Wednesday, December 14, 2016

Nir Shaviv Debunked



I recently came across an old email (sorry, it got lost in the bustle) from a reader who asked me to review the work of a particular climate-change denier – Nir Shaviv. What makes this request interesting is that this individual is scientifically qualified. He is a full professor of astrophysics at the Racah Institute of Physics in the Hebrew University of Jerusalem and has numerous awards.

On his About the author webpage of his blog, ScienceBits, he states, 
“I started this website in 2006 after I realized that I need a venue unrelated to the university where I can express my non-standared (but correct) views on global warming.” 
So, let’s take a look at some of his claims and see just how correct they really are. I was only able to locate two postings directly addressing his claims on climate change and comment on both of them below.



Dr. Shaviv addresses the question of whether changes in the global temperature are the result of anthropogenic emissions of greenhouse gases or from natural variability in the solar output, stating, 
“As I try to demonstrate below, the truth is probably somewhere in between, with natural causes probably being more important over the past century, whereas anthropogenic causes will probably be more dominant over the next century. Following empirical evidence I describe below, about 2/3's (give or take a third or so) of the warming should be attributed to increased solar activity and the remaining to anthropogenic causes.”
Later, in the same posting, he states, 
“Such a link is potentially important for global warming because over the 20th century, solar activity has been increasing.”
The fatal problem with Dr. Shaviv’s claim that increased solar activity is responsible for global warming is that solar activity is decreasing, not increasing. https://www.skepticalscience.com/solar-activity-sunspots-global-warming.htm

He dismisses this fact by stating, 
“…the total solar irradiance variations are relatively small (a few 0.1%), the latter are most likely not the explanation of climate variability.”
A heart of Dr. Shaviv’s claim concerns the incoming flux of galactic cosmic rays varies as a function of solar activity and is, therefore, responsible for climate change. It is true that cosmic rays affect our climate and cosmic ray flux is affected by solar activity. This was part of a submission to my $10,000 Global Warming Skeptic Challenge and I addressed it in the submission The Cloud Mystery (Cosmic Rays) where I made the observation, 
“They claim (correctly) that as solar activity goes down, more GCRs reach the planet and create more clouds. As more clouds are made, temperature goes down. The problem is that solar activity is dropping, we are seeing more GCRs, but the temperature is going up.”
Dr. Shaviv produces a plot of the number of sunspots to support his claim that solar activity has been increasing, resulting in decreasing numbers of cosmic rays, which results in fewer clouds and increasing temperatures. Unfortunately, his plot actually shows the sunspot numbers have been decreasing since the mid-20th century. Hence, by his claims, global temperatures should have been going down since the 1960s, but they have actually been climbing.

He concludes with the claim that AGW isn’t real because there is a likely alternative explanation, stating, “Solar activity can explain a large part of the 20th century global warming, on condition that there is a strong solar/climate link through modulation of the cosmic ray flux and the atmospheric ionization. Evidence for such a link has been accumulating over the past decade, and by now, it is unlikely that it does not exist.”
I agree with Dr. Shaviv that there is a link between solar activity and the climate. However, he is certainly wrong in his claim that solar activity has been increasing. By his very argument, we can rule out solar activity as the cause of global warming. Poetically, Dr. Shaviv proved this point himself with the data he provided.

Sorry, Nir, your claims on this topic are not correct.



This is more of Shaviv’s effort to make the case that global warming is due to galactic cosmic rays. This time, he claims there is a 140-million year cycle to ice ages and this correlates with the solar system passing through spiral arms of the Milky Way galaxy. As we pass through these arms, the amount of galactic rays reaching Earth varies, leading to changes in the climate. There are a number of issues, the biggest being that the solar system doesn’t pass through spiral arms every 140-million years. There is no such correlation between spiral arm passages and ice ages. Oops. You can read a nice summation of the issue here.

Another issue is the fact that we don’t enter and exit spiral arms on the scale of decades. It takes the solar system at least 225 million years to orbit the galaxy one time. The orbital velocity of spiral arms is different from the rest of the galaxy because they are not structures, but regions. Basically, spiral arms are waves of star formation. As new stars are made in these regions, the biggest and brightest stars light up the region. But, these stars are also the shortest-lived and come to an end relatively quickly in supernovae explosions, leaving behind the longer-lived, but dimmer stars. As the area of star formation advances, the spiral arm advances.

Because they are regions, and not structures, spiral arms do not rotate around the center of the galaxy as the same speed as the stars (including our’s). Since there is a difference in speed, it is, at least in theory, possible to enter and/or leave spiral arms. Shaviv’s claim is that as we approach the spiral arms, the amount of cosmic rays will increase because they come from supernovae and we will be getting closer to those cosmic events. 

The Milky Way galaxy has two main spiral arms and we are nowhere near either of them. However, there are spurs to these arms and we are located in the Orion Arm, which is a spur of the main Perseus Arm. In order for Shaviv’s claim to be accurate, we would have had to have made a significant approach to this arm in the last 60 years and we know that isn’t the case. I can’t find any reference to when we might have entered the Orion Arm, but it didn’t happen recently. We can tell this by looking at the constellations. Many of our most recognizable constellations are located in the Orion Arm, including the constellation Orion (hence, the name), and these constellations have been mapped for thousands of years and there has been very little change over the course of recorded history and the amount of change that has occurred since 1960 is so small it can be detected only with very accurate scientific instruments. In fact, it is possible our solar system was created in the Orion Arm and we have been in it all along.

In any event, I cannot find any evidence to suggest our location in the cosmos has changed so much over the last 60 years that is has led to a change in the cosmic ray flux large enough to change the climate as much as has been witnessed.

The whole issue of solar activity and cosmic rays has been thoroughly covered elsewhere. Here is one such excellent review. There are also tabs on that page for intermediate and basic level discussions. I particularly love the statement at the end:
“That’s a coffin with so many nails in it already that the hard part is finding a place to hammer in a new one.”

Again, the science doesn’t support Dr. Shaviv’s claims. I'm sure he's a capable astrophysicist, but he needs to leave climate change alone.

As I said, these were the only two postings I could find on his blog that addressed climate change. There might be more, but these two are most certainly not scientifically valid. Which goes to demonstrate the point, once again, that there is no scientifically credible evidence to suggest manmade climate change is not happening.

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