You could have the global warming raising the sea level, creating violent storms, and having large ice sheets calving off in the antarctic, like we have now. The bergs could hit ships like barbarians (i think TheLopez worked out the code for it). Paradoxically, some areas would get colder as some currents would stop or reverse direction.
Nuclear Warfare, on the other hand, might lead to warming or cooling, as the burning cities release gigantic amounts of CO2 and other greenhouse gases, but the dust reflects light back, encouraging the growth of glaciers, which could create a new ice age.
The world's climate is inherently unstable, and in the long run, a venus type climate is the most likely. All life on earth has nearly been eradicated several times, which could be why the galaxy isn't swarming with spacemen; extinction events before you can get interstellar space colonies viable are very very likely.
Even a disease could kill all of humanity. One single plague, like the one causing contagious cancers in tasmanian devils. We take things for granted, and view ourselves as masters of nature. We are ants, lording it over a pile of sand... and the tide is coming in.
and yes basshunter sucks!
