The amount of carbon dioxide in the atmosphere exceeded levels not seen for 3 million years -  an alarming 400 parts per million for the first time since researchers began tracking the data. The level is a worrying new milestone. Carbon emissions caused by burning fossil fuels are dangerously warming the planet and must be controlled. Without this they will cause irreversible climate change.

'We are in the process of creating a prehistoric climate that humans have no evolutionary experience of,' according to Bob Ward, a climate change expert at the London School of Economics.

Carbon dioxide can stay in the atmosphere for almost a century, so levels now may cause warming for decades. The concentration has now increased by more than 40 percent from the pre-industrial mark of 280 parts per million.

The UN's 2007 report also said that atmospheric CO2 in the range of 400 to 440 ppm could lead to sea level rise of as much as 1.7 meters. That would threaten coastal cities from New York to London and Bangkok.

Some more startling facts on Climate Change:

-       Past 10 years hotter than 80 per cent of the past 11,300 years.

-       One-degree temperature variation that took 11,300 years to occur has been repeated in the last 150 years.

-       Earth expected to be warmer in year 2100 than it has been for 11,300 years