Climate Change for Dummies
I recently came across a great Twitter thread by Michael Nielsen that compiled key climate change data points and trends that we should all be familiar with.
Inspired by its simplicity, I decided to build on it a bit more. My goal was to write something to help anyone understand the data behind statements like “climate change is real” or “it’s an existential threat to humanity.”
The data reviewed is broken down into 3 different questions:
- Is climate change real?
- It is caused by humans?
- Does it represent an imminent, existential threat to humanity?
I hope this helps.
Is the Earth Getting Warmer? — YES.
Below is a surface heat map of the observed changes in the average temperature of the earth from 1901 to 2012.
How you should read this heat map:
- Blue: it’s cooler now.
- Orange: kinda hotter now.
- Red: definitely hotter now.
- Purple: it’s wayyy hotter now.
How does the map look to you? To me: it’s mostly deep red; quite a few purple spots; a little orange mostly over oceans; and hardly any blue (cooling/neutral).
So yeah, it’s definitely getting warmer.
Are Greenhouse Gases Really the Cause? — YES.
The laws of thermodynamics tell us that an increase in temperature of a system is the result of adding and failing to subsequently release energy to that system. We can use this idea to determine the root cause of the warming observed.
In our context, the system we are trying to make sense of is a combination of the earth’s atmosphere and its ground-level surface.
While pleading ignorance, I tried, off the top of my head, to think of energy sources that could explain the warming we saw over the last 100 years. I found 3 plausible ones:
- The sun is sending more energy toward the earth;
- The earth’s core is burning hotter and radiating more energy out;
- Or the earth’s atmosphere is less capable of releasing heat.
Let’s quickly look at each hypothesis to find the right one.
Hypothesis 1 — is the sun sending more energy toward the earth?
This is called irradiance and is usually measured by satellites. You’ll see below a graph from NOAA that shows that total solar irradiance has NOT changed much over the past 30+ years (outside of regular solar cycles). This hypothesis must be wrong.
Hypothesis 2 — is the earth’s core radiating more heat than before?
Technically, heat from the core of the earth is also added to our system (again, surface+atmosphere). This heat is produced from both radioactive decay of isotopes in the core and leftover heat from the earth’s formation.
The problem for this hypothesis is that it would require for this heat to be somehow increasing over time. However, the chart below shows that the core temperature of the earth has been continuously decreasing. If anything, this is helping reduce the effect of surface warming. Regardless, this hypothesis is thus also incorrect.
Hypothesis 3 — is the atmosphere less capable of releasing heat?
Since heat can only escape our system toward space (inner core heat transfer being net neutral as our system entirely surrounds it), we logically conclude that, at some point in the past few hundred years, something in the system must have started blocking some of the heat from escaping.
Given that I’m not seeing Aliens with big space mirrors, the only logical explanation would be a change in the atmosphere’s ability to transfer heat out. So perhaps we should look at the chemical composition of the atmosphere and how it has changed over time.
When you do so, scientists find that mostly CO2, CH4 (methane), and N2O (nitrous oxide) molecules have had significant concentration change over the past few hundred years.
Now, just because the concentration of these gases is increasing, we can’t yet conclude that they must be responsible for trapping the heat. For this, we need to look into something called radiative forcing data. First though, what’s radiative forcing? From Wikipedia (emphasis is mine):
Radiative forcing or climate forcing is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space. […] Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling.
In other words, it’s a measure of how much energy is captured by our system when it fails to release the energy added to it by the sun. So what does the radiative forcing data say?
The graph below is fairly clear: the increase in the concentration of the three greenhouse gases shown in the previous graph has led to a significant increase in energy captured by our atmosphere+surface system (over the same period of time).
So there you have it. We reviewed the data and found that it points to a clear, undeniable link between the atmosphere inability to release as much energy as it used to per unit of time, and the increase in greenhouse gas concentration.
Are Humans Responsible? — YES.
So in recent years, I have noticed that the current debate around climate change has mostly shifted to arguing whether or not humans are responsible for it. As a result, scientists have spent a lot of time looking for other potential natural sources of greenhouse gases that could explain this increase in atmospheric concentration.
They found none.
We could spend time reviewing those findings, but I think that’s overkill because a five-year-old could look at the following two graph I’m going to show you and form a conclusive opinion.
Below is (again) what the rise in greenhouse gas concentration looks like over the past 200–300 years:
Next, we know from combustion chemistry that the primary source of human CO2 (the main greenhouse gas) is the combustion of fossil fuels like gasoline, natural gas, coal…etc that power our civilization. The graph below shows the increase of fossil fuel use over time for the U.S. and the world. The rise in use of fossil fuel overlaps spectacularly well with the rise in the atmospheric concentration of greenhouse gases.
A well-versed observer might point out that fossil fuels are not the only culprit, which is correct. Cement production, burning trees, and other industrial processes also produce CO2 emission. For completeness’ sake, I’ll also provide the graph below.
Is Climate Change an Existential Threat? — YES.
First, I will admit that I personally failed for many, many years to appreciate how climate change represents an existential threat to life on earth.
Previously I had always heard about the risings seas threatening trillions in real-estate investments, the monster hurricanes and typhoons that (already) knock out entire cities for weeks, the reduced agricultural yields, the droughts and ensuing endless wildfires, and the sweltering heat-waves.
Yet despite all of this, I always sort of thought that life would find a way.
Then I recall watching Interstellar, where a hypothetical blithe rapidly condemns our entire planet to suffocation and starvation. It was scary to see that scenario play out in a movie and led me to ponder whether there was some doomsday scenario in store for us as well. Scenarios that aren’t just limited to poor countries, but apply to America and Western Europe as well.
The short answer: yes, there are, but again we must first look at the data.
Heat Could Kill You
My first finding when searching for imminent, existential threats was that heat presents the gravest imminent danger to human life.
Now, I’m not talking about the kind of heat that causes rising seas, accelerating desertification, or the summer weather that now regularly kills a few thousand people each summer. No — I’m referring to heat so hot, you literally will die if you are exposed to it for more than a few hours.
To understand how, I first want to introduce the principle of wet-bulb temperature, which is a way to normalize temperature readings to account for local humidity. Wet-bulb temperature also happens to better represent a temperature’s human survivability.
As you know, your body cools itself by evaporating water off your skin (“sweat”). Unfortunately, this process is far less efficient when the ambient air is already loaded up with water (“humidity”). This is exactly why 38°C (100°F) in humid Houston, TX, feels significantly hotter than the same temperature in arid Tucson, Arizona. However, if you report the wet-bulb temperature instead, Houston’s temperature would be higher than Tucson.
So, in terms of wet-bulb temperature, how hot can it get before a human overheats and die from heat exposure? A good study out of MIT found the answer: 35°C (95°F). That’s the upper limit on human survivability. Furthermore, the study acknowledges that the livable limit is probably quite lower given the experimental setup they used wasn’t exactly your routine stroll to the local corner store:
Our [35°C] limit applies to a person out of the sun, in gale-force winds, doused with water, wearing no clothing, and not working.
Let’s repeat that again. If it’s 35°C (95°F) wet-bulb temperature or above, you, a perfectly healthy person, can be sitting in the shade, butt-ass naked, with a fan on full-blast, and you will still eventually die.
As you can see below, parts of the globe have already crossed this theoretical threshold (data is from 2015).
Going further out, a different study published in Science used IPCC climate modeling to predict where and when unsurvivable zones might arise on land. They chose to model India.
As you can see above, large swaths of the country would become inhabitable over prolonged periods of the year under the 4°C average temperature increase. For context, the IPCC climate model below show this happens by 2100 or sooner (red line is business as usual; blue line is Paris agreement).
Now obviously, America, Europe, Japan…etc aren’t at the same latitude as the Middle-East or India. But if the chemical composition of the atmosphere continues to see a rise in greenhouse gases, the aforementioned inhabitable zones would logically move north.
Heat Could Also Starve You
While pouring over data, I also eventually came to realize that we might starve to death. This is somewhat similar to the Interstellar plot. To be honest, I’m a bit more skeptical that this happens in my lifetime; but it might happen during my kids or grand-kids’.
For context, as a teenager I spent a lot of time on my grand-parents’ farm in Nebraska, hanging out with small Midwest farmers, and hearing them discuss how much rain had fallen the night before, and whether their corn futures were in the money — I’m not even kidding. I also remember being told that fertile soil in farmable climate is a rare and precious resource. In fact, within the context of climate change, my fear is that we eventually run out of arable land in farmable climate.
First, according to this study out of the University of Washington and Stanford University, with just a 4°C increase in global temperature (again by 2100 under business as usual scenario), we would see a nearly 50% drop in corn yield in America.
This drop in yield is quite problematic since the U.N. is expecting the population to nearly double to 11.2B over the same period. Corn is also pretty drought tolerant; other staple crops might be worse. So basically, we might end up with half the food, but twice the people. Generally, the agriculture industry is quite good at engineering its way out of issues like these, so I suspect they will solve this.
But assume that it’s so hot in the Midwest that you can’t farm anymore. Well, we’d have to move farming closer to polar latitudes (sup Canada!). This would definitely work until we have to move so far up north that we start to hit present-day tundra. At that point, since tundra soil is pretty poor in nutrients, we will have run out of arable land in climates that can be farmed.
I’m far less convinced we can find a large-scale solution for this one.
Summary
Obviously, new data will continue to be produced by the global scientific community, but we can feel fairly confident at this point that the following is true based on the above data:
- The Earth is definitely getting warmer.
- It can be attributed to greenhouse emissions from human activity.
- This warming, if left unchecked, absolutely poses an imminent, existential threat to humanity.
As a last point, if you feel powerless, don’t. You can do something and I don’t believe it has to involve reducing your quality of life. For example, many U.S. utilities are starting to offer 100% renewable electricity programs. You can also make sure your next car is an electric vehicle (those cars are way more fun anyways). Organic produce are probably better as well. Lastly, you don’t have to be a die-hard environmentalist to tell your friends about why this is real and why it matters. You now have all the data to do so.
Edit: removed some sections for brevity.
