Scientists, politicians and officials gathered in Bonn for the UN's annual climate change conference, with attention focused on whether China is poised to take a more important role in global warming.

It is the first such gathering since US President Donald Trump announced the US was pulling out of the 2015 Paris climate agreement in which governments pledged to limit global temperature rises.

Trump's abandonment of one of the keynote policies of his predecessor, Barack Obama, has created a leadership vacuum on climate change that only China can fill, according to analysts and observers.

The US will still have a place at the table in Bonn. Trump's decision to withdraw from the Paris deal does not come into force until 2020. But with Washington having effectively written itself out of the script, China is the logical successor as the key promoter of global warming mitigation.

Cooperation between the US and China had been a central driver of the negotiations that led to the Paris accord. Since Trump's decision to withdraw, Chinese officials have restated Beijing's commitment to the Paris deal and encouraged others to do likewise.

President Xi Jinping, hosting Trump on an state visit to China earlier this month, said in his speech to the 19th CPC National Congress last month that China was ready to assume the role of "torchbearer in the global endeavor for ecological civilization".

Officials have stressed that the issue is too important to be seen in terms of a narrow competition for political leadership. At the end of the day, China would prefer to see the US inside the climate tent rather than outside it.

Speaking ahead of the Bonn conference, Xie Zhenhua, China's special representative on climate, acknowledged that the US withdrawal announcement had dented global confidence on the issue.

However, he encouraged Washington to remain involved and said: "We hope the US can come back to the big family of the Paris pact again."

China is taking its own practical measures to fulfill the Paris agenda, including preparations for a national carbon trading scheme. It is also likely to beat its own goal of achieving a peak in carbon emissions by 2030.

Elsewhere, there are signs that the United States' threatened departure has spurred the determination of environmentalists, not only in the rest of the world but also within the US, to push forward with the Paris climate agenda.

The UN's top climate negotiator has even ended up thanking the US president. "Trump's announcement provoked an unparalleled wave of support for the treaty," according to Christiana Figueres. "He shored up the world's resolve on climate action, and for that we can all be grateful."

California's Governor Jerry Brown appears to agree. The leading climate activist was in China earlier this year for a meeting with President Xi that came just after Trump's announcement on quitting the Paris accord.

Ahead of his China visit, Brown told an interviewer: "As Trump does his climate denial, that paradoxically is a catalytic force that mobilizes those who don't agree with him and those who see climate change as the threat I think it is."

With Trump administration officials promoting the continuing role of fossil fuels, Brown is helping to fund a US pavilion in Bonn that will push the benefits of alternative climate change policy.

He predicted the US would soon rejoin the rest of the world in the face of continued scientific evidence of the negative impact of global warming.

The latest such evidence came just this week. As delegates assembled in Bonn, the UN's World Meteorological Organization informed them that 2017 was set to be among the three hottest since records began in the 19th century.