This solution applies to the following devices: Virtex-II/-II Pro, Spartan-3, Spartan-3E. When ambient temperature is changed, the thermal characteristics change, but overall power does not change. Why?
This issue is fixed in the ISE 8.1i release of the design tools.
Temperature has a large impact on quiescent power; as leakage becomes worse, temperature rises. Temperature has a much smaller impact on dynamic power (~5%). At this time, XPower does not take temperature into consideration for its power estimates. All power is for typical room temperature (25C).