In my opinion, it is not possible for the earth to explode because there is no explosive with that capability. It is also not possible for the world to return to ice age because of the current advancement in technology.
I can't imagine what you mean by the earth "exploding"; that has never been considered a probability. - When it comes to ice ages, those have been occurring like clockwork every 100,000 years as determined by the orbital Milankovitch cycle. http://en.m.wikipedia.org/wiki/Ice_age#_ Warm periods (intelglacials) have varied in length from 10 to 30 thousand years and orbital indications are that even without any help from human activity we would have an unusually long interglacial. In conclusion I'd say we will probably have a comfortable climate for quite a while and warm is better than cold.
There is no natural process that could cause the planet to explode. However, ice ages are fairly common and re-occur every few 100,000 years. It is very likely that at some point in the future another ice age will occur, but not anytime soon.