Too hot to work?

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Climate change could slash labor productivity in some countries by as much as 25 percent over the next 30 years, according to a report by Verisk Maplecroft on Wednesday.

The risk consultancy firm found that rising global temperatures and humidity could cause a dramatic increase in the number of days where it would be unsafe to do physical work.

"Incremental rises in global temperature and humidity due to climate change are likely to increase the number of working days exceeding safe levels of heat stress, which can cause absenteeism through dizziness, fatigue and nausea and even death in extreme cases," Verisk Maplecroft said in its report.

"Crops and livestock are also highly susceptible to heat stress, driving food shortages, poverty, and migration — factors that can increase the risk of conflict and instability."

It calculated "heat stress" as when the wet bulb globe temperature (a measure that includes the effect of humidity) exceeds 25 degrees Celsius.

Each of the last three decades has been warmer at the Earth's surface than any preceding decade since 1850, according to the Intergovernmental Panel on Climate Change's 2014 report. It forecast that heat waves will "very likely" occur more frequently and last longer in the 21st century and that between 2016 and 2035, the Earth's surface temperature will warm by 0.3-0.7 degrees Celsius.

Forecast labor capacity fall in SE Asia by 2045 due to 'heat stress'

The fast-growing economies of Southeast Asia will be by far the worst affected, according to Verisk Maplecroft, with productivity in Singapore seen slumping by one-quarter over the next three decades. Productivity in Malaysia and Indonesia is seen declining by 24 percent and 21 percent respectively, and by 16 percent in both Cambodia and the Philippines.

Southeast Asian economies are expected to post some of the world's fastest growth in the coming decades, but Verisk Maplecroft warned that the potential hit from "heat stress" had been largely overlooked.

"Many countries in this region have a limited financial and technical capacity to adapt to climate change impacts, which may deter some investment as the awareness of climate-related financial risks grows," the report said.

Verisk Maplecroft added that countries dependent on agriculture, construction and manufacturing, such as Thailand and Cambodia, were particularly vulnerable. Investors in countries like these could be exposed to rising costs for manufacturing and health care provisions, as well as disruption in their supply chains.

Some developed countries were also judged susceptible, with Australia at "extreme risk" of future heat stress and the U.S., Italy and Hong Kong at "high risk."

"While these countries are in theory more resilient to slowdowns in labor productivity, lost productivity and absenteeism can have significant economic impacts due to the size of their economies," said Verisk Maplecroft.

— By CNBC's Katy Barnato. Follow her on Twitter @KatyBarnato.

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