The Simple Proof of Man-Made Global Warming

The Simple Proof of Man-Made Global Warming

The two most basic Smoking Guns proving that carbon from fossil fuels is warming the Earth.  


by Brian Dunning

Skeptoid Podcast
#549

December 13, 2016

Listen:

I encourage everyone to listen to this episode, or to read and
share its transcript online. Today I'm going to talk about some simple
factual observations that anyone can make, that unambiguously prove
human activity is driving warming of the Earth. I'm not going to mention
climate models, politics, predictions, economics, or how many
scientists agree or disagree — any of the topics on which there is
debate. I'm only going to share a few of the most solid basics, the
results of absolute measurements, over which there is no debate. These
are the things nobody disagrees with, but so few people understand.
Despite its contentious topic, this episode is intended to be — and
should be — completely non-controversial.


I am only going to make two points today, and they are to share two
of the "smoking guns" by which we know that this is happening. They are
simple to understand, and they are based on basic science that everyone
should remember from school. They do not depend on models or
predictions, but upon simple direct observations. They are that the
rising CO₂ (carbon dioxide) in the atmosphere is definitely produced by human activity, and that that same CO₂
is warming the planet. Nothing in this episode is disputed, or is
subject to alternate explanations, but too few people are aware of these
facts. So let's begin with:

Proof that the atmosphere's excess CO₂ is human generated

You might think that carbon is carbon, and that if we find there's more CO₂
in the atmosphere, its source can't easily be proven. But chemistry is a
bit more complicated than that; there are different kinds of carbon, as
there are of most elements. They're called isotopes. One isotope of
carbon is carbon-14. Cosmic rays bombard the Earth at a rate that is
more or less constant over time. When they do, they strike atoms in the
upper atmosphere, kicking out neutrons. These neutrons then collide with
the most common atoms in our atmosphere, nitrogen. This collision kicks
a proton out of the nucleus and turns the nitrogen into carbon with two
neutrons too many: the unstable and radioactive carbon-14, instead of
the normal stable carbon-12.


You've heard of carbon dating; this is done by comparing the relative
amounts of carbon-12 and carbon-14 in a sample. Living things, like
animals and trees, are in equilibrium with the atmosphere. As they eat
and breathe and interact, they contain the same proportions of carbon
isotopes as the atmosphere. When they die, that carbon-14 decays over a
long time, and since the organism is no longer eating and breathing, no
new carbon-14 comes in, and eventually the only carbon remaining is
carbon-12 (and some carbon-13). Fossil fuels like oil and natural gas
come from plants that died millions of years ago and have no carbon-14
left. The CO₂ produced by burning fossil fuels contains only carbon-12.


When a forest fire burns, the CO₂ in the smoke came from
living or recently dead fuel, so the smoke contains the same proportions
of carbon-12 and carbon-14 as the atmosphere. This is the case with
nearly all natural sources of CO₂. We can carbon date the CO₂
in the atmosphere, and tell exactly how much of it comes from humans
burning fossil fuels. It's a direct measurement. It leaves no room for
interpretation.


There is one natural source of CO₂ that contains only
carbon-12, and which is often pointed out by climate deniers as the real
source of all of this new carbon-12: volcanoes. Volcanoes worldwide
constantly erupt, both on land and under the sea. They do so at a fairly
constant rate. We measure their output, and we know that annually,
worldwide volcanic activity averages about 200 million tons of CO₂
added to the atmosphere, all with carbon-12, which is indistinguishable
from the carbon-12 produced by burning fossil fuels. However, each
year, we measure a total of about 29 billion tons of CO₂
added to the atmosphere. That's more than 100 times the amount volcanoes
can account for. The only possible source of all the rest of that new
CO₂ is fossil fuel burned by humans.


This, in short, is the "smoking gun" that proves the increase in CO₂
in the atmosphere is caused by humans burning fossil fuel. It's not a
conjecture or a model or a prediction, it's a measurement that anyone
can reproduce, and isotopes are isotopes, and don't have alternate
explanations.


Some have said that 29 billion tons is not a problem, because of how
small that is compared to the atmosphere's total existing carbon load.
It's true that 29 billion tons is a drop in the bucket compared to the
750 billion tons that moves through the carbon cycle each year, which is
our name for the natural processes by which carbon is exchanged between
the atmosphere and the oceans and vegetation. Each year, of that 750
billion tons, the ocean absorbs a net gain of about 6 billion, and
vegetation absorbs a net gain of about 11 billion. They're only able to
absorb about half of the 29 billion we're adding. The other half — about
15 billion tons each year — remains in the atmosphere, after maxing out
the Earth's ability to absorb it into its system. These numbers, too,
are reproducible measurements; not conjectures, models, or predictions.
The system is provably absorbing all it can, but still unable to keep
up.

Proof that that human-generated CO₂ is warming the planet

We
also do not need models or predictions to directly measure the source
of heat in the atmosphere. There are five gases that are primarily
responsible for the greenhouse effect. They are CO₂, methane, water vapor, nitrous oxide, and ozone. We can tell this because of spectroscopy.


Spectroscopy is a method of detecting elements by looking at how
electromagnetic radiation passes through them. Different elements have
electrons in orbits at varying energy levels, and this affects the way
they resonate. It's the reason why neon lights produce different colors
depending on what gases we fill them with. It's also the way we're able
to tell what proportions of hydrogen, helium, and other elements are in
distant stars: the spectrum of light coming from them has peaks and
valleys that are chemical fingerprints of exactly what gases are in
them.


The Earth's surface is warmed by the sun, and as a warm globe in
space, the Earth itself emits that same heat right back out, as infrared
radiation. If we go outside and point a spectrometer at the sky, we can
see there are peaks and valleys in the infrared spectrum. Some
wavelengths of heat fly right out into space unhindered, while other
wavelengths are absorbed by the atmosphere, and that heat stays there,
where we're able to detect its wavelength with our spectrometer. And
exactly the same way as we're able to identify the elements in a distant
star, we're able to identify exactly which greenhouse gases are
trapping the Earth's radiative heat. This is how we were able to
identify those five main gases. And this isn't new; we've understood
this for 200 years. It's a direct measurement that anyone with a
spectrometer can reproduce. Not a model, not a prediction, not a guess.


Water vapor, which is the most prominent, defines the basic shape of
the greenhouse spectrum. Most of the infrared radiation that escapes the
Earth goes through a window left open by water vapor, which we call the
infrared window. This window in the spectrum, which is pretty wide, is
centered around a wavelength of about 10 µm (micrometers). At higher and
lower wavelengths, water vapor absorbs much of the Earth's radiated
heat, so the Earth has always relied on this open window in the spectrum
to allow the excess heat to escape. One end of the infrared window is
overlapped by CO₂'s absorption range, which is centered around 15 µm. The amount of CO₂ in the atmosphere acts like a sliding door which widens or narrows the infrared window. As CO₂
increases, the infrared window is narrowed, less radiation escapes into
space, and more heat is absorbed by the atmosphere. At the other end of
the infrared window, around 7.5 µm, methane has a similar effect,
contributing about 1/4 as much warming as CO₂.


Spectroscopy is hard science. We don't have to model or predict.
Simply by pointing our instruments at the sky, we can, right now,
directly observe and identify the greenhouse gases, and measure exactly
how much radiative energy the atmosphere is absorbing and keeping here
on Earth. This direct, non-ambiguous spectroscopic reading is the
"smoking gun" that proves the excess heat energy being trapped in our
atmosphere is due to CO₂. That excess CO₂ is produced by humans burning fossil fuels.


We've also measured the Earth's infrared spectrum from space, looking
down from satellites, to see which wavelengths of heat energy are being
trapped by gases in the atmosphere, and which wavelengths are escaping.
We started this in 1970 with the IRIS satellite, giving us a baseline
to compare against future measurements. It was followed in 1996 with
the Japanese IMG satellite, and again with the AIRS satellite in 2003,
and the AURA satellite in 2004. They paint a very clear picture. We
subtract new readings from the old readings to see the delta, to see
exactly where in the spectrum any change has occurred. Within that
infrared window defined by water vapor, there is one big spike. It is
the 15 µm range of CO₂. This is explicit, unambiguous proof that the increased heat in our atmosphere is due to CO₂.
It has nothing to do with models or predictions; it is a direct
observation, it is hard chemistry and basic physics, not guesswork or
extrapolation.


As we burn fossil fuels, the CO₂ in the atmosphere
increases, the infrared window narrows, less heat radiates away from the
Earth, and more heat goes into the Earth's system. These are simple,
solid facts.


In this episode, I've tried to limit everything to just facts that
are not in dispute. That means I haven't included any estimates or
predictions. Why? Because I'm trying to take opinion and ideology-driven
spin completely out of the picture. I don't have an answer or a
solution for people who prefer to view this particular science question
through the filter of an ideology. Earth science measurements and facts
are ideology-free, just like astronomy and mathematics and zoology. The
impact that human use of fossil fuels is measured to have already made
to the Earth system is bewildering. It is from this point, from the
non-ambiguous, factual, black-and-white characterization of our
atmosphere and oceans, that we must ask ourselves whether any
ideological twisting of the facts is truly the best path forward. We
have to accurately understand a problem in order to devise a properly
informed solution.


Please, if you have any curiosity about any of the topics we've just
discussed, see the references section at the bottom of this transcript,
where you'll find links to articles and videos that are both thorough
and easy to understand. You can go into much greater depth if you're so
inclined. What's important is what you choose to do with this
information, and that part I will leave up to you.



By Brian Dunning

Cite this article:

Dunning, B. "The Simple Proof of Man-Made Global Warming." Skeptoid Podcast. Skeptoid Media,
13 Dec 2016. Web.
4 Sep 2017. <http://skeptoid.com/episodes/4549>

References & Further Reading

Cheng,
L., Trenberth, K., Fasullo, J., Boyer, T., Abraham, J., Zhu, J.
"Improved estimates of ocean heat content from 1960 to 2015." Science Advances. 10 Mar. 2017, Volume 3, Number 3.


Editors. "Empirical evidence that humans are causing global warming." Skeptical Science. John Cook, 11 May 2008. Web. 10 Dec. 2016. <http://www.skepticalscience.com/empirical-evidence-for-global-warming.htm>


Editors. "Which produces more CO2, volcanic or human activity?" Hawaii Volcano Observatory. US Geological Survey, 15 Feb. 2007. Web. 10 Dec. 2016. <http://hvo.wr.usgs.gov/volcanowatch/archive/2007/07_02_15.html>


Lallanila, M. "What Is the Greenhouse Effect?" Planet Earth. Live Science, 12 Apr. 2016. Web. 10 Dec. 2016. <http://www.livescience.com/37743-greenhouse-effect.html>


McClain, C. "A Story of Climate Change Told In 15 Graphs." Deep Sea News.
Craig McClain, 23 Sep. 2015. Web. 10 Dec. 2016.
<http://www.deepseanews.com/2015/09/a-story-of-climate-change-told-in-15-graphs/>


Monroe, R. "How Much CO2 Can the Oceans Take Up?" The Keeling Curve.
Scripps Institution of Oceanography, 3 Jul. 2013. Web. 10 Dec. 2016.
<https://scripps.ucsd.edu/programs/keelingcurve/2013/07/03/how-much-co2-can-the-oceans-take-up/>


NOSAMS. "What is Carbon Dating?" National Ocean Sciences Accelerator Mass Spectrometer. Woods Hole Oceanographic Institution, 10 Mar. 2015. Web. 10 Dec. 2016. <http://www.whoi.edu/nosams/page.do?pid=40138>


Riebeek, H. "The Carbon Cycle." Earth Observatory.
National Aeronautics and Space Administration, 16 Jun. 2011. Web. 10
Dec. 2016.
<http://earthobservatory.nasa.gov/Features/CarbonCycle/page1.php>