As the planet marked its fourth hottest year on record, a study published in the journal Nature found increasing levels of carbon dioxide will lead to thinner ocean clouds and reduce their cooling impact, causing temperature rises of at least 5.6F (3C) over the course of the century.

The team of scientists said the findings show some climate models have been too “optimistic” and previous estimates of a minimum temperature rise of only 2.7F (1.5C) could now be discounted. The optimistic models did not properly assess the impact of water evaporation, which sometimes rises only a short distance into the atmosphere and causes updraughts that reduce cloud cover, the study found.

”These models have been predicting a lower climate sensitivity but we believe they’re incorrect,” Professor Steven Sherwood, from the University of New South Wales, told The Sydney Morning Herald.