[sPlOrYgOn]

the melting of icecaps is not a good thing..
it dilutes the salt water so much that all the oceans will have a very low level of salt.
and that means the oceans can be frozen..
It'll start from the caps then move all over..
what you get is an ice age..

and also if the caps are hot the ocean "convyer belts" stop moving and water near the caps no longer drop to the bottom of the ocean and travel to the equator where it warms the water and the water raises to the surface to be brought back to the caps to cool off and fall to the bottom again and keep going..
this cycle keeps the entire ocean from freezing also..

all you really need to know is that when the world gets hot enough it will turn into an ice age..

[edit]
a little bit of radiation?!?!
what if there's a solar flare? (they aren't rare you know..)
it'll spread a whole lot of radiation..
it'll just completely kill us cuz of the cancer..
[/edit]