An interesting post on the official Google blog estimates the energy used to perform an average search query. Remember the news article which said that two Google searches uses the same amount of energy as boiling half a kettle of water (post subsequently revised).
Not quite. Calculations by Google engineers say that an average query takes around 1 kJ. To put this into context, the human body radiates around 100W, or 100J/s doing nothing in radiated heat. A top cyclist can generate around 600W or 600 J/s when pedalling furiously. So that action of typing a query into Google does still take a significant amount of energy. The Carbon-Dioxide produced by a search is around 0.2 g.
Multiply that by the thousands of queries that are being generated per second and that is an awful lot of energy. Next time you search perhaps you should think a bit more carefully about your search terms before pressing the search button.