Secretary of State John Kerry on Thursday tried to spur slow-moving U.N. climate talks in Peru, telling governments to stop blaming each other for global warming and urging developing countries to not take the cheap route of high-polluting coal to grow their economies.

In a speech in Lima, Kerry said neglecting to mount a collective response to fight climate change would be judged as a "moral failure of historical consequences."

"If we don't lead, future generations will not forgive us," Kerry said. "We must take giant measurable clear steps forward that will put us on a new path."

He also took a swipe at U.S. politicians who continue to deny the assessment by an overwhelming majority 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.

Negotiators in Lima are trying to define the elements of a global climate agreement that is supposed to be adopted 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 during the two-week session as age-old splits between rich and poor countries re-emerged over who should do what.

Some delegates said they were surprised that China continued to take a tough stance 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.

Since his days in the U.S. Senate, Kerry has attended every major climate change conference since the 1992 Rio Earth Summit that was the first of now 20 rounds of U.N. talks and he has made action a personal priority.

As the top U.S. diplomat, he has delivered several similarly strong speeches in the past on the issue, accusing climate change skeptics of being members of the "flat earth society" and warning that recent extreme weather patterns and natural disasters could be harbingers of worse to come if climate change is not addressed urgently.

Kerry reminded the audience, which included former Vice President Al Gore, that the two had first heard scientific testimony on the issue in the 1980s.

"This issue should be personal for absolutely everyone, man, woman and child," Kerry said.

Earlier Thursday, U.N. 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.

"I'm really urging them to follow suit," Ban said.

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."