Unfortunately, graphs do not seem to post on this blog site, so I included weblinks where the graphs were supposed to be.
I have avoided blogging on climate change, as it has gotten politically-hot and ladden with "correct" views. However, I've tried to stick with the "facts" as I see them with a minimum of snide comments of my own.....
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I have a photo hanging in my office of four smiling children with looks on
their faces that seem to be saying “Dad, aren’t you done yet?” They are standing next to a marker that
established the extent of Jasper National Park’s Athabasca Glacier in 1982. Since the photo was taken in 1994 and
the glacier can be seen about 100 yards behind the marker, it provides concrete
evidence that the glacier had receded about 100 yards in only 12 years. In fact, it has retreated about 0.92 miles
since observations started about 125 years ago. It’s hard to argue that glaciers are not receding when you
have this one glacier’s history staring you in the face.
In the early 2000’s I became intrigued by how long the ice
remained on Lake Mendota in the beautiful town of Madison, Wisconsin. I had a bird’s eye view of the lake
from my 12-floor office for many years and felt privileged to be able to watch
its magnificent changes with the seasons.
I started to keep track of how long the lake was frozen and subsequently
learned that the North Temperate Lakes program at U.W. Madison had ice duration
records for this lake going back to 1855—the longest such record for any lake
in the United States. I took this nearly 150-year history and plotted a graph of
how long the ice had remained on the lake each year from 1855 to 2002. It was obvious that in the mid- to late-1850’s
there was ice on the lake for as long as five months each year, which
contrasted sharply with some of my own observations in which the ice lasted only
two to three months. (Happily,
the data set is continually updated, and ice data is available online through
2009*. You can plot it yourself!) In briefly scanning the raw data, it is
clear that the trend I observed continues through 2009, with ice duration being
not more than 90 days. What a
change—during the lives of my great-grandparents, southern Wisconsin winter’s
lasted six months, but during my children’s lives, it has only lasted about three
months. Sometimes data is so
obvious you don’t need to do a statistical analysis to tell an apple from an
orange.
These personal and anecdotal observations prompted me to
write an article in 2002 titled: “Grab your shorts and sandals, it’s getting
warmer,” which was published in the now-defunct Wisconsin Outdoor Journal (amazing
that my efforts did not reverse the Journal’s apparent decline, don’t you
think?) Writing the article was great
fun, as it forced me to read a lot about climate change, starting with the
Medieval Warm Period, which began in the 1200’s and ended in 1350 with the
onset of the Little Ice Age, a bitterly cold period that lasted 300 years. In 1850, the climate started to get
warmer, a trend that continues to the present day. I found that the Lake Mendota ice duration data was entirely
consistent with this warming. But interestingly,
the ice duration has not changed much in the past 20 years—it seems to have
plateaued at about 60 – 90 days (more on this later).
Well, it’s always more fun if you have a theoretical model in
mind when you watch the world unfold.
And to this day I still ask some contacts in Madison to let me know what
the ice is doing on Lake Mendota.
And my brother keeps track of ice duration for Hultman Lake in northern
Wisconsin, continuing a tradition begun in the 1930s by friends and family.
So partly due to my interest in Wisconsin ice data, I’ve
kept a casual eye on the ebbing and flowing of the climate change debate. As I
see, it the controversy has three main thrusts:
1. Is
the planet getting warmer?
2. If
so, what is the cause—is it the so-called “greenhouse gases” such as CO2
and methane?
3. What
role has Homo sapiens played?
The first question, is the planet getting warmer, seems to
be resolving into a consensus of “yes,” at least up until very recently. The pros and cons of the argument
have been interesting to watch, as they illustrate science in action: the good,
the bad, and the ugly, complete with pronounced political overtones.
When discussing climate change or global warming, as it used
to be called, it is hard to avoid the “impact of humans” controversy. However, in this blog I’m going to
stick to the first and second questions—is the planet getting warmer and is CO2
involved—and postpone the issue of “anthropological forcing” (the impact of
humans on climate change through the release of “greenhouse gases) until a
later blog post in this series.
So, what is the scientific evidence that the planet is
getting warmer?
Whether we look at glacial retreat in both the northern and
southern hemispheres or the amount of time that ice remains on lakes, there
seems to be pretty good observational data to support the thesis that the
climate is getting warmer. I mean,
how could you explain it any other way? Glacier ice and lake ice melts as it gets warm and freezes as
it cools, and data tracking this cycle integrate both the intensity of the
heat/cold and length of the warming/cooling period.
And indeed there are many, many worldwide reports of glacial
retreat. On all continents. In all 19 glaciated regions of the
world, including the Rocky Mountains, the Cascade Range, the Himalayas, the
Alps, the southern Andes, and Mount Kilimanjaro. Even the high mountains of Papua New Guinea, north of
Australia, have lost most of their ice caps since the 1900’s. There are also examples of glacial
advance, but it seems the “retreats” have it by a long shot.
Further, the huge ice sheets of Greenland and Antarctica are
diminishing, and the glacier data and ice sheet data are concordant (based on information
from a May 17, 2013 article in Science magazine).
So this would be pretty much a “case closed” situation in
favor of global warming, right?
Well, not exactly—because glacial retreat can be explained not
only by warming but also by reduced precipitation. Without precipitation in the form of rain, snow, and ice, a
glacier can’t grow. But what is the relative importance of reduced
precipitation vs. warming? Some
studies indicate that reduced precipitation can account for about half of at
least SOME of the glacial retreats—like those on Mt. Kilimanjaro in Tanzania
and the Great Aletsch Glacier in Switzerland. In fact, some scientists have
argued that humidity, cloudiness, air temperature, and precipitation have a
greater impact on tropical glaciers (such as those on Mt. Kilimanjaro, in New
Guinea, and in the South American Andes) than does air temperatures alone.
As in all areas of science, parsing out the truth is
difficult.
In a perfect world we’d have surface temperature data over,
say, 25,000 years. The problem is
that the thermometer, as we know it today, was not invented until 1724, and thus
has been in use for less than 300 years. Initially, at least, their distribution was not uniform
around the world, and who knows when they became standardized? So instrumentation data has its
limitations.
So how DO scientists get a long-term perspective on global
temperature if instruments like thermometers have only been around for a few hundred
years?
They use what are called “proxies.” That is, substitutes for actual
temperature data. Glacial data is a “proxy.” Ice duration data is a “proxy.” But they are only good for
observational data going back, say, 150 years. Fortunately, there are other proxies that allow us to gather
temperature data going back hundreds of thousands of years. Such as “layer-counted proxies.”
Say what—layer-counted proxies? Yes, scientists examine actual
layers of something as a stand-in for thousands of years of temperature data
(think of the poor graduate students doing this work!). And what kinds of things do they count? Layers of tree rings. Or layers of sediments, carefully taken
from lakes, oceans, caves, etc., and examined for changes from one to another. (For example, the type of pollen in a
particular sediment layer indicates the type of plant living in that place at
that time, and therefore the type of environment, and therefore the type of
climate). And ice cores. Layer upon layer of ice—because each
one of them includes tiny air pockets that are, in effect, “samples” of the air
that existed at the time the ice formed (more on this below). Or even the layers in the core of a
cave stalagmite or stalactite.
It appears, however, that the most powerful and widely-used
temperature proxy is 18O, an isotope of oxygen. Normal oxygen has 8 protons and 8
neutrons, so it is called oxygen-16 or 16O. Another type of oxygen has 8 protons
and 10 neutrons, so it is called oxygen-18 or 18O. 18O (“heavy” oxygen) is an
isotope of 16O (“light” oxygen).
Here’s the deal:
“heavy” oxygen is actually heavier than “light” oxygen. So water (H2O) made with
heavy oxygen weighs more than water made with light oxygen. This means that when the ocean warms
up, the water molecules with light oxygen evaporate first, leaving the water
molecules with heavy oxygen behind and making the ocean water richer in heavy oxygen. Conversely, when temperatures fall and water
vapor condenses into droplets to form precipitation, the water molecules with
heavy oxygen condense first, leaving behind the water molecules with light
oxygen and thus making the remaining water vapor in the atmosphere richer in light
oxygen than it was before. So,
evaporation and condensation are two ways that the ratio of these two isotopes
of oxygen can become altered. Is
that cool or what?
Consequently, when water evaporates from the ocean and moves
to mountaintops as snow that then gets compacted into a glacier in Alaska or an
ice cap in Greenland, it becomes richer in light oxygen as the temperature gets
colder—because the heavy oxygen has dropped out along the way. As a result, snow in the interior of
Antarctica, for example, has about 5 percent less 18O than ocean
water does.
By looking at the ratio of heavy to light oxygen preserved
in individual layers of ice, scientists have been able to build up a record of
temperature change over many thousands of years. More heavy oxygen means it is getting colder. More light oxygen means it is getting
warmer. Further, by examining the bubbles
of trapped air inside each layer, scientists can determine the atmospheric concentration
of other gases such as CO2 and methane at the time that particular
ice was formed. Pretty powerful
stuff.
Ice cores have been drilled at many sites around the world,
and reconciling them is a huge challenge, as you can imagine. The two most famous ice core sites are
in Greenland and Antarctica, and one data set from the Vostok site in
Antarctica caused a bit of a shock wave in the climate community.
Here is the graph of a 400,000 year history of temperature,
CO2, and dust concentrations:
The first graph shows how temperature has fluctuated (using 18O
analysis), with the valleys depicting
ice ages and the peaks depicting non-ice ages. You can see, for example, that about 25,000 years ago, we
were in a deep freeze (with Wisconsin buried under a glacier that was one mile thick!). And you can see that the time from one
ice age to another is about 100,000 years. And finally, you can see that this cyclic pattern predicts
that it’s about time for another ice age.
From the second graph, it is clear that CO2
levels have fluctuated along with temperatures—when CO2 is high, it
is warm, and when CO2 is low, it is cold. It looks very much like CO2 and temperature are
in “phase.” Interestingly, the
third graph plots “dust” (whatever
that is), and it seems to show that as dust increases it gets colder. Which makes sense, I guess, as increased
dust would block out more sunlight.
What makes less sense is that a very careful analysis of CO2
concentrations and temperature (hard to see on this graph) indicates that
temperature increased BEFORE the CO2 concentration did—about 800
years before, according to scientists who have studied this data in minute
detail. This data set was thus
rather inconvenient for those who believe that increased CO2 CAUSED
the temperature increases—how can a cause occur after the effect? This is a CO2 anomaly that
has definitely caused some head scratching.
It has been partially explained very recently (March 2013)
as follows: If CO2
bubbles are mobile (rising upward over time), it is possible for CO2
that was originally trapped in an older (lower) layer to eventually end up in a
younger (higher) layer. This would create a lag in the
temperature/CO2 data because the younger layer that was formed after
temperatures started increasing would unexpectedly have more CO2 than
the older layer that was formed at the time the temperature increased. Or an ice layer formed at a time of higher
temperatures might have decreased levels of CO2 in
comparison with a lower (earlier) ice layer that was formed at a time of colder
temperatures—which is the opposite of what you would expect if the higher
temperatures were caused by increased CO2.
The problem is that when all the ice core data at four
different locations is corrected for this effect, there is STILL a 200-year
anomaly—that is, the increase in CO2 lags behind the increased temperature
by 200 years. This throws a monkey
wrench into the argument that CO2 elevation was what CAUSED
temperature increases in the first place.
In fact, some scientists believe that past ice ages were
caused by changes in the earth’s orbit, spin angle, and tilt, which amazingly
occur at predictable intervals.
These Milankovitch cycles, as they are called, correlate very well with
ice ages, and they predict that we should now be in a cooling period.
But it is clear from the above graph that we are instead in
a WARMING period. And that long,
long ago the earth was even warmer than it is right now. And that CO2 levels in the
past were greater than they are today—if you go back millions of years, they
were apparently five times higher than they are at present. However, just this week the CO2
level in the atmosphere exceeded 400 parts per million (on a volume basis) for
the first time in at least 400,000 years.
As you can see from the graph, the highest
previous CO2 level never exceeded 380 ppm.
From all the evidence, it seems clear that yes, the earth has
been warmer in the distant past than it is now. But just how good is the evidence (besides glacial retreat)
that the planet is continuing to warm TODAY?
A January 2013 article in Geophysical Research Letters reported on 170 different
“proxies” for temperature. These
included not only ice core data, but also data from coral and lake and ocean
sediments—40 biological proxies (like tree rings) in all. So in other words, this paper pretty
much examined all of the proxy data to date, from 1730 to the present. And ALL of the data shows that warming
continues today.
So it seems pretty clear to me that the preponderance of the
evidence shows the planet is warming. The birds and the bees and the trees and the
ice say so. As do historic
temperature readings. In the face
of all this proxy data, I don’t see how anyone can argue that the temperatures
are “unchanged.”
I’d say the case is closed—the planet is getting warmer. It also seems reasonable that a warming
planet causes CO2 to de-gas from the earth’s surface, both water and
land. And if you held a gun to my
head, I would say that the periodic orbital changes of the Milankovitch cycle have
resulted in warming and cooling over time and that this accounts for the fact
that C02 concentrations have lagged behind temperature increases in
the past.
I should also point out, however, that although the overall
trend seems to be one of warming, cooling periods (cycles?) still occur. There was the Little Ice Age mentioned
above, when the ice on Wisconsin’s Lake Mendota lasted perhaps 6 months and when
Thames river in Great Britain froze over. The last time this occurred was in 1814—almost
a hundred years ago—but previously it had frozen 25 times, starting in
1408. All the ice-skating stories
and cheery oil paintings showing canals freezing in the Netherlands are from
this period. And much more recently
(from about 1950 until 1990), arctic temperatures were below those observed
during the historic 100-year warming trend from 1850 to 1950 (the recent arctic
warming didn’t start until about 1990).
So what the future holds remains to be seen. Clearly the impact of human activity on
greenhouse gas emissions is a new variable in earth’s geological history. And how increased greenhouse gases such
as CO2 and methane might interact with, foil, exacerbate, and
complicate underlying mechanisms, such as the cooling predicted by the
Milankovitch cycle, has yet to be determined. Not to mention other phenomena that could affect the
temperature of the earth, such as volcanic activity, sunspots, and ocean
currents.
But if science teaches anything, its that, as Darwin said,
“nature guards her secrets well,” so we will probably be surprised.
I should also point out that in the course of researching
this blog, it has been interesting to note the “tone” of the articles
discussing the CO2/temperature anomaly. Many scientists, as well as members of the press, appear
almost apologetic about the fact that the anomaly even exists. It is almost as if some scientists WANT
there to be a cause-and-effect relationship between CO2 and the historic
warming that we have seen in recent years.
And that is because, as we all know, there is the widely-held
theory that human activity has caused the current warming trend. One should keep in mind, however, that just
in the past 2,000 years, there has been: a cold period from 2000 years before present (“BP”) until
1,000 years BP, a Medieval Warm Period from 1,000 BP until 650 BP, a Little Ice
Age from 650 BP to 150 BP, and another warming trend from 150 BP to the present
(all times approximate). Review
the following graph and tell me there is not a cyclic pattern to our past.
http://en.wikipedia.org/wiki/File:2000_Year_Temperature_Comparison.png
Of course the spike in 2004 makes one wonder if the up-tick
in this historic record will be with us forever, or whether it will, in time,
start to fall back. Will
greenhouse gases exacerbate any natural cycling? Are they now?
I will conclude with an article that just came out on
January 15, 2013, written by James Hansen, one of the climatologists who in
1988 first postulated global warming and is its most public advocate. I mention
this because if a scientist of such high stature publishes data that seems to
be an exception to the position he has taken for most of his professional life,
then you can pretty much believe what he says. In this most recent report he says: (1) the global surface temperature is
1.0 degrees Fahrenheit warmer than the 1951-1980 base average and (2) ….wait
for it, wait for it….. “The 5-year mean global temperature has been flat for a
decade….”
Further, and then I promise to stop, a more recent article published
in March 2013 reviewed 20 different climate prediction models. That is, the
authors looked at 20 mathematical models and asked how well they predicted the
temperature TODAY based on data from 1950. What they concluded is that the temperatures we are
observing today are at the LOW END of what the models predict. Or, to say it differently, the
temperatures we are seeing today are lower than what was forecasted.
And if global temperatures have not changed in ten years even
though CO2 concentrations in the atmosphere have continued to
increase, there is obviously something OTHER than greenhouse gases causing
global warming. Right?
From the current data, it appears that this almost has to be
the case, and there are certainly a great many factors influencing climate that
could be the culprit. The problem
is that they interact in complex ways that make it difficult to sort out what’s
really going on.
This is the way science progresses, folks. Observation, theory, new observations,
new theories. Eventually the
“truth” emerges, but probably long after the public is totally confused. Kind of sounds like the saturated fat
story I addressed in previous blogs.
Oh, and I haven’t said anything yet about sunspots. Or Atlantic ocean currents. And there is certainly a lot more that
should be said about climate modeling….
Next up: more
climate confusion.
Useful references:
*http://nsidc.org/data/lake_river_ice/freezethaw.html
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