Trump, who will return to the White House in January, has pledged to reverse the green policies of President Joe Biden and could pull the United States out of international efforts to limit global warming to 1.5 degrees Celsius above preindustrial times.
This year is almost certain to be the hottest on record, with rising temperatures unleashing a deadly torrent of floods, heatwaves and storms across the world.
In a new analysis of countries' climate plans, the Climate Action Tracker (CAT) project said Trump's potential retreat from the green transition could increase global temperatures by around 0.04C by the end of the century.
Bill Hare of Climate Analytics, one of the groups behind the tracker, said the effect could be "really quite small".
"The damage it would do emission-wise to global climate action, if just confined to the United States and over four to five years, is probably recoverable," he said.
But he said the impact could be significantly greater if other countries use shrinking ambitions from the US, the world's second biggest emitter, as an excuse to slow walk their own climate actions.
That will become clear in the coming weeks and months, with nations expected to submit new and improved emissions-reduction commitments to the United Nations by February.
Hare said that a "fundamental" question will be the reaction of China, the biggest greenhouse gas emitter.
- 'Flat-lined' -
The CAT project calculated that the current crop of climate promises would see the world warm 2.6C by century's end, with very little change in the outlook in the past three years suggesting that government action has "flat-lined".
In a separate report released Thursday, CAT looked at the plans of the biggest greenhouse gas polluters.
The US, which accounts for the largest share of historical greenhouse gas pollution, has said it will cut emissions from all sectors in half by 2030 from 2005 levels.
CAT said US emissions would need to drop 65 percent this decade and 80 percent by 2035 to align with the 1.5C limit.
China, which has yet to outline a pledge covering emissions from all sectors, would need to slash carbon pollution 66 percent by 2030 from 2023 levels and 78 percent by 2035.
"If one looks at the rapid drop in emissions needed, it is reasonable to ask: How could this be possible?" Hare said of the China projections.
"The short answer is it's mainly because we can decarbonise the power sector nearly everywhere, quite quickly. And the first thing to do is to get out of coal."
The report comes after research published on Wednesday found that carbon dioxide emissions from fossil fuels rose again this year to a new record, meaning the cuts needed in the future are even sharper if the world is to meet its warming target.
Emissions of CO2 from coal, which account for 41 percent of the global total from fossil fuels, ticked up 0.2 percent this year, according to the projections by the Global Carbon Project, with decreases in the US and European Union and increases in China, India and the rest of the world.
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