Orbit
Earth's Extraordinary Journey

Southern Summers

Cooler than in the North

Sailing the Southern Ocean
Sailin the Southern Ocean

The presence of a glacier is evidence that rather than being hotter, summers in the southern hemisphere are actually cooler than those in the northern hemisphere. In fact, on average there a full 4°C cooler, despite the added boost that perihelion gives to the southern hemisphere summer. So something else is at work here, counteracting the effects of perihelion. To discover what it is, I'm heading back out to sea.

Well, we are now out in the open ocean and I have to say, if you're not a sailor, it makes you feel very small.

We're sailing in the Southern Ocean where strong winds and icebergs have made these waters notorious as a sailors graveyard. This is a very exposed stretch of water. To the west is the Pacific ocean, whilst to the east is the Atlantic. To the south, the nearest landmass is Antarctica. It's the very vastness of this expanse of water that's the reason why summers in the southern hemisphere are so cool.

If you look at the whole of the southern hemisphere, over 80% of it is covered by oceans and these huge expanses of water have a powerful effect on the climate. That's because water has an important characteristic. It takes a lot more of the sun's energy to warm up the sea than it does the land. In other words, water has a high heat capacity. This means that, even in midsummer, and even with the added warmth provided by perihelion, the oceans in the southern hemisphere are still cool. And this keeps the air cool too.

The vast expanse of the Southern Ocean
Oceanic Vastness - The Southern Ocean

Even at this time of year, when the Earth is physically closest to the Sun, and the southern hemisphere is tilted towards it, the influence of the oceans keep it much cooler. It's a sobering thought that without perihelion, southern hemisphere summers would be even cooler than they are now.

The Earth's slightly off centre orbit is a reminder that we live on a planet that's hurtling through space around the sun. This journey is controlled by the immense power of the sun's gravity. But the sun's gravity is also responsible for significant dangers.