Which process produces rising air due to unequal heating of earth’s surface?
when a layer of air with temperatures above freezing sits above a layer of subfreezing air near the ground, which type of precipitation is likely to form?

The answer for the first question is localized convective lifting. Air in the atmosphere rises when there is unequal heating of the Earth's surface. This is due to its buoyancy. Colder air then sinks, as the hotter air replaces it. 

The answer for the second question is freezing rain. Freezing rain is formed when snow passes through above freezing air atop a layer of below freezing air near the surface of the Earth.

Increasing the release of greenhouse gases and pollution

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!