Common Sense and The Perils of Predictions

12 06 2009

Guest essay by Michael R. Smith, C.C.M.

PredictionsForDisaster

Forbes, “Absolute Return” column, April 21, 2008, page 246:

Here’s another name you should own, Freddie Mac ($29 per share)…Freddie is cheap at 1.1 times book [value].

Less than five months later, Freddie Mac’s stock was worth 25¢ per share, a loss of 99%.  It has since recovered to 70¢ per share, so the loss is “only” 97.6%.

A forecast of a stock of a single company five months into the future seems easy.  The company had government backing (federally sponsored corporation).  What could go wrong?

Yet, the forecast published by Forbes, short of an outright bankruptcy, could not have been more inaccurate.  It is worth examining how a situation that seemed rock solid (government-backed securities!) became catastrophic to see if there are any lessons that might apply to the atmospheric sciences.

The assumptions that Freddie Mac (and other financial stocks) were low risk was primarily a result of computer models.  As one expert stated (using pseudonym at http://blogs.zdnet.com/Murphy/?p=1265 ), Read the rest of this entry »


Comments : 80 Comments »

Categories : forecasting, modeling

Suggestions of “strong negative cloud feedbacks” in a warmer climate

12 06 2009
Natural heat engine - the cumulonimbus cloud, transports heat from the lower to upper levels of the atmosphere. Source International Space Station/NASA - click for large image

Natural heat engine - the cumulonimbus cloud, transports heat from the lower to upper levels of the atmosphere. Source International Space Station NASA - click for large image

I thought this post on clouds and climate modeling below from Steve McIntyre’s Climate Audit was interesting, because it highlights the dreaded “negative feedbacks” that many climate modelers say don’t exist. Dr. Richard Lindzen highlighted the importance of negative feedback in a recent WUWT post.

One of the comments to the CA article shows the simplicity and obviousness of the existence of negative feedback in one of our most common weather events. Willis Eschenbach writes:

Cloud positive feedback is one of the most foolish and anti-common sense claims of the models.

This is particularly true of cumulus and cumulonimbus, which increase with the temperature during the day, move huge amounts of energy from the surface aloft, reflect huge amounts of energy to space, and fade away and disappear at night.

Spot on Willis, I couldn’t agree more. This is especially well demonstrated in the Inter Tropical Convergence Zone (ITCZ) The ITCZ has been in the news recently because early analysis of the flight path of Air France 447 suggests flying through an intense thunderstorm cell in the ITCZ may have been the fatal mistake. There is a huge amount of energy being transported into the upper atmosphere by these storms.

Here are some diagrams and photographs to help visualize the ITCZ heat transport process. First, here is what the ITCZ looks like from space. Note the bright band of cumulonimbus clouds from left to right.

The ITCZ from space. Source: NASA Earth Observatory. Click for larger image

The ITCZ from space. Source: NASA Earth Observatory. Click for larger image

Here is a pictorial showing a cross section of the ITCZ with a cumulonimbus cloud in the center. Read the rest of this entry »


Comments : 151 Comments »

Categories : Science, modeling, weather