More Questions and Answers About Climate Change
Forrest M. Mims III
A recent editorial in The Citizen
Scientist (Questions
and Answers About Climate Change, 25 March 2005)
raised questions about the connection of global warming
with the retreat of glaciers and the melting of sea
ice. This topic can be studied by both citizen and professional
scientists, and the purpose of this related editorial
is to set the stage for field and lab research that
more clearly reveals why the retreat of glaciers may
have little to do with global warming.
Briefly reviewing, the previous editorial
about climate change was suggested by a single item
in Ralph Coppola's "Wanderings" column (25
March 2005) about John
L. Daly's web site, which linked to historical temperature
graphs from many stations around the globe. Daly's site
points out that urban heating effects have distorted
the temperature record at many sites. It features many
dozens of temperature time series from rural locations
that do not appear to show any significant long term
warming or cooling trends. Also provided are time series
that show distinct warming associated with urban development.
But even if there is no overall warming,
why are glaciers around the world in rapid retreat?
For example, as discussed in the previous editorial,
Alaska's huge Bering
Glacier is the largest in North America. Even though
the temperature records at towns east and west of the
glacier show no
obvious warming trend in mean annual temperature
since about 1910, the glacier is in obvious retreat.
Part of the retreat may be due to natural cycles of
the glacier. But that doesn't explain why glaciers around
the world are also in retreat.
Soot versus
Ice
As explained in the previous editorial,
Goddard Institute of Space Studies scientists James
Hansen and Larissa Nazarenko may have found an important
reason for the retreat of glaciers. They blame the powdery
form of black carbon commonly known as soot. In a remarkable
paper entitled, "Soot
climate forcing via snow and ice albedos" (Proceedings
of the National Academy of Science, 101, 423-428
2004), Drs. Hansen and Nazarenko show that soot may
be causing significant melting of global ice and snow.
In their paper, Drs. Hansen and Nazarenko offer an intriguing
hypothesis that seems not to have attracted the attention
it deserves: "We suggest that soot contributes
to near worldwide melting of ice that is usually attributed
solely to global warming."
Carbon particles can greatly reduce
the albedo (reflectance) of snow and ice, thereby increasing
the absorption of sunlight and speeding up the melting
of ice and snow. The process has positive feedback,
for the soot layer atop the snow or ice may be joined
by older soot as the melting front progresses downward.
The global atmosphere includes a significant
soot component. The soot comes from the burning of fossil
fuels and large scale agricultural burning around the
world. There is also soot from massive forest fires
in Alaska, Canada and Russia.
Even though the soot versus ice hypothesis
appeared in a distinguished journal of science, it is
not largely known or accepted. This can be seen simply
by reading the latest articles that blame the retreat
of glaciers and the melting of arctic ice solely on
global warming. For example, I sent letters to three
scientists asking why glaciers are in retreat around
the world. The two who replied wrote that global warming
is the villain. They made no mention of soot. At the
recent meeting of the National Science Teachers Association,
none of the teachers with whom I spoke were aware of
the soot hypothesis. Instead, all of those I asked blamed
the melting of glaciers solely on presumed global warming.
Yet the impact of dark substances on
the melting or sublimation of snow and ice is familiar
to anyone who has visited or lived in a cold climate.
A year ago I made a trip to New Mexico to capture smoke
particles from massive fires in Southeast Asia. A few
weeks before the trip a major dust storm swept across
southern New Mexico. While I was there, smoke from half
way around the world was passing overhead. I photographed
bands of it in the sky at twilight and measured the
increase in optical depth that it caused.
Figure 1 shows how snow reacted to
a dark piece of wood in a field of snow near the National
Solar Observatory in the Sacramento Mountains of southern
New Mexico. A very similar effect is shown for the spruce
saplings in Fig. 2.
Look closely at these photographs,
and you will see that the snow is quite dirty. As Fig.
3 shows, the upper layer of snow was covered by considerable
dust from the dust storm. Some of the dust is gypsum
crystals that blew up to the mountaintop from White
Sands National Monument. Black carbon and vegetation
are also present. Also shown in Fig. 3 is the relatively
clean snow under the dirty layer. "Relatively clean"
is an appropriate choice of words, for this snow is
also contaminated by tiny bits of dust and soot. It
also contains a host of living microorganisms, which
I discussed in a previous
article in The Citizen Scientist. Figure
4 is a microscopic view of molten snow from this site.
Objects in the melt appear to include gypsum crystals,
soil, vegetation, black carbon and possible spores.
All the material in these dirty snow
photographs have much lower albedos than pristine snow.
Therefore, their presence quickens the melting of snow.
These contaminants are not unique to the mountains of
New Mexico. They are present all around the earth. Indeed,
recently a major blob of dust from the Sahara Desert
passed over Iceland on its way to Greenland. If Saharan
dust is deposited on Greenland's ice cap and the sun
has a chance to appear before the next snow fall, then
melting or sublimation will occur as the dust is warmed
by sunlight.
Why is Arctic
Lake Ice Melting Early?
The New Mexico field trip was very
much on my mind as I read another recent global warming
paper in the Proceedings of the National Academy
of Science (PNAS) that seemed to have
a strong connection with the soot-versus-ice hypothesis.
In "Climate-driven
regime shifts in the biological communities of arctic
lakes," (PNAS 102, 4397-4402, 2005)
John P. Smol and colleagues described significant changes
in the algae and fauna of arctic lakes caused by early
ice melt attributed to climate change. Surprisingly
there was no mention of the soot paper by Drs. Hansen
and Nazarenko that was published earlier in the same
journal. Nor did the paper include any of the arctic
temperature records that show no obvious warming trends.
These omissions seemed so puzzling that I sent the following
inquiry to John Smol.
E-Mail to Dr. John P. Smol
9 March 2005
Dear Dr. Smol,
This is an inquiry on behalf of The
Citizen Scientist ( www.sas.org/tcs
), where I serve as editor. The Citizen Scientist
is a nonprofit publication of the Society for Citizen
Scientists. Two significant questions are raised by your
recent paper in PNAS on "Climate-driven regime
shifts in the biological communities of arctic lakes,"
which observes: "Climate-driven regime shifts in the
biological communities of arctic lakes14). Each of these
interrelated thresholds is ultimately linked with length
of the ice-free season, itself directly modulated by
climate. Snow and ice appear to exert increasingly dominant
roles with latitude, whereas the onset and duration
of thermal stratification becomes more important in
subarctic lakes (13, 14).... and "Polar regions are
affected by stratospheric ozone destruction and by deposition
of persistent organic pollutants and other anthropogenic
compounds (acids, nutrients, and metals). However, these
phenomena are largely restricted to the latter half
of the 20th century, thus postdating the observed initiation
of algal and faunal changes by several decades."
1. The Temperature Record
Why does the paper not include specific
temperature time series for non-urbanized sites
that are near locations cited in your paper where temperature
has been measured for 50 years or longer? I have just
checked the temperature times series for four subarctic
sites (Svalbard, Danmarkshavn, Franz Josef Island and
Ostrov Vize) from 1951 to 2000, and there is no obvious
warming in these records. Longer records at more
southerly sites also show no warming signal, including
the 1909-1996 time series at Cordova and Yakutat in
Alaska. The latter two sites are, respectively,
west and east of the rapidly thinning Bering Glacier,
the largest glacier in North America. Why this
glacier is thinning in the absence of measured [temperature
increase] is the subject of Question 2.
2. The Soot Problem
Why does the paper not mention or cite, "Soot
climate forcing via snow and ice albedos" by James Hansen
and Larissa Nazarenko in Proc Natl Acad Sci (101(2):
423–428, 2004)? The paper by Hansen and Nazarenko, which
was published in PNAS only 14 months before your paper,
would seem to be of critical importance to your paper,
for it raises major questions regarding the relative
roles of climate warming and soot deposition on the
retreat of glaciers and the melting of ice....Your paper
mentions deposition of "...organic pollutants and other
anthropogenic compounds (acids, nutrients, and metals)."
but does not mention soot and dust. Also, your paper
states, "However, these phenomena are largely restricted
to the latter half of the 20th century, thus postdating
the observed initiation of algal and faunal changes
by several decades." Yet deposition of carbon and dust on
glaciers and ice over lengthy intervals are extensively documented.
Enhanced soot deposition on arctic ice may be related
to massive forest fires in Alaska, Canada and Siberia.
Similarly, enhanced dust deposition on arctic ice may
be related to major dust storms originating in
[Asia] and reaching Alaska and Canada. Hansen and Nazarenko suggest
with authority on p. 427 that global warming alone
is insufficient to explain the ice conditions attributed
solely to global warming in your paper. Instead, Hansen
and Nazarenko suggest that soot may be responsible for
the rapid retreat of glaciers in China and Tibet over
the past 120 years, a region with little or no warming. This
finding may also explain the significant thinning of
the Bering Glacier (cited above) in the absence of any
obvious warming trend....
Thank you kindly for responding to
these two questions. Your response will be very helpful
to a review article I am preparing on global climate
change.
Best regards,
Forrest
Forrest M. Mims III
www.forrestmims.org
Geronimo Creek Observatory
Editor, The Citizen Scientist
www.sas.org
Response from Dr. John Smol
Dr. Smol is a university professor, and
my inquiry arrived at a very busy time. Nevertheless,
he took time from his schedule to send a detailed response
to my questions. While there are still unanswered questions
about exactly why those Canadian lakes are melting earlier,
Dr. Smol shows that the issue is complex. He has kindly
given TCS permission to publish his reply.
Dear Forrest:
Thank you for your interest in our PNAS paper,
and in the email you sent me (appended below). As you
may appreciate, this is a very busy time in the academic
year, and so I have tried to provide a detailed response,
but there are time restraints!
1) Regarding your first major point,
as to why we do not include temperature time series
records for the non-urbanized sites that are near locations
in your paper.
The main focus of this PNAS paper was to look
at changes in our biomarkers (primarily diatoms, but
also other indicators, such as chrysophytes, cladocerans
and chironomid insect larvae), and to use these data
to infer any environmental and ecological changes.
This is what we did in this paper.
However, the paper is a compilation of 55 profiles collected
by 26 co-authors from many regions. Many of the
profiles in this paper are published in much more detail
and analyses, or are now in press in similarly detailed
papers. In many of these papers, the authors do work
with any available time series data, and the trends
are confirmatory. I know my lab's profiles better, and
will mention a few here, and co-authors could provide
more details for specific sites I am sure.
The biggest problems, of course, is
the lack of appropriate time series monitoring data.
The changes we are referring to in this paper occur
before any time series data were available. Remember
also that we would not expect linear responses to these
changes; a main focus of this paper is the crossing
of ecological thresholds, which are often not linear;
see cited paper 15 for a review of ecological thresholds
etc, Scheffer et al). And in any event, very
little appropriate time series data are available. However,
when we do/can compare the paleo data to monitoring
data. Of course, we deal with lake sediments, which
do not have annual resolution (at least not the ones
we are using). So we are looking at overall trends.
For example, looking at some of the data in the PNAS
paper associated with my lab, let's start at the northernmost
part of Ellesmere Island (Self Pond) which actually
is near the Alert Military base, which has temperature
data for 30 years. Our paleo diatom data closely
match the warming trend. This should appear as part
of paper very soon: probably out in April.
Antoniades, D., Douglas, M.S.V., and Smol, J.P.
Quantitative estimates of recent environmental changes
in the Canadian High Arctic inferred from diatoms in
lake and pond sediments. J. Paleolimnology
(in press).
Now how about the site we have on Melville
Island, in the Canadian western high Arctic (Keatley
et al. 2005). Here the best we can do
is get the 29 year record from Mould Bay on Prince Patrick
Island (1948-1996). Yes, there is no major change
in that temperature record over this short relatively
period. And that is exactly what we have in the diatom
record. No major change since ca 1948; BUT we
did have big changes in the early 20th century. So this
is consistent with whatever temperature record we have.
Keatley, B., Douglas, M.S.V. and Smol, J.P. 2005. Early-20th
century environmental changes inferred using diatoms
from a small pond on Melville Island, N.W.T., Canadian
High Arctic. Hydrobiologia (in press).
A major part of this paper is that 16 of the 55 profiles
are from Northern Quebec and Labrador (work primarily
led by Reinhard Pienitz). This is a key area, and will
come in again with the soot argument below. As
I am sure you know, this area is well known to be not
warming, or certainly nothing like rest of Arctic (for
a variety of reasons dealing with ocean currents etc.,
well discussed in many other places). This is an important"control"
areas for us (as we note repeatedly in our paper). But
again, temperature data here are relatively flat, and
our 16 profiles here are flat, as discussed in paper.
The examples go on in Europe and farther east as well.
Well, for example, Finish Lapland. If you look up reference
13, this may explain this area better to you and the
data available and the comparisons.
Sorvari et al. 2002. Lake diatom response to
recent Arctic warming in Finnish Lapland. Global
Change Biology 8: 171-181.
Figure 4 may be of special interest to you; a comparison
of the fossil data to temperature data.
Or you mention Svalbard in your email.
The record here is actually longer than the 50 years
(starting in 1912). On Svalbard there is a documented
temperature rise, especially annual temperature from
1912 to 1930s and 1960s to today (see Birks et al
2004 J. Paleolimnology 31 403-410).
In fact, Vol 31 and issue 4 of the J. Paleolimnology
is an issue dedicated to the paleolimnology of the Svalbard
lakes (led by Drs Birks, Jones, and Rose). It provides
details of all the records available, and concludes
climate is the main driver. You might want to
study these 9 papers in this special issue.
You can get titles and abstract free
at:
ssue.asp?wasp=pe669uj0wq7rpgdf0vtk&referrer=parent
&backto=journal,7,66;linkingpublicationresults,1:100294,1
and you can of course get full text articles if you
have a subscription
You may also be interested in looking
at:
Isaksson et al. 2003. Ice cores from
Svalbard - useful archives of past climate and pollution
history. Physics and Chemistry of the Earth
28: 1217-1228. See for example, Figures 2 and
3!
And compare to our paleolimnological data of warming
to those in the ice cores...
But in any event, our goal in this PNAS was
different; to explore biological responses to any environmental
changes over the last 2 centuries or so. And so we had
not the space etc to go over all this again in PNAS;
not in 6 pages. And again, as noted above, comparisons
are in other papers we cited.
On a broader sense (and again, this was not a focus
of this 6 page PNAS paper), we do also compare our trends
to instrumental data in a general sense even here in
this paper. For example, the bottom of Figure 3, And
if you compare our overall patterns with data in, for
example the cited Serreze et al paper (ref
7) and Moritz et al (ref 5), the overall patterns
we have are generally consistent.
Anyway, we certainly look at instrumental data where
available. BUT it is often not available on the time
scales we need, and this is exactly why we used the
paleolimnological approach.
2) Your second point deals with soot
and your citation of Drs. Hansen's and Nazarenko's paper.
You ask why we do not cite it. As you probably
know, a PNAS paper is limited to 6 pages and a set number
of references. We used every inch!
Nonetheless, this paper you note was an important and
thought-provoking contribution.
As an aside, we certainly do not ignore soot, and in
fact it is a part of some of our research programs,
including mine.
For example, Nancy Doubleday (now a professor at the
Carleton University) did her PhD in my lab on using
soot and black carbon as a paleoenvironmental tool.
And in fact, we should have published in next month
or two a massive monograph describing the taxonomy of
arctic black carbon particles (many years in the working);
Doubleday, N.C. and Smol, J.P. 2005. Atlas and
classification scheme of arctic combustion particles
suitable for paleoenvironmental work. J. Paleolimnology
(accepted).
So we are not ignoring soot at all!
But in response to your questions:
As Drs. Hansen and Nazarenko' noted in the 2003 PNAS
paper in the last line of the abstract, that anthropogenic
gases are still the predominant cause of warming. "soot
contributions to climate change do not alter the conclusion
that anthropogenic greenhouse gases have been the main
cause of recent global warming and will be the predominant
climate forcing in the future". We agree.
Drs. Hansen and Nazarenko are not claiming, based on
my previous read of the paper, that soot by itself is
causing any changes in the landscape, but that it is
an indirect mechanism affecting the albedo and hence
radiation fluxes.
We also agree (and note many times in paper) that arctic
lakes are under multiple stressors, including deposition
of black carbon etc. If you look at my publication list
on my web site, you would see large list of various
applications of paleolimnology in a variety of papers,
including a
textbook and several other books.
I also fully agree that soot and black carbon is a very
important aspect of environmental research, and their
work is very interesting and thought provoking. And
we also acknowledge that the cite as other parts of
the planet are under "multiple stressors" and soot is
part of this (one of the "contaminants").
However, we did not go into soot in any detail as it
could NOT explain any of the many trends we show in
our PNAS paper.
Perhaps the strongest evidence against any noticeable
effect of black carbon on our profiles is the 16 profiles
from N. Quebec and Labrador. As noted above, this is
the only region known to be not warming (for many good
reasons). It was our "control" in many ways. It was
also a control for any effect of soot. Surely soot would
be highest in this region: closest to sources, near
trees and fires and so forth. It would probably have
the highest soot or black carbon of any North American
sites at least. Yet, we have no changes in the paleo
profiles in diatoms, or chrysophytes, or invertebrates.
No warming; so no biological changes.
Okay, lets take this one more step. As noted above,
we do analyse soot (black carbon) in some of our cores.
For example, as part of her PhD thesis, Nancy Doubleday
had analysed soot in some Cape Herschel material, the
site of several of our Ellesmere Island sites (see Table
1). Now the Cape Herschel sites (Ellesmere Island),
like the top figure in Figure 1 (Col Pond) in our PNAS
paper, had the largest species changes of any cores.
Essentially 100% species turnover happened at Cape Herschel.
An area of marked warming. YET, Nancy showed there was
almost NO soot particles in these sediment cores. Again,
exactly opposite to predictions if soot was major factor.
Thanks again for your interest. I hope these comments
are useful to you.
Best wishes, John
---------------------------------------
John P. Smol, FRSC
Professor
Canada Research Chair in Environmental Change
Editor, Journal of Paleolimnology
Editor, Environmental Reviews
Paleoecological Environmental Assessment and Research
Lab (PEARL)
Dept. Biology, 116 Barrie St.
Queen's University
Kingston, Ontario K7L 3N6, Canada
---------------------------------------
Dr. Smol's reply to my inquiry provides important information
for anyone wishing to pursue a study of the impact of
warming and the deposition of soot and dust on ice.
As Dr. Smol notes, the issue is complicated, and as
both he and Drs. Hansen and Nazarenko also note, there
is a need for more data.
This topic is where some careful work
by an individual or a team of citizen scientists can
make a major contribution and possibly result in a first
rate science fair project or a scholarly paper. At least
two principal topics need to be studied.
First, is warming actually occurring
throughout in the arctic? Or is the warming that has
been reported occurring only at or near towns and cities?
Second, how can the impact of soot
and dust on the melting or the sublimation of ice be
carefully quantified? Many experimental methods are
available, some of which can be as simple as carefully
measuring over time the impact of direct sunlight on
ice samples that have been sprinkled with known amounts
of soot or dust or both. This experiment will be of
high value if the change in the albedo of the contaminated
ice can also be measured.
Comments about these study suggestions
and the issues of global warming and glacier retreat
are welcomed. Please insert "Backscatter"
in the subject line and send them to "Backscatter."
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