As the world’s leaders gather this week at a major summit to discuss ways to address the effects of global warming, one of the greatest obstacles they face is disinformation.

Among the biggest sources of false or misleading information about the world’s weather, according to a report released this week: influential nations, including Russia and China, whose diplomats will be attending. Others include the companies that extract fossil fuels and the online provocateurs who make money by sharing claims that global warming is a hoax.

They spread diverse and frequently debunked falsehoods: Humans are not responsible for climate change; recent wildfires were enabled by arson rather than hotter and drier conditions; the world is cooling; oil and gas giants are leading the charge toward carbon neutrality; and warnings about the environment are an excuse for authoritarian elites to destabilize the developing world and force everyone into lockdown and onto a diet of insects and lab-grown food.

Their efforts have already significantly eroded the public pressure and political will needed to prevent a dire future for the planet, experts said.

“What has dramatically shifted is how central to public life mis- and disinformation about climate has become,” said Jennie King, an author of a new report by Climate Action Against Disinformation, an international coalition of more than 50 environmental advocacy groups.

The unfounded claims, the coalition warned in its report, have increased conspiracy theories, social divisions and harassment. The report noted an “alarming mobilization to violence” against those associated with climate change work, including Spanish meteorologists who reported on extreme spring weather and then faced ominous threats and accusations that they were “murderers.”

The campaign against meaningful action to curb emissions is powered by an ecosystem with “weird informal allegiances and overlaps” among countries, corporations and people — all with disparate agendas and motivations but united in their desire to discredit the climate change threat, Ms. King said.

“It’s actually about the normalization of disinformation, rather than just the sheer volume,” said Ms. King, who is running the coalition’s intelligence unit at the summit. “That’s what concerns me the most — how high-traction and how emotionally resonant this kind of content seems to be.”

Researchers expect disinformation and misleading characterizations of the summit’s goals to spike as delegates meet in the United Arab Emirates for the summit, which is known as COP28. Already this week, unsupported conspiracy theories circulated on social media claiming that governments were using climate change as a pretext to seize land from farmers and cause deliberate food shortages.

The United Arab Emirates is a top oil exporter known less for its climate commitments than for the voracious resource consumption of its most populous city, Dubai. This summer, a disinformation expert in Qatar discovered at least 100 fake social media accounts defending the summit’s location and its president, the Emirati oil executive Sultan al-Jaber. An internal document revealed this week that the Emirates planned to use its hosting role to pursue oil and gas deals around the world.

Social media content promoting outright climate denial increased before last year’s summit, which was held in Egypt, researchers said. Such posts have continued this year to rack up views and citations from top politicians and pundits. The content has sometimes riled up followers; a report this spring from the watchdog group Global Witness found that 73 percent of climate scientists regularly featured in the media had experienced online harassment or abuse as a result of their work.

Climate activists like Greta Thunberg were targeted by Chinese state media, which falsely accused her of calling for an end to the use of chopsticks and denounced her as a “Swedish princess” after she pushed for more emissions reductions from China. RT, a Russian state television network, derided Ms. Thunberg in March as “Dr. Climate Gollum” after she received an honorary Ph.D. from the University of Helsinki.

The E.U. Disinfo Lab, a nonprofit group studying disinformation, said in a report this year that it had found dozens of active websites in Europe and the United States that exclusively focused on climate disinformation — a “striking” departure from most other disinformation websites, which tend to compile a hodgepodge of questionable topics.

Climate Action Against Disinformation found that, in every month since COP27, the hashtag #climatescam generated more retweets and likes than #climatecrisis and #climateemergency on X, the platform formerly known as Twitter. The hashtag appeared in widely circulated posts that falsely blamed arson committed by migrants for wildfires or repeated debunked claims that television broadcasters were manipulating weather maps.

Researchers attributed much of #climatescam’s traction to a small group of influential accounts, which they said tended to be far more vocal about climate denial on X than on platforms like Facebook and Instagram. One account, which researchers said had originated as an anti-vaccine forum on Telegram before shifting to climate denial on X this year, had only a few hundred followers when it shared its first #climatescam post in March; it now has more than 250,000.

Some of the sites pushing climate disinformation made money from ads — a revenue stream that researchers said was enabled by more than 150 advertising exchanges owned by some of the largest tech companies. The marketplaces, which largely use automated auctions to buy and sell online ads, placed ads on at least 15 websites known for hosting climate denial content, according to the report. Doing so flouted policies set up by many of the exchanges to block climate denial content and other disinformation from being monetized.

Ads for McDonald’s and L.L. Bean appeared next to one opinion column this fall that described “an overbearing ‘climate change’ agenda” as “implementing socialism under the guise of saving the planet” by “tyrannical central planners around the globe.”

Some climate disinformation was spread by countries like Russia and China, which often target such content to parts of the world where they seek to wield influence at the expense of the United States and the rest of the West. The report found that Russian state media had framed emission-reduction plans as a form of “Western imperialism” engineered to undermine the development of the so-called global south, or the southern part of the world, which includes some of the poorest and least industrialized countries. (Experts say global warming is a financial threat to developing nations, which are more vulnerable to climate change shocks despite contributing a disproportionately small share of greenhouse gas emissions.)

Russia’s propaganda around climate change, which routinely downplays the phenomenon as exaggerated or even positive, has become increasingly entangled in geopolitics. The country framed economic sanctions against it after it invaded Ukraine as evidence of the importance of its fossil fuel exports in maintaining global energy security. Climate disinformation also figured in a campaign in Brazil that promoted the views of Aleksandr Dugin, a prominent proponent of Russia’s imperial ambitions, according to the U.S. State Department’s Global Engagement Center.

Researchers from Climate Action Against Disinformation found, however, that Russian climate disinformation was opportunistic and, thus, inconsistent. The report noted that “fossil fuel investments in Africa were condemned as attempts to steal the continent’s resources when linked to Western countries, but hailed as championing economic development when related to Russia.”

In China, disinformation about climate change has had a long history, according to a study in May by Annie Lab, a fact-checking project at the University of Hong Kong. For years, calls to fight climate change were portrayed in China as a tool used by the West to stunt China’s economic growth, rather than as an attempt to address a global problem.

Even after China accepted the need for international action, agreeing for the first time at COP15 in Copenhagen in 2009 to set goals for reducing emissions, misinformation and disinformation on the issue remained rife in Chinese media, the lab wrote.

Climate Action Against Disinformation also said China’s state oil giant, the China National Petroleum Corporation, was among the international energy companies making misleading claims about their environmental practices, a strategy known as “greenwashing.” The company’s ads, which often targeted countries in Asia and Africa, sometimes used an increasingly popular tactic that researchers call “nature-rinsing”: employing images of landscapes and scenery in its marketing to create a false and more forgiving association between nature and fossil fuels.

One Facebook advertisement from this year, which researchers said had cost $120 to $595 to place and reached one million viewers, featured emojis of blossoms, a worker in a hard hat and a green heart.

“With the arrival of spring, let’s enjoy the beautiful flower fields covering the oil field!” the ad said.