The damning case against CO2 (pt 2)

(5 min read) Eliminating other natural drivers of warming

Last week we ruled out the Sun as the source of recent warming. This week, we’ll rule out the remaining potential causes to prosecute CO2.

The summer of 1816 was a disaster. Unseasonably cold, damp, and rainy weather caused catastrophic crop failure across Europe and North America. Grain prices increased 3x. Speculators took on credit to cash in on future grain harvests, spurring overproduction as the crops recovered the following year. As creditors defaulted, banks collapsed and the Panic of 1819 sucked America into its first major depression. 

On the other side of the world in 1815, Mount Tambora exploded in the largest eruption in recorded history. The ash ejected into the atmosphere worked its way around the world, blocking out the sun and plunging global temperatures by more than 5℉ for over a year.

Natural forces on Earth’s climate

The story of 1816 makes it painfully clear that natural events can have a devastating effect and literally write history. But, are these forces responsible for the climate change we’ve observed over the last 200 years?

In order for temperatures to change, the energy balance must be changing. We know that the amount of energy received from the sun isn’t changing, so it must be the Earth itself that is changing. For the Earth to warm, it must be trapping more heat or reflecting less heat.

Let’s investigate:

  1. Volcanos: eruptions of sunlight blocking dust into our atmosphere

  2. Oceanic Currents: powerful ocean current anomalies (El Niño & La Niña)

  3. Reflectivity (Albedo): reflecting sunlight off ice and clouds

  4. Other GHG: other gases like N2O or Methane trapping heat

(1) Volcanic Eruptions

“Ok, I get that the macro-systems aren’t changing… but what about natural occurrences like volcanos that impact us immediately?” - Reasonable person

Volcanoes affect the climate through two mechanisms: blocking the sun and cooling the ocean. Immediately after an eruption, a volcano spews sulfur dioxide into the atmosphere which transforms into a sulphuric acid aerosol that reflects sunlight back towards space, cooling the earth. The immediate impact of this can be dramatic, leading to crop failures and “the year without a summer

While sunlight is blocked by ash, the ocean cools, which can have lasting cooling effects on our climate for years after the explosion. Although the impact of massive eruptions is severe, these changes persist for a few years before the atmosphere recycles these particles back to Earth’s surface and regains equilibrium. Oh, and this cools the planet (remember, we’re concerned about warming).

(2) Oceanic Currents

“I’ve heard the the El Niño affect is responsible for most droughts and floods” - RP

Besides Volcanoes, the Earth has other anomalies that cause radical climate differences. El Niño and La Niña are naturally occurring phenomena in the Pacific ocean that change the balance of warm water (and air) in the world. As the ocean shifts between these extremes every 5-6 years, parts of the world become wetter and hotter, while others cool and dry out. 

However, these effects are not permanent and reliably oscillate as warm water sloshes back and forth. So, we’ll see occasional peaks at each extreme, but the trend line would otherwise be flat.

2016 was the hottest year on record (at the time) and it was an exceptionally strong El Niño year. While we see that it contributed 0.1C of warming that year, the Earth is still 0.8C warmer than usual (source)

(3) Clouds & Ice (a.k.a. Albedo)

“What if natural changes in the amount of cloud cover or ice is causing more solar radiation to reach the surface, increasing temperature?” - RP

This is where things get a little more complicated. On one hand, increasing temperatures (particularly in the arctic) cause glaciers to melt and recede. Receding ice means less of the surface is white (reflective) and more of the surface is dark (absorbing), leading to an increase in solar radiation entering the atmosphere, warming the planet

As for clouds, increasing temperatures can lead to increasing cloud cover as more water evaporates off the oceans to form clouds. However, the exact impact is still up for debate. Similarly, aerosol emissions (like from diesel vehicles) help clouds form by providing a ‘seed’ particle for the water vapor to bond around. Increased cloud cover can act as both a heat trap and reflector. The current effect of clouds is regional, warming some areas and cooling others.

First, both of these changes are second-order impacts of rising temperatures or emissions. They are not the source of temperature change, rather feedback loops to other effects. Taken together, the net effect of changes to albedo is cooling. Huh?

Scientists have measured (with high confidence) that the increasing cloud cover from pollution and warmer oceans has helped to offset warming by up to 30%.  

So, if there was no other heat entering the environment, it would actually be much cooler. But as we mentioned, these effects would not happen unless Earth was already warming.

(4) Other Greenhouse Gases (GHG)

“I’ve heard that other GHGs like methane are way more potent than CO2. Are those to blame? - RP

It’s true that the greenhouse effect is caused by the aggregate impact of several gases, but some contribute more than others. To measure a gas's impact, we need to understand the warming potential.

Each gas reflects a different amount of heat back towards Earth. Gases also break down in our atmosphere, meaning they don’t last forever. The combination of reflectivity & duration allows us to estimate the warming potential. We summarize a gas’s impact in terms of CO2 equivalents based on the quantity of emissions.

Put another way, the other gases are important, but given the vast volume of emissions, CO2 still has the greatest warming potential.

Ok, so CO2 is the primary culprit… now what?

The world’s atmospheric scientists have analyzed all potential forcing agents and concluded that it’s not the sun, volcanoes, clouds, currents, or other gases. It’s CO2 that’s the primary culprit.

The really bad part of all of this is that many of these effects can take centuries to be fully realized. Meaning, even if humans disappeared tomorrow, the effects on Earth’s climate will continue to be felt for centuries to come. 

But wait… how are we so sure that humans are responsible for CO2 at all?

Up next: Proof that humans are driving higher CO2 levels.

Followed by: How humans are emitting so much CO2.

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Until next time,


Want more?

This article is (mostly) abstracted from this extremely comprehensive NASA Study. I recommend the exec summary if you are into long science papers like me. 

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.