Urban Heat Island...?

I refers to the phenomenon in which the temperature is high temperature of the inner city,
such as Tokyo compared with the suburbs around it the heat island phenomenon.

If you look at the isotherm of annual regional heat island phenomenon is happening is heat island phenomenon.
It is the origin of the name areas of high temperature 's come to the island.
This problem is due to those who made people such as terrain is not necessarily a cause.

Data long to stay in the more than 30 degrees in the summer that is about two times higher than 20 years ago,
for example, it were out in the example near Tokyo has come out from the Ministry of the Environment.

What would have caused the temperature the higher the better inner city on earth ?