Weather: Antarctica/Arctic

The unrelenting cold of the glacial continent of Antarctica boggles the mind. Much of the ice-covered Arctic Ocean melts or breaks up each summer. By contrast, all but roughly two percent of the Antarctic landmass is sealed year-round beneath a mass of ice up to 4.8km/3 miles deep. There's so much ice that, were it all to melt, it would raise the planet's sea level by more than 70m/230ft. Furthermore, a seasonal ice pack roughly doubles the breadth of Antarctica's ice each winter and spring.

Nearly all of this cold continent lies within the Antarctic Circle, but it's by no means a symmetric land. Most tourists only make it to the Antarctic Peninsula – a narrow, volcanic tendril that extends toward South America as if reaching for Patagonia. In mid-summer, the peninsula's temperatures seldom get far above freezing point or much below it, making spells of either snow or rain possible. Cruise ships passing through the Drake Passage and around the peninsular islands are often forced to adapt their itineraries to changeable weather, including fogs and coastal storms. The same upper-level vortex that helps create the famed ozone hole also steers low-pressure centres around Antarctica's perimeter, where ice meets sea. Particularly in spring and autumn, streams of cold air pour off the elevated plateau and flow down the continent's margins toward offshore lows. The winds that result can easily exceed hurricane force, occasionally topping 320kph/200mph in spots where they flow through mountainous channels. Coastal storms can produce “herbies” (hurricane-strength blizzards) and “whirlies” (tornado-like whirlwinds that spin up in the unstable air caught beneath an outflowing cold pool). The relentless outflow also helps drive continental ice seaward, thus compensating for the inland snow that's light but that never melts.

If Antarctica has a metropolis, it's the McMurdo and Scott research bases, nestled on an island off the rugged Scott Coast. Roughly a thousand scientists and other visitors assemble here each summer, and a few dozen hang on through winter. Near 78°S, this is the closest coastal settlement to the South Pole. Summer days at McMurdo and Scott often push above freezing, and the winter cold – while admittedly fierce – pales next to that of the interior. Most of Antarctica lies in the Eastern Hemisphere, forming a grand plateau visited by hardly anyone but research teams. Even with 24-hour sunlight, mid-summer temperatures across the plateau never even come close to the freezing point, and when the sun disappears this is the coldest place on Earth (Vostok notched the world's lowest low at –88°C/–127°F). Winter temperatures bob up and down within a bone-chilling range, inching above –30°C/–22°F at best, and dipping below –73°C/–100°F at worst. Rather than bottoming out in July, the average highs and lows change little from April to September – a “coreless” winter unique to the Antarctic. Clear, calm spells produce the most bitter cold. It takes only a little wind (it's breezy but seldom gale-force here) to disrupt the tissue-thin inversion and bring down air that may be 25°C/40°F warmer. Ice crystals often materialize in the air itself rather than falling from above. Although covered by ice and snow, Antarctica is technically a desert: some spots haven't seen a measurable rainfall or snowfall for millennia.