But sometimes it can be hard to grasp what all the numbers and stats mean. For instance, when scientists say the Earth’s average surface temperature has gone up about 1 degree Celsius over the past 150 years or so, what does that really mean? Besides, hasn’t the Earth’s temperature always fluctuated?
Before scrolling through it, check out those axes.
Along the x-axis is temperature change. And each vertical block of color is 1 degree Celsius or 1.8 degrees Fahrenheit.
On the y-axis, we’ve got time. The whole cartoon, which starts at the end of the last ice age, represents about 22,000 years. People have been around for about 200,000 years. The dinosaurs were around about 65 million years ago. And Earth is 4.5 billion years old. So the graph is only a teeny-tiny period of the Earth’s lifetime.
“The cartoon is fantastic!” says Curt Stager, a paleoecologist at Paul Smith’s College.
“Really seeing the temperature changes over the long time scale helps you grasp, on a gut level, what we’re doing to the Earth,” he adds.
But there’s one problem with the graphic that makes it a bit misleading.
As you scroll up and down the graphic, it looks like the temperature of the Earth’s surface has stayed remarkably stable for 10,000 years. It sort of hovers around the same temperature for some 10,000 years … until bam! The industrial revolution begins. We start producing large amounts of carbon dioxide. And things heat up way more quickly.
Now look a bit closer at the bottom of the graphic. See how all of a sudden, around 150 years ago, Munroe changes the dotted line depicting average Earth temperature to a solid line. He makes this change because the data used to create the lines come from two very different sources.
The solid line comes from real data — from scientists actually measuring the average temperature of the Earth’s surface. These measurements allow us to see temperature fluctuations that occur over a very short timescale, say a few decades or so.
But the dotted line comes from computer models — from scientists reconstructing the Earth’s surface temperature. This gives us very, very coarse information. It averages the Earth’s temperature over hundreds of years. So we can see temperature fluctuations that occur only over longer periods of time, like a thousand years or so. Any upticks, spikes or dips that occur in shorter time frames get smoothed out.
So in a way the graphic is really comparing apples and oranges: measurements of the recent past versus reconstructions of more ancient times.
In fact, if you take the modeling method used to create the dotted line and extend it all the way out to the present, the recent spike in the Earth’s temperature would be partly smoothed. Kevin Anchukaitis, a paleoclimatogist at the University of Arizona, ran that exact experiment Tuesday and showed his results on Twitter.
“It isn’t possible to confidently compare annual observations v. millennial-scale reconstructions, he writes, without accounting for these differences in the data’s resolution.
Still, at the end of the day, the conclusion about climate change is the same, Anchukaitis says: “We are taking the planet into a fundamentally different state.”
Andrea Dutton, a geochemist at the University of Florida, agrees.
“One to 2 degrees Celsius sounds really small when you hear scientists talk about it,” she says. “But it’s a big deal when it comes to the climate of the Earth. And it means really enormous changes for coastlines around the world.“
This graphic, she says, helps us make the connection between the numbers and their impact on life, even if the cartoon itself isn’t perfect.