Other Answers (17)

• Florence is right in that there is a natural cycle of surface warming and cooling but do you mean when did humanity%26#039;s influence begin to change it?
  The most common answer would probably be when the industrial revolution reached its peak and %26#039;pollution%26#039; became wide scale. Also, Thomas Midgely Jr (1889-1944) solved the problem of %26#039;knocking%26#039; in car engines by adding tetra-ethyl lead (TEL) to petrol; strangely, Midgely also invented chlorofluorocarbons (CFCs) which destroy ozone, leading to the %26#039;hole%26#039; we all know.
  
  Hope that helps,
  
  Pax,
  Ape general knowledge
  
  
  
  
  
  http://greenhome.huddler.com/wiki/global...