The State We're In

Hot temperatures, cooling trees

Aug 4, 2022

By Jay Watson, Co-Executive Director

Like many New Jersey summers in recent years, this one has been a scorcher. For five consecutive days in Newark in late July, temperatures exceeded 100 degrees Fahrenheit, setting new heatwave records for the city. Other cities throughout this state we’re in sizzled as well.

In the midst of the heatwave, I had the opportunity to visit Camden City for a community cleanup with several groups beginning in Northgate Park in the North Camden neighborhood. Temperatures were in the high 90s, but a saving grace was the shade provided by the park’s maturing trees.

Those beautiful trees at Northgate Park hold a special significance for me, as I managed the original grant for the development of the park project over 30 years ago when I was with the New Jersey Department of Environmental Protection’s Green Acres Program. They were just saplings then – you could easily circle their trunks with the fingers of one hand.

Over three decades, the trees grew tall and sturdy, with spreading canopies thanks to the City’s good care. They now stand as a reminder that we as a society must keep planning ahead for the needs of future generations. Today’s children can cool off in the shade of Northgate Park and other neighborhoods because of trees planted by earlier generations – perhaps even their parents or grandparents!

Trees are urgently needed in all of New Jersey’s cities because of “urban heat island effect,” in which temperatures in city settings can be up to 7 degrees hotter than those in surrounding suburbs and rural areas because of a lack of trees and greenery and an excess of heat-absorbing asphalt and concrete. Adding to the problem is heat produced by buildings, vehicle engines and industry.

Newark was identified last year as being the second-worst heat island among 159 U.S. cities in a study by Climate Central, a Princeton-based research organization – behind only steamy New Orleans.

The heat island effect can be hazardous to human health. In addition to causing heat exhaustion, high temperatures induce more asthma attacks, as the heat concentrates air pollution and speeds up smog formation. Studies show that excessive heat also takes a toll on cognitive function, literally making it harder for people to think.

Not surprisingly, there’s an environmental justice aspect to all this. A term that’s been used lately is “heat inequality,” which simply means that the urban heat island effect is having the most severe impacts on minority and low-income residents.

“Climate change is disproportionately felt by low-income communities of color who already suffer from disproportionate environmental impact and inadequate infrastructure,” said Mathy Vathanaraj Stanislaus of Drexel University in a webinar last week on heat inequality.

A solution is to plant more trees on city streets, parks, schoolyards, in parking lots and vacant lots. Stepping from direct sunlight into the shade of a tree lowers the “feels like” temperature by 10 to 15 degrees, providing instant relief. (Direct sunlight can heat surfaces to well above air temperature.) In addition to providing shade, trees cool the air by releasing droplets of water that draw heat, turn to fine mist and evaporate, a process called “evapotranspiration.”

Trees also improve air quality by absorbing pollution and trapping particulate matter from the air. In addition, they help filter and clean water supplies; and reduce water runoff, flooding, erosion and storm water management costs. They muffle city noise, provide habitats for birds and animals, and make cities more attractive to residents and businesses.

This week, the nonprofit Groundwork Elizabeth celebrated both the completion of its first “microforest” on a 30-by-50-foot lot behind a branch of the Elizabeth Public Library, and the receipt of a grant from the Bezos Earth Fund to plant four more. These microforests, which New Jersey Conservation Foundation helped plan, will help reduce the urban heat island effect in Elizabeth, and soak up storm water in flood-prone areas.

More funding for planting trees could come from the proposed federal Inflation Reduction Act of 2022. The legislation would allocate over $5 billion for trees and forests – including $1.5 billion to support urban and community forests, and $700 million to conserve private forestlands threatened by development.

For years, the state of New Jersey has recognized the value in planting trees. Twenty years ago, then- Governor James McGreevey’s administration launched the “Cool Cities” initiative to plant 100,000 trees in New Jersey’s urban areas. The goal wasn’t fully realized, but tens of thousands of street trees went in the ground between 2003 and 2010 to cool urban areas and decrease the need for air conditioning, thereby lowering electricity use and consumer costs.

Overall, the Cool Cities initiative succeeded in increasing urban tree canopy, according to a 2021 follow-up assessment. That work recommends continued plantings in the future, with a diversity of tree species and the addition of younger trees to make sure there are replacements for older trees nearing the end of their lives. A destructive insect called the Emerald Ash Borer is killing many ash trees that have long been a staple along urban streets, and Bacterial Leaf Scorch is affecting many oak trees.

An old Chinese proverb advises that “The best time to plant a tree was 20 years ago. The second-best time is now.”

For the health of all New Jersey residents, now is the time to make sure we keep planting trees along city streets and in urban parks, and create new microforests that “re-wild” vacant lots. As climate change brings more periods of extreme heat, they’re exactly what we need.

And importantly, we must launch a public campaign in our cities to make sure that tree planting projects are welcomed and understood. Planting a tree is just the beginning of a long relationship. The tree must be cared for – watered, pruned and loved – so that the full measure of its benefits is derived.  If trees are valued and taken care of, future generations will look back and thank us for what we’ve done NOW!

For more information about “tree equity,” go to the American Forests website at To learn more about the impacts of extreme heat and view a map showing current hot spots in the U.S., go to

And to learn more about preserving New Jersey’s land and natural resources, visit the New Jersey Conservation Foundation website at or contact me at

About the Authors

Tom Gilbert

Co-Executive Director

Alison Mitchell

Co-Executive Director

John S. Watson, Jr.

Co-Executive Director

Michele S. Byers

Executive Director, 1999-2021

View their full bios here.


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