"Why has it not happened before now..." Cumulative effect, maybe?
"Global warming has been disproved..." Sources? And, again, like it or not this contradicts the scientific consensus, as today's report illustrates.
"When all aircraft were grounded in America following 9/11 the mean temperature actually rose 2 degrees..." This is disputed see
http://www.nature.com/news/2008/081231/full/news.2008.1335.html#B3 ) -- but actually strengthens my case far more than yours. Therein lies the sad irony. You claim that global warming has been disproved. Firstly, you mean Human-caused Global Warming -- average temperatures in the last twenty years or so are higher than previously, so no one can dispute that the World is warming up at the moment. Secondly the correct term is climate change -- depending on where you are the world may heat up, or not. Thirdly, if a small change in human activity over three days can lead to a 2 degree Celsius change in temperatures virtually overnight, what do you think a huge change in human activity cumulated over centuries will lead to? Nothing? How can you possibly believe that this makes any sense? It's just the most bizarre cognitive dissonance... step back and look at it for a second and tell me how you can hold two such opposing views at the same time. That we can have a massive impact on local temperature noticeable over three days, and no impact at all from far larger changes and effects.
And, anyway, again, even if Climate Change were a hoax (by which you mean, wrong -- Scientists can be wrong, but there's no reason to believe that they are deliberately being wrong) -- why should it matter? The changes in lifestyle and energy sources being proposed have the benefits firstly of returning to dependence on local resources and secondly to more long-term ones. Both of these in themselves have the potential to be hugely beneficial, regardless of how the climate changes or does not.
As regards the Arctic sea ice, point, this is an example of selective reporting. The ice levels have been decreasing significantly overall in the last few decades -- but rose in 2011. Aha, so one year's rise against the general trend and the whole claim is ruined, sceptics cry. No, that's not how things work. We are interested in general trends, not seasonal fluctuations, and as evidenced too by the fact that suddenly the US and Russia and ither countries are fighting over rights to the newly-opened shipping channels in the Arctic Ocean, it doesn't take long to realise that this has only been possible recently because overall the ice is melting (see also
http://www.climatecentral.org/news/arctic-sea-ice-hits-6th-lowest-level-on-record-16492 ).
Climate-change sceptics are highly selective in their use of evidence and often end up tying themselves up in knots trying to contradict themselves. And in the mean time the changes are still happening, plain to see. We can't say for sure what will happen in future, and how the climate will change, and in the meantime it's possible that other weather factors will cycle around to hide our own impact. But, again, the same question: giving the extensive levels of deforestation, destruction of species almost wherever we find them... it's not hard to see that humans can have a deadly and irreversible impact on our world. We may as well try to do something to reduce that impact while we can.