The report encouraged the adherence to the Paris climate change accord, which was signed in 2016. File Photo by Free-Photos/Pixabay/UPI

Oct. 9 (UPI) -- Just 20 energy companies are responsible for more than a third of all worldwide carbon emissions over the last half-century, climatologists said in a new study Wednesday.

The Climate Accountability Institute said in the analysis the top five polluters are Saudi Aramco, Chevron, Russia's Gazprom, ExxonMobil and National Iranian Oil Co.


The remaining 15, in order of emissions, include, British-based BP, Royal Dutch Shell, Mexico's Pemex, ConocoPhillips, Iraq National Oil Co. and Brazil's Pertobas.

All told, the 20 companies have contributed 480 billion metric tons of carbon dioxide and methane -- mainly from the combustion of their products -- of all fossil fuel and cement emissions since the mid-1960s.

RELATED Study calls for stronger protections for emperor penguins

The CAI said the report quantifies "how much each of the largest oil, natural gas, and coal companies has contributed to the climate crisis since 1965."

"In my view, fossil fuel firms were morally and legally obliged to warn that continued use of carbon fuels threatens our health and welfare, and to accelerate the conversation on how to reduce the threat," CAI co-Director Richard Heede wrote in an editorial in The Guardian Wednesday. "Instead, the industry has for decades invested millions in climate denial obfuscation in order to delay legislative action and avoid losing market share."

The institute started with 1965 because that was the year it says the fossil fuel industry first learned of the potential for climate change.

Sixty-seven nations recently pledged to be carbon-neutral by 2050, but the list doesn't include some of the largest polluting countries. U.S. President Donald Trump has withdrawn the United States from the Paris climate change pact, which seeks to keep the rise in the average global temperature to well below 2 degrees Celsius above pre-industrial levels and limit the increase to 1.5 degrees Celsius. The agreement was signed in 2016.

"It is incumbent on companies that value their social license to operate to respect climate science, manage corporate risks accordingly, commit to reducing future production of carbon fuels and their emissions in alignment with the Paris Agreement," the institute said. "Companies leading this transition will prosper and laggards will perish."