As the headline piece for this year's Red Nose Day campaign, four brave female celebrities head to the Arctic Circle to take part in Comic Relief's coldest ever challenge.Laura Whitmore, Alex Scott, Sara Davies and Vicky Pattison attempt a four-day, 50km polar expedition that involves climbing thousands of feet as they circumnavigate the Markusfjellet Peak. They have to use fatbikes, snowshoes and cross-country skis, and pull everything they need behind them on sledges that weigh over 20kg each.In this unforgiving landscape, temperatures drop as low as -30C and wind speeds exceed 100mph. Frostbite, hypothermia, avalanche and the risk of getting lost in a white-out are the daily dangers faced by these four intrepid women.