World must do all 'humanly possible' on climate change: Merkel

German Chancellor Angela Merkel delivered the keynote speech at Harvard University's 368th commencement ceremony AFP/Allison Dinner

"Climate change poses a threat to our planet's natural resources," Merkel said in her commencement address delivered at Harvard University in the United States. "It and the resulting crises are caused by humans."

"We can and must do everything humanly possible to truly master this challenge to humankind," said Merkel, whose government stands accused of dragging its feet on reducing carbon emissions.

"It is still possible. However, each and every one of us must play our part (and), I say this with a measure of self-criticism, get better," she added in a speech delivered mainly in German at the prestigious university.

"I will therefore do everything in my power to ensure that Germany, my country, will achieve the goal of climate neutrality by 2050."

Merkel received an honorary doctorate in law at Harvard's 368th commencement.

In a 35-minute speech often interrupted by applause, Merkel - whose governing coalition was bruised by a poor showing in the European elections - lauded the benefits of the European Union, transatlantic cooperation and multilateralism.

Without saying the name of US President Donald Trump, with whom she has had a difficult relationship at best, the German leader deplored attacks on free trade, "walls" of any kind and "lies (described) as truth."

"We can find good answers even to difficult questions if we always try to see the world through the eyes of others (...) and if we don't always act on our first impulses," she said.

She urged the graduates never to take democracy or peace for granted.

The 64-year-old Merkel, who has been in office since 2005, also mentioned in enigmatic terms the end of her time as chancellor. Her term ends in 2021.

"I believe time and time again we need to be prepared to keep bringing things to an end in order to feel the magic of new beginnings," she said.

"Who knows what life will bring after my time as a politician?" she mused.

"It's completely open. Only one thing is clear - it will again be something different and something new."