We looked at various climate forcin

We looked at various climate forcing factors, we looked at the snow loading, we looked at wind convergence and the melt season length of the previous summer," lead author Rachel Tilling, from University College London, told BBC News.
"We found that the the highest correlation by far was with the melt season length - and over the summer of 2013, it was the coolest of the five years we have seen, and we believe that's why there was more multi-year ice left at the end of summer."