LIMA, Peru -- Secretary of State John Kerry tried to spur slow-moving UN climate talks Thursday, telling nations to stop bickering over who is to blame for global warming and to shun the cheap route of high-polluting coal to grow their economies.

In a speech during a brief stop in Lima, Kerry said neglecting to seize the moment and forge an effective plan to fight climate change would be judged a "massive, collective moral failure of historical consequences."

"If we don't lead, future generations will not forgive us," Kerry said. "They will want to know how we together could possibly have been so blind, so ideological, so dysfunctional and, frankly, so stubborn" by failing to act on overwhelming scientific evidence.

Kerry also took a swipe at U.S. politicians who continue to deny the preponderant view of scientists that climate change is man-made, mainly caused by emissions from burning fossil fuels.

"You don't need a Ph.D. to see that the world is already changing," Kerry said. "You just need to pay attention. Thirteen of the warmest years on record have occurred since 2000, with this year, again, on track to be the warmest of all."

He called adopting a global pact next year to rein in heat-trapping greenhouse gas emissions an "urgent necessity" and warned against getting "bogged down in abstract debates."

Rich nations have to play a major role in cutting emissions, "but that doesn't mean that other nations are just free to go off and repeat the mistakes of the past," Kerry said, noting that more than half of global emissions are coming from developing countries.

How to divide the emissions cuts that scientists say are needed to avoid dangerous levels of warming is a major sticking point in the negotiations toward an agreement a year from now in Paris.

The optimism injected into the negotiations last month by a joint U.S.-China announcement on their planned efforts to limit emissions has faded in Lima as splits between rich and poor countries re-emerged over who should do what.

Some delegates said they were surprised that China -- the world's No 1 greenhouse gas polluter -- continued to take a tough stance at the Lima talks on keeping clear dividing lines between the climate action expected from developed and developing nations.

"I thought that they would not be as stern as they used to be in the past," said Tony de Brum, the foreign minister of the Marshall Islands, which is among the small island states that fear they will be submerged by rising seas caused by global warming.

Liu Zhemin, the deputy head of the Chinese delegation, stressed that rich countries have a greater responsibility to fight climate change and called China's announcement last month that it would peak its emissions by 2030 "a very ambitious target" that would require tremendous action.

Chinese experts are still calculating how high emissions will be when they peak but "it will be a very big volume," Zhemin said.

Earlier Thursday, UN Secretary-General Ban Ki-moon urged big carbon polluters to follow the examples of China, the U.S. and the European Union and announce emissions targets for the Paris deal. India, Russia and Japan and other major carbon emitters haven't made pledges.

Governments are supposed to submit their pledges by the end of March, though many have indicated they need more time.

Rich countries insist the pledges should focus on efforts to control emissions and are resisting demands to include promises of financing to help poor countries tackle climate change.

Scientific reports say climate impacts are already happening and include rising sea levels, intensifying heat waves and shifts in weather patterns causing floods in some areas and droughts in others.

Ban said the message from scientists that emissions need to come down urgently is unambiguous.

"They are even shouting from the rooftops," he said. "Scientists are saying that climate change is happening much, much faster than we expect, than we realize."