Do-it-yourself citizen scientists need to conduct proper data analysis to reach valid conclusions.
In this post I show how the blogger Inconvenient Skeptic misleads himself on the role of the Atlantic Multi-decadal Oscillation in global warming because he misinterprets his own trend charts and implies causation from correlation.
Inconvenient Skeptic’s Post on The All Natural Cause of Global Warming
On his Inconvenient Skeptic blog, John Kehr has written a post titled “The All Natural Cause of Global Warming“. The post presents John’s investigation into the relationship between the AMO and Hadley-CRU global land-ocean temperature anomaly; it includes 4 trend charts, 2 covering the period 1855-2005, 1 covering period 1913-1945 and one covering the period 1971-2005.
Here’s John’s 1st chart which shows the 1856 – 2005 AMO and 1971 – 2005 Hadley CRU data series.
John notes “The first thing that stood out was the rate of warming for both the AMO and the CRU global-average was essentially the same. The correlation is so close that I was simply stunned. When I focus only on the period from 1971-present the results are simply astounding.”
John then plots the 1971 – 2005 trends for AMO and Hadley – CRU in this chart.
John states “Here is a natural cycle of the Earth that has been going on for at least that past thousand years that perfectly correlates to all of the modern global warming.” He then shows a similar chart for the 1913-1945 period.
Based on these charts, John reaches some strong conclusions:
- “Once again [the 1913-1945 period] the very natural cycle of the AMO caused the average temperature of the Earth to increase over the exact same period of time that the AMO was increasing.”
- “Two times in the past 100 years the Atlantic Multidecadal Oscillation has transitioned from cool to warm. In both instances the average temperature of the Earth increased in near perfect lockstep with the changing temperatures of the Atlantic Ocean.”
- If the AMO is responsible for all or most of the current warming period that has taken place since the 1970′s, then that is proof that the activities of mankind have had little to no impact on the Earth’s climate and CO2 has not been a factor. Even if it is not the only cause, it is impossible to separate the warming caused by the AMO and that of other factors. In effect it is impossible to state that any warming has been caused by the increase in CO2.
While I have several problems with John’s analysis, I will discuss 2 issues: 1) his selective use of just rising AMO time periods and 2) his “correlation implies causation” conclusion that “.. the AMO caused the average temperature of the Earth to increase..”.
Issue 1: Long Term Trend Chart versus Rising AMO Periods
I think that John’s trend charts mislead him because they only showed him part of the long term trends. Here’s my long term trend chart that compares the AMO and Hadley – CRU data series over the full 1856-2005 period.
My chart shows the trends for 4 periods, the 2 rising AMO periods that John used (1913-1945; 1971-2005) and the 2 declining AMO periods that John ignored (1856-1912; 1946-1970). My chart provides a more complete picture of the situation; including the conflicting trends in the 1946-1970 period when AMO trended down and Hadley-CRU trended up.
Also note that the Hadley-CRU trend has generally been up since 1917 when the anomaly was -0.5 C. By just focusing on the 1970 – 2005 period, John ignored the 1917 – 1970 upward trend in Hadley – CRU. The Hadley – CRU anomaly was less than the AMO from 1856 until about 1970, when the relationship reversed.
Clearly the situation is much more complex than John implies in his post; it warrants much more analysis than John has given it to reach any firm conclusions.
Issue 2: Correlation Does Not Imply Causation
John has fallen into the well known “correlation does not imply causation” trap. He observes that CRU increases when AMO increases, therefore the AMO increases cause CRU increases. While this is possible, John did not address at least two other possibilities:
- CRU increases cause AMO increases
- CRU and AMO increases may be caused by a 3rd variable
John provides no basis for his assertion that rising AMO causes rising Hadley – CRU beyond the correlation. He offers no rationale for his conclusion, just the correlation when the AMO is rising.
The AMO, like the PDO, ENSO, AO and other climate oscillations, describes part of the complex climate picture. I’ve written about climate oscillations in several previous posts (here, here, here, here).
John has not demonstrated that the AMO has caused global warming. To me, this is an example of do-it-yourself citizen climate science over-reach. To be credible citizen climate scientists, we need to substantiate our conclusions. John has more work to do to substantiate his conclusion.