Posts tagged ‘Lubo Motl’

Stupid Math Tricks

James Hansen, head of NASA's GISS and technical adviser on An Inconvenient Truth, wrote recently

Thus there is no need to equivocate about the summer heat waves in Texas in 2011 and Moscow in 2010, which exceeded 3σ – it is nearly certain that they would not have occurred in the absence of global warming. If global warming is not slowed from its current pace, by mid-century 3σ events will be the new norm and 5σ events will be common.

This statement alone should be enough for any thoughtful person who here-to-fore has bought in to global warming hysteria out of vague respect for "science" to question their beliefs.

First, he is basically arguing that a 3σ event proves (makes it "nearly certain") that some shift has occurred in the underlying process.  In particular, he is arguing that one single sample's value is due to a mean shift in the system.  I don't have a ton of experience in process control and quality, but my gut feel is that a 3σ event can be just that, a 3σ event.  One should expect a 3σ event to occur, on average, once in every 300 samples of a system with a normal distribution of outcomes.

Second, and a much bigger problem, is that Hansen is gaming the sampling process.  First, he is picking an isolated period.  Let's say, to be generous, that this 3σ event stretched over 3 months and was unprecedented in the last century.  But there are 400 3-month periods in the last hundred years.  So he is saying in these two locations there was a 3σ temperature excursion once out of 400 samples.  Uh, ok.  Pretty much what one would expect.

Or, if you don't like the historic approach, lets focus on just this year.  He treats Moscow and Texas like they are the only places being sampled, but in fact they are two of hundreds or even thousands of places on Earth.  Since he does not focus on any of the others, we can assume these are the only two that have so-called 3σ temperature events this summer.

It's hard to know how large to define "Texas"  (since the high temperatures did not cover the whole state) or "Moscow" (since clearly the high temperatures likely reached beyond the suburbs of just that city).

Let's say that the 3σ event occurred in a circular area 500km in diameter.  That is an area of 196,250 sq km each.  But the land surface area of the Earth (we will leave out the oceans for now since heat waves there don't tend to make the headlines) is about 150 million sq km.   This means that each of these areas represent about 1/764th of the land surface area of the Earth.  Or said another way, this summer there were 764 500km diameter land areas we could sample, and 2 had 3σ events.  Again, exactly as expected.

In other words, Hansen's that something unusual is going on in the system is that he found two 3σ events that happened once every 300 or 400 samples.  You feeling better about the science yet?

Luboš Motl has a more sophisticated discussion of the same statement, and gets into other issues with Hansen's statement.

Postscript:  One other issue -- the mean shift in temperatures over the last 30 years has been, at most, about 0.5C  (a small number compared to the Moscow temperature excursion from the norm).  Applying that new mean and the historic standard deviation, my guess is that the Moscow event would have still been a 2.5σ event.  So its not clear how an event that would have been unlikely even with global warming but slightly more unlikely without global warming tells us much of anything about changes in the underlying system, or how Hansen could possible assign blame for the even with near certainty to anthropogenic CO2.

Hold off on the Funeral for Special Relativity

Harvard physicist LuboÅ¡ Motl throws some cold water on recent claims to have broken the speed of light.  He argues:

Two years ago or so, Robert Helling
explained what these experiments are all about. As far as I can say,
there is nothing new about Nimtz's findings or observations and not
much interesting about them either. He's been doing the very same
things for decades.

He builds a setup in which the maximum
of a wave moves faster than light (although you need amplifiers to find
where the maximum is at the end). That's of course possible. In fact,
it's very easy. You can make such things with normal classical
electromagnetic waves as long as you have a layer of material where
they exponentially drop. In analogy with Schrödinger's equation, you
may realize that tunneling can be very fast.

microscopically, no signal or information is moving superluminally and
nothing is violated about special relativity whatsoever because all
these waves perfectly satisfy Maxwell's equations where the speed of
light is safely bounded. Nimtz must know that, I think, so his behavior
seems dishonest to me.

Diminishing Return

I know a number of readers are tired of my writing about climate, so I am instead taking a shot at writing a comprehensive skeptic's argument on Anthropogenic Global Warming.  A free pdf will be available for download next week, with a bound copy available for purchase at manufacturing cost.

In the mean time, Luboš Motl presents one of the core skeptics arguments, that CO2 heat absorption is a diminishing return relationship to concentration, making frequent predictions of runaway climate scenarios a real head-scratcher.

In terms of numbers, we have already completed 40% of the task to
double the CO2 concentration from 0.028% to 0.056% in the atmosphere.
However, these 40% of the task have already realized about 2/3 of the
warming effect attributable to the CO2 doubling. So regardless of the
sign and magnitude of the feedback effects, you can see that physics
predicts that the greenhouse warming between 2007 and 2100 is predicted
to be one half (1/3 over 2/3) of the warming that we have seen between
the beginning of industrialization and this year. For example, if the
greenhouse warming has been 0.6 Celsius degrees, we will see 0.3
Celsius degrees of extra warming before the carbon dioxide
concentration doubles around 2100.

It's just like when you want
your bedroom to be white. You paint it once, twice, thrice. But when
you're painting it for the sixteenth time, you may start to realize
that the improvement after the sixteenth round is no longer that

If CO2 is not responsible for all the 0.6C of historic warming (a proposition for which there are good arguments) then future warming is even less.  Read it all for more detail, or look for my paper next week which covers this topic and many, many others in more depth.  There are lots of complications - aerosols, dimming, feedbacks - that are discussed in the paper.

What Do We Know and How Well Do We Know It

"Consensus" is an absurd word to apply to science.  It is more accurate to say that we have a series of hypotheses about the universe with varying levels of confidence.  LuboÃ…¡ Motl has a post to get all you physics geeks arguing:  His estimate of the probability certain hypotheses about the universe are correct.  Some examples:

  • 99.999% - String theory is a mathematically consistent theory
    including quantum gravity, even non-perturbatively, at least in some
    highly supersymmetric vacua
  • 99.999% - General relativity
    correctly predicts phenomena such as frame dragging and classical
    gravitational waves in the real world
  • 99.995% - Black holes exist  ...
  • 60% - At very high energy scales, a GUT theory with unified gauge
    interactions becomes more natural zeroth approximation: GUT is correct
  • 50% - Supersymmetry will be found at the LHC
  • 40%
    - The Hartle-Hawking wavefunction or its generalization that will
    require the author(s) to cite Hartle and Hawking correctly predicts
    non-trivial features of the initial conditions of the Universe...
  • 0.0001% - Loop quantum gravity, with the metric as the only and
    well-defined degree of freedom and with quantized area, is a correct
    description of gravity in the real world at the Planck scale
  • 0.00001%
    - One of the ESP phenomena measured in the Princeton lab actually
    exists and can be measured again with a similar equipment

Many more here.

Here are some of my own:

  • 95% - Probability that the Raiders, Browns, and Lions will all botch their first draft picks next weekend
  • 85% - Probability someone will introduce legislation in Congress in the next 7 days in direct response to the Va Tech shooting rampage
  • 80% - Probability that man-made CO2 is contributing a non-zero effect to global temperature
  • 70% - Probability that Barry Bonds will break the home run record this season
  • 60% - Probability that Prince Charles will ever serve as King of England
  • 50% - Probability that all-electric vehicles will make up more than 10% of the auto market in the US in ten years
  • 5% - Probability that man-made CO2 will contribute more than 2 degrees C warming in the next 50 years
  • 5% - Probability of meaningful earmark reform getting passed in Congress
  • 5% - Probability that ethanol or other bio fuels will make any measurable reduction in oil imports.
  • 1% - Probability that the costs of CO2 reduction will be less than the benefits of CO2 reduction
  • 1% - Probability that a true libertarian candidate will be elected president in the next 20 years