A scientific conundrum that has puzzled climate experts for years may have been solved with the publication of research showing how an increase in carbon dioxide levels in the atmosphere contributed to rising temperatures millions of years ago.

The paper, published on Wednesday in the journal Nature, has wide-ranging implications for climate science, because the question of whether a rise in carbon dioxide leads to an increase in temperature – or whether rising temperatures lead to an increase in carbon dioxide – has been seized on by climate sceptics eager to disprove a link between atmospheric carbon and global warming.

It also suggests that imminent “runaway” climate change – whereby our actions in pumping greenhouse gases into the atmosphere contribute to melting permafrost or sea changes that release stores of methane – is a real possibility.

Commenting on the findings, Prof Mark Maslin of University College London said: “[This] should put paid once and for all to the false claim that the rise in carbon dioxide was a passive response to increased global temperatures.”