Y'know, I was going to make this post about the new pact between California and Nevada to reverse the decreasing clarity trend in Lake Tahoe, but then I found something more disturbing.
Anthony Watts blames the warming of Lake Tahoe on its decreasing clarity.
Now, to me, this intuitively seemed outlandish. While Tahoe's clarity is decreasing [as evinced by the figure shown on his Web site, shown below, not of his making, but properly attributed to the UC Davis Tahoe Environmental Research Center (TERC)], it isn't exactly mud-clear yet. Now, yes, more suspended matter would probably absorb radiation, but for this to be significant, it would have to be a pretty big change to overcome the basic air temperature effects that maintain the temperature of a body of water.
Now, let's review some basics here. Bodies of water and caves are similar -- left to themselves, they will equilibrate at the average temperature of their region. This actually works really well with outdoor swimming pools; if you want to know what the average temperature (diurnally) was over the past few days, go to your local outdoor swimming pool and check the temperature early in the morning. It'll be within a degree or two of the average. Lakes are an extended temporal version of this; they will equilibrate to the regional average. And it takes a considerable change in the regional average to change them. Not a slight increase in the concentration of phytoplankton in what is still a very oligotrophic (not even close to mesotrophic) body of water.
Now, I read all the comments. But before I did that, I found this paper (which one of the commenters mentioned, and another provided a link to).
The warming of Lake Tahoe
The Watts Up With That article was written in 2009, so maybe this wasn't as easily findable then. It sure was easy for me now.
Anyway, here's the abstract:
"Abstract. We investigated the effects of climate variability on the thermal structure of Lake Tahoe, California-Nevada, 1970–2002, and with principal components analysis and step-wise multiple regression, related the volume-weighed average lake temperature to trends in climate. We then used a 1-dimensional hydrodynamic model to show that the observed trends in the climatic forcing variables can reasonably explain the observed changes in the lake. Between 1970 and 2002, the volume-weighted mean temperature of the lake increased at an average rate of 0.015 ◦C yr−1. Trends in the climatic drivers include 1) upward trends in maximum and minimum daily air temperature at Tahoe City; and 2) a slight upward trend in downward long-wave radiation. Changes in the thermal structure of the lake include 1) a long-term warming trend, with the highest rates near the surface and at 400 m; 2) an increase in the resistance of the lake to mixing and stratification, as measured by the Schmidt Stability and Birge Work; 3) a trend toward decreasing depth of the October thermocline. The long-term changes in the thermal structure of Lake Tahoe may interact with and exacerbate the well-documented trends in the lake’s clarity and primary productivity."
So, basically, the climate is driving the temperature increase of the lake, and the clarity decrease might be somewhat related to that, but it is more due to increased nutrient input from increased development around the lake.
But here's the best part:
AW: " 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. [I found the paper searching with "Lake Tahoe" and "warming" and "trend".]
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
As far as I can tell, he never said another word about the subject. "I was wrong" might've been too simple.
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