Solarpower wrote:

So what do you think Akasofu was referring to when he claims they “have not examined the natural component?” I have a feeling he is a respectable scientist, although not specialising in this field

First, Akasofu's claims are not entirely new by any means. Most of the content of his (2006) paper and main claims already appeared in a paper 4 years ago by Sallie Baliunas and Willie Soon. The main item of contention by Akasofu, is the claim of a temperature rise of 0.4C between 1910 and 1940, while most of the increase in greenhouse gases occurred after 1940.

Akasofu also goes one better presenting a number of graphs which he claims shows a "linearity" that contradicts the IPCC panel claim of a 0.6 C rise in temps.

As to the claims of both contrarian papers, it's difficult to specifically assign a source for their so-called "natural causes". Perhaps the most definitive paper ever on the possible variations of the solar constant was: 'Solar constant - Constraints on possible variations derived from solar diameter measurements' Sofia, S.; Okeefe, J.; Lesh, J. R.; Endal, A. S. (Science vol. 204, June 22, 1979, p. 1306-1308.)

Their data, acquired for the interval between 1850 and 1937, set limits of variation on the solar radius to about 0.25 arc second. The Sun's actual aperture in seconds of arc is ~ 1920". So we are talking about 1.3 parts in ten thousand of change.

Generally, in terms of solar gas dynamics and with considerations of hydrostatic pressure balance, e.g.

dP/dr = - GM(r) rho(r)/ r^2

If the 0.25 arcsec change is a contraction of the diameter we can expect heating, while if it is an expansion we get cooling.

The authors' modeling of the Sun indicates that the solar constant did not vary by more than 0.3 percent during that time, either way.

Meanwhile, John Eddy's radio-carbon data for the "little Ice Age" (cf. 'Historical and Arboreal Evidence for a Changing Sun' in The New Solar Physics, AAAS Selected Symposium, Westview Press, 1979, pp. 11-33) falls well within the tolerance parameters assigned by Sofia et al. That is, there is no evidence whatever that the cooling extended beyond the threshold limits allowed for solar constant variance, OR that such cooling is still going on. Indeed, Eddy pointedly notes the decline in his Fig. 2 and a zero norm level is attained by 1890. (For the de facto termination point of the little Ice Age)

In addition to this, an exhaustive series of studies of temperature - solar sunspot number correlations have already been done and they are listed in the monograph Sun, Weather & Climate, by John R. Herman and Richard A. Goldberg, Dover, 1978, p. 127 - Table 3.5)

A total of eight periods are listed under column three, with their correlation coefficients, which include:

1891- 1917 (-0.44)

1870 - 1918 (-0.33)

1893 - 1924 (-0.25)

1888 - 1920 (- 0.24)

1892 - 1920 (-0.38)

1862 - 1920 (-0.33)

1867- 1923 (-0.46)

1871 - 1920 (-0.38)

Note that all entries exhibit a negative correlation coefficient, indicating an inverse relationship between sunspot number and temperature. Meanwhile for Period 2 (Column 4) the Table shows:

1925 - 1957 (- 0.1)

1921 - 1954 (+0.21)

1926 - 1954 (+0.32)

1921 - 1947 (+0.16)

1921 - 1950 (- 0.29)

1921 - 1953 (+0.24)

1924 - 1953 (+0.10)

1921 - 1950 (+0.23)

These coefficients mostly disclose positive correlation, the notable exception being the 5th entry from top. The authors note (cf. p. 128) that for the entire data set:

"the correlation coefficient for annual temperature and sunspot number (11-yr. cycle) was -0.38 up to 1920, but for the period 1921- 1950 the correlation had reversed and the coefficient was +0.23".

I maintain these results are totally consistent with the hypothesis of anthropogenic global warming. In their respective papers, Akasofu, and earlier Baliunas and Soon, argue the opposite, but they forget - or neglect to factor in - the 100 year delay time for CO2 deposition and retention in the atmosphere. Thus, inputs at the time of the onset of the industrial revolution, ca. 1845, would not manifest significantly until 100 years later.

And indeed, we see the inversion of averaged correlation coefficients from -0.38 (up to 1920) to +0.23 up to 1950, a total net change of +0.61 in the positive direction, which can take into account a total variability (explained by it) of some 36% (the total change - squared). It is clear, certainly to me, that Akasofu, Baliunas and Soon have drawn exactly the wrong conclusion from their respective results. Indeed, in the latter’s paper ( Fig. 1), showing the IPCC data and the temp. rise of 0.4C between 1910-1940, the accumulation of CO2 in the atmosphere is surely taken into account. Their conclusion that “the 'CO2' signal does not commence until 1940” is precisely what is in error.

This sort of error, neglecting time delay for signal exposure, is not unique and has been made many times by professionals who should know better.

Given this, Sofia et al's results remain generally the most credible, given they are tied to actual observed physical changes in the solar diameter.

One can only conclude from this that the conclusions of Akasofu as well as Baliunas & Soon are specious on their face, since they have no external and credible source of "natural warming" on which to pin the changes reported by the IPCC.

Akasofu's conclusion, it is also important to note, controverts the climate science position statement of the largest scientific body in the U.S. devoted to the study of climate change, the American Geophysical Union.

As that statement noted (cf. Eos, Vol. 84, No. 51, p. 574:

"Human activities are increasingly altering the Earth's climate. These effects add to natural effects present over Earth's history. Scientific evidence strongly indicates that natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century.

Human impacts on the climate system include increasing concentrations of greenhouse gases, air pollution, increasing concentrations of airborne particles and land alteration. A particular concern is that atmospheric levels of carbon dioxide may be rising faster than at any time in Earth's history, except possibly following rare events like impacts from large extraterrestrial objects