The Paris Climate Change Agreement could fall apart because of Brexit, according to a report published by the Institute of International and European Affairs.
The IIEA claim the UK has been a leader on climate change within the EU, and their loss may make the union less ambitious on reaching its targets.
A new report from the group says EU leadership and ambition will suffer even in the case of a soft Brexit.
It may result in the EU having to submit a less ambitious pledge to the Paris accord.
IIEA director general Barry Andrews said this analysis of the impact of Brexit on climate change shows different results to other areas of policy they are exploring.
"In most areas, the UK will be disproportionally negatively affected by its decision to leave the EU, be it in trade, foreign policy or security," he said.
"However, when it comes to climate change, under all Brexit scenarios the most profoundly negative consequence are not felt by the UK, but by the EU and internationally," he added.