Rising temperatures and humidity due to climate change are likely to increase the number of days with unsafe "heat stress," putting Southeast Asia at great risk of significant drops in productivity, a research firm said on Wednesday.

Southeast Asia over the next three decades could lose 16 percent of its labor capacity due to rising heat stress, which could cause absenteeism due to dizziness, fatigue, nausea and even death in extreme cases, the British firm Verisk Maplecroft said.

The company predicted the biggest losses in productivity in Singapore and Malaysia, with 25 percent and 24 percent decreases from current levels. Indonesia could see a 21 percent drop, Cambodia and the Philippines 16 percent and Thailand and Vietnam 12 percent.

"Climate change will push heat stress impacts to boiling point with significant implications for both national economies and the health of vulnerable workers," said James Allan, head of environment at Verisk Maplecroft, in a statement.

The company used climate projections to calculate the drop in labor capacity, based on the occurrence of conditions that prompt heat stress and leave workers unable to perform physical activity.

It said by 2045 the number of heat stress days in Singapore and Malaysia will rise to 364 (from 335 and 338 respectively); to 355 from 303 in Indonesia; and to 337 from 276 in the Philippines.

Calculating potential lost productivity for 1,300 cities, the company found 45 of the 50 highest risk cities were in Southeast Asia, including Kuala Lumpur, Singapore and Jakarta.

Twenty of the 50 highest risk cities are in Malaysia, 13 in Indonesia, four in the Philippines and three are in Thailand.

High-risk cities outside the region included Cartagena, at the top of the list, and Barranquilla in Colombia, Panama City and Arraijan in Panama, and Manaus in Brazil.