March 30, 2019
Yes, solar variability does indeed affect the Earth's climate.
Stergios Misios, a postdoctoral researcher at the University of Oxford, said, "We deal with a very short record of observations in the tropical Pacific, and we must be very careful with how we filter out other interannual fluctuations. After a careful treatment of the data covering the last 60 years, we detected a robust slowdown of the Walker cell during years associated with solar-cycle maxima." The analysis shows that in tandem with changes in the wind anomalies, the dominant patterns of tropical precipitation shift to the central Pacific during solar-cycle maxima. As a result, rainfall decreases over Indonesia and in the western Pacific, and increases over the central Pacific Ocean.
How could miniscule changes in incoming solar radiation produce significant climate signatures?
"Soon enough, we realized that the magnitude of the wind anomalies that we detected in observations simply could not be explained by radiative considerations alone. We thought that if it comes from the sun, there must be another mechanism that amplifies the weakening of the Walker circulation," said Prof. Lesley Gray of University of Oxford. With the aid of a global climate model, this mechanism was found in the dynamical coupling between the atmosphere and ocean circulation in the tropical Pacific.
Averaged over the globe, the surface temperature imprint of the solar cycle barely reaches 0.1 K in a solar maximum—almost eight times weaker than the global warming trends observed in the 20th century. Yet, even such a weak surface warming influences the Walker circulation through changes in global hydrology. As the surface warms, water vapor in the atmosphere increases at a higher rate than is lost by precipitation, necessitating a weakening of the Walker cell. This is a well-tested mechanism in model simulations of increased CO2 concentrations but it turns out that is operating under the 11-year solar cycle, too.
S. Misios said, "Our model showed westerly wind anomalies in the Pacific region even when we considered only changes in global hydrology, but the magnitude was far too weak. We hypothesized that atmosphere-ocean coupling, essentially the Bjerknes feedback, can amplify the solar signal."
Our understanding of water vapor and it's effect on climate is still in the horse-and-buggy stage. This clearly illustrates that fact.
Oh, and by the way, we just learned that the sun's magnetic field is ten times stronger than previously believed.
Taken separately these two stories may not seem to amount to much, but together they make a powerful statement about how much we don't know and how these things work together to influence the Earth's climate.
A number of years ago, reading an article that had something or other to do with science, I was struck with a remark the author, a prominent scientist, made, which was (I'm quoting loosely because this was, as I said, many years ago) to the effect that "Anytime we write about science, we ought to always preface anything we say with 'at our current stage of ignorance.'" It's a great shame that today's crop of "climate modelers" don't have that kind of humility.
Posted by: Dana Mathewson at March 30, 2019 01:40 PM (rIYC+)
Science is an ever-evolving thing, not "settled".
Posted by: Timothy Birdnow at March 31, 2019 11:13 AM (1eXJd)
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