Migratory birds are especially at risk for endangerment due to the extreme dependability on temperature and air pressure for migration, foraging, growth, and reproduction. Much research has been done on the effects of climate change on birds, both for future predictions and for conservation. The species said to be most at risk for endangerment or extinction are populations that are not of conservation concern.[40] It is predicted that a 3.5 degree increase in surface temperature will occur by year 2100, which could result in between 600 and 900 extinctions, which mainly will occur in the tropical environments.[41]