There was an interesting story in the Las Vegas Journal Review on August 20th. which had a passage and quote from California Senator Diane Feinstein (emphasis mine):
Both U.S. Sen. Dianne Feinstein, D-Calif., and Ensign announced that they and other members of their delegations will reintroduce a bill in Congress to provide $390 million for additional preservation projects at Lake Tahoe.
Ensign said some have called the summits “publicity gimmicks,” but they are an important way to focus at what still needs to be done.
He said he has noticed how the dense forest around the Nevada side of the lake has been thinned dramatically in an effort to prevent forest fires. Feinstein praised Nevada for its efforts to stop fires, adding she wishes she saw the same results in California.
Unlike other officials, Feinstein blamed global warming for the degradation of Lake Tahoe.
“The real culprit in my mind is global warming,” she said.
Since 1970, the water temperature of the lake has risen by about three degrees, according to scientists.
I have no dispute about the temperature rise, but I do have a dispute with her assignment of blame, especially since she is my senate representative. I’ve found something interesting that leads me to think that global warming and Lake Tahoe’s water temperature are not significantly connected.
First about her statement. Perhaps Senator Feinstein is recalling this article on Lake Tahoe from 2004 in the San Francisco Chronicle.
There was a weak caveat in that article that Feinstein likely ignored if she read it:
No one can be certain if any given change is due to human activity, but the widely held assumption is that emissions of carbon dioxide and other heat-trapping greenhouse gases are involved.
I’d like to add a reason of my own for Senator Feinstein and the Chron: turbidity.
For those who don’t know, water turbidity is defined by the EPA as:
Turbidity is a principal physical characteristic of water and is an expression of the optical property that causes light to be scattered and absorbed by particles and molecules rather than transmitted in straight lines through a water sample. It is caused by suspended matter or impurities that interfere with the clarity of the water. These impurities may include clay, silt, finely divided inorganic and organic matter, soluble colored organic compounds, and plankton and other microscopic organisms.
The EPA definition comes from the publication American Society for Testing and Materials, ASTM (2000) D1899-00 Standard test method for turbidity of water. Annual Book of ASTM Standards, Vol. 11.01.
Water clarity and turbidity has been a big issue with Lake Tahoe for many years, and there have been campaigns to reduce the amount of runoff into Lake Tahoe that is a direct consequence of the building boom that has occurred around the Lake in the last century. “Keep Tahoe Blue” is one of those and you’ll see these bumper stickers all over California:
Senator Feinstein is certainly aware of this effort to reduce turbidity and maintain clarity in Lake Tahoe, in fact she is one of the champions of the cause. She drafted the Lake Tahoe Restoration Act in 1999
Her own website has quite a section on it:
http://feinstein.senate.gov/tahoe_restoration_act.html
In that web page is this passage and graph related to it:
Sediment and algae-causing phosphorus and nitrogen, all of which contaminate the water in the lake, continue to flow into Lake Tahoe from a variety of sources. Destruction of wetlands, wet meadows and stream habitat has compromised Lake Tahoe’s ability to cleanse itself of pollutants.
There’s not one word on Feinstein’s Lake Tahoe Restoration Act web page about global warming or climate change. Zilch, nada, zero. I’ll also point out that it looks like the page has not been updated in quite some time. Perhaps after passing the act in 1999 her interest waned.
The graph above can also be found in a different form from the 2009 State of the Lake Report from the UC Davis Tahoe Environmental Research Center (TERC):
TERC writes about the clarity as defined by the Secchi depth measurement:
Secchi depth (the point below the lake surface at which a 10-inch white disk disappears from view) is the longest continuous measurement of Lake Tahoe clarity. The annual Secchi depth is the average of 20 to 25 readings made throughout the year. While lake clarity has improved for brief periods since 1968, the overall long-term trend has shown a significant decline. In the last eight years, Secchi depth measurements have been better than predicted by the long-term linear trend. Statistical analysis suggests that the decline in Lake Tahoe’s clarity has slowed, and is now better represented by the curve below than a straight line. In 2008, the Secchi depth was 69.6 feet and virtually the same as 2007. With the exception of 2005 and 2006, precipitation has been low during the past 8 years. The response of the Secchi depth to a series of normal and above normal years will be very instructive.
What is interesting is that the top two values of the TERC graph occurred in 1997 and 1998, the years of the super El Nino and massive amounts of rainfall (and runoff) in California. I wasn’t surprised to see those years as the peak of low clarity of the last 40, but I was surprised that TERC does not mention it in the report. Perhaps it is counter to the TERC mission to blame nature for peak values.
So we’ve established two things:
1) The water temperature of Lake Tahoe has been increasing. From the LVJR news article:
Since 1970, the water temperature of the lake has risen by about three degrees, according to scientists.
2) As measured by TERC, the turbidity of Lake Tahoe has been increasing, thus reducing the clarity.
While lake clarity has improved for brief periods since 1968, the overall long-term trend has shown a significant decline.
I should add, I think it is a good thing to reduce the runoff issues that contribute to the reduced clarity of Lake Tahoe. This is a clear case where human activities have made a measurable impact on an ecosystem. That said, I believe that same human impact affects the lake temperature. As Dr. Roger Pielke Senior argues, land use and land cover changes have significant local and regional impacts. Lake Tahoe’s clarity decline has been established to be a result of increased runoff and pollutants resulting from the local population increase around Lake Tahoe in the last century.
This USGS publication, Stream and Ground-Water Monitoring Program, Lake Tahoe Basin, Nevada and California, defines the issue:
Lake Tahoe has long been admired for its alpine setting and the clarity of its water. During the last half-century, however, human activity in the lake basin has increased while the lake has been losing water clarity at a rate of about 1 foot (ft) per year.
Now, for a look at what I believe to be a significant contributor to the water temperature increase in Lake Tahoe.
One thing nobody seems to be talking about is the relationship between water turbidity and temperature. It is a quite simple physical mechanism, and quite well established.
For example, here is a peer reviewed study, published in International Journal of Biometeorology on mosquito larvae and increased turbidity contributing to increased water temperature.
The effect of water turbidity on the near-surface water temperature of larval habitats of the malaria mosquito Anopheles gambiae
K. P. Paaijmans &W. Takken & A. K. Githeko & A. F. G. Jacobs (full PDF here)
In that study they write in the abstract:
Water turbidity affects water temperature, as suspended particles in a water column absorb and scatter sunlight and hence determine the extinction of solar radiation. To get a better understanding of the relationship between water turbidity and water temperature, a series of semi-natural larval habitats (diameter 0.32 m, water depth 0.16 m) with increasing water turbidity was created. Here we show that at midday (1300 hours) the upper water layer (thickness of 10 mm) of the water pool with the highest turbidity was on average 2.8°C warmer than the same layer of the clearest water pool. Suspended soil particles increase the water temperature and furthermore change the temperature dynamics of small water collections during daytime, exposing malaria mosquito larvae, which live in the top water layer, longer to higher temperatures.
That is a small scale experiment in shallow water. On a larger scale there are lots of other scientific references available that demonstrate a relationship between increased water turbidity and increased water temperature. Here’s one published in BAMS from the Naval Research Lab looking at turbidity in the Black Sea and water temperature relationships. (Kara et al 2005, PDF here)
The K.P. Paaijmans et al study above writes about the Kara et al 2005 Black Sea Study:
In larger water systems, turbidity is known to change the water temperature. In seas, for example, a high turbidity changes the sea surface temperature (SST), and model simulations of the SST should include turbidity to account for variations in solar radiation extinction (Kara et al. 2004). Kara et al. (2005) demonstrated that using a clear-water constant attenuation depth assumption as opposed to turbid water type to model the SST of the Black Sea, resulted in monthly SST biases as large as 3°C in the summer period.
What I find amazing is that Senator Feinstein, who championed a bill to save Lake Tahoe from reduced clarity, apparently has no idea of the relationship between water clarity and water temperature. Apparently TERC doesn’t see it either, and prefers to blame increased water temperatures on climate change.
Of course, if we take the “global warming” route followed by Senator Feinstein, it can be argued that Lake Tahoe’s increasing air temperature is a significant contributing factor to the Lake Water temperature:
Source: NASA GISTEMP
But then you see what the measurement station looks like. Then of course that station’s data purity is brought into question for reasons of siting as well as local development nearby in Tahoe City.
Of course, we don’t know exactly what the magnitude of contribution to warmer temperatures at this station from those siting issues are, and the burn barrel has since been removed from the USHCN station enclosure shortly after I highlighted it in June 2007. The tennis courts surfaces nearby may have an effect on air temperature also.
What is important to note though, and this fact is lost on many politicians, is that the lake itself, as a large solar insolation heat sink, has more effect on local air temperatures than the other way around. The reduced clarity contributing to increased water temperature issue likely is a factor in the USHCN weather station data, given it is just a few feet from the lake.
And that brings us back to the quote from the original newspaper article:
Since 1970, the water temperature of the lake has risen by about three degrees, according to scientists.
Eyeballing our Tahoe City USHCN station graph from GISS above, it looks like we have a trend since 1970 not far from that value. Using air temperature from our world renowned center for global warming data, NASA GISS, one can certainly draw a correlation between the air temperature of the Tahoe City station and the water temperature of the lake.
But as we’ve heard so many times, correlation is not causation.
Feinstein appears to completely miss the physical connection between increased water temperature and the Lake Tahoe water clarity cause she championed. Now the need for an additional $390 million. Before she spends more citizen’s money chasing this global warming issue, let us hope she gets some “clarity” on the issue soon.
Ever wonder where some of that money goes? See TERC’s headquarters. Nice digs for studying a lake. The field station is not too shabby either.
While TERC has a really nice LEED certified HQ, I can’t find a single publication on their website about water temperature and turbidity. Unfortunately I can’t scan the content of the papers on their website since so few are posted in full text form, just titles.
Given the huge public relations effort to preserve Lake Tahoe’s clarity and, by the view of the lake’s most famous patron, Diane Feinstein, and the apparent connection to global warming, one would think that a water turbidity-temperature study would be something they would want to pursue. Either to confirm it, or to rule it out.
If I’ve missed such a study, please feel free to post it in comments.
Addendum: Additional References on turbidity (originally from comments)
Here is one where reflectivity is examined in the context of turbidity.
Citation: Witte, W. G., C. H. Whitlock, R. C. Harriss, J. W. Usry, L. R. Poole, W. M. Houghton, W. D. Morris, and E. A. Gurganus (1982), Influence of Dissolved Organic Materials on Turbid Water Optical Properties and Remote-Sensing Reflectance, J. Geophys. Res., 87(C1), 441–446.
http://www.agu.org/pubs/crossref/1982/JC087iC01p00441.shtml
“From these data it is clear that dissolved organic materials decrease upwelled reflectance from turbid waters. ”
Here is a primer on suspended solids in water from the City of Boulder Water Quality Monitoring:
http://bcn.boulder.co.us/basin/data/BACT/info/TSS.html
“High TSS (total suspended solids) can also cause an increase in surface water temperature, because the suspended particles absorb heat from sunlight.”
Here is another identical passage from the New York Harbor Survey that cites TSS and water temperature:
http://www.nynjcoast.org/NYCDEPHarbor_survey/docs/water_clarity/total.htm
“High TSS can also cause an increase in surface water temperature, because the suspended particles absorb heat from sunlight.”
From Brockport University
http://vortex.weather.brockport.edu/~jzollweg/oakorchard/docs/waterquality.pdf
On page 1 under TDS (Total Dissolved Solids):
“Similar to TSS, high concentrations of TDS may also reduce water clarity, contribute to a decrease in photosynthesis, combine with toxic compounds and heavy metals, and lead to an increase in water temperature.”
For a fairly recent and mostly comprehensive study of Lake Tahoe’s warming, see Coats et al 2006
http://www.springerlink.com/content/6384855p5513l393/fulltext.pdf
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A very fine report, Anthony. Feinstein has always struck me as rather dense. If Dan White hadn’t shot Harvey Milk and Mayor Moscone, she might have spent her whole political career in San Francisco.
Antony,sorry.
None of your references did say that turbidity increases the mean temperature of any lake.
On the contrary .The study about the Black Sea turbidity(that the author of the article cites)affirms that the simulations (yes,simulations)showed that ,when they introduce the rss turbidity,the simulated temperature DIMINISHES from 2C to 1.04C(compared to the real climatology).
So ,as i argued on my previous post ,the turbidity has a global cooling effect.
REPLY: I disagree. The way I read the Black Sea study is just the opposite. Note they didn’t put a minus sign in front of the 3C bias statement.
And lets not jump off topic, we aren’t discussing a global cooling effect here, we are talking about the water surface temperature of a lake, so lets not get outside of the discussion context. As I asked before, show me a reputable citation anywhere that equates increased water turbidity to lower water surface temperatures. I’ve shown several for water quality in general that demonstrate increased turbidity equals increased water temperature. There were no size caveats about puddles, ponds, lakes, or seas listed, in any of them.
– Anthony
pyromancer76 (03:20:52), per your request about info re: Feinstein & her hubby: click. [The link in the first sentence of the article goes to the original exposé.]
She used her position as Chair of the Senate’s military construction appropriations subcommittee [MILCON] to funnel $Billions in taxpayer loot straight to her husband’s companies in open ended, no-bid contracts. [Since California is a community property state, Feinstein’s wrongdoing amounts to conversion.]
When she was caught, she was forced to resign as committee Chair. But of course, they didn’t have to pay the money back to the U.S. Treasury, and Feinstein wasn’t sent to San Quentin like other thieves.
Betcha didn’t hear anything about that in the media.
Alexandriu,
Here is yet another citation from a water quality agency saying that increased turbidity equals increased water surface temperature.
In this citation, they very clearly mention larger bodies of water, like reservoirs. The state of Kentucky has some very large ones.
http://kywater.org/ww/ramp/rmtss.htm
(Kentucky Water Watch, main page http://www.water.ky.gov/ww/ )
I’ve now quoted several water agencies all saying the same thing about increased turbidity resulting in increased water temperature.
The onus is now on you to provide credible citations showing that this is not true. – Anthony
I don’t know why Anthony and other bloggers and posters would ignore a 28 page peer reviewed article by Coats et al. (2006) titled: The warming of Lake Tahoe. This paper is freely available as a PDF at several sites including the publshers web site:
http://www.springerlink.com/content/6384855p5513l393/fulltext.pdf
The analysis for this paper is based in part on weekly measurements at 2-15 m intervals to 100 m since 1969, biweekly measurements every meter to 125 m since 1996 and less frequent measurments to 400 m. This paper shows that Anthony’s speculation that lake warming is can be atributed to increased turbidity does not hold up.
I would agree that a good part of the increase in turbidity is due to increased runoff and nutrient loading. Anthony’s point about the El Nino effect is well supported . Certainly, when weather or climate results in increased runoff and nutrient loading, this results in increased turbidity, while droughts lead to increased water clarity.
Warming, by reducing the mixing depth, also leads to increased turbidity. These interactions between mixing depth, warming and turbidity, which are quite complex, are discussed in the Coats et al. paper. It does not make sense to ignore a readily available paper that is directly relevant while mixing good points with speculation that can easily be dismissed.
REPLY: Thanks for this, Bill. You make an unsupported assumption that this paper was ignored. I’ve done a lot of searching on turbidity TSS, and TDD and this never came into view. But I’ll have a look now. – Anthony
Follow up: Bill again thanks for this, I’m going to add it to the list of citations at the bottom of the article. A couple of points about your claim of “ignoring” this paper. First, I’m not in the mainstream academic world as you are, I’m in the business world, so things that are “givens” for you being exposed to with periodicals and such (paid for by your university) are not part of my world. 2) Given that you do biology of lakes, (love those daphnia, spent hours loking at them as a kid) I’m sure your were already aware of this study a couple of years ago. This convenience of being in mainstream academics that I don’t have sets you up to unfairly judge me for “ignoring” a paper that I wouldn’t have the same opportunity to be pre-exposed to that you do.
Me, I have to find such things with Internet searches. The word “turbidity” is not mentioned anywhere in the Coats et al paper, so I didn’t find it in searches. Oddly with all the measurements they made, that is the one thing that paper didn’t cover.
There’s a lot of interesting things in the Coats paper, much of which I agree with, some that I don’t, and some that supports my idea. I’ll have more in the next couple of days. – Anthony
1.Anthony
Tahoe lake warmed from top to bottom With 3C.
I agree with you that turbidity is warming the surface of the lakes
But in the same time it cools the bottom(and may generate stratification)
2.From the article you pointed.
“From these data it is clear that dissolved organic materials decrease upwelled reflectance from turbid waters. .. Changes in backscatter coefficient are moderate, indicating minimal changes in particle scattering.”
As i explained ,at the surface ,there is ~zero reflection.
Once in the water,as there is no ‘mirror’, the photons will go down indefinitely.
The only chance for them to go up is the backscatter (who,as you see, does NOT change)
3.the text in the “black sea “article is explicit.
“In particular, when using the clear-water constant attenuation depth as opposed to using spatial and temporal kPAR, basin-averaged rms SST difference with respect to the Pathfinder SST climatology increases ∼46% (from 1.41°C in expt 1 to 2.06°C in expt 3)”
It is clear: when they use clear water(instead of kpar=turbidity) the temperature INCREASES!
4.the physics behind this effect is obvious:more you warm a thinner surface, more you loose the heat.
5.I live in Roumania and the Black Sea is no more what it once was.
Mais ou sont les neiges d,antan?
REPLY: We agree on points 1 and 2. On 2 I never claimed there was a “mirror” that was your argument, I said from the beginning that turbidity increases radiation absorption. On point 3 I still don’t see it your way. Point 3 conflicts with point 1. The logic seems backwards, but then again we are talking a model and a satellite. The question remains though, in the abstract they mention a 3°C bias, but do not give a negative sign, why? I’ll have a look again.
Point 4 I think what you are defining there is a heat sink of lower volume, in which case, yes it would lose heat faster than one of a large volume. In the case of a lake warmer water strata, that would transfer the energy as LWIR into the air above it. This is consistent with point 1.
Point 5. I have no doubt the Black Sea has similar issue to Lake Tahoe.
It seems possible to verify the turbidity question experimentally.
Use two containers, one containing pure distilled water, and the other containing, say, 10% India ink and 90% distilled water.
Place them side by side in direct sunlight for several hours, then compare temps.
It seems intuitive that the darker water would be warmer; an experiment like this would definitively answer the question.
Smokey
For a container is true because the reflection from the bottom is important and the ink will stop the light going up.
For a lake is not: there is no bottom reflection if the lake is deeper than the attenuation length in water.
IF you put ink in a lake you will warm the surface(who will rapidly loose the heat during the night) and you will cool the bottom (who receives less energy).
Globally it will be a cooling effect
About five (??) months ago an AWGer posted here that the increasing temperatures of lake water supported the case for global warming and discredited the oceanic data showing no warming. It appears to me that this increasing lake-turbidity factor is an effective counterpoint to his claim.
Likely the oceans are getting more turbid too, from increased runoff of topsoil, agricultural fertilizers, sewage, etc. There should maybe be a correction for these, showing that the oceans would be cooling in their absence.
Antony
Thank you for the last article citation(Coats& al. 2006)
It is in fact very comprehensive and informative .
May be,one day, you will publish a comment on it .
Pamela Gray (08:16:42) :
The forest practices you speak highly of was called thinning.
It used to be practiced.
That was then.
This is now, 40 years after those practices were dumped in favor of clear cutting and herbicides.
Yellowstone worked because it wasn’t messed with.
The National Forests failed because they were subjected to pure greed (aka overharvesting).
They continued to fail as restoration efforts were subjected to lawsuit gridlock (it’s natural for it all to burn faster than it can recover).
Diane Feinstein stared blankly as it all took place, and still does.
Anthony I agree with you on most things and turbidity might have some affect on temperature. However I think it is slight, It would also be hard to separate cause and effect. Warmer water creates more algae growth and thus more measured turbidity. Land use and residential discharge certainly affect the nutrient availability and thus algal growth. However there is a much more dynamic factor that I hope become more clear from the linked graphs.
What is missing from the Coats et al paper and this discussion is the affect of inflows and outflows from Lake Tahoe. The affect of cold water coming in and warmer surface water leaving certainly seems as if it would be a major contributing factor. The outflow is controlled by a dam also located in Tahoe City. The Coats et al paper shows a definite increasing trend in temperature with a few cooling periods. He goes to great lengths to attribute the cooling of in 82 and 83 to Pinatubo. Much closer to home we see that year had peak snow pack and maximum lake discharge. It is curious that Coats et al would ignore such an obvious factor.
I have linked to a jpeg I made containing 3 graphs. Top is the Lake Tahoe temperatures from Coats et al. Notice the 2 main warming trend that go from 1975-1982 and from 1983-1994. The next graph show the amount of discharge from Lake Tahoe. Notice the 2 periods of very low discharge coincide with the warming trends. The bottom graph shows snow depth anomalies based on the 1970-2002 average and computed from California’s Dept of Water Resources Snow Surveys for 7 Lake Tahoe sites, Squaw Valley and Mt Rose. All available on line. We see the heavier snow packs are during the cooling periods Coats cites. Less cold water entering lake means less warmer surface water being pushed out over the dam. Here is the link . I apologize that the images are a bit small as a result of converting the document into an image.
http://farm3.static.flickr.com/2658/3851020563_550606911e_m.jpg
I would appreciate any comments.
REPLY: Linked images are so small I can’t even see it. Thumbnail sized. – A
Jim Steele (00:37:24) :
Anthony I agree with you on most things and turbidity might have some affect on temperature. However I think it is slight, It would also be hard to separate cause and effect. Warmer water creates more algae growth and thus more measured turbidity. Land use and residential discharge certainly affect the nutrient availability and thus algal growth. However there is a much more dynamic factor that I hope become more clear from the linked graphs.
Jim:
I am not a physical limnologist, but I have looked at quite a few heat budgets for lakes. Except for very shallow lakes with residence times of weeks or months and high flow reservoirs, the effects of water inflows and outflows are negligible for heat budgets. According to a Google search, the water residence time for Lake Tahoe is an exceptionally long 700 years. This confirms that effects of water inflow and outflow on water temperature and total heat are completely negligble.
Very impressive Anthony.
Enjoyed the reminisces and the many fillers supplied by your readers, especially those of Layne Blanchard. Must have been a magic time.
Keep up the good work.
Given a constant atmospheric condition, I would tend to think that if the water surface is warmer from increased turbidity absorbing more solar energy at the surface then it will also radiate more heat back out while blocking more solar energy from reaching the bottom thus making the bottom colder. So increased turbidity should reduce a lake’s total heat energy overall with the bottom utltimately losing more heat than the surface gains.
Wouldn’t temperature measurements at the bottom put this debate to rest?
Better yet… let’s send Dianne down to the bottom with no wet suit to discover how cold it is down there.
Beyond Lake Tahoe: effects turbidity and climate on lake temperatures
One of the big advantages of studying lakes is that there are so many of them. I am privileged to be participating in studies on the effects of climate warming on the food chains of large European subalpine lakes. These lakes experienced high nutrient loading and reduced clarity (increased turbidity) during the 1960s and 1970s due to high phosphorus detergents, increased human populations and poorly treated sewage. This is an environmental success story–large investments in sewage treatment and restricted use of detergents with phosphate has resulted in great reductions in phosphorus, improvements in water quality and, in most cases, substantial increases in water clarity back to pre-1960 values.
These intensive long term monitoring studies that started mostly in the late 70s to assess the effect s of P remediation have proven very important in documenting effects of climate warming on lake water temperature and lake food chains. Lake Constance (Europe’s second largest lake, bordering Germany, Switzerland and Austria) showed probably the biggest decrease in phosphate loading and greatest improvement in water quality (and water clarity) during the 80s and 90s. During this period it also showed a trend of warming very similar to that of Lake Tahoe. Much of the work on the effects of warming on Lake Constance and its food chain has been published by Dietmar Straile of the University of Konstanz (search under Google Scholar under Straile, Lake Constance and Climate change for PDFs).
Direct effects of P loading from a lake’s watershed can have strong effects on water clarity and my guess (after reading only a few specific studies on this lake) is that these effects have probably been dominant in Lake Tahoe, as suggested in Anthony’s original posting.
There is, however, also evidence that warming, through its effects on thermal stratification, mixing depth and food chain interactions can have negative effects on water clarity (increased turbidity). This seems to be the case in Lake Maggiore (Italy and Switzerland) where warming and altered predator-prey interactions may be overriding a 50% reduction in phosphorus. I am coauthor of a study (in press) on Maggiore that looks at effects of warming on a specific predator-prey interaction. Effects of warming on water clarity is not a significant topic of my study. However, my Italian coauthor has presented evidence of a eutrophication-like effect of warming in this lake (search Manca, Maggiore and climate warming).
It’s also clear from the Maggiore data (included on my paper in press) that warmer winters are resulting in shallower water mixing and more algal growth (and increased turbidity) during winter, the period of clearest water. Like Lake Tahoe, Maggiore never freezes. Colder winters lead to mixing at uniformly cold temperatures (about 5oC) to hundreds of meters. Even though the water is relatively clear, few algae can grow under such low average light.
Heads up–A special issue of Limnology and Oceanography titled something like “Lakes as sentinels and integrators of climate change” is in press. A part of the volume focuses on paleolimnology which uses sediment chemistry and fossils to study past climates but many studies present data for the past 20-30 years. Authors of L&O have the option of paying to make their articles open access. Thus, many of these (40 articles or so) and other recent studies are or will be available at the American Society of Limnology and Oceanography web site (www.ASLO.org). You can also find PDFs of all L&O articles between 1947 and 2005 freely accessible.
This posting has lead to comments on how or whether warmer air temperatures can influence water temperature (in lakes and oceans). Work by David Livingstone shows that warming in Lake Zurich over the last 50 years is tied to higher nighttime minimal temperatures rather than an increase in maximal temperature. Thus, lake warming seems to be mainly linked to less heat loss during warmer nights. Here’s a PDF of probably the best study (in my opinion) on effects of climate warming on lake temperatures. (http://homepages.eawag.ch/~living/downloads/2003/Livingstone%202003.pdf.)
I appreciate Anthony’s earlier comment that he does not have ready access to much of the scientific literature, nor does he have the time to read a large number of studies. This does, however, raise the risk of reaching and posting conclusions that are contrary to a substantial body of already published and well documented scientific evidence. I also don’t have the time to read hundreds of original studies outside of my field of expertise. This is the reason that I largely restrict my posting on blogs to areas where I have professional interest.
On a windy day, large lake temperatures are colder due to mixing from wave action. On a still day, large lake temperatures are layered (warm on top with a rather definitive transition to cold). Turbidity is likely both a cause and an effect in bodies of water surrounded by development. However, to say that a lake is in better health because it is clear is very iffy. The very thing that is necessary for the food chain to stay intact from top to bottom will cloud the water.
Well it is my understanding that historically, Lake Tahoe water has had very high clarity, and apparently relatively low biological content; in other words it is/was very clean water; and of course it is very deep.
So as someone else observed it is likely 4 deg C at the bottom.
The clearer thbe water is, the further down the incident sunlight propagates; and the spectral components containing the most sloar energy are the ones that propagate to the greatest depths.
As a result the incident solar energy is distributed throughout a very large volume(mass) of water, so the average temperature rise is quite small. Thjat warm water is going to conduct somewhat to the deeper colder waters, but also the vertical temperature gradient, si going to set up a vertical convection currnet; which might be relatively small because of the great depth over which the incident solar energy is distributed. But the result should be a vertical temperature gradient that is relatively small, because of the water clarity.
So now fast forward to a more turbid present condition, where particulates, and biological materials make the water less clear and mor ehighly scattering.
A direct result of this is that incident soalr energy is going to be more strongly abosrbed at shallower depths. The total absorbed energy isn’t going to be any different; it will be a very good black body approximation (for a natural object), but all that energy is now depoasited in a smaller volume of water; which is still pegged at 4 deg C at the bottom.
With the same flux of solar energy deposited as heat in a smaller shallower volume (mass) of water; the mean temperature of that smaller mass of water has to go up as the turbidity increases.
I still believe that the main heat loss from the lake is through the surface to the atmosphere, because the convection current should trump the downward conduction to the colder depths.
So I believe it is as simple as that; the higher the turbidity/absorptance, the smaller the mass of water over which the constant influx of soalr energy is distributed, so the higher the mean temperature must get.
George
And speaking of the energy (E), and the temperature (T); the two are clearly related.
Everybody is familar with E = mc^2 but that is only part of the story. We could say:-
E = (1/2)mv^2 = mc^2 = hf = kT etc
Here f is a substitute for the Greek “nu” = c/(lambda) in the Einstein relationship between quantum energy and em radiation frequency; (h) of course is Planck’s constant. And then there is that kT where k is Boltzmann’s constant = 1.38066 e-23 J/K (joules per Kelvin), and the (E) in this case is the mean energy per particle in a heated body.
If we multiply k by Na ; Avogadro’s number = 6.0221367 e+23 we of course get R , the Universal Gas Constant (not to be confused with the Rydberg Constant which is something else).
But in any case, it is Boltzmann’s constant which relates energy to Temperature (and hence to “heat” that awful word) ; and just incidently irretrievably links heat to matter, since it specifies the mean energy per particle of matter, directly in terms of the abolute temperature (Kelvins).
From there of course you have to get into the statistical mechanics of the random motion of particles (above zero K), and the Maxwell Boltzmann distribution of particle kinetic energies or velocities.
A classic textbook derivation of the specific heats of solids at low temperatures done by Sir James Jeans starts off by assigning an energy of kT to each degree of freedom of each particle in a system, and computing the total energy for the system. The number of possible modes of oscilaltion in the sytem is astonomical, and in the process of developing his solution Jeans made a simplifying assumption that allows the accurate expression to be reduced to one that is much simpler to understand. That simplifying assumption was to set the value of one of the factors to the value 1. It was a pretty brazen step because the factor that he said was approximately one happened to be Avogardo’s number that is really 6 x 10^23. That is a pretty approximate substitution in anybody’s language; but you have to understand that the quantity of which the Na term was a nuisance factor he wanted to get rid of, also included the term factorial of Avogadro’s number; so really he was just leaving off one number in the factorial.
Somehow I think the factor he approximated as one was only the square root of Avogadro’s number; I seem to recall a term (Na + 1/2) inside a square root term, and that half in there was bloody awkward to say the least.
Hey it was 50 years ago, so I have forgotten exactly how to do the derivation; but that part I remember.
But the important thing is that it closely ties the concept of the mean energy per particle in a system to its heat content, and absolute temperature.
So that discussion with Nassif was not just idle chatter or opinion; important fundamental concepts were at stake.
But we can have such discussions on a forum like this, without upsetting the whole United Nations General Assembly.
George
PS; Don’t forget next time someone asks you; “what’s nu? “, you can smartly answer; ” E/h !”
George’s reasoning above is largely, but not completely correct. A number of studies have shown that in small lakes, increased turbidity leads to stronger heating of a thinner upper layer through which light from the sun is attenuated.
However, Mazumder and Taylor show that this turbidity effect mainly applies to small to medium-sized lakes <12.5 km2 in surface area. It would not apply to great lakes or Lake Tahoe (about 500 km2) or oceans. This is because the greater wind fetch and greater turbulent mixing of large water bodies is such that the mixed depth is determined by wave action and turbulent mixing and is independent of turbidity and light penetration. For larger lakes, mixing by wind trumps heating by the sun in determining the thickness of the upper warm, mixed layer. This is shown in several studies, including one paper in Science. The following paper in Limnology and Oceanography is available as free access from the ASLO.org web site.
http://aslo.org/lo/toc/vol_39/issue_4/0968.pdf
feinstein has been in office way too long. the problem is not global warming, the problem is the kind of industrialization the world participates in. what is feinstein’s “carbon footprint” over the years?
A great and interesting article and thread. I cant help reaching the conclusion, from just visitng the place a few times, that the problems with Lake Tahoe are directly related to the homes and businesses built around it (Some right on
the shores) and the huge year round tourism from the Bay area and elsewhere. Perhaps I missed something, but I assume there have been no long term
studies related to the effects of this.
Every time I saw that Tahoe sticker on the backs of cars (it’s amazing which states it turns up in and once or twice in Mexico) I could’nt help thinking what … why dont you stop living or going there if you cared so much about it!
“”” BillD (11:09:45) :
George’s reasoning above is largely, but not completely correct. A number of studies have shown that in small lakes, increased turbidity leads to stronger heating of a thinner upper layer through which light from the sun is attenuated.
However, Mazumder and Taylor show that this turbidity effect mainly applies to small to medium-sized lakes <12.5 km2 in surface area. It would not apply to great lakes or Lake Tahoe (about 500 km2) or oceans. This is because the greater wind fetch and greater turbulent mixing of large water bodies is such that the mixed depth is determined by wave action and turbulent mixing and is independent of turbidity and light penetration. For larger lakes, mixing by wind trumps heating by the sun in determining the thickness of the upper warm, mixed layer. This is shown in several studies, including one paper in Science. The following paper in Limnology and Oceanography is available as free access from the ASLO.org web site. """
Bill, I don't have any disagreement with your point that stirring the lake up will spread the heat around and complicate the simplified picture I drew.
But is there data on how significant an effect that would be in lake Tahoe. It seems to me that Tahoe is a relatively calm lake. Maybe that's a bad assumption on my part. I would actually be quite surprised if in fact wind driven surface turbulence can effect more than a fraction of the depth which I believe gets direct solar heated.
I guess if Tahoe is 500 squ km that puts it around 25 km diameter; so it certainly is large compared to its depth; but then it also has mountain peaks all around.
But I'm sure you are correct, that wind driven mixing somewhat counters the process I described.
But lets say that wind driven mixing completely obliterates any trace of the effect I mentioned.
Bottom line is that deep lakes and oceans are effectively black body absorbers, since the total Fresnel reflection from the surface is 2% at normal incidence, and maybe 3% integrated over the hemisphere; so the total solar energy input would be the same turbidity or no.
So what sort of Secchi disk data or history do they have for Tahoe to give some actual quantitative turbidity measurements.
It's amazing how speculative one gets in the absence of data; I couldn't even begin to guess at the long wave ir heating from the atmosphere over Tahoe; given its altitude; don't know a thing about the humidity history to guess about evaporative cooling.
I would place my bets on the increased population and activities; if looking for extra energy input. One thing is for sure that the water turbidity would have no effect whatsoever on the long wave IR heating; which wouldn't make it deep enough to discover there was any turbidity. That pretty much leaves local atmospheric or surface heating due to climate change if any.
But I wouldn't sign on to the Feinstein bandwagon; that's just a photo-op for her.
George:
The pictures that I have seen of Lake Tahoe suggest a relatively calm lake. However, since its surface area is 40X greater than the empirically derived boundry between lakes where there is a shift from turbidty to turbulent mixing being more important, then is safe to assume that turbulent mixing by wind is more important.
I am also skeptical about Feinstein’s comment about causes of increased turbidty in Lake Tahoe.
Looking at the Coats et al paper, I believe that the mixed upper layer (epilimnion) of Lake Tahoe is about 30 m thick in fall. Evidently the lower depth (30 m) is deeper than significant heating by light. I don’t know the details of the Lake Tahoe sampling regime. If they have been measuring temperature over the upper 30 m every two weeks for the last 40+ years, as the Coat’s paper notes, it seems safe to assume that the research group also has regular Secchi measurements and also measured light transmission with depth using a light meter, probably also over the upper 100 m. It’s a well funded research programs and Charles Goldman for UC Davis has been the research leader for all or most of the 40 years.