Hathaway: “Sun’s contribution is small compared to volcanoes, El Nino and greenhouse gases”

I’ve no objection at all and much praise when scientists actually make falsifiable predictions based on their understanding of the science. Thus when David Hathaway predicts that Solar Cycle 24 will be as large or larger than Solar Cycle 23, I applaud that boldness.

In this article on space.com, several aspects to the current solar minimum are discussed:

The sun’s surface has been fairly blank for the last couple of years, and that has some worried that it may be entering another Maunder minimum, the sun’s 50-year abstinence from sunspots, which some scientists have linked to the Little Ice Age of the 17th century.

Could a new sunspot drought plunge us into another decades-long cold spell?

It’s not very likely, says David Hathaway a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Ala.

Fair enough. Perhaps if I used IPCC-speak, we’d give that a 10-20% probability?

Hathaway continues to make bold observations and predictions:

The sun’s energy drives all climate and weather on Earth. And Hathaway does agree there are good indications that fluctuations in solar output related to sunspot cycles influence the Earth’s climate. And the Maunder minimum isn’t the only evidence — scientists have linked two smaller sunspot minimums (periods of time with very few sunspots) in the early 19th century to cold spells, as well as periods before the Maunder minimum deduced from tree ring records, he said.

But the sun isn’t the only thing that influences our climate: volcanic eruptions, large-scale phenomena such as El Nino, and, more recently, the accumulation of greenhouse gases in the atmosphere also affect the global climate.

Prior to the industrial revolution, the sun probably accounted for about 10 to 30 percent of climate variability, Hathaway told SPACE.com, but now that greenhouse gases have started to build up, “the sun’s contribution is getting smaller and smaller,” he added.

So the pre-industrial climate change on Earth was only 10-30% driven by solar variability. I wonder what the other 70-90% were.

Hathaway hints that volcanic eruptions have an effect, but as far as I am aware such eruptions only cool for perhaps 2 or 3 years, hardly causing a blip in a climate trend [unless we’re talking about supervolcanic events which can cause climate cooling for decades, but we haven’t had one of those for 70,000 years with the Toba explosion]. Is the rest caused by the ENSO cycle?

What of the current solar minimum and the sputtering start to Solar Cycle 24?

Signs of the current, new solar cycle (which actually overlaps with the last cycle) showed up in November 2006, and its first sunspots were seen in January of this year, and again in April, Hathaway said. So already that rules out another Maunder minimum, Hathaway says, since this solar cycle has already begun producing spots, even if there haven’t been many of them yet.

This cycle is just simply “off to a slow start,” Hathaway said.

The last three solar cycles were also what Hathaway calls “big cycles,” meaning they had more than the average number of sunspots (the average is around 110 to 120 sunspots on any given day during the cycle’s maximum). It’s not unusual for such a spate of prolific cycles to be followed my more muted solar cycles (such as the cycle that preceded the last three biggies).

Hathaway says that solar physicists are divided on their predictions of this new solar cycle — some say it will be small, others say it will be another doozy. Predictions have ranged anywhere from 75 to 150 maximum spots during its peak. “There really are two camps,” Hathaway said. Whatever the number ends up being, though, “it’s not zero,” he added.

That depends on whether the Maunder Minimum was really devoid of sunspots or had sporadic “Tiny Tim” spot groups which were not seen because of the technology used at the time.

It’s doubtful that it was really zero during that time.

Here’s the clincher:

Why the sun is so fickle in its sunspot production is still something of a quandary. “We still don’t fully understand how the sun does this,” Hathaway noted.

Now that statement I regard as the most important of the article. It might not be a popular statement with people on either side of the argument, but as far as solar cycle prediction is concerned, nobody knows for sure what will happen with the Solar Cycle next week, never mind next year or five or ten years hence.

The science of the variation of the Sun’s solar cycle is in its vary early stages. No-one, not even David Hathaway, knows what will happen next. That’s why he’s checking the Sun every day.

As Kenneth Tapping has already reported (and I blogged his observation) long solar cycles are not that unusual historically and are not in themselves indicative of how powerful are the succeeding cycles. Tapping noted that the long and weak Solar Cycle 20, (which occurred during a global cool period on Earth), was succeeded by Solar Cycles 21, 22 and 23 all of which were relatively powerful (and coincided by chance with a global warming on Earth).

But on the point of whether even a Maunder Minimum style collapse would cool the Earth, Hathaway admirably sticks with the IPCC-derived consensus:

One idea springs from the fact that the sun emits much more ultraviolet radiation when it is covered in sunspots, which can affect the chemistry of Earth’s atmosphere. The other is that when the sun is active, it produces tangled magnetic fields that keep out galactic cosmic rays. Some scientists have proposed that a lack of sunspots means these cosmic rays are bombarding Earth and creating clouds, which can help cool the planet’s surface.

But these ideas aren’t yet proven, and anyway, the sun’s contribution is small compared to volcanoes, El Nino and greenhouse gases, Hathaway notes.

Even if there were another Maunder minimum, he says, we would still suffer the effects of greenhouse gases and the Earth’s climate would remain warm. “It doesn’t overpower them at all,” Hathaway said.

So according to Hathaway, greenhouse gases are warming the Earth to such an extent that solar variation becomes unimportant. Never mind whether I agree with him (and who am I to disagree with an expert?), I applaud David Hathaway for making such scientifically falsifiable statements.

I hope he’s right about the warming. So far, during the current warming, we’ve had the major deserts contract, the tropics expand and possibly a general reduction in hurricane frequency globally during the 20th Century.