Archives for August 3, 2007

Readers may already have seen the ABC News story ‘Big brown Asian cloud blamed for glacial melting.’ This story is based on a new paper published in the weekly journal Nature, also featured in the News and Views section.

The paper, which looks at the effect of the so-called Asian brown clouds (the aerosols formed by the burning of wood and fossil fuels), is published by a group of scientists from the University of California San Diego and the Nasa Langley Research Center. Up to now, it has been recognised that aerosols can cool the Earth’s surface by scattering the Sun’s rays (global dimming), which is the explanation often used in order to try and explain the global cooling during the 1940’s to the 1970’s, despite rising levels of atmospheric CO2. Researchers now say that they also have a significant warming effect on the atmosphere, dependent on the altitude.

According to the BBC:

“We found that atmospheric brown clouds enhanced lower atmospheric solar heating by about 50%. “[The pollution] contributes as much as the recent increase in anthropogenic greenhouse gases to regional lower atmospheric warming trends,’ they suggested. ‘We propose that the combined warming trend of 0.25 Kelvin per decade may be sufficient to account for the observed retreat of the Himalayan glaciers.”

Also:

“The scientists said there remained a degree of uncertainty because, until now, estimates had largely been derived from computer models.”

Another problem for computer models on which the IPCC base there certainty about climate change.

This new paper adds to the concerns about the reported UK plan of burning more home grown wood in order to help reduce CO2 emissions.

There is also a concern that the Asian Brown Clouds are having a significant effect on the patterns of Australian rainfall via a climate ‘teleconnection.’

Professor Ramanathan concludes, “a huge proportion of the cloud comes from people burning wood and dung to cook their food, so if enough people converted to cleaner fuels, the cloud would quickly dissipate.”

Paul Biggs

‘Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature’

There’s nothing really new in this paper, which is a review partly written in response to the controversial Wag TV documentary ‘The Great Global Warming Swindle.’ Not good news from the point of view of being objective, and I doubt that it’s a coincidence that the paper has found it’s way into the same journal that published Svensmark’s cosmic ray-cloud experiment. The Royal Society are very excited too: ‘Global warming: A Proceedings A paper shows that the Sun is not a factor in recent climate change!’

The Abstract states:

“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.”

An extract from the paper says:

“…it is possible that the decline seen since 1985 marks the beginning of the end of the recent grand maximum in solar activity and the cosmogenic isotope record suggests that even if the present decline is interrupted in the near future, mean values will decline over the next century. This would reduce the solar forcing of climate, but to what extent this might counteract the effect of anthropogenic warming, if at all, is certainly not yet known.”

The paper concludes:

“There are many interesting palaeoclimate studies that suggest that solar variability had an influence on pre-industrial climate. There are also some detection–attribution studies using global climate models that suggest there was a detectable influence of solar variability in the first half of the twentieth century and that the solar radiative forcing variations were amplified by some mechanism that is, as yet, unknown. However, these findings are not relevant to any debates about modern climate change. Our results show that the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified.”

L&F are therefore supportive of a past and relatively recent solar influence on climate, with an ‘unknown’ amplification mechanism. Furthermore, they acknowledge that the ‘grand maximum’ of solar activity seems to be coming to an end, which raises the possibility of global cooling, long predicted by the likes of Fairbridge and Shirley (1987).

Let’s take a look at some of the contentious points relating to L&F and TGGWS :

1. Solar cycle length v temperature

The use of the 1991 Friis-Christensen and Lassen graph of solar cycle length plotted against mean surface temperature attracted much criticism because the correlation diverged after the paper was published. The graph was lifted directly from F-C & L in order to demonstrate a solar link to climate.

The sunspot cycle length data finishes after 1980 – at least 1985 – the graph just looks like it finished in 1980 because the dots are plotted in the centre of the cycle.

Additionally, cosmic ray data goes back to the 1950’s, so Lockwood is the one ignoring data that doesn’t suit him by starting the graphs at 1975 which we know was a turning point in temperature.

2. Smoothing and sunspot cycle length

When Lockwood smoothes his graph to expose the long-term trends, he basically averages the readings over the length of one sunspot cycle. Like F-C & L, he plots the result in the MIDDLE of the data range. So each point on his graph is a combination of the previous 5 years’ data with the 5 years in the FUTURE. This is the same as the FC& L graph, but Lockwood uses it to make it look like the solar activity started to fall away long before it actually did.

3. The data itself

There are several different sets of data used:

a. Total solar irradiance TSI – amount of energy arriving from sun – correlated with sunspot cycle.

(There has been some debate about the preference for Frohlich’s own PMOD data set over the ACRIM data, and the adjustment to the Lean TSI reconstruction data 2 months before the publication of the L & F paper, but I don’t intend to dwell on that here!)

b. Number of sunspots observed – averaged over a month

c Length of sunspot cycle (varies 9-11.5 years)

d Direct measurements of cosmic rays – cosmic rays are lower when sunspots higher because the solar magnetic field blocks them.

(N.B. The Berrylium10 proxy for cosmic ray flux is formed by 1 GeV cosmic rays, whereas it is 10 GeV cosmic rays that are of interest and responsible for atmospheric ionisation. Ion chambers are sensitive to very high cosmic ray energies of 10’s of GeV.)

Comparing Lockwood’s paper with Lassen’s, the main difference is that Lassen’s stops in the late 1980s whereas Lockwood’s includes one more sunspot cycle peaking in 2001.

The sunspot cycle peaks grow higher through the 1970, 1980 and 1990 peaks, which are all very large in the context of the last 150 years, and 2001 is considerably lower.

Equally, the minima in cosmic ray flux (measured at the edge of space by Lockwood) get deeper up to 1990, but the 2001 one is shallower again – about the same as 1980.

So any divergence between the solar record and the temperature record only begins in the last ten years or so, even failing to allow for the “middle of cycle plot” – not in the last 20 like Lockwood says.

L & F says that “Earth’s surface air temperature does not respond to the (11 year) solar cycle…..(due to)…long thermal time constants associated with……the oceans”

In other words, 10 years is far too short a time to show any effect from long-term solar changes. Interestingly, the temperature graph seems to level off around 2003 – as you would expect if there were a lag.

However, a new GRL paper by Camp and Tung, published 18th July 2007, claims that: “By projecting surface temperature data (1959–2004) onto the spatial structure obtained objectively from the composite mean difference between solar max and solar min years, we obtain a global warming signal of almost 0.2°K attributable to the 11-year solar cycle. The statistical significance of such a globally coherent solar response at the surface is established for the first time.”

Summary:

The ‘science’ is far from ‘settled.’

Solar activity is higher than it has been for at least 1000 years.

IPCC AR4 rates the ‘level of scientific understanding’ of ‘solar irradiance’ as ‘low,’ other solar factors have a LOSU of ‘very low.’ The emphasis is always on irradiance rather than eruptivity, which I believe is much more important.

Small solar changes seem to have a much larger influence on climate than expected, suggesting an unknown amplification mechanism.

Global mean surface temperatures have levelled off since the 1998 El Nino, and there has been little or no ocean warming for the past 5 years according to the ARGO network.

Solar cycle length, sunspots, irradiance, are general indicators of solar activity. Nir Shaviv sees no reason why the length of the solar cycle should be related to solar activity – it could be a coincidence, and it is largely a phenomenon of the Northern Hemisphere. That said, the correlation between solar cycle length and a long mean surface temperature series has also been observed at Armagh Observatory in Northern Ireland.

There is also an interesting paper from 2005, by Hengyi Weng entitled ‘The influence of the 11 yr solar cycle on the interannual-centennial climate variability.’ There is also a summary here entitled ‘Influence of the 11-year solar cycle more significant than previously thought.’

The full paper is here:

http://tinyurl.com/94dtf

Any hypothesis involving correlations between 2 variables out of many is likely to diverge at some point. The attempted 20th century correlation of CO2 and temperature diverged from the 1940’s to 1970’s, yet the hypothesis wasn’t abandoned. Instead cooling due to sulphate aerosols was touted as an explanation. A cue for another blog post perhaps!

Paul Biggs