Governments of several countries responsible for the largest shares of historical greenhouse gas emissions knew about the dangers posed by fossil fuel-driven climate change decades before they acknowledged them in international negotiations, according to a report released by the Center for International Environmental Law (CIEL). The report, Early Warnings: Government Knowledge of Climate Change and Legal Responsibility for Climate Harm, argues that officials in major emitting countries, including the United States, Canada, the United Kingdom, France, Australia, Germany, Norway and Russia, had access to credible scientific warnings about climate risks from at least the 1960s, and in some instances much earlier.
The findings arrive a week before the first anniversary of the International Court of Justice’s landmark advisory opinion on climate change, issued on July 23, 2025. The ruling affirmed that all countries have binding obligations under international law to prevent and mitigate climate harm and may face legal consequences, including reparations, if they fail to act.
Drawing on government archives, scientific papers, official memoranda and media reports, the 67-page report directly challenges claims made by several high-emitting countries before the ICJ that governments could not reasonably have been expected to act on climate change before the late 1980s or early 1990s. “The question of what governments knew about climate change and when they knew it is not just a matter of historical record, but it is a matter of legal responsibility,” the report says.
According to CIEL, the scientific basis for the greenhouse effect had already been established by the mid-19th century, while the consequences of burning fossil fuels began to be modelled and debated in the late 1800s. By the middle of the 20th century, scientists had begun measuring excess carbon dioxide in the atmosphere, and by the 1960s researchers and policymakers in several industrialised countries were aware that fossil fuel combustion could alter the climate and cause severe environmental damage.
The report notes that much of this early research was funded by governments and carried out in institutions created to advise states. Findings were widely disseminated through scientific journals, mainstream newspapers and government reports, meaning climate science was “not a niche issue discussed only within scientific circles.”
The United States, the world’s largest historical emitter, released an estimated 420 gigatonnes of carbon dioxide from fossil fuels between 1850 and 2021. Yet, in its submission to the ICJ, Washington argued that “general awareness” of climate risks emerged only in the late 1980s.
CIEL points to a series of earlier warnings. In 1951, the US Air Force published a meteorological compendium discussing carbon dioxide and climate change. Between 1956 and 1957, oceanographer Roger Revelle briefed the House Committee on Appropriations on how fossil fuel combustion was increasing atmospheric carbon dioxide and driving global warming.
A 1963 conference report, circulated to universities and government libraries across the country, warned that continued fossil fuel use could melt polar ice caps and that “many life forms would be annihilated”.
By 1965, President Lyndon Johnson’s Science Advisory Committee had dedicated an entire section of its report to atmospheric carbon dioxide, warning of rising temperatures and catastrophic sea-level rise. The report concluded that fossil fuels were the only significant source of additional carbon dioxide entering the atmosphere.
CIEL argues that similar evidence exists across Europe. Germany, Europe’s largest historical emitter with 93.1 gigatonnes of fossil fuel-related carbon dioxide emissions between 1850 and 2021, told the ICJ that meaningful scientific understanding emerged only with the Intergovernmental Panel on Climate Change reports in the 1990s.
However, German government scientist Hermann Flohn had published one of the country’s earliest papers on climate change in 1941. In the 1970s, Germany hosted major conferences examining the carbon cycle and fossil fuel emissions, with participants warning that rising atmospheric carbon dioxide could trigger profound consequences for society.
The report further documents that climate science was increasingly moving from laboratories into political discussions during the 1960s and 1970s. By 1979, scientists were already describing climate change as an “immediate environmental control problem” because the transition away from fossil fuels would take decades. One study estimated that swift action could stabilise atmospheric carbon dioxide concentrations at around 403 parts per million. Atmospheric carbon dioxide concentrations today exceed 420 ppm. CIEL contends that the historical timeline is crucial because international law links legal responsibility to what governments knew and when they knew it. The ICJ held that states have obligations under customary international law and human rights law to prevent significant environmental harm once risks become foreseeable. Those obligations include regulating fossil fuel production, licensing and subsidies.
Lindsay Fenlock, senior researcher at CIEL, said governments can no longer argue that they lacked sufficient knowledge.
“Governments have argued that they couldn’t act because they didn’t know. The historical record tells a different story,” Fenlock said. “The science establishing the dangers of fossil fuels did not emerge overnight in the late 1980s. Governments were engaging with that science decades earlier. That evidence matters because accountability for the climate crisis depends not only on what governments did or did not do, but on what they knew, and when they knew it.” The report also warns that countries continuing to expand fossil fuel production face growing legal risks.
“This evidence makes clear that major emitting States knew we needed to ditch fossil fuels to avert climate disaster for decades before they entered into UN climate negotiations,” said Nikki Reisch, senior attorney and director of CIEL’s Climate and Energy Programme, to TNIE.
“To foresee harm and not act to prevent it is worse than to unwittingly cause damage. The countries and companies that have generated the largest cumulative shares of greenhouse gas emissions should bear the largest shares of responsibility for the ensuing harms,” she said. Reisch added that the ICJ opinion had put governments “on notice”.
“Countries that continue pouring fuel on the raging climate fire by expanding oil, gas, or coal production are hard-pressed to defend their conduct under international law. Continuing to expand fossil fuel production, or to license and subsidies such expansion, may violate international law and subject a State to the full panoply of legal consequences.”
The report stops short of assigning legal responsibility to any individual country, noting that proving liability requires linking emissions to specific harms.