Men sleep on a temporary shade built over a drain next to a slum during a heatwave in New Delhi, India, May 28th, 2015. Photograph: Reuters/Anindito Mukherjee

Increase in heat stress, which reduces people’s capacity to work, could also increase poverty and inequality in some regions. This will be an effect of reduced income or increased risk of death as people become pressured to maintain livelihoods.


Increasing global temperatures will affect more than one billion people’s ability to work and perform daily activities (workability) and 20 million people’s ability to cope with heat (survivability) especially in tropical and sub-tropical developing countries, according to a recent study by a team of scientists led by Dr. Oliver Andrews.

The study, published in The Lancet, looked at the risks associated with 2.5°C of global warming above pre-industrial levels. It calculated the wet-bulb globe temperature — factors including the effect of temperature, humidity and other environmental factors on humans.

The threshold for workability is a monthly average of daily maximum temperature of 34°C, after which it is too hot to work safely for a large part of the month. This is supported by the recommended heat exposure limits of the US National Institute of Occupational Safety and Health.

The threshold for survivability is a maximum daily temperature of 40°C for three consecutive days, after which the body’s core temperature will increase to potentially fatal levels.

This increase in temperature will affect urban more than rural areas, which will be amplified by urbanization and changes in land use.

Cities will experience more heat stress than rural areas

Exposure to high temperatures can cause heat exhaustion and heat stroke that could reduce labour productivity and increase the risk of deaths. Some countries have already seen the effect of rising temperatures. In 2015, India and Pakistan experienced a heat wave that caused the deaths of at least 3,500 people. In fact, climate-change driven heat stress might have already caused rural to urban migration in Pakistan. Central North Africa is also already experiencing extreme risk of heat exposure.

However, as global temperature change (GTC) increases, more regions will be exposed to extreme heat and heat stress. At 1.5°C above pre-industrial levels, more areas of Africa such as Mali and Niger, South Asia, and the Middle East such as Iraq and Saudi Arabia will be exposed to extreme heat.

At 2°C above pre-industrial levels, the risk of extreme heat stress will spread across north and central north Africa and central South America and at 3°C above pre-industrial levels, this would affect Brazil and Peru and subtropical Africa.

In addition, population growth is projected to be highest in regions at the highest risk of heat exposure such as Central and West Africa and South and Southeast Asia. The study then emphasises the importance of adaptation strategies.

Increase in heat stress, which reduces people’s capacity to work, could also increase poverty and inequality in some regions. This will be an effect of reduced income or increased risk of death as people become pressured to maintain livelihoods. This will be true especially for poor rural communities and subsistence farmers who will be exposed full sun outdoor heat.

According to the researchers, this highlights “the need to build on the Paris Agreement regarding global temperature targets, to protect populations who have contributed little to greenhouse gas emissions.”

The Paris Agreement states that the global temperature change must stay below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C. However, current commitments by countries through their nationally determined contributions show that these commitments are not enough and will lead to global temperature change of at least 3°C.


Published for the Tyndall Centre