Most southern summers, we take a ski trip in Europe or North America. This started years ago as an extension to an annual business trip in January to the Pacific Northwest. It puts seasons into stark contrast. The hot Australian summer is about as different from a snowy mountain as you can get. There have been extremes in the past. One year, we got on a train in Switzerland at -25C and came out of the airport at home to find +40C.

The mid and late winter in the Northern Hemisphere this year has been usually severe. After an extraordinarily warm and dry early winter in North America, the ski fields are full of metres of snow and severe avalanche conditions. There are tornados in the mid West, over 20 metres of snow fell in Hokkaido this winter and a huge cold snap killed hundreds in Eastern and Central Europe. The ski resort in Colorado where we were last month just had a big storm go through leaving the better part of a metre of fresh snowfall (damn!).

Recently, here in Australia, it’s been very wet and warm. People have been flooded out in the river valleys and low-lying farm lands in NSW and Victoria again. The main reservoir in Sydney overflowed yesterday creating even more flood danger. This follows the floods in Queensland last year which put a part of that state bigger than France and Germany underwater for weeks at a time; downtown Brisbane had a river flood that wiped out large sections of the City. Over the last couple of summers, an inland reservoir in NE Victoria has fully recovered from the drought – it overflowed last spring for the first time in over 15 years:

Lake Eildon Levels Jan 2009 - Mar 2012

Our return from the US to Australia this week brought the contrast home to us – up close and personal. The day we left the Rockies, it was -20C and very dry. 30 hours later, it was almost tropical in Melbourne and Sydney: mid-30s and extremely humid. As I write, it’s raining outside for the 5th day straight. From 1995-2010, it hardly ever rained late in the summer in SE Australia. Now, moisture is being dragged all the way across the dry Australian interior from the Indian Ocean.

This is something more than El Nino and La Nina. The basic pattern of weather has exhibited a big departure from historical norms. There have always been floods when droughts break in Australia. The last time there was a drought that lasted a decade was in the 1890s and the rains surely followed – but not for two years and not like this. The last time there were tornados in the mid West in February was… never, at least not on record. The last time the Black Sea froze on the Romanian coast was in the Medieval Ice Ago hundreds of years ago. They’ve never measured 70 feet of accumulated snow on Japan’s northern island since reliable record-keeping began. Last northern summer, a weather event in the Carribean disrupted the jet-stream resulting droughts and fires in Russia and deluges in South Asia and the Arctic sea-ice melted almost completely away.

The nightmarish thoughts of some climate apocalypse aside, all of these change evoke some serious worries. Has the weather become so destabilised that its becoming hazardous? Certainly – people are dying all over the world from storms and floods and droughts. Has the weather changed from the gentle seasons of my childhood? You bet – every year seems to bring some high level of intensity to climate-releated news. Is the ice melting and the sea rising? Certainly – no quantitative doubt about it from any reputable scientist. Are food and water supplies changing because of the weather? It looks that way – the markets are reacting quite strongly to nations withholding export supply to satiate domestic demand.

Medium term, this is likely to spill over into some social, economic, political and even some military activity. With a half of mankind overall in cities (85% down here), the resilience of human society to changing weather has paradoxically become concentrated. Farmers are directly subject to the forces of nature but urban dwellers are subject to a finely tuned just-in-time supply chain of foodstuffs. The agribusiness supply chain managers have seen to it. It’s the economically rational thing to do. But if hungry and thirsty people living crammed into larger and larger cities find empty supermarket shelves because of some weather event, things can get very ugly very quickly.

For me, I’m glad my brother-in-law has a hobby farm on high ground just outside the City. We all know what to do up there and how to do it together. The food and water from that property tastes much better than the stuff in the supermarkets. Hope we never need to use that place as a last line of defence…