A new batch of emails and other documents from the University of East Anglia's (UEA) Climatic Research Unit has been released on the internet.
There are more than 5,000 emails, while other documents include working papers relating to the Intergovernmental Panel on Climate Change (IPCC).
A similar release in 2009 triggered the "ClimateGate" affair and accusations of fraud that inquiries later dismissed.
Now, as then, the release comes shortly before the annual UN climate summit.
The university says it has "no evidence of a recent breach in our systems", and says that the sheer number of documents - posted on a Russian server - makes it impossible to confirm that all are genuine.
"These emails have the appearance of having been held back after the theft of data and emails in 2009 to be released at a time designed to cause maximum disruption to the imminent international climate talks," it said in a statement.
UEA's belief that the newly-released material comes from that original hack is backed up by BBC News' examination of the messages, which shows that in at least two cases they derive from email chains that were also released in 2009.
"This appears to be a carefully-timed attempt to reignite controversy over the science behind climate change when that science has been vindicated by three separate independent inquiries and number of studies - including, most recently, the Berkeley Earth Surface Temperature group."
A text file included with the batch, apparently written by someone involved in the release and headed "FOIA 2011 - Background and Context", reads: "'One dollar can save a life' - the opposite must also be true.
"Poverty is a death sentence. Nations must invest $37 trillion in energy technologies by 2030 to stabilize greenhouse gas emissions at sustainable levels."
It then picks a number of phrases from the email batch, whose senders and recipients include UEA's Phil Jones and Keith Briffa, and Michael Mann from Penn State University in the US.
The excerpts talk of issues such as "science being manipulated to put a political spin", the deletion of emails to avoid Freedom of Information (FoI) requests, and agreeing on a "message".
UEA says these extracts "have been completely taken out of context".
Prof Mann - cleared of misconduct last year by a panel convened by Penn State - described the new release as "truly pathetic".
"Agents doing the dirty bidding of the fossil fuel industry know they can't contest the fundamental science of human-caused climate change," he told BBC News.
"So they have instead turned to smear, innuendo, criminal hacking of websites, and leaking out-of-context snippets of personal emails in their effort to try to confuse the public about the science and thereby forestall any action to combat this critical threat."
The writer of the "FOIA 2011" file claims to possess 220,000 more emails.
The first "ClimateGate" material arrived on the web almost exactly two years ago, just before the UN climate summit in Copenhagen that was scheduled to see about 140 heads of state and government deciding on a new global climate treaty.
A hacker entered a backup server at the university and downloaded a file containing administrative passwords, which were subsequently used to access a vast number of files and emails dating back to 1997.
Three inquiries in the UK in 2010 found that the CRU team had not acted fraudulently or tried to manipulate data, as they were accused of doing.
But the university accepted it needed to revise its policy for dealing with Freedom of Information requests, which it has now done.
CRU has also released all of the data it held from weather stations around the world - even some that the original owners of such data wanted kept private.
In partnership with the UK Met Office, CRU maintains one of the three most important global temperature records that have been used to demonstrate the reality of 20th Century warming.
A police investigation into the hack is still ongoing.
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