Last week we explained why the Earth isn’t frozen over. This week, we’ll start to rule out other potential sources of warming.
In the 1850’s, a scientist filled cylinders with different gases to observe the potential heating effect. She notes that air saturated with water absorbs and maintains heat much better than dry air, an observation that can be intuited by a humid summer day. However, a surprising candidate, carbon dioxide, absorbs and retains heat shockingly well. Eunice Foote had just discovered the greenhouse effect and concluded “An atmosphere of that gas would give to our Earth a high temperature”.
What’s all this hype about CO2?
If you’re reading this, you’ve probably heard that, rather abruptly, global temperatures have started to skyrocket. As we discussed previously, this system should be in equilibrium and not change suddenly. You’ve also probably heard that CO2 is the super villain of the 21st century and it will take an Avengers-level effort to defeat.
But how did we come to this conclusion? There are numerous other factors that affect how much heat the Earth receives. How are we sure that CO2 is the main source to be concerned about?
Surely, it must be the sun...
I mean obviously, right? All of our energy comes from that big exploding ball of gas so any reasonable person would conclude that even tiny solar changes would have massive effects on Earth. To figure it out, let’s model what happens to temperature as we pull different levers. As a reminder from our previous edition, there are a few factors to consider for incoming energy:
The Intensity: is the amount of energy emitted changing?
The Distance: are we getting closer to the sun?
(1) The Intensity
“If the sun emits so much energy, couldn’t a small increase in the amount of energy it emits have a big impact on us?” - Reasonable person
Turns out that the sun’s energy is always changing in 2 main ways: solar cycles, and solar aging.
In the near term, the sun cycles through solar maximum and minimum every 11 years. During this cycle, the sun becomes increasingly active & spews additional radiation and particles into space as its magnetic fields switch.
However this only changes solar irradiance by 0.15%. Some records from the 1600’s suggest that the sun can go through longer periods of max or min, but this direct irradiance does not explain recent warming.1
Over its lifetime, the sun has been steadily increasing in intensity as the sun’s core becomes denser and hotter. Today’s sun is about 30% more intense than it was 4.5bn years ago during Earth’s formation (more here).
However, these changes happen super fucking slowly, like 1% every 150mn years. Put in human terms, ~0.2% increase in solar forcing over the entire existence of our species. This effect has been studied, and (unsurprisingly) concluded to play a very minor role in the warming experience over the last 250 years.
(2) The Distance
“The Earth’s orbit changes and summons ice ages! We’re just nearing the end of another interglacial period where things change dramatically.” - RP
It’s true, the Earth’s orientation to the sun does change overtime as other celestial bodies (like Jupiter) pull on the Earth. Specifically, the distance from the sun (eccentricity), angle of the earth (obliquity), and the wobble (precession) change how much solar radiation the Earth receives. However, these changes occur over long 40,000-100,000 year cycles.
Earth is currently in:
Least extreme orbit (most circular), reaching ‘crazy seasons’ in ~50,000 years
Neutral tilt, trending towards ‘ice-age worthy’ minimal tilt in ~9,600 years
Wild south wobble, creating more seasonal variation in the southern hemisphere; this trend will reverse in ~13,000 years
This predictable wobble is what leads to ice ages and the following interglacial period that we’ve been enjoying for the last 10,000 years. So, while this effect does have a large impact on our climate in the long-term, it is not the cause of recent changes. Therefore, we can conclude that recent changes in temperature cannot be attributed to our solar energy system (for at least another 10,000 years).
But wait there’s more!
So if it’s not the sun, there must be another natural explanation, right?! What about Volcanoes, Currents, and other greenhouse gases?
We’ll dig into that next time...
Up next: How are scientists so sure that it’s CO2 (part 2)?
Followed by: How are we so sure that humans are responsible for the CO2?
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Until next time,
Extra disclaimer: Science is never done and we’re always learning more. What’s presented here is the current global consensus from an ensemble of climate scientists across leading government organizations (i.e. NASA, IPCC).
Usual disclaimers: I’m not an expert and will never claim to be. I’ll probably be lacking context, too vague, or flat-out wrong frequently & I hope folks will hold me accountable. After all, the fastest way to find the right answer is to post the wrong answer visibly on the Internet. Lastly, there is a ton of great information online already (e.g. Drawdown, Breakthrough Energy playbooks). I will synthesize and cite as I go.
Understanding how Coronal Mass Ejections during solar maximum impact our magnetic field / atmosphere is an open area of research