India is set to lose 3.6% of annual daylight work hours by 2025 due to rising temperatures, reveals an IndiaSpend analysis of data in a new United Nations report.

The loss of daylight work hours could increase to 5.2% in 2055 and 8% in 2085, assuming a consistent rise of 2.7°C, according to Climate Change and Labour: Impacts of heat in the workplace, released by the United Nations Development Program.

Exploring the link between rising temperatures and productivity loss, the UNDP report said South Asian countries will be the most affected by rising temperatures, while European and South American countries will be the least affected. The report is the latest to warn of productivity losses resulting from climate change.

The worst-affected countries globally will be Burkina Faso, Cambodia, Pakistan and Maldives.

In May, India recorded its highest-ever temperature of 51°C in the town of Phalodi in the western state of Rajasthan. In the southern state of Telangana, as many as 315 people died this year (until May) from heat-related causes, and as IndiaSpend reported in April 2016, heat-wave deaths in India increased 296%, or three times, over the last 23 years.

2015 was the third-warmest year recorded in India since record-keeping began in 1901 and as many as 22,563 people have died in heat waves across India between 1992 to 2015.

Excessive heat while working, generally at temperatures above 35°C, creates occupational health risks and reduces work capacity and labour productivity. Maintaining a core body temperature close to 37°C is essential for health and human performance, and large amount of sweating as a result of high heat exposure while working creates dehydration risks.

Outdoor workers with a moderate and heavy workload exceeded the threshold limit value of 28°C and experienced 18-35% productivity loss, according to this 2014 study from Chennai.

4°C temperature rise can lead to 13.6% work-hour loss

The projected loss of daylight work hours by 2085 can further rise if temperatures do.

In India, an 8% loss in daylight work hours due to heat extremes can be reduced to 7%, if the temperature rise is limited to 2.4°C, but the work-hour loss will surge to 13.6% if the temperature rises by 4°C.

A large part of southern India, the eastern and western coasts, has so far been unaffected by heat waves. But that will no longer be the case after 2070, it has been projected, and these areas will be exposed to extreme heat-stress conditions, intensification of heat wave and heat-stress leading, to increased mortality, IndiaSpend had earlier reported.

India will lose 1.8% of its GDP due to climate change

Those in the lowest-income group – heavy labour and low-skill agricultural and manufacturing jobs – are among the most susceptible to climate change, according to the UNDP report.

India has 263 million farm workers and 13 million workers in factories. Without changes to current global behaviour on climate change, India would see economic losses equivalent to 1.8% of annual GDP by 2050, widening to 8.7% by 2100, predicted this 2014 report from the Asian Development Bank.

If mitigation and adaptation steps keep the temperature rise below 2°C, economic losses could be limited to below 2% of GDP by 2100, the ADB report said.

Labour productivity impacts could reduce output in affected sectors by more than 20% during the second half of the century, according to estimates in the Intergovernmental Panel on Climate Change fifth assessment report. The global economic cost of reduced productivity may be more than $2 trillion by 2030.

This article first appeared on IndiaSpend, a data-driven and public-interest journalism non-profit.