For the first time in human history, the concentration of climate-warming carbon dioxide in the atmosphere has passed the milestone level of 400 parts per million (ppm). The last time so much greenhouse gas was in the air was several million years ago, when the Arctic was ice-free, savannah spread across the Sahara desert and sea level was up to 40 metres higher than today.

These conditions are expected to return in time, with devastating consequences for civilisation, unless emissions of CO2 from the burning of coal, gas and oil are rapidly curtailed. But despite increasingly severe warnings from scientists and a major economic recession, global emissions have continued to soar unchecked.

The world's governments have agreed to keep the rise in global average temperature, which have already risen by over 1C, to 2C, the level beyond which catastrophic warming is thought to become unstoppable. But the International Energy Agency warned in 2012 that on current emissions trends the world will see 6C of warming, a level scientists warn would lead to chaos. With no slowing of emissions seen to date, there is already mounting pressure on the UN summit in Paris in 2015, which is the deadline set to settle a binding international treaty to curb emissions.

The extreme speed at which CO2 in now rising – perhaps 75 times faster than in pre-industrial time – has never been seen in geological records and some effects of climate change are already being seen, with extreme heatwaves and flooding now more likely. Recent wet and cold summer weather in Europe has been linked to changes in the high level jetstream winds, in turn linked to the rapidly melting sea ice in the Arctic, which shrank to its lowest recorded level in September.

http://greenalerts..com/2013/05/global-carbon-dioxide-in-atmosphere.html