Is anyone else in the mood for some cold hard science?
In a world besieged by misinformation and sensationalism, science feels warm and fuzzy these days.
If you’re reading this, you likely know a thing or two about global warming. A 12-word summary: it’s real, it’s serious, we’ve caused it, and we can fix it.
This is a brief introduction to the fascinating science behind the greenhouse effect, whose strengthening has spawned a global climate emergency.
You might remember learning about air’s composition in an earth science or environmental science class. If not, here’s a refresher on the chemical composition of the atmosphere.
Dry air is about 78.09% nitrogen and 20.95% oxygen. That’s 99.04% accounted for. What about the other ~0.96%? 0.93% is argon. Other trace gases make up 0.03%.
So we still have a tiny little sliver left. Ah yes, that pesky molecule resulting from two oxygen atoms combining with one carbon atom. We know it as carbon dioxide.
Once upon a time, in an era not too far away, that tiny sliver was about 0.028%, hence the 0.03% designated for “trace gases”. Except that’s no longer the case. Carbon dioxide — the main trace gas — now comprises about 0.0415% of the atmosphere. What happened? How did humans alter the chemical composition of the atmosphere?
Great question! Therein lies the rub. That number reflects the story of climate change. It represents the current concentration of carbon dioxide in the atmosphere. The figure is commonly expressed in terms of parts per million.
Looking back at those percentages, air used to have about 280 parts of carbon dioxide per million. Today, air has about 415 parts of carbon dioxide per million. Again, what the hell happened? Humans happened. More accurately, fossil fuels (and some other things, like deforestation and industrial agriculture) happened.
Ok, but what’s the big deal about carbon dioxide going from 0.028% of the atmosphere to 0.0415% of the atmosphere?
Here’s the scientific issue: an increase of atmospheric carbon dioxide leads to an increase in radiative forcing. You’re probably wondering what ‘radiative forcing’ is, no?
Almost all of the energy that affects Earth’s climate comes from the Sun. Earth’s atmosphere absorbs and reflects some of that energy. Longer-wave energy is radiated back into space. But the atmosphere absorbs some of that reradiated longer-wave energy.
The balance between absorbed and radiated energy, also known as the radiation balance, dictates global temperatures. And the effect that entails the atmosphere absorbing reradiated long-wave energy is something you’ve likely heard of: the greenhouse effect.
Back to the radiation balance: it is affected by various factors like the intensity of solar energy, reflectivity of clouds or gases, absorption by various greenhouse gases or surfaces, and heat emission by various materials.
Much of the energy from the Sun is reflected by the Earth’s surface and passes harmlessly through the atmosphere back into space. But some of it is absorbed, and the absorption of solar energy produces infrared radiation.
Where does that infrared radiation go? If the atmosphere were composed entirely of nitrogen and oxygen, it would probably go back into space. Elements like nitrogen and oxygen are electrically balanced, so they are undisturbed by radiation. But 1% of the atmosphere contains gases that are electrically imbalanced; infrared radiation does affect these gases.
Why? Imagine the best disco concert of all time, except it never ends, you can’t see it, and it happens miles above your head. Infrared radiation is the disco ball; it gets the greenhouse gases groovy!
Thus, the properties of these gases allow them to retain that radiation (aka heat) like a greenhouse. Among them are water vapor, methane, ozone, nitrous oxide, and chlorofluorocarbons. And then there’s the most climatically influential one, the invisible molecule whose properties and abundance could destroy the planet: carbon dioxide.
Radiative forcing captures the difference between solar energy absorbed by the Earth and solar energy radiated back to space. It is measured in terms of watts per square meter (W/M2).
The Earth’s surface receives about 340 W/M2.
Elevated greenhouse gas levels since 1750 have heightened radiative forcing (measured in W/M2) as follows (according to the Intergovernmental Panel on Climate Change, as of a 2007 report): 1.88 W/M2 from carbon dioxide, 0.49 W/M2 from methane, 0.4 W/M2 from ozone, and 0.17 W/M2 from nitrous oxide. Overall, radiative forcing has risen by about three W/M2 since 1750.
This is in essence the science behind the harm of adding carbon dioxide (and other greenhouse gases) to the atmosphere. This scientific experiment is akin to tinkering with the knob of the planet’s oven. Even a tiny adjustment will warm the oven a few degrees.
Long story short: we’ve put the atmosphere out of balance.
Likewise, the tiny atmospheric adjustment derived from a ~50% increase in concentrations of a gas that constitutes less than five-hundredths of one percent of the atmosphere has already warmed the planet over one degree Celsius. If we keep emitting, temperatures will keep rising. Even if we stop emitting right this second, warming will continue.
Stop and think for a second about that. We have warmed an entire planet by over one degree Celsius. Disregarding the inherent harm of that outcome, it is simply astonishing.
And that warming hasn’t stopped, far from it. Since 1981, the rate of global temperature increase has risen to 0.18 degrees Celsius per decade.
The current level of carbon dioxide in the atmosphere — measured at the iconic Mauna Loa Observatory in Hawaii high above the Pacific Ocean — stands at about 415 parts per million, or ppm. Every year, coronavirus or no coronavirus, TikTok or no TikTok, Trump or no Trump, that number rises by about 2.5 ppm.
Atmospheric carbon dioxide levels haven’t been this high in millions of years. The Earth was a very different planet back then.
The story of anthropogenic climate change (and environmental degradation writ large) can effectively be told through the prism of ppm. No singular figure better represents the extent of the problem and the degree of amelioration required to stabilize the planet and solve the biggest emergency in human history.
On that last point, scientists generally agree that the threshold of carbon dioxide needed to keep the planet stable is about 350 ppm. 350 is quite a long way from 415.
So not only must we drastically reduce emissions. We need to remove greenhouse gases from the atmosphere.
How much? At least half of all greenhouse gases ever emitted by human activity.
And the more we emit, the more we must remove.
Let’s say, for instance, that the global atmospheric concentration of greenhouse gases peaks at 450 ppm (a realistic estimate if emissions peak about 10 to 15 years from now). To keep the planet safe and sound, we’d need to cut that number below 350 ppm.
Since pre-industrial ppm stood at around 280, that scenario would entail removing at least 10 out of every 17 molecules of greenhouse gases we’ve ever admitted.
So when the atmospheric disco stops spinning, we’ll still need to clean up the giant mess from the party.
That cleanup effort will be the most critical one in human history.