Randall Munroe, from XKCD, uses a very comic pictorial way to describe the significant impacts of 4.5°C changes in global temperature. The 4.5°C is derived from the difference between the norm temperature of 20th century and the coldest temperature during last ice age. Randall calls every 4.5°C be 1 "Ice Age Unit" (IAU).
(1) If we are -1 IAU (4.5°C below) then Randall's neighbor (in Boston, U.S.A.) will be 1/2 mile under ice.
(2) If we are -4 IAU (18°C below) then the whole earth will be a snowball.
(3) If we are +1 IAU (4.5°C above), which will be 86 years from now, Randall is not sure how the earth will be...
(4) If we are +2 IAU (9°C above) then the sea level will be 200 meters above today, no more ice on North and South Poles, and palm trees will grow on the poles.