Guest post by Craig Loehle, Ph.D.
A fundamental principle of physics is that causation is unidirectional in time. An event must follow its cause. Forgive me for stating the obvious, but you will soon see why I begin with such a simple statement. Outside of temporal anomalies in sci-fi movies, time travel is forbidden by thermodynamics, among other reasons (and not just because you could kill yourself at an earlier time and create a multiple-worlds crisis which calls for Spock to give future technologies to past counterparts of Scotty…).
In the climate change debate, by contrast to physics, the force of GHGs and human evil is so great that it transcends time. Bad things happen BEFORE their cause. It is simply amazing.
Let’s establish the time frame for the analysis. When can we say that human activities began to influence the climate in a significant way? According to the IPCC it is sometime after 1950 (in their attribution section). Before that, whatever small effect GHGs and land use change had on the climate was not detectable because too small—remember, GHGs are rising, it is not a black/white single event like shooting someone but a matter of quantity. Specific attribution studies give 1950 (Thompson, D.W.J., J.M. Wallace, P.D. Jones, and J.J. Kennedy. 2009. Identifying signatures of natural climate variability in time series of global-mean surface temperature: Methodology and insights, J. Clim., 22, 6120-6141, doi:10.1175/2009JCLI3089.1) or 1960 (Hegerl, G.C., P.D. Jones, and T.P. Barnett. 2001. Effect of observational sampling error on the detection of anthropogenic climate change, J. Clim., 14, 198-207) as dates for detectability. And yet, these dates are ignored in much of the debate. I will note 3 cases here.
First, the IPCC implicitly counts warming that occured before 1950. In calculating trends, it lists the 100 year 20th Century trends, and leaves it implicit that all of the warming over this period is human-caused. It never explains the warming pre-1950 or clearly disavows it. In the public debate also, the entire 100+ year warming is noted as alarming (“the world has warmed 0.8 deg C during the past 100 years” is given as “proof” of how bad it is), but the first 50 years of this could not be human caused.
Second, particularly in blog debates or press commentaries, the melting of glaciers is given as indisputable evidence for warming (often in responding to concerns like the CRU email scandal or the surfacestations project). Let’s consider the well-documented case of glaciers in Europe. During the LIA glaciers advanced and crushed many farms and villages. Between 1750 and 1800 many began to recede. They were thus receding for between 150 and 200 years before human activity could have been the cause, yet this melting is taken as proof of AGW.
This assumption is once again based on time travel: the human impact since 1950 melted glaciers beginning in 1750. In some cases it is argued that the melting in recent decades is human caused, even if earlier melting was not. This is special pleading, with no empirical support. One must demonstrate that the cause has changed, not assume it. Assuming it creates circular reasoning: the melting of glaciers after 1950 is different than before 1950 because of AGW, and it is therefore evidence supporting AGW! The proper analysis is that melting of glaciers before 1950 does not require AGW as a cause, and therefore melting after 1950 does not need AGW as a cause unless it can be proven.
As a side-note, it is important to understand that since glaciers are slow to respond to climate changes, and slower the larger they are, the only thing a receding glacier tells us is that it is currently warmer (and/or drier) than when it reached its last maximum extension. So, it is currently warmer than in 1750 or 1800, but we do not know if it is getting warmer and warmer by looking at receding glaciers. This would only be true if glaciers were in instant equilibrium with climate, which is of course not true.
Third, the impacts claimed by the IPCC to be likely in the distant future are claimed to be already evident. The “climate resistance” blog, I believe, coined the term “future present tense” for this phenomenon. In many essays or editorials, the actual argument for present impacts invokes future impacts.
And yet, in most cases in which historical data are sufficient to compare recent with historical data, no trends for increasing bad things can be detected (see Pielke jr blog for many examples), and even the IPCC admits that effects on agriculture and forestry have so far been limited (see also R. Seppala, A. Buck, and P. Katila, eds. Adaptation of Forests and People to Climate Change—A Global Assessment Report. IUFRO World Series Vol. 22. Helsinki. 224pp. [PDF]).
There may also be the following reasoning involved:
Climate change will cause bad things, and climate change is happening.
Therefore, if bad things happen it is due to climate change. This line of argument is qualitative but climate change is not discrete but quantitative, and the bad things that are claimed to be likely consequences depend on the magnitude of the climate change, not just the existence of climate change. This type of argument also misses the necessary/sufficient distinction.
Climate change is not necessary for bad things to happen (since they have happened throughout history and even before human history), it can only be assessed by the frequency of bad things (of course ignoring the existence of good things…).