Sent by Alec Rawls, 2-18-2011, to a dozen scientists who dismiss a solar explanation for late 20th century warming on the grounds that solar activity was not increasing in the late 20th century


Dear Professor ________________:

 I am writing a post on your work for the Watts Up With That climate website, hosted by meteorologist Anthony Watts. You are one of about a dozen scientists (mostly solar scientists) who have at some point have argued that late 20th century warming cannot be attributed to the 20th century's high level of solar activity because solar activity did not show any upward trend over the over the late part of the century. (Citations below. I  am sure there are many more, but you are the one's I bookmarked over the past few years.)

Professor Benestad made this argument about post 1950 warming. Professors Usoskin, Schüssler, Solanki, Mursula made it about post 1970 warming, and Professors Lockwood and Fröhlich made the same argument about post 1986 warming.  I am hoping that at least some of you will be willing to elaborate. In your mind, does this argument depend on an unstated assumption that ocean temperatures must have already equilibrated to the "grand maximum" levels of solar activity that began in the 1920's? In the instances that I am citing, none of you addressed the question of whether equilibrium had been reached, but without this assumption, your statements seem to be quite obviously wrong.

The assertion you all have been making is that steady maximum levels of solar forcing cannot drive warming: that only continued increase in solar activity could cause continued warming. That is equivalent to saying that it isn't possible to heat a pot of water by turning the burner to maximum and leaving it there. Rather, heating will only occur if one turns the flame up gradually, as if it is the act of raising the level of the flame that heats the water, rather than the level that the flame is raised to.

It seems unlikely that any of you would actually be making such a basic mistake. More likely, there is an unstated assumption. If equilibrium temperatures had been reached by 1970 or by 1986, then your statements would make scientific sense. From a position of equilibrium, only a change in forcing will cause temperature to change. But if you have been making this assumption, I would urge that it needs to be publicly stated and addressed, so that scientific debate can be directed to the correct point: is there good reason to believe that by 1970, or by 1986, ocean temperatures had equilibrated to the 20th century's high level of solar activity?

If not, then grounds for dismissing a solar explanation for late 20th century warming disappears. On the other hand, if the case for equilibrium having been reached is solid, then the solar explanation fails. Thus the question of whether equilibrium was reached is THE key point for distinguishing the main competing climate theories: whether late 20th century warming was due to the sun or to CO2. This question should properly be front and center, yet you all appear to have tucked it away as an unstated assumption.

I am guessing that most of you probably have some equilibrium arguments in mind, reasons why you think--or thought in the past--that equilibrium must have been reached before the sun dropped into its recent funk, and I am hoping that you will be willing to share these reasons with the public, so that this crucial issue can be brought to the fore where belongs. Some of you might have changed your minds. An awful lot has happened in recent years, with the sun going quiet. Any updates on your thinking would be very welcome. And if any of you want to maintain that it really is not the level of forcing that creates warming, but the change in the level, regardless of whether equilibrium has already been reached, that would be interesting too.

List of citations below.

Thank you all for your consideration,

Alec Rawls

Palo Alto, CA



Professors Usoskin, Schussler, Solanki and Mursula (2005):

The long term trends in solar data and in northern hemisphere temperatures have a correlation coefficient of about 0.7 — .8 at a 94% — 98% confidence level. …

Note that the most recent warming, since around 1975, has not been considered in the above correlations. During these last 30 years the total solar irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most warming episode must have another source.

Solanki and Krivova (2003):

Clearly, correlation coefficients provide an indication that the influence of the Sun has been smaller in recent years but cannot be taken on their own to decide whether the Sun could have significantly affected climate, although from Figure 2 it is quite obvious that since roughly 1970 the Earth has warmed rapidly, while the Sun has remained relatively constant.

Professors Lockwood and Fröhlich (2007):

Abstract: There is considerable evidence for solar influence on the Earth's pre-industrial climate and the Sun may well have been a factor in post-industrial climate change in the first half of the last century. Here we show that over the past 20 years, all the trends in the Sun that could have had an influence on the Earth's climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.

Professor Benestad (2004, 2005):

Svensmark and others have also argued that recent global warming has been a result of solar activity and reduced cloud cover. Damon and Laut have criticized their hypothesis and argue that the work by both Friis-Christensen and Lassen and Svensmark contain serious flaws. For one thing, it is clear that the GCR does not contain any clear and significant long-term trend (e.g. Fig. 1, but also in papers by Svensmark).

A further comparison with the monthly sunspot number, cosmic galactic rays and 10.7 cm absolute radio flux since 1950 gives no indication of a systematic trend in the level of solar activity that can explain the most recent global warming.

Professor Phil Jones (interview with the BBC, February 2010):

Natural influences (from volcanoes and the Sun) over this period [1975-1998] could have contributed to the change over this period. Volcanic influences from the two large eruptions (El Chichon in 1982 and Pinatubo in 1991) would exert a negative influence. Solar influence was about flat over this period. Combining only these two natural influences, therefore, we might have expected some cooling over this period.

Dr Piers Forster (quoted by the BBC, October 2009):

The scientists' main approach was simple: to look at solar output and cosmic ray intensity over the last 30-40 years, and compare those trends with the graph for global average surface temperature.

And the results were clear. "Warming in the last 20 to 40 years can't have been caused by solar activity," said Dr Piers Forster from Leeds University, a leading contributor to this year's Intergovernmental Panel on Climate Change (IPCC).

Professor Johannes Feddema (quoted in the Topeka Capital-Journal, September 2009):

Feddema said the warming trend earlier in the century could be attributed to anything from solar activity to El Ninos. But since the mid 1980s he believes data doesn't correlate well with solar activity, but does correlate well with rising CO2 levels.

Professor Kristjánsson (2009):

Kristjansson also points out that most research shows no reduction in cosmic rays during the last decades, and that an astronomic explanation of today’s global warming therefore seems very unlikely.