There is a lot of debate about the sun’s role in global warming and climate change. Some scientists argue that the sun plays the dominant role, making human activity insignificant.
Much of this argument is based on statistical analysis of very long proxy records. One can see a very good example of this thinking, as well as the debate surrounding it, in a recent article on Judith Curry’s Outstanding “Climate, Etc.” science blog.
The article is titled “Nature Unbound VI Centennial to millennial solar cycles.” In keeping with blog practice, the author is simply Javier. (Who the author is, is generally considered irrelevant.) As the “VI” indicates, this is the sixth in a series of detailed reviews of important aspects of natural variability, all written by Javier.
Curry’s blog is a great place where climate science gets discussed and debated in detail, with all sides well represented. Many of the articles are long and somewhat technical. In fact Climate Etc. is often very much like a scientific journal. The extensive comments are what is called post publication peer review in the journal world.
There are over 850,000 comments to date, many quite technical. This blog may be the best place in the world to see the climate science debate in action. Its educational value is unparalleled.
Most of these articles are what would be called review articles in a journal. Many journals publish review articles and some publish nothing else. These articles attempt to summarize a specific body of research. In this case we have a review of some of the numerous correlations that have been found between very long term climate change and changes in solar activity.
The article is quite long and somewhat technical in places. The starting summary gives the flavor of the piece:
“Summary: Holocene climate has been affected in different periods by several centennial to millennial solar cycles. The ~1000-year Eddy solar cycle seems to have dominated Holocene climate variability between 11,500-4,000 years BP, and in the last two millennia, where it defines the Roman, Medieval, and Modern warm periods. The ~208-year de Vries solar cycle displays strong modulation by the ~2400-year Bray solar cycle, both in its cosmogenic isotope signature and in its climatic effects. The Centennial, and Pentadecadal solar cycles are observable in the last 400-year sunspot record, and they are responsible for the present extended solar minimum that started in 2008.”
The basic problem with the sun-climate connection is our lack of understanding of how it works, even while the evidence for it is quite strong. Javier puts this nicely in the introduction, as follows:
“The study of solar cycles and their climatic effect is hampered by a very short observational record (~400 years), an inadequate understanding of the physical causes that might produce centennial to millennial changes in solar activity, and an inadequate knowledge of how such changes produce their climatic effect. Despite this lack of a solid theoretical framework, paleoclimatologists keep publishing article after article where they report correlations between solar proxy periodicities and climate proxy periodicities, and the observational evidence is now so abundant as to obviate the lack of a theory or well defined mechanism.”
The US Global Change Research Program spends well over $2 billion a year on so-called climate research, but almost none of that is on trying to understand the hugely important sun-climate connection. Instead, the research program assumes that climate change is due to human activity, so it is focused on things like the carbon cycle. This questionable assumption stands out in the USGCRP’s highly alarmist “Climate Science Special Report.”
If the assumption of human causation is false, which seems likely, then the science is misdirected and the money wasted. It is time for the multi-billion dollar USGCRP to focus on understanding the sun-climate connection. We need to see the sun in climate change.