The last time the average global temperature was below zero degrees celsius was in 1950

Mean global temperatures then stabilized at roughly 14.0°C (57.2 °F) until the 1980s. The world has mainly grown hotter since 1980, at a rate of nearly 0.2 °C (0.36 °F) per decade.

Explanation:

Hope this helps.

i am positive it is c. condensing but i may be wrong

c.more precipitation,but only when emission levels.