With the direst warnings yet of impending environmental disaster still ringing in their ears, representatives from nearly 200 nations gathered yesterday in Poland to firm up their plan to prevent catastrophic climate change.

The U.N. climate summit comes at a crucial juncture in mankind's response to planetary warming. The smaller, poorer nations that will bare its devastating brunt are pushing for richer states to make good on the promises they made in the 2015 Paris agreement.

In Paris three years ago, countries committed to limit global temperature rises to well below two degrees Celsius (3.6 degrees Fahrenheit) and to the safer cap of 1.5C if at all possible.

But with only a single degree Celsius of warming so far, the world has already seen a crescendo of deadly wildfires, heatwaves and hurricanes made more destructive by rising seas.

In a rare intervention, presidents of previous U.N. climate summits issued a joint statement as the talks got underway in the Polish mining city of Katowice, calling on states to take "decisive action... to tackle these urgent threats." "The impacts of climate change are increasingly hard to ignore," said the statement, a copy of which was obtained by AFP. "We require deep transformations of our economies and societies."

A key issue up for debate is how the fight against climate change is funded, with developed and developing nations still apart in their demands. Poorer nations argue that rich countries, which are responsible for the vast majority of historic carbon emissions, must help others to fund climate action. But wealthy states, led by the U.S., have so far resisted calls to be more transparent in how their contributions are reported, something developing nations say is vital to form ambitious green energy plans.