A new World Wildlife Fund has a new report out reporting that they expect summer sea ice to completely melt sometime between 2013 and 2040. Their reasoning is a logical one: positive feedback. The ice at the arctic circle, being very white, reflects back a larger proportion of the sun's radiation. Less of the heat is absorbed into the ground and everything stays cooler. However, as glaciers and polar ice melts, there is less ice to reflect back this radiation. Everything gets warmer faster. More ice melts. More radiation is absorbed into the ground. Everything gets warmer. More ice melts. Et cetera, Et cetera.
This type of positive feedback is a big problem, because it can be difficult to get back into a balance. We would need a really cold winter in the Northern Hemisphere to make up for the loss of ice, but it's harder to do that because more radiation is naturally being absorbed.
Of course, there's always another possibility, something that's been discussed in the past and a very strange result from global warming: the Northern Hemisphere is a deep freeze. You may have heard about this before if you like big summer movies. The article is an interesting read. According to the theory, fresh water melting and entering the salt water ocean will disrupt the North Atlantic current, shutting down the flow of warm water into northern reaches of the Atlantic, which in turn causes massive temperature drops in portions of North America and Europe.
This is why climate change is so complicated and the reason that people say "What global warming? It's snowing in Buffalo!" or "You could fry an egg out here! Because of global warming!" are both equally wrong. It's nuanced. It involves not only the the atmosphere in your home town, but the atmosphere and oceans in the entire world. There's a lot more to consider than the local 10-day forecast. The more people that realize this, the better.