Hot cities getting hotter faster

With the summer sun baking up the earth and cities growing in number, hot cities will grow even hotter, says a new study.

It is known that cities retain more heat than rural areas, and the above finding suggests that the increasing temperature in urban areas would take a toll on the comfort and health of people who live in cities around the world, especially those who don't have access to air-conditioning.

"If you've been exposed to hot temperatures during the day and you expect relief over night, that becomes increasingly difficult as temperatures at night get warmer. We have to prepare to live in a warmer world," Discovery News quoted Richard Betts, a climate scientist at the United Kingdom's Met Office, as saying.

In a concrete jungle, roads and buildings absorb sunlight and trap heat, which also flows as waste out of cars, air-conditioning units and even just the breathing of millions of people crammed into a busy grid of streets.

Thus, cities create their own, warmer microclimates— a phenomenon called the urban heat island effect.

Scientists have known about urban heat islands for many decades.

Still, most climate models are based only on conditions in rural areas, where soil, trees, lawns and fields don't absorb and reflect sunlight the same way that asphalt crosswalks and concrete skyscrapers do.

To see how climate change might interact with urbanization and population growth, the researchers created a new model that compared future climate scenarios in cities with predictions for rural areas.

The results found that the urban heat island effect is most extreme in dry, subtropical regions, where the differences between nighttime and daytime temperatures are greatest.

With projected increases in heat-trapping carbon dioxide, the model predicted that between now and 2050 daytime temperatures will increase equally in cities and rural areas.

But over the same time period, city nights will get much warmer than rural nights.

In the Middle East, where the effect will likely be most extreme, the study predicted that CO2 emissions will lead to a night time rise of about 5.4 degrees Fahrenheit both inside and outside of cities, with an extra 5.4 degrees Fahrenheit rise within city limits.

Among other places, nights will also get significantly warmer in the urban areas of East Africa, Central Asia and the western United States.

The study is published in the journal Geophysical Research Letters.