Are we headed for a new solar minimum?


by Judith Curry

We can conclude that the evidence provided is sufficient to justify a complete updating and reviewing of present climate models to better consider these detected natural recurrences and lags in solar processes. – Jorge Sánchez-Sesma

In pondering how the climate of the 21st century will play out, solar variability has generally been dismissed as an important factor by the proponents of AGW. However, I think that it is important that scenarios of future solar variability and their potential impacts on climate should by considered in scenarios of future climate change.

I have been cursorily following the literature on this topic. I have recently been in communication with Jorge Sanchez-Sesma. He has new paper that was just accepted for publication in Earth System Dynamics, an interactive open-access journal published by the EGU. I am featuring this paper in a post since it provides important new analysis and insights on this topic, and also provides a useful assessment of the literature and current state of knowledge on this topic.

The significance of this paper is reflected in the EG

U metrics link  that indicates that this paper has been downloaded 1531 times so far (before it has been formally published).

For full text of the Curry post, see here:

JC reflections

This is a remarkable paper in many ways. This paper has a single author — Jorge Sanchez-Sesma, who is a climatologist (not a solar physicist). I have been in contact with Jorge and will be posting an interview with him in several weeks. He has a remarkable story to tell.

This paper indicates that the case is increasingly compelling for millennial-scale variations in solar activity. The arguments for a forthcoming Grand Solar Minimum are also increasingly compelling.

To what extent a Grand Solar Minimum will influence

the Earth’s climate remains uncertain.   As discussed on a previous blog post IPCC: solar variations don’t matter, the IPCC AR5 Ch 8 stated:

Nevertheless, even if there is such decrease in the solar activity, there is a high confidence that the TSI RF variations will be much smaller in magnitude than the projected increased forcing due to GHG.

The previous post also describes different perspectives on this from Svensmark and a 2013 NRC report (see also Effects of solar variability on climate; 21st century solar cooling.)

Solar indirect effects on climate remain at the knowledge frontier, and ar

e associated with substantial uncertainty and ignorance. This uncertainty and ignorance is not a rationale for ignoring solar effects on the 21st century climate (and 22nd, 23rd centuries). And anyways, is the solar uncertainty (we understand the sign) really so much more greater than that associated with the effects of clouds on climate (see my recent post The cloud climate conundrum), where even the sign of the feedback is uncertain and the magnitude of cloud forcing swamps greenhouse gas radiative forcings.

But we are starting to see some ideas emerge as to how these solar effects and processes could be included in climate models. Independently of climate models, the statistical forecast technique used by Sanchez-Sesma provides the basis for creating alternative scenarios of the 21st century climate. I find his arguments about lags to be particularly important as we sort out the solar-climate effects.

Tackling the variability of solar activity and solar indirect effects seems more tractable than the cloud-climate problem and untangling the myriad of scales of ocean oscillations, so I would hope to see much more emphasis put on unraveling the solar-climate connections.

The policy significance of this issue is clear:  if we are headed to a

mid-20th century solar minimum, or a Grand Solar Minimum for the next two centuries, this will offset greenhouse warming to some extent.  The extent of the offset depends on whether climate sensitivity to CO2 is on the larger or smaller end of the range of estimates, and the magnitude of the solar impact.  But the sign of the solar offset is becoming increasingly clear: towards cooling.

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