The U.S. withdrawal from the Paris climate pact could “in a worst case scenario” add a 0.3°C rise in global temperatures over the 21st century, the UN said on Friday.

The head of the World Meteorological Organisation’s atmospheric research and environment department, Deon Terblanche, underscored, however, that the likely impact of U.S. President Donald Trump’s widely-condemned decision remains far from clear.

“We haven’t run new models overnight but the indications are that it could be in the worst case scenario in the order of 0.3°C,” Mr. Terblanche told reporters in Geneva, referring to a possible rise over pre-industrial temperatures.

“That is the worst case scenario and this is probably not what will happen,” he added.

Under the Paris deal agreed in 2015, world nations vowed steps to keep the worldwide rise in temperatures “well below” 2°C from pre-industrial times.