Days ahead of United Nations’ COP26 climate conference, top executives of major Western oil companies will testify before the US Congress on their alleged role in downplaying the impact of climate change. In a statement, the House of Representatives Oversight Committee said the companies had for decades “spread denial and doubt” about the harm of their products despite being aware of the effects of global warming since 1977.

Some major companies also publicly supported action to prevent climate change while privately stalling reforms, the statement added.

The CEOs of Exxon, Chevron and BP America, the president of Shell and the heads of lobby firms the American Petroleum Institute and the US Chamber of Commerce will testify before the committee on Thursday, BBC reported.

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Democratic Representative Ro Khanna, who chairs the Subcommittee on the Environment, told Reuters that the hearing was the start of a year-long investigation.

“The idea is for them to admit to the American people what they have done,” he said.

Khanna said other industries including advertising and social media could also face the probe.

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Shell and BP are among a group of companies that wrote to Congressional leaders earlier this month to pledge their support for climate action and reduce greenhouse gas emissions.

The companies said in a letter they are “deeply committed to combating climate change and promoting clean and renewable energy and energy efficiency. The companies said they had taken significant steps to reduce emissions and “embrace climate-forward business strategies”, the letter said.

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The hearing is being compared to House’s Big Tobacco investigation in the 1990s, which concluded that cigarette companies had tried to cover up evidence that their products were addictive and harmful.

A total of 197 countries that have signed the UN Framework Convention on Climate Change will meet for the annual COP26 climate change summit from October 31 to November 12 in Glasgow, Scotland.