It’s not climate change – it's climate reversal

The climate has always changed, but it has never been driven backwards at this speed — what took millions of years to sequester has been released in the last 150 years, writes David Higginbottom.

THIS ARTICLE WAS PROMPTED BY a discussion with a neighbour who, with absolute authority, told me “climate change has always existed”. Whilst technically correct, it is also one of the most misleading things climate change sceptics say.

The "climate has always changed" argument is used as a sedative: Things have been different before; they'll be different again, nature adapts, continue with life, enjoy.

But that framing completely misunderstands the changes that occurred before.

Yes, Earth's climate has changed throughout its history. It's been much warmer and colder than it is today. Glaciers have swallowed continents. Deep seas have covered what are now mountain ranges. There has always been climate change.

But here is what that argument almost always leaves out: while Earth has experienced thermal shocks in its past:

The overall trajectory, for tens of millions of years, was moving in a particular direction. In just 150 years, we have reversed it.

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What we have done — the big exhale

Beginning about 500 million years ago, and accelerating during the Carboniferous period (about 360 to 300 million years ago), vast forests of ancient trees collapsed into swamps and were buried under layers of sediment before they could fully decompose. Marine microorganisms died and sank to the seafloor by the trillions. With each burial, carbon that had been floating in the atmosphere as CO2 was captured and locked underground.

And this process was incredibly slow. It took place over timescales that make human civilisation look like a rounding error. Over millions of years, atmospheric CO2 dropped. The planet cooled. Stable, temperate climates became possible. The conditions that made complex animal life (and eventually us) viable were the result of this planetary carbon removal.

By the time our species appeared, and certainly by the time we built our first cities, the atmosphere had settled into a steady, rhythmic cycle. Pre-industrial CO2 fluctuated within a safe range and was around 280 parts per million during warm times – low by the standards of deep geological history – ideal for humanity to flourish.

Climate stability was the inheritance of hundreds of millions of years of CO2 burial.

Undoing epochs in 150 years

Beginning with the Industrial Revolution in the early nineteenth century, we began digging up those ancient, buried forests and burning them. We drilled for the compressed remains of marine organisms and burned those too. In doing so, we began releasing carbon that had been underground since before the dinosaurs - carbon that nature had spent unimaginable spans of time removing from the air.

By 2025, atmospheric CO2 had reached about 425 parts per million — a 50 per cent increase over pre-industrial levels, achieved in 150 years.

Hundreds of millions of years of sequestration. One hundred and fifty years of reversal.

The University of Chicago climate scientist David Archer, in his indispensable book The Long Thaw (2009), puts it precisely:

'The carbon we are releasing took millions of years to accumulate underground — once released, a significant amount will stay in the atmosphere for hundreds of thousands of years.'

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The rate is the point

Here is where the "climate has always changed" argument collapses completely.

Natural climate change does happen. It happens slowly. Scientists drilling into Antarctic ice can read 800,000 years of atmospheric history in those cores — bubbles of old air trapped layer by layer as snow compacted into ice. The British Antarctic Survey has carefully analysed these records. The fastest natural increase in CO2 they have ever measured is about 15 parts per million over about 200 years.

We are in fact increasing CO2 by 15 parts per million every six years. That is not a faster version of natural climate change. It is a categorically different event — closer in geological terms to a mass extinction trigger than to a natural cycle.

The Czech-Canadian scholar Vaclav Smil (2017) also makes an important point about fossil fuels:

'They are ancient stores of solar energy, accumulated over geological ages by biological processes and compressed by time and pressure. When we burn them, we are not merely using energy — we’re liquidating a geological inheritance that took epochs to build.'

The direction matters

Climate change proponents and sceptics have a long history of arguing about the extent of change and how quickly it is occurring. But the bigger point is about vector: which direction did the planet go, and which way are we pushing it now?

For tens of millions of years, the general trend was toward lower CO2, cooler temperatures, and greater climate stability. Over the last 35 million years, in particular, Earth was on a slow trajectory toward the conditions that eventually allowed humanity to flourish.

We have not merely accelerated climate change. We have reversed its direction, and at a speed that has no geological equivalent.

The IPCC’s Sixth Assessment Report (2021) – the most comprehensive scientific synthesis ever produced on the subject – confirms there is no precedent in the 800,000-year ice core record for what is currently happening to atmospheric CO2. Not in rate, not in magnitude for this era.

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What this means

Understanding the geological scale of what we have done is not a counsel of hopelessness — it underscores the urgency. Whilst we play war games, our planet is approaching a tipping point — and don’t believe that your country, location or privilege will make you immune.

We inherited a planet that had spent hundreds of millions of years cooling itself, sequestering its carbon, and creating the stable conditions for complex life. In a geological instant – a century and a half to be exact – we have begun to undo that work.

The climate has always changed. But it has never been driven backwards at this speed, liquidating millions of years of planet history in a matter of decades. We didn’t just change the climate; we put it in reverse — and we are compressing that change into a human lifetime. What took millions of years to sequester has been released in the last 150 years.

The climate system will eventually find a new equilibrium. The question is whether civilisations and ecosystems that we depend on can survive the transition.

David Higginbottom is a member of the coordinating committee of the Independent and Peaceful Australia Network (IPAN) and coordinator of the Make Peace A Priority campaign (mpap.au).