Well if we are to believe some top climate scientists the answer could even be forever. As some top climate scientists calculated levels of carbon dioxide and other greenhouse gases emitted from today's homes, cars and factories will continue to heat up our planet for hundreds of thousands of years. This is contrary to belief that world should see quick recovery once we stop current levels of greenhouse gas emissions.
These results are pretty much shocking because most people believe that once we cut carbon dioxide emissions we should very soon see atmosphere that would clean itself of harmful levels in no more than one century of time. But if we are to believe Professor David Archer of Chicago University and his associates "the climatic impacts of releasing fossil fuel carbon dioxide into the atmosphere will last longer than Stonehenge, longer than time capsules, far longer than the age of human civilization so far. Ultimate recovery takes place on timescales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste."
Proffesor Archer believes that oceans play key role in absorbing CO2 and "the ocean is getting fed up with absorbing our CO2," he says. The surface waters, about 100 metres deep, which used to sop up the gas quite fast, are now getting saturated with it – turning acid in the process – and so decreasing their uptake. Oceans need to be replaced with fresh water from deep down, but this overturning circulation "takes centuries or a millennium". And global warming is expected to slow this down: the hotter the surface layer becomes, the longer the replenishment takes.
It looks like vast amounts of carbon dioxide in the atmosphere will require eternity (from our current point of view) before being removed. And as carbon dioxide emissions continue to rise this eternity looks longer and longer.
You can say that world's governments are under a real pressure to agree a new international treaty, that would put greenhouse gas emissions to "acceptable levels" and give us a decent chance to fight against global warming. Hopefully they will learn from mistakes made in Kyoto protocol to actually ensure decrease in global CO2 emissions, not only on paper, but in reality as well. This could well be our last chance to fight global warming and climate change.