When people do awesome things to highlight vast global problems, sometimes it’s easier to talk about what they did than why they did it. So it is with the six Greenpeace climbers who scaled the Shard this week. It is impossible not to be overawed by their skill. It is incomprehensible how they could complete such a feat.

photo from Greenpeace

But none of that should be the point. Or, at least, it shouldn’t be the main point. Because this was not an Olympic climbing contest. This was a protest. It was a demand not that we look up in awe, but North, in horror.

Four years ago, I was running a workshop on climate change for a group of sixth formers in Gloucestershire. We were discussing what climate scientists call feedback loops.

They were a bright and well informed bunch, so I thought I’d test them. “Does anyone know what the albedo effect is?” one hand shot up. “Is it the way that white ice reflects the sun’s rays back into space, keeping the earth cool? And it means that, as the ice melts, more and more rays are absorbed by the dark tundra underneath it, making the planet warm even faster?”.

The precocious student was, of course, dead right. This phenomenon is a classic example of a positive feedback: the changed climate triggers a change in the planet, which changes the climate even more. These loops have a terrifying implication: once we reach a certain tipping point, climate change could become irreversible.

And this loop is what’s happening in the far North right now. Over the last 30 years, we’ve lost 80% of the Arctic’s sea ice. The vast, heat reflecting mirror on the top of our planet has been smashed. Unless we can save what remains, our bad luck will run for more than seven years.

But feedback loops don’t just appear in physical geography, and there’s something else going on too. When they emerge in capitalism, we sometimes call them death spirals. In this case, the term is apt.

As the ice has vanished, it has revealed not just dark tundra, but also black gold. And so now, those same organisations who sparked the fire are looting the building. Companies like Shell are drilling for oil only accessible because of ice melted as a result of a climate changed by the oil they drilled out before.

When thinking about the future of our civilisation, it is important to remember one very simple equation. There is enough carbon in conventional reserves to take us beyond the tipping point. If we burn what we have already discovered, we will no longer be able to limit the extent of the changes in the climate to something with which we believe our civilisation can cope.

The likely effects of such changes in the climate are, of course, well documented – desertification of farm land on which we all depend for food, mass flooding of the low lying lands inhabited by a large swathe of our species, chaotic weather making farming ever harder, etc, etc.

This means something else very simple. If we allow Shell and their chums to hunt for new fossil fuels to burn, on top of those known reserves, we are allowing them to endanger the very future of our civilisation. It is easy to sound a little high pitched when talking about these things, so I’ll just say this. Vast numbers will die unless they stop. They have been told this by the leading scientists in the world. They refuse to stop.

The actions of six women from Greenpeace were incredible, awe inspiring, brave. Let’s not forget what they were trying to tell us.