On the day US President Donald Trump rejected his own administration’s dire report on the economic consequences of climate change, China says it will strive to do better to improve outcomes.

The US National Climate Assessment, quietly unveiled on Friday, warns that natural disasters are worsening because of global warming.

It says warming-charged extremes “have already become more frequent, intense, widespread or of long duration.”

The report notes the last few years have smashed US records for damaging weather, costing nearly $US400 billion ($A553 billion) since 2015.

The President’s response on Monday was, “I don’t believe it.”

Mr Trump, administration officials and elected Republicans frequently say they can’t tell how much of climate change is caused by humans and how much is natural.

In contrast, China’s top climate envoy Xie Zhenhua says his country will work to achieve and surpass its existing greenhouse gas targets.

“I believe the promises we make will be 100 per cent completed and we will strive to do better,” said Mr Xie, speaking to reporters on Monday before a new round of climate talks in Katowice, Poland on how to implement the 2015 Paris agreement.

Although we have encountered a lot of difficulties, a lot of problems, our targets and our resolution will not change.”

China, the world’s biggest source of climate-warming carbon dioxide, has pledged to halt its rise in emissions by “around 2030” through cleaner forms of energy, boosting efficiency and encouraging high-technology industries.

However, overseas researchers have suggested that China’s emissions already reached a peak of 9.53 gigatonnes in 2013 and declined in the three years that followed, suggesting that Beijing’s targets were far too conservative.

Mr Trump said last year that he would pull the US out of the 2015 agreement, arguing that it was too lenient on China.

The economic effects of climate change are becoming apparent. Photo: AAP

Mr Xie said Trump’s decision to withdraw hurt the confidence and resolution of many other countries, but its impact was now beginning to wane, and China’s own commitments to clean, low-carbon development were unbending.

China has already met a target to cut carbon intensity – the amount of CO2 emissions per unit of economic growth – by 40-45 per cent from 2005 levels by 2020, and it is also on course to bring the share of non-fossil fuels to 15 per cent of total energy consumption by the end of the decade, Mr Xie said.

China was the world’s biggest investor in renewable energy and is in the process of establishing the world’s largest carbon trading exchange, he added.

Mr Xie said he hoped developed countries would honour their commitments to the Paris agreement and provide the promised financial and technical support to poorer nations.

He also called on nations to use the upcoming G20 meeting to reaffirm their commitment to combating climate change.

“We hope that this meeting can send out a strong political signal that these economic powers should continue to make efforts to carry out the Paris Agreement and 2030 sustainable development goals,” Mr Xie said.

-With AAP