If you work backwards from the numbers, the conclusion is inescapable – we only have a short time to start rapidly reducing emissions, or global warming is going to slip out of control. Some say it already has, but we think that if enough of us take action, we can avoid disaster.
The argument for a 2015 deadline:
First, there is broad agreement that if we keep global temperature increases below 2 degrees Celsius, it is “likely” that we’ll avoid irreversible, runaway climate change. Likely, but not for certain, and there is ongoing debate that an increase of even 1.5 degrees above the global, average, preindustrial temperature would be too risky to chance. Bottom line: everyone agrees that warming above 2 degrees would be a disaster.
Second, given the relationship between emissions of heat-trapping pollution and resulting increases in temperature, there is also broad agreement that to avoid this 2 degree increase in temperature, emissions from developed nations need to peak by 2015 and rapidly decline for many years after.
If we miss the 2015 deadline, atmospheric CO2 levels continue to rise and we have to cut back even more steeply, over a shorter time period, to avoid runaway climate change. In short, if we don't start reducing by 2015 -- which will already be hard work -- then it is very unlikely we're going to get it done at all.