Climate change sceptics have been emboldened to press their case in the countdown to the Copenhagen talks after seizing on a clutch of e-mails sent to and from climate change experts appearing to show them plotting to manipulate data and hurling abuse at their sceptical peers.

The exchanges, purported to have been written by British and US scientists at the UK's University of East Anglia, debate data and whether it should be released and include abusive language aimed at climate change sceptics.

One e-mail from Phil Jones at UEA to several climate scientists spoke of using a “trick” to hide “the decline” of temperatures. It is not clear from the context what he means exactly but sceptics said it showed that scientists were concealing temperature data that appeared to run contrary to the idea of global warming.

Prof Jones said the “trick” e-mail “caused a great deal of ill-informed comment” but had been taken out of context. “The word ‘trick' was used colloquially as in a clever thing to do. It is ludicrous to suggest it refers to anything untoward.”

In other e-mails, one scientist expressed anger at a journal that had questioned his work, and another threatened to “beat the crap out of” a prominent scientist who takes a sceptical view of global warming.

Sceptics hailed the e-mails – uncovered through a hacking operation targeting the UEA – as the “smoking gun” they had been looking for, proving that climate change scientists were engaged in dubious practices and personal attacks on their opponents, as well as failing to give out certain data on request.

Myron Ebell, director of global warming and international environmental policy at the Competitive Enterprise Institute, a think-tank in the US, said the e-mail exchanges were a “scandal that has knocked down the global warming house of cards”.

Bob Ward, policy director at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics and Political Science, called for a thorough investigation into the matters raised by the e-mails. He said: “The selective disclosure and dissemination of the messages has created the impression of impropriety, and the only way of clearing the air now would be through a rigorous investigation . . . There needs to be an assurance that these e-mail messages have not revealed inappropriate conduct in the preparation of journal articles and in dealing with requests from other researchers for access to data.” He was more sympathetic about the e-mails railing against sceptics, saying climate researchers had been the target of “an aggressive campaign by so-called ‘sceptics' over a number of years”.

The leak came as climate change sceptics stepped up their campaign ahead of the Copenhagen summit that begins in less than a fortnight. Last week, Conservative MEPs hosted a conference of global warming sceptics at the European Parliament in Brussels.

The meeting featured Canadian economics professor Ross McKitrick, who was hailed by sceptics for challenging the calculations underlying a graph of global temperatures that was created by the UN Intergovernmental Panel on Climate Change.

Some climate change experts moved to discount the damage done, arguing that the language used against sceptics amounted to little more than the normal banter used on e-mail among colleagues, and that the basics of climate change science were not called into question by the e-mails.