In mathematics, a function is used to represent the dependence of one quantity upon another.
Let's look at an example. Syracuse, New York has the highest annual snowfall of any US city because of the “lake effect” snow coming from cold Northwest winds blowing over nearby Lake Erie. Lake effect snowfall has been heavier over the last few decades; some have suggested this is due to the warming of Lake Erie by climate change. In December 2010, Syracuse got 66.9 inches of snow in one 12 day period, all of it from lake effect snow. See Table