Editor’s Note: Mark Lynas is a writer on climate change, and visiting fellow at the Alliance for Science at Cornell University. The opinions in this article belong to the author.

CNN —  

To get a full grasp of climate change, you need to take a geological perspective. Wind the clock back all the way through human history, past the Romans and through the Stone Age, to the time before modern humans evolved, and our ape ancestors roamed in Africa.

Roughly three million years ago, in an epoch called the Pliocene, was the last time carbon dioxide levels were as high in the atmosphere as they are now. In other words, today’s CO2 concentrations – at about 410 parts per million – are higher than at any time during the existence of Homo sapiens.

Sea levels were as much as 30 meters higher than now, suggesting that even today’s carbon dioxide levels will be enough to eventually (albeit over many centuries) melt so much ice from the polar regions that all major coastal cities will be drowned.

But it’s the rate of change that is really off the charts, even geologically. Humans are now transferring 10 billion tonnes of carbon from the earth’s crust – in the form of combusted coal, oil and gas – into the atmosphere each year.

Smoke billows from a large steel plant in Inner Mongolia.
Kevin Frayer/Getty Images
Smoke billows from a large steel plant in Inner Mongolia.

This is a rate of carbon release probably 10 times faster than anything scientists can find in the geological record for the past 300 million years, including cataclysmic volcanic eruptions that are linked with several of the mass extinctions of life that have occurred during that time.

Ocean warming, coral bleaching

So it’s perhaps hardly surprising that each new climate-related news headline seems to be worse than the last.

Just recently scientists announced that the oceans are warming much faster than they had previously thought. The amount of heat now being absorbed in the seas equates to the energy generated by exploding at least three Hiroshima-sized atomic bombs in the oceans every second, according to a calculation by The Guardian.

No wonder the coral reefs are dying – also at a rate that is much more rapid than anyone previously thought. When I wrote my 2007 book “Six Degrees,” looking at the predicted degree-by-degree impacts of climate change, it was expected that reefs would be undergoing regular bleaching events in about 2030.

Sadly, it’s already happening. More than 90 percent of the Great Barrier Reef was affected by coral bleaching just over two years ago – the devastation was so severe that the marine scientists surveying the aerial data wept.

Australia's Great Barrier Reef faces severe climate change.
WILLIAM WEST/AFP/Getty Images
Australia's Great Barrier Reef faces severe climate change.

I am currently working on an updated edition of Six Degrees. It’s a scary task because many of the impacts that I had previously put in later chapters – equating to three or more degrees of global warming – have had to be moved forwards, because they are happening already.

Another example is the worsening of climate extremes, like hurricanes. In 2007 I imagined a monster storm, worsened by global warming, hitting Houston in about 2040. Well that happened already too – in 2017 Hurricane Harvey poured so much water on the Houston area that it equated to the flow of Niagara Falls for 110 days.

Scientists later calculated that Harvey’s rainfall was likely intensified by as much as a third because of the changing climate, in particular the warming oceans which act as rocket fuel for tropical cyclones.

The flooding from hurricanes is often aggravated by storm surges, which are worsened in turn by rising sea levels. There is news here too: this week scientists announced that the melt rate in Antarctica has increased six-fold since the 1980s, which contributes to sea-level rise.

Greenland’s melt rate has also shot up, increasing four-fold between 2003 and 2013. This week scientists announced that the giant northern polar ice sheet has likely already crossed a “tipping point” of irreversible decline. Recent Greenland melt rates are now without precedent for hundreds, and probably many thousands, of years.

Interactive: Greenland’s melting glaciers may someday flood your city

Icebergs breaking off a glacier in Greenland.
Joe Raedle/Getty Images
Icebergs breaking off a glacier in Greenland.

Closer to worst-case scenarios

When I wrote Six Degrees back in 2007 I felt that there was at least an odds-on chance of stabilizing global temperatures at or below 2 degrees Celsius, the policy target that was later agreed by world leaders at the Paris climate conference in 2015.

This now looks deluded. Achieving the two-degrees target would require the whole world to cut its net carbon emissions to zero by mid-century, and to go carbon-negative – somehow hoovering up hundreds of billions of tonnes of extra carbon dioxide using technology yet to be invented – from the atmosphere for decades thereafter.

In the real world, the opposite is happening. Emissions reached a new record last year, dragging us ever closer to the worst-case scenarios employed by climate models, which yield four degrees or more by the end of this century.

Perhaps the scariest thing of all is that millions of people – including the President of the United States – are still climate skeptics. For them, conspiracy theories and mass psychological denial serve to justify business as usual.

Optimism risks letting us off the hook

It is customary to end articles like this with an optimistic call to arms, a rousing finale making that case that it is not yet too late to act to avoid the worst if only we scale up zero-carbon technologies fast enough to urgently cut emissions.

But that risks letting us off the hook. Instead, consider this.

There is no known geological precedent, for at least the last half-billion years of the history of life on earth, for climate change of the magnitude now projected this century to take place over such a short period of time.

To think that young people alive today will experience all of this within their lifetimes is an extraordinary thought indeed.