However, this in itself is not enough to define what
level of warming is «dangerous,» especially since the projections of
actual impacts for any
level of warming are highly uncertain, and depend on further factors such as how quickly these
levels are reached (so how long ecosystems and society have had to respond), and what other changes are associated with them (eg: carbon dioxide concentration, since this affects plant photosynthesis and water use
efficiency, and ocean acidification).