Forests have a localised cooling effect, and in tropical areas where deforestation has occurred, outdoor workers are now feeling the heat more
17 December 2021
Deforestation in tropical regions of Asia, Africa and the Americas has reduced the cooling effects of trees, decreasing safe working hours – by an average of at least half an hour per day between 2003 and 2018 – for about 2.8 million outdoor workers.
“The temperature change associated with deforestation over the 15-year [study period] is equivalent to a century of global warming, happening almost instantly, at these locations,” says Luke Parsons at Duke University in North Carolina.
Tropical forests are known to have a localised cooling effect, not only through providing shade, but also via a process called evapotranspiration, in which water is sucked up from the soil and evaporates from the leaves.
Now, by using data from population surveys and mapping tree cover loss over a 15-year period, Parsons and his colleagues have estimated the effect of deforestation on outdoor workers – in, for instance, agriculture, fishing or forestry – across 41 countries.
“Climate change has already pushed tropical locations right to the edge of what would be considered safe for heavy outdoor labour. Deforestation tips those locations into being even more unsafe,” says Parsons.
Parsons and his colleagues used land surface temperature measurements from satellites, and humidity data from weather balloons, to estimate how hot an average day felt to outdoor workers in regions which either lost or maintained tree cover between 2003 and 2018.
“The study focuses on what you would think of as a ‘feels-like’ temperature, it takes into account how well you can cool yourself by sweating [which is affected by humidity], as well as the temperature,” says Parsons.
The team calculated the number of hours during an average day in each region that the apparent temperature fell within a threshold with a maximum temperature of around 29°C that is deemed safe for heavy labour. Above this threshold, health guidelines suggest more breaks should be taken to avoid heat-related issues such as kidney injury and potentially fatal heat stroke.
The researchers then turned to population surveys to estimate the number of outdoor workers in these areas.
This revealed that some 2.5 million outdoor workers in Asia lost at least half an hour of safe work per day, between 2003 and 2018, due to increased temperatures in deforested regions.
In the Americas, nearly 200,000 outdoor workers lost half an hour of the safe working day between 2003 and 2018 in regions with depleted tree cover. Meanwhile, deforestation in Africa was associated with some 31,000 people losing this amount of safe work time each day. Regions that maintained forest cover generally stayed cool, and substantially less work time was lost.
It is important to remember that, due to the scale of the study, the team didn’t measure actual worker hours on the ground across the entire tropics, says Parsons. This means the assessment of lost worker hours is based on theoretical considerations rather than direct observations of behaviour.
“Removing tropical rainforest not only contributes to global climate change, but also threatens the livelihoods and well-being of local communities. Future deforestation combined with climate change will be a one-two punch for those who are most vulnerable,” says Parsons.
He and his colleagues are currently looking at how replanting trees could decrease local temperatures. “This work shows there’s a clear incentive for local populations to replant trees to regulate local warming,” says Parsons.
“These results emphasise the need for policies that take into account local contexts to reduce and eventually stop deforestation and implement workers’ protection,” says Shouro Dasgupta at the Euro-Mediterranean Center on Climate Change.
Journal reference: One Earth, DOI: 10.1016/j.oneear.2021.11.016
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