Heat Wave in Northeast Provides Glimpse of What Awaits Us in a Warmer World

By Rose Winer, Intern

The severe heat wave that blanketed the U.S. mid-Atlantic and Northeast at the end of last week indicates a trend of heat-related climate change impacts that will intensify over the next century, according to the U.S. Global Change Research Program (USGCRP) and Environmental Protection Agency (EPA). On Thursday temperatures reaching the mid- to upper 90’s stretched from Vermont to North Carolina, the National Weather Service stated, with heat expected to continue according to forecasts in the low 90’s and high 80’s across the mid-Atlantic over the next few days. The heat wave sparked brownouts in New York City and forced utilities across the Northeast to ask customers to conserve electricity.

Several reports claim that climate change has had and will play a major role in intensifying heat waves. According to the USGCRP, the U.S. average temperature has risen over 2 °F over the past 50 years, causing heat wave frequency to rise steadily since the 1970’s. Moreover, nationwide temperatures are expected to increase by 5-9 °F over the next century, which will bring more intense, more frequent, and longer lasting heat waves in the coming decades. The USGCRP predicts that this increased severity will lead to more heat-related illness and death, particularly among vulnerable groups like the poor, the elderly, children, and people of color.

Major cities are particularly vulnerable to heat-related climate change impacts due to a phenomenon called “urban heat island effect” (UHI). City development replaces vegetation with buildings, roads, and other infrastructure, lowering evaporative cooling by making once permeable, moist surfaces impermeable and dry. This causes urban areas to become warmer than rural surrounding areas and thus creates an “island” of higher temperatures. Cities with over 1 million people, the EPA asserts, can have an annual mean air temperature up to 1.8–5.4°F hotter than nearby rural areas. Hence UHI exacerbates heat waves in large cities and increases overall national vulnerability to heat waves as urban areas and populations grow.

Governments and organizations across the U.S. and the world are adopting measures to mitigate UHI and related heat wave impacts.  Some particularly promising strategies for reducing UHI include green roofs, cool roofs, tree planting, and cool pavements. Green roofs—vegetated roof surfaces covered in part or in whole with plants—provide a space-efficient way to reduce cooling energy use and associated air pollution and can remove air pollutants and help lower the risk of heat-related illnesses.  Cool roofs, characterized by a reflective white coat, are a less labor-intensive alternative to green roofs that can lower cooling energy use, air pollution, and heat-related incidents.  These strategies can produce significant climate and related benefits: a new report by the Natural Resources Defense Council and UCLA School of Law’s Emmett Center on Climate Change and the Environment finds that “if green roofs or cool roofs were installed on 50 percent of the existing roof surfaces in urbanized Southern California, the resulting direct energy savings from reduced building cooling energy use could be up to 1.6 million megawatt-hours per year, saving residents up to $211 million in electricity costs and reducing greenhouse gas emissions by up to 465 thousand metric tons of CO2 equivalent annually.”[1]  Tree planting is an alternative method to achieve benefits similar to what green and cool roofs provide.  Finally, cool pavements—pavements made with materials designed to reflect more solar energy, enhance water evaporation, or otherwise remain cooler than traditional pavements—can indirectly help reduce energy consumption, air pollution, and greenhouse gas emissions. Each of these mitigation options can be more or less effective depending on a city’s configuration.

EPA has spearheaded efforts to implement these UHI mitigation strategies through its Sustainable Skylines Initiative (SSI), in which government, nonprofit, and private agencies collaborate to support individual cities in UHI alleviation efforts. SSI programs are already underway in Dallas, Philadelphia, and Kansas City. An excellent example of a proactive city is Houston, where the Cool Houston program sets forth a comprehensive strategy to mitigate UHI within 10 to 15 years through policy and land cover alterations.

New York has also taken several steps to address UHI. The City’s 2007 comprehensive climate change plan, PlaNYC, was updated in 2011 to include enhanced green infrastructure measurements to mitigate UHI. The 2008 New York City Building Code revisions requires most new buildings to have a roof that is 75% reflective or ENERGY STAR® rated.[2] The “NYC Cool Roofs” Program mobilizes volunteers to meet this code by painting NYC rooftops with reflective white coatings. And the NYC Regional Heat Island Initiative (NYCRHII), formed in 2006 among scientists, academics, and state and local governments, evaluated a range of UHI reduction strategies according to projected NYC temperatures. The NYCRHII study noted that while living roofs, light roofs, and tree planting have comparable cooling effects, street tree planting is more cost- and space-effective than cool roofing. Accordingly, a tree-planting project called the “Greening the Bronx Initiative” was established as a pilot project to monitor the temperature impacts of curbside planting.  Sustainable South Bronx has developed goals for green/cool roof projects and community green roof education.

With new data pointing towards carbon emissions rising even faster than recent predictions, we can expect more sweltering days here in NYC and across the country in the coming years.  This bleak reality makes initiatives to alleviate UHI even more important to lessen the severity of heat waves and other heat-related climate change impacts. It should also help remind us why, in addition to these important adaptation measures, we must continue to aggressively push for strategies to mitigate climate change.

The full National Climate Assessment released by the U.S. Global Change Research Program can be accessed here.

The EPA’s “Where You Live” page, mapping government and local initiatives across the U.S. that seek to mitigate UHI, can be found here.

Reducing Urban Heat Islands: Compendium of Strategies, compiled by the EPA, describes the causes and impacts of urban heat islands and promotes strategies for mitigating UHI impacts in the U.S. It is accessible here.

The nonprofit International Council for Local Environmental Initiatives (ICLEI), an international association of national and regional government organizations, runs an Urban Heat Island Initiative program that provides assistance to local governments in mitigating UHI. Find more information here.


[1]  Noah Garrison & Cara Horowitz, Looking Up: How Green Roofs and Cool Roofs Can Reduce Energy Use, Address Climate Change, and Protect Water Resources in Southern California 3 (NRDC & UCLA School of Law Emmett Center on Climate Change and the Environment June 2012).

[2]  See N.Y.C. Admin. Code, Tit. 28, Ch. 7 § 1504.8 (West 2012).