Research published in an astronomy journal suggests that high solar output seen in the second half of the last century was a once in 3,000 year event.
This astronomical finding based on a careful analysis of sunspot activity has clear implications for climate science as the so called “grand maximum” in solar output identified by the researchers and observed between 1950 and 2009 co-incided with the rapid warming of global surface temperatures seen during the second half of the 20th century.
The international team of space scientists from Finland, France, Switzerland and Russia who authored the paper, “Evidence for distinct modes of solar activity” which appeared in the journal Astronomy & Astrophysics, do not explicitly link their results to climate science.
They state that the sun has several modes of activity and oscillates between periods of higher and lower output. “The distribution of solar activity is clearly bi-modal, implying the existence of distinct modes of activity. The main regular activity mode corresponds to moderate activity that varies in a relatively narrow band between sunspot numbers ≈ 20 and 67. The existence of a separate Grand minimum mode with reduced solar activity, which cannot be explained by random fluctuations of the regular mode, is confirmed at a high confidence level,” they state.
There is an indication that the Grand maximum seen between 1950 and 2009 also corresponds to a separate mode of activity, they state, “but the low statistics does not allow us to firmly conclude on this, yet”. The low statistics they refer to are because the solar output seen during this period was only observed once during the 3,000 or so years covered by the study.
The research was based on analysis of carbon-14 and magnetic evidence contained in sediments and rocks to reconstruct solar activity over a 3,000 year period.
The implications of this result are controversial as they appear to fly in the face of evidence presented by the Intergovernmental Panel on Climate Change (IPCC) and accepted by many climate scientists that increases in atmospheric carbon dioxide (CO2) have been the main factor driving up global temperatures in the industrial age and that the sun has played a minor role.
This finding that the period of most intense global warming has coincided with an unprecedented peak in recorded solar output will add pressure onto the IPCC to look again at the interconnection between the sun and the climate.
This is not the first paper this year to potentially finger the sun as an agent in recent global warming. Earlier this year reportingclimatescience.com reported on research from China published in a peer reviewed Chinese language journal that claimed that there is a strong correlation between solar output and the warming of the Earth. The paper implied that the climate models used by the IPCC may have “underestimated” the impact of natural factors on climate change.
The study claimed to demonstrate the existence of significant resonance cycles and high correlations between solar activity and the Earth’s averaged surface temperature during centuries, according to an accompanying press release. The press release also claims that a peer reviewer of this paper stated “this work provides a possible explanation for the global warming”.
The press release stated: “climate models of IPCC seem to underestimate the impact of natural factors on the climate change, while overstate that of human activities”. It added that the study “implies that the “modern maximum” of solar activity agrees well with the recent global warming of the Earth. A significant correlation between them can be found”.
This key finding of the Chinese research that there has been a recent peak in solar activity is consistent with the key finding of the Astronomy & Astrophysics paper.
Aims. The Sun shows strong variability in its magnetic activity, from Grand minima to Grand maxima, but the nature of the variability is not fully understood, mostly because of the insufficient length of the directly observed solar activity records and of uncertainties related to long-term reconstructions. Here we present a new adjustment-free reconstruction of solar activity over three millennia and study its different modes.
Methods. We present a new adjustment-free, physical reconstruction of solar activity over the past three millennia, using the latest verified carbon cycle, 14C production, and archeomagnetic field models. This great improvement allowed us to study different modes of solar activity at an unprecedented level of details.
Results. The distribution of solar activity is clearly bi-modal, implying the existence of distinct modes of activity. The main regular activity mode corresponds to moderate activity that varies in a relatively narrow band between sunspot numbers 20 and 67. The existence of a separate Grand minimum mode with reduced solar activity, which cannot be explained by random fluctuations of the regular mode, is confirmed at a high confidence level. The possible existence of a separate Grand maximum mode is also suggested, but the statistics is too low to reach a confident conclusion.
Conclusions. The Sun is shown to operate in distinct modes – a main general mode, a Grand minimum mode corresponding to an inactive Sun, and a possible Grand maximum mode corresponding to an unusually active Sun. These results provide important constraints for both dynamo models of Sun-like stars and investigations of possible solar influence on Earth’s climate.