Friday, July 4, 2014

Lying with Statistics about Global Warming

A very contentious contemporary issue in global warming is whether or not the global temperature has advanced over the last two decades or so.  It is a very popular meme among global warming skeptics and deniers that planet has actually gotten colder over this time, or at least has not changed at all thus contravening the claims of the Warmists altogether.  To make this happen though is to engage in one of the well-used methods of lying with statistics, "cherry picking".  The Cato Institute, for example, published an article asserting that the global temperature is declining.  To get that result, however, they had to begin their time series of temperatures with one very close to 1998 which happened to be a year that experienced a "super" El Nino, a phenomenon that increases global temperatures over and above the secular trend.  This made the trend look negative.  El Nino is a separate occurrence from the increasing trend of global temperatures due to the increase in atmospheric CO2.   Cherry picking a "super" El Nino year to begin your time series virtually guarantees a negative trend in global temperatures even though the El Nino has nothing to do with the underlying secular trend due to atmospheric CO2.

It is important to understand that there are several processes involved in determining global temperatures and the ENSO, that is, the El Nino, La Nina, cycle is one of them.  Another is the impact of the sun.  These and other factors add and subtract from the secular trend due to atmospheric CO2.  The goal of any analysis is to find the underlying secular trend controlling for these events that are irrelevant to the impact of CO2.  To tease out the true increase of global temperatures requires having irrelevant events with the right properties. If these events were to always be in one direction we'd have a biased result.  To keep that from happening we need a longer time series of temperature where all of the irrelevant actions both add and subtract.  We need to include El Nino events that raise the temperature as well as La Nina events that lower them.  Then we can see the underlying secular trend by using statistical methods that control out the irrelevant events.  Anything else is lying with statistics.

The Cato Institute realized their error and asked another expert to produce an analysis without the "cherry picking" --  Global Warming: Correcting the Data. Even the Cato Institute, stolid deniers of global warming, have been forced to conclude that they were wrong, that there's an increasing secular trend.  This underlying trend has slowed, but very likely some underlying process is having an impact.  Scientists believe that much of the heat is going into the oceans.  That the impact of atmospheric CO2 is right now more on the oceans than the global atmospheric temperature doesn't mean that we won't have to pay for what we are doing to our planet.