Meteorologist Tamsin Gray releases a weather balloon at the British Rothera research station on the Antarctic Peninsula to help record temperature and other data from the freezing air. Apart from helping predict the weather, the balloons are also giving scientists clues to global warming.

As you can see, it starts off about 2 metres across but how big it is when it reaches about 25 km above the ground?

a) it shrinks to the size of a tennis ball

b) it swells to the size of a double-decker bus

c) it drifts off into space unchanged

Gray, of the British Antarctic Survey, says that data from the atmosphere about 5 km above Antarctica are helping to confirm findings by the U.N. Climate Panel that greenhouse gases are warming the planet.

She says that layer is warming three times faster than the global average during winter, or about 0.75 Celsius over 30 years, which is what computer models predict if man-made emissions are to blame for raising temperatures.

“It’s confirming the theory that warming is caused by greenhouse gases,” she said.