The study conducted through a computer model found that  adding 10% of new green spaces to their sample city (Manchester, England) will reduce the surface temperature of the city by 4 degrees Celsius (about 7 degrees Fahrenheit) by the year 2080. (The study assumed that greenhouse-gas emissions will continue to increase in the future at the current rate.)

The Ennos team also studied infrared maps of other cities. They found that wooded areas are, on average, 12 degrees Celsius (about 22 degrees Fahrenheit) cooler than the centers of cities with no trees.

Green spaces with vegetation and trees, even green roofing (roofs covered partially or totally with soil and vegetation), cool city temperatures by taking water absorbed within such greenery and evaporating it into the atmosphere. The effect is similar to perspiration on a human body.

Other studies have already shown that if city people do not alter their lifestyles, then heat stress and other heat-related health problems will become an increasing problem in the summer months of the year.

The Ennos team concludes that new park space is not the only solution for accomplishing a 10% increase in green space in order to get a four degree (Celsius) reduction in temperature. Planting trees and shrubs, altering present roof types, and other such environmental methods can also help to accomplish the goal.

One way to help retain water is to capture rainwater and retain it in artificially built ponds so that it does not wash away (run-off) into streams and rivers, and eventually into the oceans and seas. In this way, the water can be used in times of drought.

The researchers indicate that their results should be verified with other tests to validate their conclusions. However, if validated, humans could offset global warming in the cities with some common sense alterations in lifestyles.

The Ennos results, with co-authors Susannah E. Gill (The Mersey Forest), John F. Handley (Manchester University’s Director of the Center for Urban Regional Ecology), and S. Pauleit, are found in the journal Built Environment under the title “Adapting Cities for Climate Change: The Role of the Green Infrastructure” (10.2148/benv.33.1.115).

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