A group of former leaders and climate experts said the annual U.N. COP climate talks were no longer fit for purpose and needed to be reformed, publishing a critical open letter mid-way through what has so far been a fractious summit.

The United Nations' COP climate talks are "no longer fit for purpose" and need an urgent overhaul, key experts including a former UN secretary general and former UN climate chief have said. In a letter to the UN, senior figures say countries should not host the talks if they don’t support the phase out of fossil energy.

For the third straight year, efforts to fight climate change haven't lowered projections for how hot the world is likely to get — even as countries gather for another round of talks to curb warming, according to an analysis Thursday.