Thursday, June 30, 2011

A new solar minimum ahead ?

Some news are trickling down to the mainstream media about the current unusual solar minimum and about the consequences it may have for the climate. This purported grand solar minimum, if it finally materializes, is however even more intriguing.

The Total Solar Irradiance (TSI) is the mean energy of the sun that reaches the higher atmospheric layers at position of the Earth in its orbit around the sun, and amounts presently to about 1370 Watts per squared meter annually average. his energy is then distributed among all components of the climate, atmosphere, oceans, cryosphere. About one third of the solar irradiance is reflected back to space by clouds, ice, and the surface of the ocean and continents. The solar energy is absorbed mostly by the surface and used to evaporate water and to be re-radiated upwards in form of infra-red radiation. The source of almost all the energy in the climate system is therefore provided by the sun. There is no doubt that variations in TSI can therefore affect the climate, the question is how large is this influence relative to the factors that also drive the climate. I would not shock anyone by saying that exactly this question is the most hotly debated between climate warmist and climate skeptics (nothing slighting here - you can also think in terms of FC Barcelona and Real Madrid FC if it sounds better).

The TSI varies over many timescales, from the vary rapid variations of minutes to the very low-frequency variations over millennia. The most known cycles are however those that rather match our life timescales: the 11-year sun-spots cycles and the Reydberg cycle of about 80 years. There are however many other {\it quasicycles}. In an interesting talk at the last General Assembly of the European geophysical Union, Jürg Beer presented an empirical scheme to predict the sun activity in the next 100 years based on a decomposition in terms of osculations of different frequencies of the reconstructed solar activity over the last 10 thousand years. He predicted that this century would be one of the periods with the weakest solar activity of the Holocene, although he could not precisely quantify his assertion in terms of watts per m2. >How lartge could the influence of a new ganrd solar minimum on Earth's temperatures. Some recent papers have tried to provide some estimations, e.g. here with the help of climate models. These estimations hinge of course on the sensitivity of a particular model to external perturbations and on the assumed reduction of the solar activity. Form a more empirical point of view, it turns out that the study of the Late Maunder Minimum around 1700, one of the most recent periods with an unusually low solar activity, could provide an analogue for the effect on Earth's temperatures. Now we see why an accurate, reliable reconstruction of the temperatures of the past centuries can provide very useful hints about future climate. If the temperatures in the LMM were only slightly subdued relative to, say the beginning of the 20th century as the hockey stick reconstruction implies, then conventional wisdom would conclude that the anthropogenic greenhouse effect will dominate regardless of what the sun does in the next decades. If, on the other hand, the LMM temperatures were clearly lower, say about 1 degree C or lower, for instance the reconstruction by Christiansen and Ljungqvist , then the future decades may look considerably different from climate model predictions, although with longer time horizons the unabated greenhouse gas forcing would finally prevail. The economic planning for coastal defenses, infrastructure, etc, has a however a life time of a few decades.

This is one of the reasons why I think that the Late Maunder Minimum is a much more interesting and policy relevant than the Medieval Warm Period. For some reason, the debate is much often framed around the Medieval Warm Period, and sometimes it seems that some participants would like to slug it out over a few tenths of a degree difference between the present temperatures and those in the MWP.

As a curious note, over the past millennium periods of low solar activity like the Late Maunder Minimum and the Dalton Minimum (around 1820), were accompanied by increased volcanism. This coincidence is one of the reasons why it has so far been difficult to disentangle the effect of solar and volcanic forcing on climate, even more so since the uncertainties in the estimation of both forcing in the past are still large. I am not aware of a robust physical mechanism that would link both solar activity and volcanism, although I am sure that one could found in the blogosphere all sorts of solar conspiracy theories to explain it. However, .. isn't volcanism increasing as of recent ?


Anonymous said...

"you can also think in terms of FC Barcelona and Real Madrid FC if it sounds better"

Was?? Ich dachte, wer einen grossen Einfluss der Sonne auf unser Klima postuliert, sei ein böser Verschwörungstheoretiker, der zuviel im Internet surft und auf die hinerhältige Propaganda der amerikanischen Rechtskonservativen und Ölmultis reinfällt! Die wahren und aufrechten Wissenschafter, die nur der Wahrheit verpflichtet sind, haben diesen Einfluss längst widerlegt (mit wasserdichten Beweisen) und sind sich in dieser Sache komplett einig.
Das ist eher ein Match zwischen Real Madrid und der Hobbykicker-Mannschaft FC Hinterpfupfigen.

Anonymous said...

Eduardo, you might like this, speculative, but close to your point ;-)

Oort, Abraham H., 1989: Angular Momentum Cycle in the Atmosphere-Ocean-Solid Earth System. Bull. Amer. Meteor. Soc., 70, 1231–1242.
doi: 10.1175/1520-0477(1989)070<1231:AMCITA>2.0.CO;2


eduardo said...

'Was?? Ich dachte, wer einen grossen Einfluss der Sonne auf unser Klima postuliert, sei ein böser Verschwörungstheoretiker'

Der Teufel steckt im Detail. Was ein Verschwörungstheoretiker meinen würde wäre, dass die Sonne jetzt, als im 20. Jahrhundert einen großen Einfluss auf das mittlere Klima gehabt hat. Das würde das IPCC bestreiten, weil im 20. Faktoren sich stärker ausgewirkt haben. In der Vergangenheit waren diese anderen Faktoren nicht da, kann also die Sonne ruhig Herr des Klimas werden. Was ich in meinem Post meinte ist, dass eventuell ist diese Argumentation nicht ganz abgesichert ist, insbesondere für die nächsten Dekaden, sollte die Sonne sich wirklich abschwächen wie vor ca 300 Jahren.

VickyS said...

Eduardo, some research done during the ADVICE project in the 1990s suggested that the circulation during the LMM was more meridional, with more negative values of NAO proxies, and also more variabilty in NAO proxies.  This also led to what seem to be more extreme swings in temperature and precipitation from one season to the next, which makes sense with blocking highs, cut-off lows, and adjacent areas of more northerly or southerly winds than normal across the hemisphere.  Of course the data are sparse, from historical records in only a few locations. The extreme events of the past few years (snowy and cold European winters, the floods in Pakistan, the increased precipitation and flooding across parts of North America) might also be related to the more meridional circulation of recent times, compared to the highly zonal flow of the 1990s.  As you say, the LMM looks more and more interesting!