Thomas Jefferson was a weather buff

Imagine a world of wildly escalating temperatures, apocalyptic flooding, devastating storms and catastrophic sea level rise. This might sound like a prediction for the future or the storyline of a new Hollywood blockbuster but it’s something quite different: it’s our past. In a day and age when we’re bombarded with worrying forecasts for future climate, it seems hard to believe that such things could come to pass. Yet almost everywhere we turn, the landscape is screaming out that the world is a capricious place. The problem is if we don’t tune in, the message is lost. We need to decipher the past and learn from it.

In some parts of the world, a few early snapshots of the weather, recorded by enthusiasts, help us. In the eighteenth century, an interest in meteorology was highly applauded. You didn’t have to be hairy and middle aged. A clean-shaven and young Thomas Jefferson kept a weather journal; from this we know it was pretty mild in Philadelphia during the Declaration of Independence on 4 July in 1776. We can go further back by looking at pictures where the weather forms part of the scene. There’s a beautiful painting by Emanuel Gottlieb Leutze showing George Washington crossing the Delaware River in 1776. The river is clogged with enormous berg-like blocks of ice. It’s a romantic piece of work that was painted some 75 years after the event but suggests a winter that would be unimaginable today. Sadly, though, paintings can only take you back so far.

Happily, when our ancestors were fighting one another, nature was recording the conditions at the time; depending on the season, trees, peat bogs, ice and mud all preserve an archive of what the conditions were like when they were formed. The trick is how to read what nature has left behind. When we do, a worrying conclusion hits us between the eyes. The average global warming of 0.8°C over the past century is beyond what is natural.

Source: National Snow & Ice Data Centre

In 2002, a chunk of Antarctic Peninsula ice known as the Larsen B shelf collapsed into the Weddell Sea, never to be seen again. It might not sound that exciting but this wasn’t just any old piece of ice. This was 3,200 square kilometres, equivalent to the size of Rhode Island. And it wasn’t something that happens every Tuesday week. The researchers who went into the area afterwards were able to show this was a one in a 12,000-year event. And it all happened in 31 days; once the shelf started to disintegrate, there was no stopping it. After all the to-ing and fro-ing of temperature during recent millennia it was only in the twenty-first century that the conditions were exceptional enough for Larsen B to collapse into the sea.

The Antarctic Peninsula is a fabulous place to observe changing climate. A 1300 kilometre long finger of land that juts far beyond any other part of Antarctica, it’s suffering from a severe case of over heating. The region has warmed 2.5°C since the 1950s; four times the global average. It was all too much for Larsen B. Melt water built up on the surface and squeezed down the crevasses, weakening the ice. The shelf managed to deal with earlier warmings but this was the final straw. After 12,000 years it was time to say goodbye. It was an extraordinary event in our planet’s history.

Larsen B is strong evidence that today’s warming is exceptional. But this is just an opening shot. Glaciers in the Andes and Europe are shrinking back to a size not seen for 5,000 years. Meanwhile, temperatures across the northern hemisphere are the highest they’ve been for at least 1000 years. These aren’t natural changes that can be explained by natural processes. We can only explain today’s warming by taking into account the billions of tonnes of greenhouse gases we’re pumping into the atmosphere each year. Our seemingly insatiable demand for fossil fuels is killing us. As other parts of the world get warmer, we’ll start to see more of these one in 12,000-year events.

We’ve been living on borrowed time but we still have a choice. We can do something about the mess we’re creating. We can listen to the warnings from the past and change our ways.