Deniers of manmade climate change will claim that our greenhouse gas emissions are not causing global warming; instead, other factors are responsible. And I've gotta hand it to them; they're very creative when it comes to explaining away Earth's warming temperatures: Milankovitch cycles, the Sun, volcanoes, too many people leaving the stove on—anything but greenhouse gases, basically, are responsible. Here I argue that the explanations they put forth cannot account for the planet's warming temperatures.
Milankovitch cycles are long-term processes that wouldn't cause the rapid rate of warming we're currently seeing. Even if they were responsible, we should be in the cooling phase of the Milankovitch cycle—so why the global warming? On top of that, even if we were in the rising phase of the cycle, this wouldn't nullify the warming effect of greenhouse gases; if anything, it would compound the warming and should thus alarm us even more. Measurements of the planet's orbital changes simply don't support this narrative.
Solar output has been largely static over the warming period, as proxy measurements via sunspots and direct measurements via satellite makes clear. The differing rates that layers of the atmosphere are warming at also support greenhouse gases as the cause—not solar energy. Volcanic greenhouse gas emissions pale in comparison to those from human activities—and the molecular signature of the CO2 being released matches up with fossil fuel emissions and doesn't match up with volcanic emissions.
Scientific analyses of the question make clear that natural forces cannot account for the warming we've observed, and it is only with manmade greenhouse gas emissions that you can explain the rising temperatures.
I came across the Milankovitch cycle argument being made on Twitter by the user "@TinPotDickTator". He shared a graph of temperature and CO2 going back over 400,000 years, and as we can see, there have been regular spikes and drops in temperature. As he put it:
"Who created the previous climate cycles, prior industrial civilizations?"
Ya know, sometimes I do actually suspect that that's the case. It sometimes seems as if the fossil fuel industry so enjoys polluting the planet that it's not enough for them to do it just the one time; they love it so much that they created a time machine to travel back and experience the joy of destroying the environment over and over again.
I'm sorry, but have any of you ever heard a single person argue that humans are the only conceivable cause of all climate change throughout all of Earth's history? This guy is attacking a strawman, plain and simple.
"Haha! You say humans are causing global warming today, but in order to be logically consistent, that must mean that they were also the cause of global warming 300,000 years ago!"
This would be like saying: "You say this person died of heart disease, but that means nobody in Earth's history could've ever died of anything else!" If the human brain was capable of having a miscarriage, this argument would be what came out.
In the course of our very productive Twitter debate, he went on to tell me that I should look up "Milankovitch cycles"—as if I've never heard of them before—arguing that these explain the past and present temperature increases.
What, exactly, are Milankovitch cycles? An article on UniverseToday.com explains:
"A Milankovitch cycle is a cyclical movement related to the Earth's orbit around the Sun. There are three of them: eccentricity, axial tilt, and precession [or wobble]. According to the Milankovitch Theory, these three cycles combine to affect the amount of solar heat that's incident on the Earth's surface and subsequently influence climatic patterns."
So the argument is that the cyclical nature of temperature changes over time proves that orbital variations—and not human activity—are the cause of our current warming. It certainly seems like a plausible explanation when you look at graphs like the one he presented us with, but when you closely examine the subject, you find that this position does not stand up to scrutiny.
TinPot tells us that "Currently we're at peak of latest cycle with cooling due."
Ah yes, cooling should be happening any minute now, so clearly there's nothing to worry about here—except for the fact that the planet is not cooling; it's instead warming at an alarmingly rapid and accelerating rate!
"Hey, these cycles which tell us that the planet should be cooling right now explain the fact that our planet is instead rapidly warming!"
I'm sorry, this just isn't a very convincing argument to me. If you're going to invoke a certain pattern to explain a set of data, shouldn't that set of data actually match up with that pattern?
The OSS Foundation puts it bluntly:
"Simply put, based on the evidence, mankind has forced the Earth climate system to depart from it's natural cycle forcing."
Maybe you'd argue that we're still in the midst of an upward spike and that's what's causing the temperature increases? Well look at the past spikes in temperature on this graph and you'll see that they took about 10,000 years to materialize. On average, these were increases of about 10*C. 10,000 years divided by 10*C = 1,000 years for each 1*C increase in temperature.
Compare that against present-day rates of warming. NASA temperature data shows us that from 1910 to 2018—a period of about 100 years—temperatures have increased by about 1.3*C. Let's just round down and say they've increased by 1*C. So this is a 1*C increase over the past 100 years compared against past Milankovitch-cycle warming rates of 1*C for every 1,000 years. That is to say, current warming rates are 10x faster than what we've seen during past warming spikes—indicating that clearly more than just Milankovitch cycles are at play here.
As the EPA points out in a report of theirs:
". . . changes in the shape of Earth’s orbit as well as the tilt and position of Earth’s axis affect temperature on very long timescales (tens to hundreds of thousands of years), and therefore cannot explain the recent warming."
And even if it was correct that we were in the midst of a Milankovitch spike right now, this wouldn't disprove or negate the idea that greenhouse gases are warming the planet. We know what effect greenhouse gases have on atmospheric temperatures, and pointing out that there's an additional source of warming wouldn't somehow magically nullify the greenhouse effect.
By analogy, imagine that I'm hanging out with my non-existent group of friends and we're roasting hotdogs in a bonfire, as I've been told twenty-somethings love to do in their spare time.
While my hotdog is being cooked by the flames from the fire, I also start roasting it with an acetalyne blowtorch at the exact same time. It would not make sense to say: "Actually, the blowtorch isn't warming the hotdog, because if you look closely, you'll see that the hotdog is in a bonfire." Two things can be true at the same time, and two different sources of heat can be increasing temperatures at the same time. It's not like these options are mutually exclusive.
So if anything, the Milankovitch cycle enthusiast is actually making an argument in favor of even more drastic measures to combat climate change, because they're basically arguing that in addition to the Milankovitch cycle warming spike, we're compounding the temperature increase by sharply increasing greenhouse gas concentrations. The truth of their argument should therefore make us more alarmed about global warming—not less.
Notice on his graph that CO2 concentrations in the modern era have skyrocketed. They're increasing at such a rapid pace that you can't even depict them on this timescale as anything other than a straight upward line. And modern CO2 levels on his graph stop at 360 ppm when really, in 2019, they're at about 410 ppm—a level that is quite literally off the chart. Doesn't this unprecedented spike in CO2 levels suggest to you that something other than Milankovitch cycles are at play here? Doesn't this make you worry that maybe the temperature increase we're seeing might be connected to that?
TinPot would argue that there's nothing to worry about, writing that: "We can't emit enough GH gas to stop the coming cooling which is due to combined forces of Milankovitch cycles"
When I read things like this, it makes me wish that the next Milankovitch cycle would send our planet straight into a black hole!
This is nothing more than a bald assertion made with no supporting evidence—or as Fox News would call it, a "fact." Please point me to the scientific literature making clear that greenhouse gas emissions couldn't possibly increase global temperatures enough to override the impact of Milkanovitch cycles. It doesn't exist. This guy is just talking out of his ass.
Just look, on his chosen graph, at the amount of time that it takes for the planet to cool as a result of Milankovitch cycles: we're talking 10–20,000 years to drop about 10*C. The planet is currently warming at a rate that's 10–20x faster than that, so please explain to me how these glacially slow Milankovitch cycles can outweigh that? It'd be like dropping one ice cube every 30 minutes into a pot of water boiling on high and expecting that to be enough to bring it back to room temperature.
Climate change deniers also seem oblivious to the basic fact that you can compare Earth's recent orbital changes against the temperature increases to see whether there's a correlation or not. Bloomberg presents us with exactly such a comparison using data from NASA GISS, and as we can see, Earth's orbit simply hasn't been changing in such a way that would account for even a fraction of the temperature increases that we've seen lately. The orbital changes have been negligible, having a net zero impact on global temperatures since 1880.
Deniers will often invoke not just Milankovitch cycles, but also an increase in solar output to explain the warming that we're seeing. The solution is obvious: We destroy the Sun.
Here's what the most boring man in the world, Patrick Moore, argues in a PragerU video:
". . . we do know there are many more factors in play than simply the concentration of CO2 in the atmosphere. Factors such as the shape and size of the Earth's elliptical orbit around the sun, activity from the sun, and the amount of wobble or tilt in the Earth's axis, among many others."
*me making snoring sounds because Patrick Moore put me to sleep* "...Oh, what? Yup, mmhmm, I'm awake."
*In unenthusastic robot voice with tone varying awkwardly*: "We do know that Patrick Moore is an extremely terrible speaker. Why does he sound so rigid when he reads a script?"
Yes, that is the Patrick Moore, former president of Greenpeace Canada who now exploits his former ties with that organization to get handsomely rewarded as a corporate lobbyist. I guess it makes sense that he speaks with a complete lack of emotion because I suspect that he's quite literally sold his soul to the oil industry.
Whenever you hear deniers invoke alternative explanations for present warming trends, pay close attention and you will inevitably notice a pattern: They never present you with actual data quantifying the exact degree to which these other factors are causing temperatures to rise. Instead, what they do is just talk broadly and generally about how other factors like Milkanovitch cycles or increased solar activity could perhaps—in a theoretical sense—cause global temperatures to rise. This is not the same thing as conclusively demonstrating that these things have been causing temperatures to rise.
It's not enough to just be like "Hey, maybe these other things are causing climate change?" You have to actually explore the scientific data and find out whether or not they are.
The question of increased solar activity is another one that's been thoroughly examined by climate scientists, and the data makes very clear that this also cannot explain recent warming trends. An EPA article on the causes of climate change writes that:
"The sun’s energy received at the top of Earth’s atmosphere has been measured by satellites since 1978. It has followed its natural 11-year cycle of small ups and downs, but with no net increase. Over the same period, global temperature has risen markedly."
And here we see an EPA graph illustrating the non-correlation between solar energy and global temperatures. Here's another graph using NOAA data presented in a 2009 report entitled "Global Climate Change Impacts In The United States." As we can see, once again, there is no correlation between solar output and worldwide surface temperatures.
You can extend this analysis even further into the past using proxy measurements of solar output—namely, sunspots, which have been carefully monitored and tracked over time. We see such an extended analysis, going back to around 1880, in the U.S. Global Change Research Program's 2017 Fourth National Climate Assessment Report. (Wow that was a fuckin' mouthful! I think I could read the entire report itself faster than I just read its title!)
As you'll notice from their graph, solar variation over the past 140 years or so has only had the most miniscule impact on global temperatures, contributing only about 0.05*F of the 2*F in warming. That means that solar variation can only account for about 1/40th of modern warming, or 2.5% of it.
We can also rule out the sun as the cause of recent warming for another reason, and that's that different layers of the atmosphere have been warming at different rates in a manner that's inconsistent with increased solar output. As SkepticalScience.com explains,
"Another human fingerprint can be found by looking at temperature trends in the different layers of the atmosphere. Climate models predict that more carbon dioxide should cause warming in the troposphere but cooling in the stratosphere. This is because the increased 'blanketing' effect in the troposphere holds in more heat, allowing less to reach the stratosphere. This is in contrast to the expected effect if global warming was caused by the sun which would cause warming both in the troposphere and stratosphere. What we observe from both satellites and weather balloons is a cooling stratosphere and warming troposphere, consistent with carbon dioxide warming"
And here we see two graphs which illustrate this dichotomy, depicting a cooling stratosphere since the late 1950s and a warming troposphere, as measured by satellite and balloon data:
You'll also sometimes see graphs like this one, presented in a Skeptic magazine article, which make it appear like solar activity has basically been correlated with global temperatures until the past 30 years or so, which could easily lead one to conclude that solar activity has been the cause of this global warming. The problem with these graphs, however, is that there isn't a 1-to-1 correlation here between the measurements on the Y-axes. What I mean by that is that an increase from 1365 to 1366 Watts/square meter doesn't translate into a 0.5*C increase in temperatures, as the graph seems to indicate.
As we read in a CarbonBrief article:
". . . it would take around a seven watts per metre squared change in TSI to result in 1C warming, meaning that the observed rise in solar activity between 1880 and 1980 would result in only 0.1C warming."
So you need to be careful when looking at graphs, and be sure to ask yourself how, exactly, certain measurements relate to one another.
…Plot twist: It turns out that it's actually the Moon that's causing global warming. All this time! There it was. Staring us in the face. But alas! It was too late...
Volcanoes are another frequently invoked cause of global warming. As we read in a YouTube comment on a PragerU video,
"Valcanos alone disprove climate change"
Patrick Moore's like "Hey, pay me enough money and I'll make a video arguing that that is how you spell 'volcanoes'!"
As another user argues,
"The top drivers of climate are:
1) Volcanic eruptions
2) Sunspot Cycles
Not surprisingly, no source is provided by either one of these people to support their claims. (They're like "What's a 'source'? Is that where you just like make shit up and pretend like you know what you're talking about? Because that's my specialty.") Once again, volcanic forcings are another thing that have been very thoroughly studied by climate scientists.
I love this whole idea, by the way, that some armchair viewer of misinformation-filled PragerU videos is the one who's figured it out, and the experts who've dedicated their lives to studying climate have just been floundering in the dark the whole time, oblivious to the possibility that something other than greenhouse gases could be responsible for the warming trends. No, the very essence of science is to devise methods of ruling out alternative explanations—and deniers bring up things like Milankovitch cycles or volcanic eruptions as if they've never crossed the climate scientist's mind before!
"Hey, maybe something else is responsible for global warming?"
"What the fuck?! We have never once even considered that! What a groundbreaking hypothesis."
It'd be like telling a coroner: "Hey, you know that instead of being murdered, sometimes people die of natural causes?"
He's like: "Yeah, buddy, I think, as a coroner, I know a thing or two about how dying works. Look, as much as I'd love to stay here and have you amateurs tell me how to do my job, I need to get back to my important work of touching and staring at naked corpses until 4 in the morning."
And then he's back in the morgue with his colleagues like: "...Well fellas, it looks like a pretty open-and-shut case where the decapitation during the car crash is what killed her. But just to be safe, we should examine her breasts one last time for tumors, because you know what they say!: Fifth time's a charm!"
Here's what the EPA writes about volcanic eruptions:
"Some volcanic eruptions released large quantities of CO2 in the distant past. However, the U.S. Geological Survey (USGS) reports that human activities now emit more than 135 times as much CO2 as volcanoes each year."
The textbook Global Climate Change presents us with an even larger difference, writing that:
"The amount of CO2 released from volcanoes . . . averages about 10,000-fold less than that from the modern-day burning of fossil fuels."
Source: p. 55, Global Climate Change: Convergence Of Disciplines, by Arnold J. Bloom. 2010.
They also point out that:
". . . on balance, volcanic eruptions cool, rather than warm, the planet. . . . Mount Pinatubo in the Philippines erupted on June 12–15, 1991 . . . and spewed vast amounts of sulfur dioxide and fine particles into the upper atmosphere. These materials quickly spread over most of the world and formed a haze of aerosols in the upper atmosphere that reflected enough sunlight to lower global temperatures by as much as 0.5*C for nearly 2 years."
Source: p. 55, Global Climate Change: Convergence Of Disciplines, by Arnold J. Bloom. 2010.
And here we see a Bloomberg graph—again using data from NASA GISS—which compares recent volcanic forcings against net temperature changes since 1880, making clear that not only are they not a primary or even partial contributor to the warming we've seen, but overall, they've slightly driven temperatures down.
Further proof that it's manmade CO2 emissions that are causing global warming comes from an analysis of the Carbon-13 to Carbon-12 ratio in the atmosphere. Here's what they write over at RealClimate.org:
". . . plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios. Since fossil fuels are ultimately derived from ancient plants, plants and fossil fuels all have roughly the same 13C/12C ratio – about 2% lower than that of the atmosphere. As CO2 from these materials is released into, and mixes with, the atmosphere, the average 13C/12C ratio of the atmosphere decreases."
And indeed, as we can see here in this graph from a 2013 Rubino et al paper, right when CO2 levels began spiking during the 1800s, the 13C ratio began declining—exactly as you'd predict if fossil-fuel emissions were the source of this carbon dioxide.
There's a very important analytical question to be asking yourself right now, and if you can think of it on your own, you get a gold star for the day.
The key question to ask is: How does the 13C ratio of fossil-fuel emissions compare against those from volcanic eruptions? Here's what Erik Klemetti writes in a Wired article:
"Consider the following rough estimates of isotopic composition for sources of carbon dioxide in the atmosphere (mainly taken from Faure ):
Volcanic gas emissions: -2 to -6‰ (for CO2)
Weathering of crustal rock: -7‰
Decay of organic matter: -25‰
Burning of coal: -25‰
Burning of oil: -18 to -34‰
. . . if you take a bunch of coal and crude oil and burn it, you will add a lot of highly negative (light) carbon dioxide into the atmosphere, thus lowering the [overall] carbon isotopic composition of the atmosphere's carbon dioxide.
Now, for argument's sake, what if you wanted to explain this without invoking the burning of fossils fuels. What would need to happen to explain the increase of carbon dioxide with an accompanying decrease in its isotopic composition? Well, if you want it to be volcanoes, then you would need both a sharp increase in volcanic emissions since 1800 and a change in the composition of the carbon dioxide they emit, from around -3 to -5‰ to something much more negative. This has not happened in either case: volcanic activity hasn't increased since before 1800 and the composition of the gases they emit hasn't changed either."
The final thing you might argue is that present warming rates are simply the result of natural variability in Earth's climate. Indeed, if you look at fine-grained temperature data over the past 10,000 years or so, as we see on GeoCraft.com, you'll see that while the trendline has been basically flat, global temperatures have fluctuated around that flat line by about 1*C or so. So perhaps what we're seeing today is simply another iteration of this randomness?
My response would be, why attribute to randomness that which is clearly being caused by something? Humans have been pumping out enormous amounts of greenhouse gases into the atmosphere. We know what impact these have on global temperatures, so what would you expect the outcome to be if not global warming?
"Well, sometimes climate just mysteriously changes and who knows what the cause is," he said, after pumping 1.3 trillion tons of CO2 into the atmosphere.
“Ah yes, the old random, steady increase in temperatures that perfectly correlates with greenhouse gas emissions. That old chestnut.”
"Look, I get that I punched you in the face 9 times in a row, but sometimes people's faces will just naturally hurt on their own!"
Natural variability is something else that's taken into consideration and accounted for by climate scientists, and this too has been dismissed as the core explanation for recent warming trends. Zeke Hausfather writes the following in a CarbonBrief.org article:
"A number of researchers have examined the potential for natural variability to impact long-term warming trends. They have found that it generally plays a limited role. For example, Dr Markus Huber and Dr Reto Knutti at the Institute for Atmospheric and Climate Science (IAC) in Zurich found a maximum possible contribution of natural variability of around 26% (+/- 12%) over the past 100 years and 18% (+/- 9%) over the past 50 years."
The IPCC's Fifth Assessment Report found that internal variability could only account for a maximum of 0.1*C of the observed 0.65*C in warming we've seen since 1950—or about 15% of it. The error bar is centered right around zero, however, so this same variability could've actually contributed to a decrease in temperatures of the same amount. So although we're unclear about which direction climate variability pushed global temperatures in, what is clear is that whatever impact it did have was very minor.
There have been many scientific analyses which look at any and all alternative explanations for our current warming trends, and from what I've seen, they all reach the same conclusion: manmade greenhouse gas emissions are to blame. And when I say "scientific analyses," I don't mean some robotic, PragerU propagandist providing us with the data-free implication that perhaps Milankovitch cycles are to blame; I don't mean some clueless person in the comments section asserting with no supporting evidence that volcanoes and solar variation are causing the warming; I mean actual scientific investigations into the subject which quantify the precise degree to which different forcing factors have contributed to the warming trends.
The OG himself, Zeke Hausfather, presents us with one such breakdown in a CarbonBrief graph created using data from the IPCC, NOAA, and ECLIPSE. As we can see, from 1850 to 2017, temperatures have increased by about 1.2*C. The solar contribution to this warming, indicated in yellow, has been negligible. The volcanic contribution, as seen in orange, has actually been net negative. It is only manmade greenhouse gas emissions that can explain the warming trends over time.
Here's what the USGCRP writes about the subject in their 2017 report:
"The likely range of the human contribution to the global mean temperature increase over the period 1951–2010 is 1.1° to 1.4°F (0.6° to 0.8°C), and the central estimate of the observed warming of 1.2°F (0.65°C) lies within this range . . . This translates to a likely human contribution of 93%–123% of the observed 1951–2010 change. It is extremely likely that more than half of the global mean temperature increase since 1951 was caused by human influence on climate . . . The likely contributions of natural forcing and internal variability to global temperature change over that period are minor."
And here we see a graph from their report showing that natural forcings alone—depicted in blue—are not enough to account for the observations. The orange line in their other graph shows that only by including manmade emissions do the forcings match up with the observations.
On top of that, we've also seen a steady increase over time in the the degree of confidence that the scientific community has in their proclamations about the manmade contribution to global warming. The Union of Concerned Scientists has a graphic on their website which shows us the conclusions reached over time by the IPCC on the amount of human-caused warming.
...and, finally, 2018, where they said "You stupid fucks must not be hearing us or something!" No, I'm joking; that last one, I obviously made up—although I do suspect that the next IPCC report will literally just be one page long, containing nothing more than a single picture of climate scientist Michael Mann completely giving up hope and just getting passed-out drunk in public.
At the risk of stating the obvious, the USGCRP tells us that:
"These increasingly confident statements have resulted from scientific advances, including better observational datasets, improved models and detection/attribution methods, and improved estimates of climate forcings."
So as we've learned, the data clearly indicates that manmade greenhouses gases are responsible for the global warming we're seeing.
Milankovitch cycles don't produce the type of rapid temperature changes we've seen lately, and the orbital changes that have taken place in recent years simply wouldn't have caused a temperature increase. Solar activity is something that's been carefully measured, and the data makes clear that this, too, cannot be described as the cause of global warming. Volcanic eruptions emit only a tiny fraction as much carbon as that emitted from human activities, and the atmospheric C13 ratio indicates that fossil fuels—and not volcanoes—are the source of our rising greenhouse gas concentrations.