The title is in reference to "Armegeddon" I would listen to "Don't wanna Miss a Thing" while reading
If I asked you what the weather was yesterday
between 6:00 AM and 7:00 AM in Bali how would you look it up? You would Google “Bali Weather 11/20”
and have the information in seconds.
What about in Kansas in 1910? You’d
have to find an old newspaper from that time or an almanac but you could most
likely find it. What about Chile in
2000 BCE or Tokyo in 10,000 BCE? This is
what we need to unlock in order to study the climates of the past.
If I have a theory about the current climate and
where it is heading, but have to wait 2 human life times to see it come to
term, I am going to have one hell of a time testing anything. However if I knew the exact climate and make-up
of the earth throughout all of its history I would be able to match my theories
about the climate with the climates of the past. Since we did not have meteorological
instruments or chemists stationed in Chile in 2000 BCE we need a different type
of Almanac. Luckily the earth has provided just that in Glaciers; giant, as old
as the earth has been cold, and constantly recording the state of the earth in
their layers of ice. Imagine every
summer since the inception of ice you wrote down the hottest day of the summer
and the coldest day of winter. Then you stacked these pieces of paper every
year… for a couple million years (the age of the current glaciers in
Antarctica). Every couple of years you
also wrote down a description of the weather that year and stuck that in there
too. This is what we are going to use to study the past climate.
Digging up
the Past
So we have miles and miles of history frozen all
over the world. The issue is this history is incredibly brittle, has to remain
frozen, and needs to remain intact and in sequence for the miles and miles it
exists. In good news, throughout the
course of American history we have been great at getting things out of the
ground (thanks oil industry!) and can drill for days. Imagine you had a 2 inch
hole-saw and drilled a hole in a 2x4.
The 2x2 inch slug of wood that we throw away is now what we are looking
to extract. Instead of a couple of
inches of wood slug however, we are looking to harvest more than 2 miles of ice
– therefore we use much bigger hole-saws!
Since these have years and years of engineering behind them it would be
insincere to pretend like I could summarize all the ways we have come up to
extract cores so I’m just going to throw up some pictures and let you imagine
from there.
What a Core
Can Tells Us
Water Ratio
Cores contain three important history “logs” we
use to recreate the atmospheres of the past. The first “log” we look at will be
the frozen water itself. Most of us know that water is made up of Hydrogen and
Oxygen or “H2O”, however not all H2O is created equal. Eventually we will cover “isotopes” in a Not So Simply Science however this is
what you need to know: There are two
common forms of water, one is heavier than the other. As most of us learned in grade school snow is
precipitation, it literally falls from the sky.
In order for it to get up in the sky it takes energy to evaporate –
think boiling a pot of water. The
heavier the water the more you have to heat it.
As in most of our examples the energy we need to evaporate the water
comes from the sun. The warmer the planet, the more heavy
water can get into the air, the more heavy water ends up in snow, the more it
is frozen in the glaciers!
The first important fact we get from the core is this ratio of heavy
water to light water.
Important Note: O18 is heavier than O16 - that's what you need to know!
While we do not have weather records for all of
recorded history, we still have a ton of weather records from both current and
ancient civilizations. We take our
weather records and compare them to core samples from that time. With the expected heavy/light water ratio and the temperature, we can reconstruct
the history of temperature by analyzing the ratio throughout the core. Even more importantly we can measure the history of temperature change! This
information is invaluable – it is how we anchor all of our climate
science. Without knowing the temperature
of the planet in the past we cannot predict what will happen in the future.
The next “log” of glacier cores is basically the climate science equivalent of Jurassic
Park! Just like the tiny mosquitos
filled with dino blood were trapped in tree sap, tiny pockets of atmosphere get pressed and frozen into the layers of
the glacier. These are basically
tiny windows into the atmosphere of the past and the time when it was present. If the first log gives us the global
temperature at the time, this second log gives us both the potential causes and
effects of this temperature. Scientists
use these tiny atmosphere samples to recreate the greenhouse gasses of the past
atmosphere. While the effects of greenhouse
gasses will have to explored in further blog posts here is chart that shows
changing temperature along with the concentration of CO2 for the
last 400,000 years. While this does not
show which is cause or effect, it shows a clear link between the two in some
way.
Dust
The last “log” we will talk about is dust and
debris. In our daily lives dust is a simple nuisance, dust that has been
trapped beneath ice for millions of years can let us know a lot about other
atmospheric conditions we cannot get from temperature and gas breakdown alone. Firstly dust and debris are actually pretty
specific in their origin. Sand from
Arizona is different than sand from the Jersey Shore is different than sand
from the Gobi desert. Secondly dust gets
into the atmosphere by being blown around.
More wind means more dust and
the further travel. The dryer the
climate is the more dust is available to get into the air. When they want to keep dust down at large
construction sites they are constantly spraying water everywhere – the earth
does the same thing. As an example of
how any of this is useful, dust in Greenland’s cores is seen to be 10-100 times
more prevalent during glacial periods.
This lets us know that in the deserts where the dust originates from, during
glacial periods, it is much dryer and windier than when the climate is
warm. The amount of dust and specific origin let us
infer even further into the climate's conditions. The previous chart shows the inverse
relationship of “dustiness” to temperature.
Potential
Issues
While I have painted a pretty simple picture of
the benefits of glacial cores, they are more like a long Indiana Jones corridor of booby traps than the almanac I presented. Firstly as we get further and further back in
time it gets harder and harder to date the ice core. Close to the surface the core looks a lot
like a tree, there are layers you can see when the ice melted and refroze in
the summer and winter. As you get deeper
and deeper, under more and more pressure these lines become essentially non-existent. This is where we use things like known
volcanic explosions and other geological events to look for changes in the ice
composition. It is a highly advanced
guessing game.
The black line is from a Volcanic Eruption ~21,000 years ago
Next, molecules (the little parts that make up
everything) do not tend to just sit still for millions of years. While the bubbles of atmosphere are trapped
in the ice and put under immense pressure many of their molecules will travel
out of the bubble and spread into the ice.
It is then up to scientist to calculate what the atmosphere
would contain based on more recent bubbles we know the correct concentrations for as
well as the amount of time these old bubbles have been in the ice.
Finally (not really finally there are just too
many issues to look into) as we handle cores whether by drilling them out, transporting them, or keeping them cool they are constantly changing. Imagine
you were reading a history book, but the more you read it the more the content changed. They can change so much that
what you thought you read the day before about Greece defeating the Persians
now reads the Persians defeated the Greeks. It is that difficult. We
cannot recreate being 2 miles beneath the surface of the earth, being undisturbed
for thousands of years as we rip the ice out of the earth, our handling of the core has to change it. All of these factors
need to be worked into any analysis that is done on an ice core.
Regardless of all of these issues, these are our
premier way of comparing today's changing climate of the future into known
quantities of the past. The power of
knowing how the climate reacted in the past is immeasurable. I have spent a lot of time talking about just
how long geological time is, and how it can be hard to even see the end of a
current hypothesis about the climate come to fruition. With Ice cores however we get to test our theories
out on hundreds of thousands of years of climate data!
Image Credit:
http://pages.uoregon.edu/rdorsey/geo334/O-isotopes.html
http://icecores.org/icecores/drilling.shtml
http://insectcop.net/two-mosquito-mistakes-that-the-first-jurassic-park-movie-made/
http://climatechange.umaine.edu/icecores/IceCore/Ice_Core_101.html
https://upload.wikimedia.org/wikipedia/commons/b/b8/Vostok_Petit_data.svg
http://icecores.org/indepth/2015/spring/nsf-press-release_waisdivide_01.jpg
http://www.crowcanyon.org/images/photos/learn_about_archaeology/ice_core.jpg
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