WASHINGTON — More than 400 climate scientists are calling on Hill+Knowlton to drop its fossil fuel clients, saying the agency’s work for Big Oil is in conflict with its role handling PR for the United Nations climate change conference in Egypt later this month.

“As scientists who study and communicate about climate change, we are constantly faced with the twin challenges of addressing the climate emergency and overcoming fossil fuel industry-backed disinformation campaigns,” about 420 experts said in an open letter to H+K CEO AnnaMaria DeSalva and WPP CEO Mark Read.

“Up until now, Hill+Knowlton has played an enabling role in these campaigns to mislead the public through its work with clients such as Saudi Aramco, ExxonMobil, and the Oil and Gas Climate Initiative,” said the letter, whose signatories include scientists from the Union of Concerned Scientists, or UCS, and Harvard University. “These clients have not taken the fundamental steps necessary to address the climate emergency and sharply rein in fossil fuels. Instead, they have used Hill+Knowlton and other PR agencies to spin, delay, and mislead, in order to continue expanding fossil fuel production and thereby increasing heat-trapping emissions.

“We firmly believe that Hill+Knowlton’s work for these clients is incompatible with its role leading public communications at the annual United Nations climate talks in 2022 (also known as COP27),” the letter said.

The letter, issued Friday, comes on the heels of a report in Open Democracy saying H+K has been hired by the Egyptian government to help organize COP27, which will be held later this month in Sharm El Sheikh.

H+K did not respond to request for comment.

Calling out H+K is the latest move by UCS and Clean Creatives, a PR and ad industry advocacy group, criticizing agencies for working with some of the world’s largest polluters.

During the annual Climate Week in September, Clean Creatives plastered parts of lower Manhattan with posters calling on agencies — most notably Edelman — to drop their fossil fuel clients.

Three days earlier, UN Secretary-General António Guterres blasted PR agencies for “raking in billions” by downplaying fossil fuel clients’ detrimental effect on the climate — and said they should pay for doing so.

And less than a week before that, federal legislators ramped up their probe into PR firms’ relationships with Big Oil companies with a congressional hearing that investigated the industry’s role in spreading deceptive information

In January, more than 450 scientists called on PR and advertising firms to stop working with fossil fuel companies.

The effort was coordinated in partnership with the Union of Concerned Scientists and Clean Creatives, which in November, launched a high-profile celebrity and influencer campaign calling on Edelman to drop fossil fuel clients.

Two weeks earlier, Edelman unveiled a series of actions it pledged to take in response to those calls, which include walking away from companies that do not meet a series of criteria on climate action. At that time, Edelman identified 20 emissions-intensive clients for follow-up discussions after a 60-day review of its portfolio.

Edelman, however, stopped short of dropping fossil fuel companies across-the-board, saying its work pushing clients toward achieving net zero goals is more productive than walking away.