It is extremely likely that human activity caused how much of the observed increase in global average surface temperature from 1951 to 2010?
A. One quarter
B. More than half
C. Seventy-five percent
D. All
Submit your answer in the comments below for your chance to win a prize worth £25!
The entry period is from 6th August 2014 to 5th September 2014.
All entries must be received by midnight on 5th September 2014.
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