Our latest Optimist View discussed how urban green space impacts heat exposure and health outcomes in cities. One of the cities grappling with this issue is Phoenix. As the hottest city in the US, Phoenix is very focused on keeping things cool in a warming world. The city has pledged to reach American Forests’ “tree equity” designation by 2030, but it will have some hurdles to overcome.

Looking at the city of Phoenix, ground temperatures and child poverty rate maps are highly correlated, with the lowest income neighborhoods also reaching the highest temperatures. Unfortunately, a large part of urban green space planting relies on private residents, but in neighborhoods like Central City South, where the majority of residents are low-income renters, there is little incentive to plant trees and families have no extra money to pay for the water and upkeep.

How can Phoenix reach its tree cover goals? Utility companies in the city will pay for trees for residents to plant on the West or South side of their properties, which lowers cooling costs, but community advocate Eva Olivas tells Vox that this isn’t enough. The city will have to identify lots where trees can be planted and pay for the upkeep. Fortunately, these initiatives will pay off with one study from Arizona State University finding that covering a quarter of paved areas in the city with trees can cool air temperatures by eight degrees Fahrenheit.

The city is also exploring reflective roofs and roads, although experts note that this is not as effective as boosting canopy cover. The good news is that the city has agreed to make urban green space a priority, taking an important step to ensure that climate change does not disproportionately impact those already more vulnerable to hot summer temperatures.

This story is part of our ‘Best of 2021’ series highlighting our top solutions from the year. Today we’re featuring science solutions.