Bots are computer programmes 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.