Computer hackers have broken into systems at the Climate Research Unit (CRU) at East Anglia University and have published thousands of documents online.
The data included personal information about individuals.
The hackers claim the data proves that global warming has been overstated.
The university has removed the server that was attacked. "We took immediate action to remove the server in question from operation and have involved the police in what we consider to be a criminal investigation," it said.
The CRU countered the claims that global warming had been overstated. "[Our] research is, and has always been, fully peer-reviewed by the relevant journals, and is one strand of research underpinning the strong consensus that human activity is affecting the world's climate in ways that are potentially dangerous."