How much time do we have to cut CO2 emissions? 20 years and the budget could be all spent!

I recently worked out for myself how long we have before we use up the 'emissions budget' that is aimed at keeping warming to 2 degrees. I was prompted to do so after reading this article on realclimate.org (see last paragraph).

If emissions were to continue at the current 3% a year (approx) growth rate, and if climate sensitivity is 3 degrees, then we have about 22 years before we've spent the entire emissions budget.

Between 2009 and 2010 emissions grew by 6%. If they kept growing at that rate we only have 17 years left in the budget.

If we had zero growth in worldwide emissions we will have a bit more breathing space - 33 years in the budget (based on 2010 emissions). If we start to reduce emissions (negative growth), we'll have a bit more time again.

After that, we're heading much hotter.

(The calculations are based on an emissions budget of 1,000 million tonnes remaining that we can use to hopefully prevent a rise above 2 degrees - and 2010 emissions of 30.6 million tonnes of CO2e/year.) 

Anyone with a child over 15 years of age will appreciate the short time frame we have. Anyone over 40 who's looked back on their life will recognise that twenty years can fly by so quickly.

I don't imagine for a minute that everyone in the world will stop emitting carbon once the budget is spent. Imagine shutting down all power plants, banning all petrol-driven motor vehicles, immediately proclaiming only horse and plough can be used on farms, stopping all transfer of goods and services by ship, diesel train and oil-powered trucks.

Insurance company, Munich Re, says that we've already missed the boat for two degrees, but that provided governments act, we are able shift to renewables. Seems the US Department of Energy is of the same opinion.  Hopefully we will not let it get too much worse than that.