Three British explorers have set off on a massive 90-day trek to the North Pole, to find out how quickly the Arctic sea ice is melting.
During the 600 mile expedition, they'll be measuring the thickness of the ice in what's said to be the most detailed survey of its kind in the region.
In recent years, satellites have shown the Arctic sea ice is melting faster than expected.
And lots of experts think global warming is to blame.
A few years ago, researchers predicted that by the end of the century the Arctic could be ice-free in the summer, but now some think that could happen a lot sooner.
Pen Hadow says scientists need to know how thick the Arctic ice and snow is
It's hoped the expedition, which is due to be completed in May, will give scientists a better idea of just how thin the ice is becoming.
Pen Hadow, Ann Daniels and Martin Hadley are the explorers who are tackling the chilly task, but it won't be easy.
As well as having to drag sledges that each weigh about the same as a very heavy rugby player, the trio also face having to swim with all their equipment in the icy waters.
Mr Hadow, who became the first person to trek solo from Canada to the North Pole in 2003, said the epic trip was about science and discovery.
"If, as scientists tell us, the ice is thinning quickly, then it should set alarm bells ringing around the world," he said.