It’s a thankless job, but green spaces save us millions by soaking up pollution and cooling us down.

Trees have a proven positive impact on cities:  They lower wind speed and thus energy consumption.  They reduce pollution and heat.  They generally improve how neighborhoods are perceived.  They make cities more livable.  But the best way to prove why cities should plant more trees might be the fact that they have a significant economic impact.

A new study published in the online journal Ecological Modelling puts a number on just how much money trees save cities.  After studying 10 megacities around the world and taking into account air pollution, storm water, building energy, and carbon emissions, the researchers found that trees have an economic benefit of about $505 million every year.  From Beijing and Cairo to London and Los Angeles, researchers from the SUNY College of Environmental Science and Forestry and Parthenope University of Naples found that trees are worth $1.2 million per square kilometer, or $35 per capita.

But in the future, those numbers could be much greater.  In megacities, which are defined as cities with more than 10 million people, tree cover today ranges from 8.1% of the metropolitan area to 36%.  But the potential tree cover ranges from 15.6% to 24%, meaning there’s significantly more space to plant trees.  “Planting more trees in potential tree cover areas could nearly double the benefits provided by the urban forest,” the researchers write.

Read more at Trees Can Save a City $500 Million Every Year