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The carbon skyscraper: A new way of picturing rapid, human-caused climate change

Changes in carbon dioxide levels in the atmosphere during the past 1 million years. (Climate Central)

Speed kills.

That’s why firing bullets from a gun is more dangerous than tossing them by hand. Why skydivers use parachutes. Why roads have speed limits. And why it’s critical to understand how quickly human activity will drive the climate to change, compared with past rates. Will we cause gradual shifts that civilization and life on Earth can adapt to — or are we igniting a wildfire that can’t be outrun?

And so it is that scientists trek to frigid Antarctica, to drill deep into its ice sheets and pull out thousands of feet of snow compressed into ice. They carefully date each layer, extract tiny bubbles of ancient atmosphere and measure the concentration of carbon dioxide, tuner of the planet’s thermostat.

2C: Beyond the Limit

From this hard work, we’ve learned the saw-toothed pattern of carbon dioxide levels over the past 1 million years. It has shot swiftly up during climbs to past warm intervals, a bit like the climate of today, and ramped slowly down into the long ice ages in between. We can also see the sharp recent increase in carbon dioxide that humans have caused, mainly by burning fossil fuels for energy. The graph used to show this jump is arguably the most iconic figure in climate science.

To me, it’s long been the most powerful illustration of climate change’s danger. At a glance, it shows how huge a departure we’ve made from normal. Yet there’s a built-in optical illusion that greatly understates human influence.

Simply put, there’s a lot of time squished between the left and right ends of the plot — almost 1 million years. The eye can hardly tell the difference between the tiny widths occupied by 100 vs. 1,000 years. While the most recent jump in carbon dioxide is clearly the tallest and steepest, it doesn’t look that much steeper than many increases that came before it.

But the recent increase is in fact way steeper than any past jump in this record or yet discovered.

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Steepness is what shows the speed of carbon dioxide increase — and speed foretells danger. The faster the climate changes, the less the ability of society, along with the ecosystems we depend on, to adapt to the new abnormal.

You can begin to see the difference by zooming in to look at only a small recent fraction of the figure’s timeline. New data from Antarctica has just given us our highest-resolution look at carbon dioxide during the past 67,000 years:

Within that period, you can see the slow decline of carbon dioxide until Earth reached the coldest point of the last ice age, about 20,000 years ago. Then, for 7,000 to 8,000 years (the period between the arrows), carbon dioxide naturally shot up, warming the planet to near its current climate — hospitable for agriculture and civilization.

The sheer spike at the far right, linked to human activity since the Industrial Revolution, is obviously much steeper. The problem is that we needed to zoom way in to see this contrast — but have to zoom way out, like the earlier figure, for the broader context.

Fortunately, there is a simple way to show the difference in speed of change together with a very long record. That is to focus on the change in carbon dioxide per period of time, instead of on the level. The result reveals the jaw-dropping “carbon skyscraper” at the top of this piece.

To my knowledge, this is the first time the historic carbon dioxide record has been depicted in this way. My hope in developing this visualization is to clearly show just how dramatic human influence has been — and how grave our situation may be.

Importantly, there is an optimistic side to this coin as well. The speed and scale of human industry can also be applied toward solutions, and today, we have the potential to move quickly to reduce emissions. Through renewable energy and other clean technologies, and with smart policy and the will to act, the world’s nations can shut the carbon dioxide floodgates much more swiftly than we pried them open — in a few decades, not centuries.

Perhaps the skyscraper plot hasn’t been tried before because we don’t have direct carbon dioxide readings for the exact years needed. There are gaps in the record: For the whole period shown, scientists have direct measurements once per 400 years or so on average — and about once per 800 years in the older parts of the timeline. Some gaps exceed 2,000 years. The reason the traditional graph looks complete is that a line is drawn between observations, essentially connecting the dots.

But from a scientific perspective, that’s not the best way to fill in the gaps.

To improve on that approach, my colleague Scott Kulp used neural networks, a form of artificial intelligence, to construct a continuous curve from the patchy data, shown just below, and allow estimates for any year. The carbon skyscraper is constructed by taking readings from the curve every 1,000 years going back from the present.

The reconstructed curve has a good fit to the data. But the 1,000-year skyscraper still understates our predicament.

Why? Time chunks 1,000 years long can’t capture the speed of the modern carbon dioxide jump, almost all of which has taken place in the past century. If we could make a 100-year skyscraper plot, its appearance would be even more stark. It would look a lot like the 1,000-year skyscraper, but with the average change per period — except the last spike — divided by 10, creating an even bigger contrast. Unfortunately, data gaps across most of the record are still too long to put confidence in a reconstruction with a 100-year resolution. Or maybe that is fortunate: The 1,000-year version looks daunting enough.

One thing is clear at any resolution: Humankind is on a crash course with rapid, destabilizing climate changes, unless we can dramatically slow down and stop our pollution of the atmosphere. After that, maybe we can even find a way to put it in reverse.

Benjamin Strauss is the chief executive and chief scientist at Climate Central, a nonpartisan climate science and communications group. Scott Kulp, a senior computational scientist at Climate Central, developed and implemented the detailed method for estimating past CO2 levels.