A temperature rise of 1.5C by the end of century could lead to a 2.2% drop in working hours - equal to 80 million full-time jobs - costing the global economy $2.4 trillion, according to projections by the U.N. International Labour Organisation (ILO).
The ILO said people would be unable to work due to the health risks posed by higher temperatures.
"The impact of heat stress on labour productivity is a serious consequence of climate change, which adds to other adverse impacts such as changing rain patterns, raising sea levels and loss of biodiversity," said ILO's Catherine Saget.
The World Health Organisation has said heat stress linked to climate change is likely to cause 38,000 extra deaths a year worldwide between 2030 and 2050.
Heat stress occurs when the body absorbs more heat than is tolerable. Extreme heat can cause heat-related illnesses, such as heat stroke and exhaustion, increase mortality, and exacerbate existing health conditions.
Agricultural workers - especially women, who make up the bulk of the 940 million labourers in the sector - will be most affected, the ILO said, accounting for about 60% of all working hours lost due to heat stress by 2030.
If global temperatures rise as predicted, the construction industry will account for about 19% of lost working hours, with the poorest countries in Southeast Asia and west Africa worst hit, the ILO added.
Transport, tourism, sport and industrial sectors are among those that will also be affected by rising heat, the ILO said.