OK, I’m going to talk about global cooling: cue, derisive laughter from Climate Scepticism’s troll-like AGW-convinced readers. I’m also – wait for it – going to talk specifically about global cooling due to a Maunder Minimum type decline in solar activity: cue almost insane high-pitched babbling from the ‘it’s not the sun, stupid’ ranks of the ‘Believers in the Pre-Eminence of His/Her Radiatively Forced Royal Highness, the One, the Magnificent, the All-Powerful, CO2’ (aka the Scientifically Naive, aka the Climatologically Challenged).
AGW alarmists have been pooh-poohing the idea of global cooling for years now, scoffing at the various hit and miss predictions and projections which have appeared on sceptic blogs throughout the years, gleefully declaring that warming is still happening in spite of declining solar activity, therefore solar variability must have very little influence on the climate and the actual variation in Total Solar Irradiance is so miniscule that the radiative forcing from solar variability is tiny in comparison to that from CO2, blah, blah, blah. That stance is becoming ever more difficult to justify. Firstly, they were wrong about the former – mechanisms have been identified whereby solar variability can significantly affect the climate – and if it turns out that they are wrong about the latter and climate sensitivity due to CO2 is on the low side, as recent observational estimates suggest, whilst at the same time, the influence of a significant decline in solar activity has been underestimated, then society may have a problem.
Meehl et al, 2013, estimated the reduction in global warming which would be caused by an upcoming grand solar minimum (GSM) to be “several tenths of a degree Celsius” between 2020 and 2070. For this they used a climate model with a high climate sensitivity of 3.2C – which is the CMIP5 multi-model mean. They concluded that the modest cooling would not reverse the warming trend, just slow it down somewhat, and by 2070, we’d be back on track for full-on Thermageddon. Other studies have shown similar. What seems highly unlikely is that Meehl et al accounted for large uncertainties in multi-decadal internal (ocean) variability forcing – expected to exert a cooling influence in the coming decades. Also, whilst their estimate assumes strong near-future GHG warming, it also fails to adequately quantify the extreme decline in solar UV which is expected during a GSM, as we shall see.
A new study has been published which looks at the expected decrease in UV solar output resulting from the sun proceeding into a grand solar minimum. Media reports (plus here) and one of the authors of the study basically confirm that, even though it will cool the earth, it will still be no big deal, quoting Meehl et al above, saying what the authors of that earlier study said, that global warming will soon outpace any modest global cooling.
A team of scientists led by research physicist Dan Lubin at Scripps Institution of Oceanography at the University of California San Diego has created for the first time an estimate of how much dimmer the Sun should be when the next minimum takes place.
Lubin and other scientists predict a significant probability of a near-future grand minimum because the downward sunspot pattern in recent solar cycles resembles the run-ups to past grand minimum events.
Despite how much the Maunder Minimum might have affected Earth the last time, Lubin said that an upcoming event would not stop the current trend of planetary warming but might slow it somewhat. The cooling effect of a grand minimum is only a fraction of the warming effect caused by the increasing concentration of carbon dioxide in the atmosphere. After hundreds of thousands of years of CO2 levels never exceeding 300 parts per million in air, the concentration of the greenhouse gas is now over 400 parts per million, continuing a rise that began with the Industrial Revolution. Other researchers have used computer models to estimate what an event similar to a Maunder Minimum, if it were to occur in coming decades, might mean for our current climate, which is now rapidly warming.
One such study looked at the climate consequences of a future Maunder Minimum-type grand solar minimum, assuming a total solar irradiance reduced by 0.25 percent over a 50-year period from 2020 to 2070. The study found that after the initial decrease of solar radiation in 2020, globally averaged surface air temperature cooled by up to several tenths of a degree Celsius. By the end of the simulated grand solar minimum, however, the warming in the model with the simulated Maunder Minimum had nearly caught up to the reference simulation. Thus, a main conclusion of the study is that “a future grand solar minimum could slow down but not stop global warming.”
Makes you wonder why Lubin and co. bothered looking into it in the first place, if all they were going to say is, ‘well, yes, it will put a small dent in global warming, but that’s all’. Are they right about this though? Is Lubin’s opinion justified by the science he presents?
The world has warmed somewhere between 0.8C and 1.0C in the last 170 years. According to climate scientists, this is a big deal. Since 1976 or thereabouts, it’s warmed about 0.6C – which in itself is not unprecedented (it warmed by as much from 1910 to 1945). Apparently though, this latter warming is an even bigger deal because the IPCC is 95% certain that all of it is due to fossil fuel emissions. 0.6C actual warming in 42 years. Contrast this with say 0.3C global cooling in maybe as little as 30 years – not unrealistic according to the above referenced study. Then consider that some Northern Hemisphere regions may experience winter cooling at least double this – 0.6C in as little as three decades. These are conservative estimates. Other studies indicate larger declines occurring during the Maunder Minimum. Then consider that every 0.1C cooling, pound for pound, is a lot more damaging to human society, to agriculture, to health, than the equivalent warming, which may even be beneficial in many circumstances. Then consider that renewables have trebled the price of electricity in some parts of the developed world – ironically, with the supposed intention of reducing global warming – resulting in a dangerous reliance upon intermittent, unreliable and expensive wind power, to meet demand. This is not a scenario that the developed nations have planned for, having been convinced by climate scientists that the only climate change threat is from GHG warming.
Global warming obsessed scientists and the media are still dismissive of the threat posed by possible decreasing temperatures; they still push the dubious notion that it is increasing global temperatures which threaten us, not ‘slight cooling’ from a dimmer, less active Sun. Literally, they are gambling with the lives of many, many thousands of people. It would be supremely ironic if, after years of alarmists telling us ‘it’s worse than we thought’ and it actually turning out to be rather better than we thought, that they now tell us global cooling will be no big deal when in fact it turns out to be pretty disastrous. Because what they conveniently forget is that future warming projections are based upon climate models which, until the latest ‘spurt’ in global mean temperature caused by Pacific warming and a powerful El Nino, were looking pretty useless. They’re going to look useless again if a GSM/internal variability offsets global warming in the next 10 years or (horror!) the world cools. It’s all very well introducing ad hoc reasons why warming won’t be quite as rapid as predicted, but the fact is, the current generation of CMIP5 climate models don’t adequately account for solar forcing or internal variability due to ocean cycles.
Lubin, for his part, makes it clear that the cooling due to a GSM is as a result of a top-down interaction of the stratosphere with the lower troposphere, precipitated by a decrease in solar UV causing a thinning of the ozone layer:
“Now we have a benchmark from which we can perform better climate model simulations,” Lubin said. “We can therefore have a better idea of how changes in solar UV radiation affect climate change.”
The reduced energy from the Sun sets into motion a sequence of events on Earth beginning with a thinning of the stratospheric ozone layer. That thinning in turn changes the temperature structure of the stratosphere, which then changes the dynamics of the lower atmosphere, especially wind and weather patterns. The cooling is not uniform. While areas of Europe chilled during the Maunder Minimum, other areas such as Alaska and southern Greenland warmed correspondingly.
Thus it would appear that the cooling effect of any possible future grand solar minimum is critically dependent upon the reduction in solar UV intensity and not merely a function of the more modest decline in TSI. Lubin and his team estimated a UV reduction during a future GSM of 6.9% below the UV intensity during the solar cycle 22 (1986-96) minimum.
Reconstructions for UV irradiance from the historical MM to the present-day vary widely. Krivova et al. (2010) estimate a difference between the MM and recent solar minima of 5.1% in the Schumann–Runge continuum (1300–1750 Å) and 1.9% in the Schumann–Runge bands (1750–2000 Å). Lean (2000) reconstructs a difference between MM and mean present-day solar spectral irradiance of ∼15% increasing to ∼30% as wavelength decreases from ∼1900 Å to ∼1300 Å. Our estimate for the interval 1250–1910 Å is 16.3% between quiet Sun and solar maximum, 11.1% between quiet Sun and median present day solar activity, and 6.9% between quiet Sun and cycle 22 minimum. Our solar analog estimate therefore appears to be intermediate between the Lean (2000) and Krivova et al. (2010) reconstructions.
Meehl et al, which Lubin references to justify his assertion that the upcoming GSM will only put a small dent in global warming, estimate the decline in spectral UV irradiance during a GSM thus:
The grand solar minimum is computed as the average of the 1976, 1986 and 1996 solar minima multiplied by (1-0.0025) across all spectral irradiances. In the prescribed SSI changes for these twentieth century minima, larger reductions (1-8%) occur in the ultraviolet range than other parts of the spectrum and this is therefore also reflected in the grand solar minima.
This is a curiously opaque way of saying they took the average of the minimum UV intensity of three consecutive solar cycle minima from 1976 to 1996 and assumed that, at the next GSM, the ‘quiet sun’ solar UV intensity would be 0.25% lower than this. As is evident, this is an order of magnitude less than Lubin’s estimate of 6.9% lower than the single minimum UV which occurred in 1986 (or 1996, depending on whether they took minimum at the beginning or end of the cycle). So it would appear that Lubin is contradicting the findings of his own research and that the expected cooling from a future GSM will be significantly in excess of what Meehl et al estimated in 2013. I guess that’s what you call being a ‘reluctant scientist’! Unfortunately, being a reluctant scientist might mean that the world is not adequately informed of the very real dangers of a possible fast approaching Grand Solar Minimum. It may even cost lives.