Cosmoclimatology, a better theory of climate change

Here is a link to a paper by Henrik Svensmark describing a better theory of climate change.

I find HS's theory credible.

Here are some excerpts.
--------------------------------------------
Low-level clouds cover more than a quarter of the Earth and exert a strong cooling effect at the surface. (For clouds at higher altitudes there is a complicated trade-off between cooling and warming.) The 2% change in low cloud during a solar cycle, as seen in figure 3, will vary the input of heat to the Earth's surface by an average of about 1.2 W m-2, which is not trivial. It can be compared, for example, with 1.4 W m-2attributed by the Intergovernmental Panel on Climate Change for the greenhouse effect of all of the additional carbon dioxide in the air since the Industrial Revolution (Houghton et al. 2001).

If cosmic-ray counts merely went up and down with the 11-year cycle of solar activity, there would be no trend in the climate. Systematic records of influx to the Earth's surface go back to 1937. Cosmic-ray changes before then can be seen in the rate of formation of radioactive isotopes such as beryllium-10, or inferred from the Sun's open coronal magnetic field. As seen in figure 5, the various methods agree that there was a pronounced reduction in cosmic rays in the 20th century, such that the maximal fluxes towards the end of the century were similar to the minima seen around 1900. This was in keeping with the discovery that the Sun's coronal magnetic field doubled in strength during the 20th century (Lockwood et al. 1999).

Here is prima facie evidence for suspecting that much of the warming of the world during the 20th century was due to a reduction in cosmic rays and in low-cloud cover. But distinguishing between coincidence and causal action has always been a problem in climate science. The case for anthropogenic climate change during the 20th century rests primarily on the fact that concentrations of carbon dioxide and other greenhouse gases increased and so did global temperatures. Attempts to show that certain details in the climatic record confirm the greenhouse forcing (e.g. Mitchel et al. 2001) have been less than conclusive. By contrast, the hypothesis that changes in cloudiness obedient to cosmic rays help to force climate change predicts a distinctive signal that is in fact very easily observed, as an exception that proves the rule.

Cloud tops have a high albedo and exert their cooling effect by scattering back into the cosmos much of the sunlight that could otherwise warm the surface. But the snows on the Antarctic ice sheets are dazzlingly white, with a higher albedo than the cloud tops. There, extra cloud cover warms the surface, and less cloudiness cools it. Satellite measurements show the warming effect of clouds on Antarctica, and meteorologists at far southern latitudes confirm it by observation. Greenland too has an ice sheet, but it is smaller and not so white. And while conditions in Greenland are coupled to the general climate of the northern hemisphere, Antarctica is largely isolated by vortices in the ocean and the air.

The cosmic-ray and cloud-forcing hypothesis therefore predicts that temperature changes in Antarctica should be opposite in sign to changes in temperature in the rest of the world. This is exactly what is observed, in a well-known phenomenon that some geophysicists have called the polar see-saw, but for which “the Antarctic climate anomaly” seems a better name (Svensmark 2007). To account for evidence spanning many thousands of years from drilling sites in Antarctica and Greenland, which show many episodes of climate change going in opposite directions, ad hoc hypotheses on offer involve major reorganization of ocean currents. While they might be possible explanations for low-resolution climate records, with error-bars of centuries, they cannot begin to explain the rapid operation of the Antarctic climate anomaly from decade to decade as seen in the 20th century (figure 6). Cloud forcing is by far the most economical explanation of the anomaly on all timescales. Indeed, absence of the anomaly would have been a decisive argument against cloud forcing — which introduces a much-needed element of refutability into climate science.

Figure 5 takes the climate record back 300 years, using rates of beryllium-10 production in the atmosphere as long-accepted proxies for cosmic-ray intensities. The high level at AD 1700 corresponds with the Maunder Minimum (1645–1715) when sunspots were extremely scarce and the solar magnetic field was exceptionally weak. This coincided with the coldest phase of what historians of climate call the Little Ice Age (Eddy 1976). Also plain is the Dalton Minimum of the early 19th century, another cold phase. The wobbles and the overall trend seen in figure 5, between cold 1700 and warm 2000, are just a high-resolution view of a climate-related switch between high and low cosmic-ray counts, of a kind that has occurred repeatedly in the past.

Iciness in the North Atlantic, as registered by grit dropped on the ocean floor from drifting and melting ice, is a good example of the climate data now available. Gerard Bond of Columbia University and his colleagues showed that, over the past 12 000 years, there were many icy intervals like the Little Ice Age — eight to ten, depending on how you count the wiggles in the density of ice-rafted debris. These alternated with warm phases, of which the most recent were the Medieval Warm Period (roughly AD 900–1300) and the Modern Warm Period (since 1900). A comparison with variations in carbon-14 and beryllium-10 production showed excellent matches between high cosmic rays and cold climates, and low cosmic rays and the warm intervals (Bond et al. 2001).

-----

• This article so far has summarized the evidence for the climatic role of cosmic rays, which underpins cosmoclimatology:
• Observations of variations of low cloud cover correlated with cosmic-ray variations;
• Experimental evidence for the microphysical mechanism whereby cosmic rays accelerate the production of cloud condensation nuclei;
• The Antarctic climate anomaly as a symptom of active forcing of climate by clouds;
• Quasi-periodic climate variations over thousands of years that match the variations in radionuclide production by cosmic rays;
• Calculations that remove an apparent difficulty associated with geomagnetic field variations.

From this secure base, we can broaden the horizons of space and time to consider the relevance of cosmic rays to climate change since the Earth was young. The climatic effects of the Sun's quasi-cyclical variations on millennial timescales are seen throughout the Phanerozoic (Elrick and Hinnov 2006). But more emphatic changes in climate become apparent on longer timescales when the galactic environment of the solar system changes and the variations in the cosmic-ray flux are an order of magnitude greater than those due to the Sun.

-----

Large, slow swings, to and fro between ice-free and glaciated climates, are evident in the geological record of the past 550 million years. Efforts went into using the greenhouse-warming paradigm to try to account for these changes, but the pattern was wrong. There were four alternations between hothouse and icehouse conditions during the Phanerozoic, while reconstructions of atmospheric carbon dioxide show just two major peaks (Cambrian-Devonian and Mesozoic) and troughs (Carboniferous-Permian and Cenozoic). A more persuasive explanation comes from cosmoclimatology, which attributes the icehouse episodes to four encounters with spiral arms of the Milky Way galaxy, where explosive blue stars and cosmic rays are more concentrated.

Nir Shaviv, an astrophysicist at the Hebrew University in Jerusalem, pioneered this interpretation several years ago (Shaviv 2002). The relative motion of the spiral arm pattern with respect to the solar orbit around the galactic centre was uncertain, but Shaviv found that reasonable assumptions gave a good fit with the climatic record, in cycles of ~140 million years. He found independent evidence linking the icehouse episodes with high cosmic radiation in a ~140 million-year cycle of clustering of the apparent exposure ages of iron meteorites by cosmogenic potassium isotope ratios (41K/40K). Later, Shaviv joined forces with a geologist, Jan Veizer of the Ruhr University and the University of Ottawa, to refine the analysis using a large database on tropical sea-surface temperatures, as seen in figure 8 (Shaviv and Veizer 2003). The matches between spiral-arm encounters and icehouse episodes are as follows:

• Perseus Arm: Ordovician to Silurian Periods;
• Norma Arm: Carboniferous;
• Period Scutum-Crux Arm: Jurassic to Early Cretaceous Periods;
• Sagittarius-Carina Arm: Miocene Epoch, leading almost immediately (in geological terms) to
• Orion Spur: Pliocene to Pleistocene Epochs.

The Jurassic to Early Cretaceous icehouse is a matter of special interest. Until recently, geologists considered the Mesozoic Era to have been warm throughout, so when Shaviv first saw that his analysis needed that icehouse, he was disappointed. Then he was reassured by recent reports of signs of ice-rafting, just as required. The first clear evidence for glaciers ~140 million years ago (Australia, Early Cretaceous) was published in 2003. That a story should become better as the data improve is characteristic of a successful paradigm. For the greenhouse theory of climate change, on the other hand, the Mesozoic glaciation was bad news, because carbon dioxide concentrations in the atmosphere were high at the time. The comparative mildness of the Mesozoic icehouse may have been due to the carbon dioxide (Royer et al. 2004) or perhaps to a relatively quick crossing of the Scutum-Crux Arm.