A study by researchers at Brown University has found a quarter of posts about climate change on Twitter were written by bots.
Bots are computer programs that can masquerade as humans to post or send messages on social media.
Researchers discovered tweets posted by bots created the impression there was a high level of climate change denial.
The paper detailing the finds has not yet been published and was first reported by The Guardian newspaper.
The research team analysed 6.5 million tweets from the period surrounding President Donald Trump's June 2017 announcement that he was removing the United States from the Paris climate accord.
The finding showed 25% of tweets on climate change were likely posted by bots. Most of those tweets centred on denials of global warming or rejections of climate science.
"These findings suggest a substantial impact of mechanized bots in amplifying denials messages about climate change," the authors of the reporter wrote, according to The Guardian.
Bots are automated to post or send messages but they must be set up by a human. The Brown University team could not identify who was behind these climate change denying bots.
Bots for both sides
Researchers used a tool from Indiana University called Botometer to determine the probability that a tweet was sent by bots or by humans. Within the overarching topic of climate change, they also broke down several subcategories.
Tweets about "fake science" were found to have been written by bots 38% of the time and 28% of tweets about oil company Exxon were posted by bots.
Posts in support of action to protect the environment were far less likely to come from bots. Researchers found only 5% of tweets advocating such action came from this type of software.
Emilio Ferrara, a research professor at the University of Southern California - who has conducted his own research on the influence of bots - explained this type of software is used to amplify a message.
"Think of a bot as a megaphone," Professor Ferrara said.
"Bots give the impression that there is organic support behind a movement or idea."
Paris climate accord
During the days directly surrounding President Trump's announcement that the US was leaving the Paris agreement, there was a general increase in the number of posts about climate change. This included the number of posts by bots - they rose from hundreds per day to more than 25,000 per days.
But because more humans were also posting about climate change during this period the percentage of bot posts was reduced. They made up just 13% of all posts during that time.
Though the Brown University study was unable to identify who set up the bots, Professor Ferrara, from USC, said there is cause for concern.
"If someone is manipulating the messages that we consumer online then there is a reason to be concerned that they are changing people's perceptions or beliefs," he told the BBC.