On March 16th I blogged about the sharp upturn in global temperatures that some liken to the blade of a hockey stick. The blog provides a link to a graph reproduced by the BBC which goes back 1000 years. Aside from questions about how data are fitted, simple changes to scales and other attributes of the graphs themselves can paint very different perspectives on seemingly straightforward scientific questions such as whether we ought to be worried about global warming. Andy Sleeper shows this in part 7 of his white paper titled HOW TO LIE WITH STATISTICAL GRAPHICS. The color-coded graph generated by the U.S. National Oceanographic and Atmospheric Administration is very alarming. However, it only provides 122 years of history and the y-axis scale is restricted to about 2 degrees C. A few figures later in Sleeper’s paper one sees another graph based on 400,000 years of temperatures estimated from core samples of Antarctic ice. It reveals cyclic temperature swings of 12 degrees C! In this context, should a less than 1 degree increase in global temperature be considered abnormal, that is, due to a special cause such as man-made carbon dioxide?
PS. Here’s something to really worry about. The November issue of Sky and Telescope features a heads-up on “The Most Dangerous Asteroid Ever Found” — a 1000-foot pile of rock called Apophis. It will just miss the Earth on April 13, 2029. If Apophis hits a narrow zone — called the keyhole, it will be dragged enough by our gravity to put it on a course that collides with Earth seven years later. One can only hope that NASA’s proposed gravity tractor will pull the asteroid off target and save the planet.
#1 by Eric Kvaalen on October 6, 2006 - 2:04 pm
The trouble with the graph showing the last 400,000 years is that it only gives the temperature at Lake Vostok in Antarctica. The present time may be a couple degrees cooler than 10,000 years ago at that remote location, but I don’t think that would be true for the global average temperature. Also, the time scale is so squeezed that you can’t tell whether the warmings of the past occurred over 1000 years or over 100 years.
So his Graph 13 is no more “truthful” than the previous graphs.
I think the graph here http://en.wikipedia.org/wiki/Global_warming#Historical_warming_of_the_Earth is better. It shows the last 2000 years, and is not as reassuring as his Graph 13.
Whether we can prove that the recent global warming is due to man or not, there is nevertheless a good possibility of that, which has not been disproved. On the other hand, the chance of Apophis hitting us is estimated at 1 in 43000! And even if it does, I doubt it would do as much disruption as the kind of global warming we may be getting into. It would be comparable to a few Krakatoas in energy.
Could one find a statistically significant correlation between people’s beliefs about global warming and their use of fossil fuels?
#2 by Mark on October 6, 2006 - 3:51 pm
Aside from our individual biases on this polarizing issue (literally so far as the Antarctic data), the Wikipedia graphs reinforce Sleeper’s point that one should be alert to differing perspectives in X (time) and Y (temp), not to mention their veracity from the outset.
Also you provide a good point about self-interest creating bias in judging the evidence.
#3 by katie on October 24, 2006 - 8:08 am
wow this sounds so interesting i will reply to this