What Causes Climate Change? The Sun, the Solar System, and the Galaxy

by Benjamin Deniston

Aug. 3, 2015—Where historical and geological records of CO₂ changes fail to correspond with temperature changes, shifts in the activity of the Sun, the characteristics of the Solar System, and the Sun's position within the Galaxy do match climate and related changes quite well. This can be clearly seen on a series of different timescales.

On the timescale of the past century, variations in Solar activity match changes in the Earth's temperature (which clearly deviate from the trends in CO₂ emissions). This has been shown with measurements of average US temperature, average Arctic temperature, and average global temperature, compared with changes in solar activity. From around 1900 the temperature increased until about the middle of the century – when CO₂ emissions were relatively low, but solar activity was on the rise. From about the 1940s to the mid-1970s, temperature held flat, or even declined – matching the easing of solar activity, but not matching the accelerated increase in CO₂ emissions. The warming from the mid-1970s to the end of the century matches both the increase in solar activity and the increase in CO₂ emissions, but since the turn of the century solar activity has leveled off and temperature has leveled off with it (while CO₂ emissions continue to accelerate)(Figure 1).

While it has been argued that the measured changes in the amount of sunlight reaching the Earth are too small to account for the observed global climate change, a new body of research is showing that there is an additional process which amplifies the effect of the Sun on the Earth’s climate: the Sun’s role in affecting the flux of galactic cosmic radiation, which plays a critical role in cloud formation (and, therefore, climate). Galactic cosmic radiation is composed of atomic particles (mostly protons and helium nuclei, with a few nuclei of heavier elements as well) traveling at extremely high speeds throughout the galaxy. Because they are charged, the Sun’s magnetic field acts to change their paths, thereby regulating the amount of high energy galactic cosmic radiation reaching the Earth’s atmosphere – a stronger Sun means the Earth receives less galactic cosmic radiation, and a weaker Sun means the Earth receives more.

In 1997 Danish scientists Henrik Svensmark and Eigil Friis-Christensen showed that the density of low-level cloud cover appeared to change in response to variations in the flux of galactic cosmic radiation. Since then they continued to develop evidence to support their new theory, showing in laboratory experiments that galactic cosmic radiation affects the processes which lead to cloud formation,[fn_1] and identifying additional responses of the Earth’s climate system to changes in the cosmic radiation flux. In a 2007 study Svensmark and Friis-Christensen showed that the global average temperature of the atmosphere rose and fell in lock step with changes in the flux of galactic cosmic radiation. In a 2009 study Svensmark and colleagues showed that the number of low level clouds, the water content in clouds, and the number of cloud forming aerosols all decreased in the days following sudden drops in galactic cosmic radiation (caused by explosive outbursts of solar magnetic activity) (Figure 2).

These studies all show that cosmic radiation plays a critical role in processes of cloud formation and thereby acts as a critical factor in determining the Earth’s climate, because clouds regulate the amount of sunlight reaching the Earth’s surface. A more active Sun not only puts out more light, but it also blocks more cosmic radiation, meaning fewer clouds and more sunlight reaching the Earth’s surface. Svensmark and colleagues have shown that just a few percent change in low level cloud cover (attributable to change in the flux of galactic cosmic radiation) could account for half of the warming in the past century.

This relatively new body of work indicates that much of the climate change over the past century has been largely driven by natural activity, meaning any effect human CO₂ emissions have had is relatively negligible, and future human CO₂ emissions are not something to worry about. This conclusion is supported by a recent study from a group in Germany which looked for cycles in temperature records covering the last few hundred years. In their own analysis they clearly identified the presence of two already known cycles, an approximately 200 year cycle in solar activity (known as the “Suess cycle” or “de Vries cycle”) and an approximately 65 year cycle in Atlantic ocean temperatures (known as the “Atlantic Multidecadal Oscillation”). When they examined the interaction of these two natural cycles they found that just these two cycles alone accounted for most of the climate change over the past centuries, including the recent warming trends – again, indicating that there is little evidence CO₂ has an effect worth worrying about.[fn_2] (Figure 3).

With this in mind, let’s look a bit further back in time. If we examine records of climate over the past few thousand years we again see that climate changes match records of variations in galactic cosmic ray flux (and not changes in CO₂). Multiple records of climate over the past thousand years indicate lower temperatures from the 1500s to the 1800s, corresponding to a period of lower solar activity and increased galactic cosmic rays. Additionally, during this time we see periods of increased glaciation in the Andes Mountains, matching periodic increases in galactic cosmic ray flux quite well. Prior to this, from around the 900s to the 1200s the temperature was warmer (the Medieval Warm Period), galactic cosmic ray flux was less, and glaciation in the Andes was less (see Figure 4).

Looking at the past two thousand years, temperature records from the Alps follow changes in galactic cosmic rays very well – while, again, changes in CO₂ levels don’t match the temperature records, changing in the opposite directions for hundreds of years (see Figure 5).[fn_3]

These records from the past one and two thousand years confirm the picture developed from examining the past 100 years, that changes in the flux of galactic cosmic radiation (regulated by solar activity) govern changes in the climate, not CO₂.

Stepping back even further in time, we see more evidence of galactic cosmic radiation being a driving factor in climate change. An examination of the galactic cosmic radiation flux over the entirety of the current interglacial period (the Holocene epoch, lasting from 12,000 years ago to the present) shows a very strong relation to records of variations in glaciation and ice flow in the Northern Atlantic Ocean.[fn_4] Additionally, shifting to a slightly finer resolution, records of variations in long-term trends in precipitation in the Arabian Peninsula, measured from 6,200 years ago to 9,600 years ago, show a very strong relationship to variations in galactic cosmic radiation flux.[fn_5] Figure 6

Taken together, we have evidence that critical factors in the Earth’s climate system respond to changes in galactic cosmic radiation on timescales of days, years, decades, centuries, and millennia – demonstrated in independent studies.

Shifting to longer timescales, the cycles of transition between ice ages and shorter interglacial periods are closely associated with changes in the Earth’s orbit around the Sun and with changes in the tilt and orientation of the Earth’s spin axis – together known as the Milankovitch Cycles. For the past one million years ice age cycles have had the strongest correlation with changes in the eccentricity of the Earth’s orbit around the Sun. For the two million years prior (from three to one million years ago) the Earth’s climate changes best correlated with changes in the tilt of the Earth’s axis. Figure 7

Taking one more step to larger timescales, even larger climate changes over tens and hundreds of millions of years correspond with the motion of our Solar System through the galaxy – likely due to larger changes in galactic cosmic radiation flux. While changes in the strength of the Sun’s magnetic field modulate the amount of galactic cosmic radiation on the order of ten percent, in different regions of the galaxy the Solar System (and the Earth therein) can experience much larger fluctuations in galactic cosmic radiation – bringing changes on the order of one hundred percent. In accordance with the work of Svensmark and his associates, this larger variation in cosmic radiation flux over geological timescales should drive large-scale climate variations. This is exactly is what the records show.

Over the past 540 million years (the Phanerozoic eon) the Earth’s climate has shifted back and forth four times between two general climate modes, icehouse and hothouse. During the hothouse modes there are no continental glaciers on Earth and temperatures are significantly higher. During the icehouse modes the climate is colder and glaciers develop and expand. We are currently in an icehouse mode, with the ice sheet over Antarctica starting to form around 34 million years ago, and the Arctic ice sheets forming only two million years ago.

In 2000 scientist Ján Veizer and his associates showed that the four hothouse-icehouse transitions over the past half billion years do not correspond with changes in CO₂ levels, and in 2003 Veizer together with Nir Shaviv showed that these climate transitions do correspond with the periods of the Solar System’s passage through our Galaxy’s spiral arms. This is consistent with Svensmark’s work, since the Galaxy’s spiral arms are expected to have significantly higher concentrations of galactic cosmic radiation, and we see that the Earth’s four most recent icehouse modes correspond with the times when the Solar System is thought to have been traveling through a spiral arm. Shaviv was also able to provide additional evidence by examining iron meteorites, which showed records of having been exposed to higher galactic cosmic radiation levels at times when the Solar System is believed to have been traveling through the spiral arms (recorded when the meteorites were still orbiting though interplanetary space as part of an asteroid).[fn_6]

Together, records of higher galactic cosmic radiation flux recorded in iron meteorites, correspond with the time when we think the Solar System has been passing through the Galaxy’s spiral arms (where we’d expect more cosmic radiation), which both correspond with the recent icehouse periods on Earth – all consistent with the work of Svensmark and associates on the relation between cosmic radiation and climate through cloud formation. Shaviv and Veizer showed that this could account for most of the large scale temperature changes over the past half billion years (whereas CO₂ was shown to have little effect, if any).

More recently, Shaviv has also shown that records of ocean temperature exhibit a 30 million year periodicity, corresponding to the bobbing motion of our Solar System above and below the plane of our Galaxy. When the Solar System is either above or below the galactic plane the galactic cosmic radiation flux is expected to be less, and ocean records show relatively warmer temperatures (as would be expected from Svensmark’s hypothesis); when the Solar System is passing through the galactic plane, galactic cosmic radiation flux is thought to be higher, and ocean records show relatively cooler temperatures (as would be expected from Svensmark’s hypothesis). Figure 8

Taken together, a growing body of evidence indicates that galactic cosmic radiation plays a major role in affecting climate change (by controlling critical aspects of cloud formation). On shorter timescales of days, to decades, to centuries, to thousands of years, changes in the strength of the Sun’s magnetic field regulate the flux of galactic cosmic rays reaching the Earth; and on much longer timescales, tens to hundreds of millions of years, different galactic environments experienced by our Solar System have much larger variations in the density of galactic cosmic radiation. For time periods in between, the most important factor appears to be related to changes in the Earth’s orbit and spin axis. Climate change (across all these timescales) is driven by cosmic processes – solar, orbital, and galactic changes – not CO₂.

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