United Nations Secretary-General Antonio Guterres said developing nations were paying a "horrific price" for the world's reliance on fossil fuels, as he toured parts of Pakistan hit by floods blamed on climate change.
Nearly 1,400 people have died in flooding that covers a third of the country - an area the size of the United Kingdom - wiping out crops and destroying homes, businesses, roads and bridges.
Guterres hopes his visit will galvanise support for Pakistan, which needs at least US$10 billion to repair damaged infrastructure.
"Pakistan and other developing countries are paying a horrific price for the intransigence of big emitters that continue to bet on fossil fuels," Guterres said in a tweet, shortly before heading to see some of the most flood-affected areas.
"From Islamabad, I am issuing a global appeal: Stop the madness. Invest in renewable energy now. End the war with nature.
Pakistan receives heavy - often destructive - rains during its annual monsoon season, which is crucial for agriculture and water supplies.
But downpours as intense as this year's have not been seen for decades.
"INSANITY AND SUICIDE"
On Friday (Sep 9), Guterres lamented the lack of attention the world gave to climate change - particularly the industrialised nations that scientists blame.
"This is insanity, this is collective suicide," he said.
Pakistan is responsible for less than one percent of global greenhouse gas emissions, but is eighth on a list compiled by the non-governmental organisation Germanwatch of countries most vulnerable to extreme weather caused by climate change.
Guterres is touring flood-hit parts of the south on Saturday, and will also visit Mohenjo-daro, a centuries-old UNESCO-designated world heritage site threatened by the deluge.
Some 33 million people have been affected by the floods, which have destroyed around two million homes and business premises, washed away 7,000km of roads and collapsed 500 bridges.