Diane Feinstein: turbidity denier?

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