A new report says planting more trees would be good for our health.
The Planting Healthy Air study from The Nature Conservancy examines the potential impact of planting trees in specific cities to lower heat and pollution, and how that could affect health, especially in regard to asthma.
The group's lead scientist, Rob McDonald, said trees provide shade and release water vapor into the air as they photosynthesize. Leaves remove particulate matter from the air around the trees, including toxins from auto exhaust and factory and power-plant emissions.
"Trees can reduce air temperatures nearby by two to four degrees Fahrenheit, and they're already doing that for tens of millions of people worldwide," he said. "They can remove up to a quarter of the particulate-matter concentrations in the atmosphere, one of the most damaging kinds of air pollution."
McDonald said heat waves are responsible for 12,000 deaths each year, killing more people globally than hurricanes or winter storms. Additionally, 3.2 million deaths annually can be attributed to fine particulate matter, a component of smog. The report said by 2050 this type of pollution could kill 6.2 million people every year.
According to McDonald, elderly people face particular risk as the global climate shifts and average summer temperatures increase.
"One forecast from the World Health Organization is that annual mortality from heat waves could reach 250,000 people by 2050 unless cities start to adapt," he added. "Smart cities are starting to think about heat action plans."
The study found if cities around the world invested $4 for every resident in tree planting, tens of millions of lives could be saved.