A latest report given by research organization Climate Central based in Princeton, NJ, reveals that Las Vegas, Albuquerque and Denver were amongst the most extreme urban islands in terms of heat.

Urban heat island is a phenomenon in which temperature of the cities goes much higher as compared to the temperature of the nearby rural places.

Alyson Kenward, lead author of the report and senior scientist with Climate Central, said that urban heat islands usually have extremely hotter days during summers and even have much hotter nights as compared to the neighboring rural areas.

As per sources, buildings made up of concrete, asphalt, shingled roofs and other infrastructure are the major factors behind making cities hotter.

The National Climate Assessment report unveiled that on an average summer temperature in U.S. has increased approximately by 2 degrees since 1970.

Kenward said, "Thanks to the dual action of urbanization and climate change, cities are not just hotter, they are getting hotter faster: 45 of 60 cities we analyzed were warming at a faster rate than the surrounding rural land".

The report also revealed that as compared to rural areas every summer there are minimum eight days in cities that have temperature over 90 degrees. Researchers said that these hot summer days are interrelated with high ozone pollution, which means that hottest days of the year are reported to have higher ozone levels. Researchers have found that sometimes this level even surpasses the safety standards set by the Environmental Protection Agency.

On the other hand, some studies that have been conducted by independent researchers have found that urban heat islands have no effect on the rising global temperature. They say urbanization is not the only factor that causes rising global warming measurements.