Subject: Roughly how much of the Earth's surface is covered in asphalt or tarmac?

If we replaced the black, heat retaining surface with a light coloured one, say 
light blue or grey (gray) wouln't this reflect a lot of heat back into space 
and so help reduce Global warming? How much of an effect could this have?  This 
could be done gradually by replacing when existing surface is worn out or by 
painting the surface with a suitable coating - Who should we contact about 
trialing some alternatives to black?

Re: Roughly how much of the Earth's surface is covered in asphalt or tarmac?