white roofs

Greenhouses and the environment

July 25, 2024 By EarthWise Leave a Comment

The use of greenhouses around the world has been growing dramatically. A new satellite mapping exercise estimated the total land area covered with permanent greenhouses at 3.2 million acres, which is an area the size of Connecticut. More than half of this is in China, where the growth of greenhouses has been driven by the rapid urbanization of the country and by a more prosperous population increasingly consuming produce like tomatoes, cucumbers, peppers, and eggplants.

The intensive agricultural methods employed within greenhouses can be harmful to local environments because of overtaxing water supplies and by polluting rivers and soils with nutrients, pesticides, and plastic waste. But the effects of vast areas of plastic coverings on local temperatures can be even more dramatic, and often beneficial.

There are so many plastic and glass roofs in many areas that they are reflecting sufficient amounts of solar radiation to cool local temperatures. Greenhouse roofs increase the albedo – the reflectivity – of the land surface typically by a tenth.

All these greenhouses are just the tip of the albedo iceberg. Many farms now temporarily cover crops with reflective plastic sheets. If these coverings are included in the satellite survey, the total reflective area would be about ten times greater – roughly the size of New York State.

A study in Almeria, on the Mediterranean coast of Spain, which grows about 3 million tons of fruit and vegetables annually, determined the cooling effects of greenhouses. Weather stations amid the greenhouses showed an average cooling of 1.3 degrees Fahrenheit compared with the surrounding area.

Greenhouses are an accidental and benign form of climate engineering. The cooling provided by greenhouses is similar to the effect of white roofs in urban areas.

**********

Web Links

Could the Global Boom in Greenhouses Help Cool the Planet?

Photo, posted September 6, 2017, courtesy of Lance Cheung / USDA via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Strategies To Cool Off Cities | Earth Wise

July 2, 2021 By EarthWise Leave a Comment

Heatwaves in cities are becoming increasingly common and increasingly intense. The warming climate is a big factor, but it is the nature of our cities that really drives up temperatures. Solar radiation stored throughout the day on asphalt and buildings is released slowly during the night, which generates significant heat stress.

A study carried out by a major Barcelona university and published in the journal Urban Climate looked at the effectiveness of various ways to mitigate the heating effects in cities. In particular, the study examined the effects of the use of white roofs on buildings and the expansion of urban green areas with daily irrigation in the Barcelona metropolitan area. It simulated various scenarios incorporating combinations of these two mitigation strategies.

The strategy with the greatest impact was a combination of the use of both white roofs and the addition of six urban parks, which is a target set by the Barcelona Urban Master Plan. This scenario resulted in an average temperature reduction of 2.25 degrees Fahrenheit. The maximum reduction occurs during the mid-afternoon with a reduction of 7 degrees and the combination still provides more than 3 degrees of reduction at 9 pm. Reducing temperatures this way also results in a reduction in energy consumption, with 26% less spending on air conditioning.

The 2-pronged strategy combines the benefits of reducing the temperature at night due to more urban green areas with the reduction of daytime heat due to both the increased reflectivity of white roofs as well as the irrigation of the green areas.

The study demonstrates how modeling efforts can help urban planners to counteract the impacts of heatwaves, which are likely to increase with climate change and intensification of urbanization.

**********

Web Links

White roofs and more green areas would mitigate the effects of heat waves in cities

Photo, posted January 16, 2011, courtesy of Sean MacEntee via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Cooling Cities With White Roofs

April 16, 2018 By EarthWise Leave a Comment

The phenomenon of urban heat islands has been well known since the 19th century. The materials from which city buildings and roads are made reflect much less solar radiation and absorb more of it than the vegetation they have replaced. The absorbed energy is then radiated in the form of heat into the surrounding air making cities warmer.