[thedoc (OP)]

"Schoeman, Thea"  asked the Naked Scientists:
   
Just heard a question on Talk Radio 702 that you could not answer, and perhaps I can help. The person asked why grass is in summer yellow underneath his car, but in winter green (he stays in Johannesburg). A short, and hopefully sweet, answer:

In summer temperatures are quite high and heat is trapped between the car and the grass. The radiation from the earth cannot 'escape' easily, as the car blocks this. Thus, this creates a 'small greenhouse' effect and the high temperature underneath the car causes the grass to 'burn' and turn yellow.

In winter temperatures are quite low and we often experience frost. In this case, the 'mini greenhouse' effect protects the grass from dying as the temperature is higher than surrounding the car. Furthermore, dew would form underneath the car (instead of frost) and thus provide water to the grass.

I enjoy your talks and really appreciate your contribution of making science accessible to so many people.

Best wishes

Thea Schoeman
 
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