A new solar theory of climate

The current position of bodies like the IPCC and the broader climate alarmist lobby is that climate change in the industrial age is predominantly caused by anthropogenic greenhouse gases primarily CO2, with relatively small natural contributions due to solar irradiance and volcanoes.

However in the last decade a new theory, developed by Henrik Svensmark a physics professor at the Danish National Space Centre in Copenhagen, about how variations in the Sun’s magnetic activity may have very a profound impact on climate on earth has attracted growing interest in the scientific community. The theory, explained below, proposes a link between fluctuations in the sun’s magnetic activity and resulting changes in the solar wind around the earth affecting how many cosmic rays hit the earth, particularly the lower atmosphere, which in turn affect the rate of low level cloud formation which in turn drives climate variability.

It is worth noting that Svensmark work has encountered heavy resistance from the climatology community which is strongly wedded to the CO2 model of climate change. Resistance to radical new ideas in science is not new but in this case any suggestion that a mechanism other than CO2 might be driving climate change prompts particular hostility far beyond the narrow group of scientists working in the field as climatology is now a hugely politicised science and there are hundreds of thousands of political activists very strongly committed to the CO2 model for idealogical reasons and who react to any alternative scientific hypothesis to the CO2 model with intense hostility and accusations of ‘denialism’.

It is also worth noting that after finishing his initial SKY experiment Svensmark found it very hard to get his paper published, he was told it wasn’t interesting enough, an odd echo of the response to McIntyre and McKitrick’s paper critiquing mann’s Hockey Stick paper. It is also worth comparing this lack of interest and (healthy) scepticism shown to Svensmark’s paper to the almost instant adoption and non sceptical response to Mann’s paper which was proposing a radical change to the previous model of the recent climate past and the rapid take up of Mann’s paper as a campaigning tool by a very large political movement.

Over the past few decades an increasing amount of knowledge about past climate changes going a long way back in earth’s history has accumulated as well as knowledge about the composition of the atmosphere in the past including CO2 levels.

It has became clear that not only has the climate fluctuated through large scale events such as ice ages and interglacials but that within these big period events many smaller, but nevertheless significant, climate variations have occurred. Some of these smaller but significant climate changes have occurred in the historical time frame, such as the Roman Warm Period (200 B.C. to A.D. 600), the Dark Ages Cold Period (A.D. 600 to 800), The Medieval Warm Period (A.D. 800 to 1300), The Little Ice Age (1300 to 1850) and the Modern Warm Period (usually called global warming AD1850 – ?).

Generally speaking the fit between past climate variations and CO2 is not good. Al Gore made much in his film ‘An Inconvenient Truth” of the similarities between the graphs showing CO2 levels in the past and the big pulses of temperature change during the various ice ages and interglacials. What he failed to explain was that CO2 level changes lagged temperature changes by several hundred years so CO2 changes could not be the drivers of those climate change events (see Does lung cancer cause smoking?). Deep in the Earth’s history there have been periods when the planet has been gripped by a very deep ice age while at the same time the levels of CO2 in the atmosphere were 10 times higher than they are today (note that human CO2 emission have only increased CO2 by 0.3 times). Clearly something other than CO2 was driving such cold periods and even increasing CO2 by ten fold (i.e. five times what man made emissions might do in the next hundred years) had not driven up temperatures.

The graph below shows the temperature and CO2 record going back 500 million years and it is clear that the CO2 level changes do not fit the temperature changes.

There are no changes in CO2 levels that can account for the various climate changes that have occurred in the current interglacial period (which is called the Holocene – see ‘Happy Holocene‘) such as the Medieval Warm Period. The only historical climate change event that is associated with a CO2 level change is the Modern Warming Period and even within that period there was a smaller cooling event between 1940 and 1975 that cannot be explained by CO2 changes. So CO2 is a poor candidate for a prime climate driver.

It has long been acknowledged that there seemed to be a very good fit between solar magnetic activity, as evidenced by sun spot levels and the waxing and waning of solar cycles, and climate changes. The British Astronomer Royal, William Herschel, noticed a correlation between sunspots and the price of wheat in England. This marked the first observation that Earth’s climate may be affected by variations of the Sun. The well-known Little Ice Age around the 17th and 18th centuries – when sunspots all but disappeared for 70 years during the Maunder Minimum, the cosmic ray flux increased and the climate cooled – seems to be merely the latest of around a dozen similar events over the last ten thousand years. However there was no proposed mechanism which could explain how changes in the solar cycle could affect the climate to the degree suggested by the historical record as the overall level of energy emitted by the sun, and thus the solar energy hitting the earth, didn’t seem to vary that much with the solar cycles.

The graph below shows the sunspot numbers since records began. Note the Maunder Minimum which exactly coincides with the Little Ice Age, the dip in the early 19th century which also coincides with a cooling period and the very high and growing level of sunspots in the 20th century that coincides with a warming period.

Although solar radiance doesn’t vary very much with changes in the solar cycle the solar wind does vary considerably. The solar wind, the stream of particles that floods out of the sun and washes over the Earth, varies with the changes in the level of solar activity and in turn the solar wind controls how many cosmic rays hit the earths atmosphere. When the sun is active and the wind is strong then fewer cosmic rays get through into the atmosphere, and conversely when the sun is relatively inactive lots more cosmic rays manage to get through to the earth. As the Sun approaches “solar maximum” its magnetic field is at its most stressed and active state. Flares and coronal mass ejections become commonplace, as do sunspots. Sunspots are a magnetic manifestation, showing areas on the solar surface where the powerful magnetic field is up welling and interacting. It is during this period of the 11-year solar cycle that the reach of the solar magnetic field is most powerful. So powerful that galactic cosmic rays (high energy particles from supernovae etc.) will be swept from their paths by the magnetic field lines en-route to the Earth in the solar wind.

It is possible, by measuring various isotopes, to get a very good record of past cosmic rays levels going back a long time in the earths history and the fit between the rise and fall of the levels of cosmic rays and the rise and falls of global temperature seems to be ready good. There is an apparent correlation between the level of cosmic rays and climate where as there is no apparent correlation between climate and CO2 levels. Until Svensmark’s work there was not a clearly understood mechanism that could explain how cosmic rays could interact with the climate.

This graph shows the pulses of the ice age through millions of years and the historical record of cosmic ray levels – there is an apparently very good correlation.

This graph shows sunspot activity in the 20th century showing an apparent correlation beteenn sunspot activity and the rise and fall of the average global temperature.

This graph shows the relationship of cosmic rays to temperature in the 20th century. In Svensmark’s hypothesis it is the rise and fall of cosmic rays which drive climate (see below) and the fit between cosmic rays changes and temperature changes looks very impressive and much better than the fit between temperature and CO2 levels.

One way to actually see cosmic rays is to use a cloud chamber. This is so simple that almost anybody can do it and the video below shows how to construct a simple cloud chamber. What happens is that a chamber is filled with a supersaturated gas (various substances can used such as water or alcohol. etc) and as the cosmic rays pass through the chamber the particles cause the super saturated gas to condense (a process called nucleation) into a string of small droplets that beautifully track and reveal the path of the particles. The video below contains some lovely footage of such nucleation strings.

Svensmark’s breakthrough was to realise that such cosmic ray nucleation activity could affect the way and the rate at which clouds form, that incoming cosmic rays could be seeding clouds. In 1995 Svensmark conducted the SKY experiment that demonstrated that cosmic Rays could indeed be playing a significant role in the formation of clouds. Building on Svensmark’s work Jasper Kirkby a scientist at CERN has set up and is currently conducting a much larger experiment called CLOUD (Cosmics Leaving Outdoor Droplets) in an experimental facility being set up at CERN. The equipment began operations in November 2009 and should be producing results pretty rapidly, and the first comprehensive quantitative analyses are expected in 2010. There is a video of a very informative lecture by Jasper Kirkby here, it explains a great deal of the background both in terms of climate history and cosmic ray records as well as the role of clouds in climate and ends with a description of the CLOUD experiment.

Clouds are very important climate drivers and water vapour, in the form of clouds, is recognised as the most important greenhouse gas, far more important in terms of its scale of impact than CO2 (see the ‘Clouds in a Changing Climate‘ video lecture). Clouds can both increase the greenhouse effect and heat the planet (in the form of high Sirrus clouds) or decrease the greenhouse effect and cool the planet (in the form of low level clouds). Because there is no functional model of the global cloud system all the existing climate models essentially insert guesses into their calculations as to what CO2 warming will do to clouds. Mostly the models assume that CO2 warming will lead to more high clouds of the warming types and thus clouds will reinforce any CO2 warming but there is little empirical evidence about the response of clouds to small climate change (and the little evidence there is seems to point in an opposite direction – see the ‘Why the IPCC climate model is wrong‘ video).

Until Svensmark’s work clouds were treated as a phenomena that was affected by climate change (and might act to accelerate or slow down change) but they were not thought of as climate change drivers in their own right. Svensmark’s hypothesis changes that by proposing that the amount of cosmic rays hitting the lower atmosphere might drive cloud formation up and down and this completely changes the role of clouds and turns them into climate drivers. To put it simply, periods of low cosmic rays (such as during periods of high solar activity such as during the 20th century) will see fewer lower clouds and a higher temperature, periods of high cosmic rays (such as during periods of low solar activity) will see more low clouds and therefore a drop in temperature.

It is very hard to get an accurate figure for cloud cover across the earth over time but using satellite data it is possible to get a reasonable estimate. This chart shows the seemingly tight correlation between cosmic ray levels and cloud cover over a period of 25 years since 1985.

To view a full length video documentary on Svensmark’s new theory and his experimental work, which includes interviews and contributions from a number of scientists, click here.

Through pure serendipity just as Svensmark theory has focussed attention on solar activity as possibly the most important driver of climate change the sun’s solar activity has started to change very dramatically.

The solar cycle, or the solar magnetic activity cycle, is the main source of periodic solar variation driving variations in space weather. Such cycles last approximately 11 years and and we have observed data on 24 such cycles. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun.

What has happened is that the end of cycle 23 became a long drawn out affair and then cycle 24 was very, very slow to start The first sunspot of cycle 24 was spotted in January 2008 but the cycle has just never got going. What solar physicists describe as the ‘onset’ – when the new cycle blossoms eradicating all traces of the old cycle – had barely happened by December 2009, with cycle 23’s prolonged minimum still clinging on in the Sun’s southern hemisphere. Comparing the Sun’s magnetic flux ratio over several cycles indicates that deviations from the norm began to occur in the southern hemisphere five or six years ago, suggesting that the Sun’s decline has a deep-rooted explanation.

Many scientists now consider that there is strong evidence that the period of high solar activity that had prevailed throughout the 20th century may be coming to an end. This long period of high activity would, according to Svensmark’s theory, have been the driving force behind the warming of the 20th centaur. If solar activity is indeed entering a period of sharp decline then this would indicate a general cooling trend over the next couple of decades.

At the time this article was written (January 2010) Solar Cycle 24 appears to be spluttering into life, and sunspots are now at last appearing, but the geomagnetic index shows a very sharp and unprecedented fall in the sun’s magnetic activity. Remember that magnetic activity  is important in relation to Svensmark’s proposed cosmic ray- cloud mechanism because the magnetic field can effect the solar wind which in turn controls (or modulates) the amount of cosmic rays getting through to earth. The most recently realised figure for measured solar magnetic activity shows it crashing lower than it has been for 165 years.

The graph below shows the index of solar magnetic activity in the last decade.

In order to put the decline in magnetic activity into a context look at this chart of observed solar magnetic activity going back 165 years and note how the figure for December 2009 dropped off the bottom to show the lowest figure since the record began.

Meanwhile the winter of 2009, following the cold winters of 2007 and 2008, is the coldest in the Northern Hemisphere for three decades and possibly longer.