very little effect on the overall trendline.

Finally, the coalition points to solar activity. It says solar output strongly correlates with observed temperature changes over the past century. Solar output rises and falls alongside temperature trends, a relationship it argues may better match the data than emissions-based models. In this case, that furnace is the sun, and human activity is unlikely to change that.

Whether the coalition is granted standing remains uncertain. What is not uncertain is the argument being advanced: the scientific foundation for the EPA’s endangerment finding is open to challenge. If that is correct, the consequences extend beyond this lawsuit.

Climate policy in the United States, and in countries such as Canada that have adopted similar approaches, rests heavily on the assumption that the science is settled.

If that assumption is weakened in court, the legal and policy structures built on it will not stand.

Lee Harding is a research fellow for the Frontier Centre for Public Policy.

Summary: Lee Harding argues U.S. courts may soon test climate science as the EPA reverses its emissions finding. Highlighting dissenting scientists, he challenges consensus claims and warns climate policy is driven more by politics than empirical evidence.