For example, the bright snow- and ice-covered landscapes of Canada and Siberia during winter reflect most solar radiation straight back into space, keeping the surface cold.

BBC: Earthshine map helps predict weather

According to the US National Snow and Ice Data Center (NSIDC), Arctic sea-ice covered 4.5 million sq km (1.7 million sq miles) at its lowest point on 12 September last year.

BBC: Arctic team targets key ice data

Drivers in Pennsylvania were traversing ice- and snow-covered streets and highways.

CNN: Storms snarl traffic, batter Midwest and Northeast

It takes seven or eight hours and strong legs to hike the whole crossing, past ice-blue crater lakes, over snow-covered ridges and through windswept mountain deserts, where totara trees cling to the soft black volcanic sand.

BBC: A return to Middle-earth