I'm a little late on this, but last month we hit an interesting environmental milestone: For the first time in a very long time, atmospheric carbon dioxide levels were measured at higher than 400 parts per million. In fact, it's the first time that atmospheric CO2 levels have ever been measured that high- considering the Earth System Research Laboratory in Mauna Loa, Hawaii which reported these numbers has only been measuring CO2 since 1958. The BBC reports on it quite well here.
CO2 is important, as I'm sure you've
all heard, because it is a greenhouse gas- meaning that it's presence in the atmosphere has a net heating effect on the Earth. CO2 is generated from nearly every fuel and process that humans use, and because of that, humanity has a huge impact on atmospheric CO2- but let's take a look at how CO2 functions as a greenhouse gas, and why 400 ppm is a number we should be worried about.
Carbon dioxide's action as a greenhouse gas is due to some interesting quantum physics effects of the
molecule- but without getting too complicated yet, lets start by taking a look at
our good old electromagnetic spectrum:
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| The Electromagnetic Spectrum |
I like this chart paticularly because
of the thermometer scale at the bottom. It's useful to remember that
nearly every object, as long as it contains significant energy, leaks that energy through electromagnetic radiation. A very high
temperature object gives off a relatively short wavelength wave,
which is higher in energy, as per the Planck Relation:
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| Where energy is E, Planck's Constant is h, the speed of light is c, and wavelength is λ |
As wavelength (λ)
decreases, energy (E) increases. And in fact, the
two main ways that the Earth as a whole gains and loses energy is
through these electromagnetic waves- electromagnetic radiation from
the Sun reaches Earth and heats it up, and then the Earth
releases it's own electromagnetic radiation, losing energy and cooling it down.
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| The Sun, a G-Type main-sequence star |
But the Sun is hot- really hot in fact. Depending on where you look in the Sun, it's departure can be between 4000 to 2 million degrees Celsius-
while the Earth clocks in around a bit more hospitable 15 degrees Celsius on average, according to NASA. Looking up at the chart above, we can see that the
Sun emits waves in the visible to UV range, while the Earth emits
it's own waves in the infrared spectrum (note that the spectrum chart has an odd scale- logarithmic by Kelvin). A fun fact- because humans are a little warmer than the Earth, we all emit infrared radiation with a little more energy than the
Earth- which is how infrared cameras can pick up humans in the dark.
So,
this is fine- the Sun warms up the Earth with UV-visible radiation,
and then the Earth cools itself with infrared radiation- and it all
balances out, usually. but what does CO2 have to do with it?
Here's
where it gets weird and quantum mechanics come into play. Just like
every object releases radiation, every object also absorbs it. But similar to how objects emit specific radiation wavelengths, objects also absorb wavelengths differently, depending on their atomic structure. CO2 doesn't absorb short wavelength light from the sun- it passes straight through
it, without heating up the gas significantly. But CO2 does absorb the infrared radiation given off by the Earth, absorbing and reflecting the heat contained within surprisingly well. So when the Earth tries to
get rid of its heat by releasing infrared radiation, CO2 sucks it
right up- and traps it in the atmosphere instead.
And here's the problem that the Earth
Systems Research Laboratory is seeing: due to human actions-
deforestation, burning of fossil fuels, and agricultural processes-
the amount of free CO2 in the atmosphere is rising, inhibiting the
Earth's natural heat dissipation process. When the Earth can't get
rid of it's own heat, the average surface temperature starts to
increase. This is the global warming effect.
400 ppm stands as a warning from
the Mauna Loa laboratory and the rest of NOAA- the National Oceanic and
Atmospheric Administration- that runs it. Without a reduction of CO2,
we'll keep seeing the Earth slowly heat up. And while the
implications of extra temperature are still somewhat poorly
understood, one thing is for certain: the world of the future could
certainly be drastically different from the world of today.
In conclusion, I've compiled NOAA's lab
data that they publish on their website here and put it in an interactive chart.
Monthly CO2 Data from NOAA
Parts Per Million Atmospheric CO2 Over Time
Red line is yearly average, blue line is monthly average
A few interesting things to note: CO2 concentration fluctuates by season because of plant growth in the northern hemisphere. Because most of the landmass of the Earth is north of the equator, as plants grow
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| The Earth, with most land above the equator |
in the northern Spring and Summer, they remove some of the CO2 from the air. As trees lose their leaves and plants decompose in the Fall and Winter, much of this CO2 is released again- and as such, the CO2 concentrations are lowest in the early Fall before trees start to lose their leaves, and highest in the early Spring, before they begin to regrow them.
Additionally, it's helpful to note that NOAA is reporting the
first actual measurement above 400 ppm- but in fact, the yearly
avereage is still slightly below that number. As Dr. James Butler
from the Mauna Loa facility remarks in the BBC article, due to the
natural fluctuation, CO2 numbers will still be dancing around 400 for
a little while to come- but in a few years, it's unlikely we'll see
numbers below 400 ppm again.
Links to references:
http://www.bbc.co.uk/news/science-environment-22486153
http://www.space.com/17137-how-hot-is-the-sun.html
http://www.co2science.org/subject/s/summaries/seasonalco2.php
ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt
http://www.universetoday.com/14516/temperature-of-earth/
http://www.chemguide.co.uk/analysis/uvvisible/theory.html
http://environment.about.com/od/globalwarming/a/greenhouse.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/grnhse.html
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