What was done
The impact of human activities on regional climate is briefly examined in a News Focus item on climate change.

What was learned
Human land-use activities, such as irrigation, deforestation, development and grazing, can have major impacts on regional climate.  However, as this information piece indicates, most climate models are "rather primitive" in their ability to model regional climates; because "processes determining regional climate can take place at too fine a scale to be captured by most climate models."

What it means
In the words of one of the scientists quoted in the article, "the global climate is the sum of [the] regions."  As such, the inability of current global climate models to correctly incorporate regional climate leaves additional "room to maneuver" for those who doubt that the buildup of carbon dioxide and other greenhouse gases constitutes a substantial threat to the environment.