In understanding causes of changes in global or regional climate, scientists often distinguish between processes external to the climate system and processes internal to the climate system. External processes include solar and volcanic forcings and the longlived greenhouse gases. Internal processes include fluctuations in water vapor, surface albedo related to vegetation or snow cover, and clouds. In addition, atmospheric and oceanic circulations rearrange heat. The influence of variations in circulation patterns is more pronounced at regional to local scales than at global scales. For example, regional climate in the Northwest is strongly influenced by atmospheric circulation in the northeast Pacific ocean; to first order, atmospheric circulation merely moves heat from place to place, cancelling out in the global average, so year-to-year fluctuations in regional averages are usually much larger than the global average.