Urban heat islands have been with us for a long time. That’s the well-documented temperature jump inside cities’ built environments, compared with the surrounding undeveloped countryside.

However, expanding development and the heating climate have turned an interesting meteorological effect into a mounting health hazard for urban dwellers. Temperatures as much as 20 degrees higher than the surrounding green areas can make the asphalt and concrete of the city a literal death trap for vulnerable people. Those with health problems such as asthma are particularly vulnerable, especially if they are too poor to afford reliable air conditioning and home weatherization. Extreme heat already causes more deaths than any other kind of natural disaster in the United States. 

What causes this urban heat island effect? The process is simple: asphalt and concrete absorb more heat from the sun faster, and without as much vegetation respiration to help cool an area off, the heat stays longer. 

The good news is at least one fix is straightforward as well: plant more greenery, especially trees. Organized neighborhood tree-planting efforts can supplement tree cover in existing neighborhoods, while urban development rules can incorporate additional tree-save and planting requirements for new development. 

A major added bonus is that this is a classic case of the “think globally, act locally” principle. Active citizens don’t have to wait for international treaties or congressional action to get these city-cooling projects moving in their communities. It’s one part of climate resiliency that can be underway while we fight for the big fixes at the state and national levels.