I just bought X-rite calibration kit but one thing makes me curious. Should I set colder white point (6500K) for summertime and warmer (5000K) for winter? Will global warming cause atmospheric effects which might meaningfully change the ambient light in my area?
Monitor calibration is for standardized color rendering among displays (nominally 6500K) or between displays and prints (typically 5000K). For any single outdoor location, skylight correlated color temperature varies widely by time of day, weather and season. Those relatively short term fluctuations (e.g. between 4000K and over 10000K) are provoked mostly from dust and water vapor; carbon dioxide has negible absorption at visible spectra.
Color temperature refers to the color a hot body appears, see http://en.wikipedia.org/wiki/Color_temperature for a complete description, but briefly, the sun seen through more atmosphere (sunrise/set, higher latitudes) looks redder, which is often called "warmer", but would be closer to the cooler 5,000 K setting. On oxyacetylene torch, by comparison, is only ~3,500 K.
BTW, newer LED lights are marked for approximate color temperature, so you compare the color temperature at hardware stores with LED lamps on display. ;-)