Alright I'm not an expert on this, so you'll probably have to verify it with someone more qualified, but here's my idea (the summary is underlined at the bottom, but I added an explanation just because):
Humans are increasing the CO2 levels in our atmosphere, trapping a lot of the sun's heat in. Increased heat increases the chance of desertification and drought, and also causes regional temperatures to go up. The sun's rays are also hitting the icecaps, but the ice itself reflects most of the sun. However, the ocean absorbs the heat, causing the water around the ice to become warmer, just enough to cause them to melt a bit. This melting makes the ocean level rise. So to wrap up, humans are changing the biosphere causing the Earth to warm up, the icecaps and glaciers to melt, regional temperatures to increase, and the chance of desertification to also increase.
It took me FOREVER to write and word this well so I hope this helps. =)
