A few days ago I was interviewed by Doron Levin, for an article to appear online on forbes.com. After having seen a draft (to make sure that I am quoted correctly), I told him good luck with getting it published, as I doubted it will. Why? Because a year ago I was interviewed by a reporter working for Bloomberg, while the cities of San Francisco and Oakland were deliberating a climate change lawsuit against Exxon-Mobil (which the latter won!), only to find out that their editorial board decided that it is inappropriate to publish an interview with a heretic like me. Doron’s reply was to assure me that Forbes’ current model of the publication online allows relative freedom with “relatively little interference from editors”. Yeah Sure.
After the article went online yesterday and Doron e-mailed so, I saw how much relative exposure it received. It had already more than 40000 impressions in a matter of a couple of hours. Impressive. All that took place while I was relaxing with my family on a Tel-Aviv beach. But this didn’t last long. Although I continued to relax at the beach, the article was taken down for “failing to meet our editorial standards”, which apparently means conforming to whatever is considered politically correct about climate change.
In any case, the main goal of this post is to provide the scientific backing for the main points I raised in the interview. Here it comes.
First and foremost, I claim that the sun has a large effect on climate and that the IPCC is ignoring this effect. This I showed when I studied the heat going into the oceans using 3 independent datasets - ocean heat content, sea surface temperature, and most impressively, tide gauge records (see reference #1 below), and found the same thing in a subsequent study based on another data set, that of satellite altimetry (see reference #2 below). Note that both are refereed publications in the journal of geophysical research, which is the bread and butter journal of geophysics. So no one can claim it was published in obscure journals, yet, even though the first paper has been published already in 2008, it has been totally ignored by the climate community. In fact, there is no paper (right or wrong) that tried to invalidate it. Clearly then, the community has to take it into consideration. Moreover, when one considers that the sun has a large effect on climate, the 20th century warming is much better explained (with a much smaller residual). See reference #3 below, again refereed).
I should add that there are a few claims that the sun cannot affect the climate because of various reasons, none holds water. Here is why:
- The first claims is that “the sun cannot have a large effect on climate because changes in the irradiance are too small to do so, and we don’t know of a mechanism that can”. This is irrelevant because given that the oceans prove that the sun has a large effect on climate, we must consider it even if we don’t know how it comes about. Often in science we are forced to accept a theory we don’t fully understand because the empirical evidence suggests so. Mendelian genetics explained reality pretty well (though we now know it is a bit more complicated) a century before Watson and Crick showed what the underlying mechanism is. Does it mean that we should have discarded Mendelian genetics for a century without knowing the mechanism? Pauli postulated the existence of the neutrino a quarter of a century before it was actually detected. Similarly, almost all cosmologists and particle physicists assume that dark matter exists, because an overwhelming amount of evidence suggests so, and because alternatives simply don’t work (mainly MOND, e.g., as a post-doc and I have shown in a paper as well as many others). However, we don’t really know what dark matter really is (there are many suggestions), but its existance has to be considered. Having said that, we actually do see very clear empirical evidence pointing to the link, as I describe below.
- The second claim is that “solar activity decreased from the 1990’s but the temperature continued to increase. So the sun cannot be the reason for the heating”. It is wrong at several levels. First, one has to realize that the temperature anomaly at a given time is not some fixed factor times the forcing at the time. This is because the system has a finite heat capacity and various interesting feedbacks. Without properly modeling it, erroneous conclusions can be reached. A simple example is ruling out the solar flux as the major source of heat because between noon time and say 2pm, the solar flux is decreasing but the temperature is increasing! (Similarly, the average solar flux is decreasing during the month of July in the northern hemisphere, but the temperature is increasing). Solar activity has been high over the latter half of the 20th century such that even after solar activity started to decreases, the temperature should continue increasing for a decade or so, albeit at a lower pace. Second, the above argument is extremely simplistic. Proper modeling has to consider that human have contributed as well to the net positive forcing. And indeed, when one considers both the large effect that the sun has, and the anthropogenic forcing, one can explain 20th century climate change if climate sensitivity is on the low side, much better than the IPCC models that exclude the large effect that the sun has, but assume a large climate sensitivity instead. See reference #3 below, as well as Roy Spencer’s short talk showing that climate models generally give a much larger temperature increase than has been observed over the past 2 decades.
- The third claim is that when 20th temperature changes are compared with solar activity and anthropogenic forcing, one doesn’t see the 11 year solar cycle in the temperature data, which can be used to place an upper limit on the solar effect. This faulty argument is related to the previous one. It too assumes that the temperature should be proportional to the radiative forcing at any instant, and because the temperature variations over the 11 year solar cycle are only of order 0.1°C, the contribution to 20th century warming should be similar since the secular increase in the solar forcing is comparable to the variations over the 11 year solar cycle. However, the large heat capacity of the oceans damps any temperature variations on short time scales. Proper modeling reveals that an 0.1°C variation over the solar cycle should actually correspond to a variation much larger on the centennial time scale, in fact, about half to two thirds of the warming (see reference #3 below and my comments about the BEST analysis from Berkeley who “proved” that the sun cannot have a large climate effect based on the above argument).
[Edit: See my more detailed rebuttal of the attack on solar forcing that appeared a day later on Forbes]
As I said above, we now know from significant empirical data where the solar climate link comes from. It is through solar wind modulation of the galactic cosmic ray flux which governs the amount of atmospheric ionization, and which in turn affects the formation of cloud condensation nuclei and therefore cloud properties (e.g., lifetime and reflectivity). How do we know that?
- When the sun has gusts in the solar wind, it causes several day long reductions in the flux of cosmic rays reaching Earth, called Forbush decreases. We see as a response changes in the aerosols and in cloud properties, just as expected. See references 4 & 5 below.
- There are large cosmic ray flux variations over geological time scales that are not related to solar activity but instead to our location in the Milky Way and the changing galactic environment. You can reconstruct the cosmic ray flux using meteorites and find that the 7 ice-age epochs over the past 1 billion years all appeared when the cosmic ray flux was high (see references 6 & 7 below). On a bit shorter time scales, the vertical motion of the solar system clearly manifests itself as a 32 million year oscillations in the temperature (15 periods over the past half billion years! See reference 8 below). Namely, there are very clear indications that independent variations in the cosmic ray flux affect the climate.
- Cloud cover varies over the 11 year solar cycle (e.g., reference 9 below). This by itself is not proof that the link is through cosmic rays, since there are several things that change with the solar cycle. However, one particularly interesting aspect is that the cloud cover variation are asymmetrical between odd and even cycles, just as cosmic rays are, and unlike other solar related variables that are blind to the fact that the real cycle is 22 years (Polarity returns back to the same state after two switches, hence, 22 years. The asymmetry arises from the fact that cosmic rays are primarily positive particles, and the sun is rotating such that there is a clear helicity to the field configuration).
- There are several experimental results showing that ions increase the nucleation and formation of a few nm sized aerosols and increase the survival of those aerosols as they grow to become 50 nm sized cloud condensation nuclei. A few examples are given in references 10-13.
One should be aware that we are still missing the last piece of the puzzle, which is to take the various mechanisms, plug them into a global aerosol model and see that there is a sufficiently large variation in the cloud condensation nuclei. This takes time, but compared with the aforementioned examples of genetics, neutrinos or dark matter, it will definitely take us much less to provide this last piece, but in any case, the evidence should have forced the community to seriously consider it already.
Nonetheless, even with the above large body of empirical evidence, the link has been attacked left and right. A really small number has been valid and interesting, but not to the extent to invalidate the existence of a cosmic ray climate link, just to modify our understanding of it. The rest has been mostly bad science, as I exemplify below.
- One of the main critiques arises when people look for the cosmic ray climate link but find none. In all those cases were no effect is seen, the authors didn’t estimate the size of the effect they expected and compare it with the noise level in the data. For example, if one considers only a small patch of the atmosphere above oceans, then the day to day fluctuations in the cloud cover are large compared with the Forbush decrease signal. Similarly, not seeing an effect over 10’s of thousands of years because of Earth’s magnetic field changes, is not surprising because switching off Earth’s magnetic field altogether is expected to give rise to a 1°C effect, which is notably smaller than the climate variations seen over these time scales (presumably because of the Milankovich cycles).
- The cosmic ray climate link over geological time scales was attacked by several papers. Only one raised a valid scientific point, which is that the original analysis of Jan Veizer and I didn’t consider the effect that the ocean pH (affected by atmospheric CO2) has on the Oxygen 18 data. When that was taken into account, we modified our best estimate for climate sensitivity to be 1 to 1.5°C per CO2 doubling. Other analyses are blatantly wrong, such as faulty statistical analysis or data handling (see summaries here and here), or even simple arithmetic mistakes! (see here).
- The last set of critiques are actually part of a healthy scientific discourse about the mechanism that is responsible for linking atmospheric ionization with cloud condensation nuclei. Papers like this discuss the possibility that ion induced nucleation could be the physical mechanism linking ionization changes with variations in the cloud condensation nuclei number density. However, even if we don’t fully understand the underlaying mechanism, ruling out a particular suggested mechanism doesn’t mean that other possibilities do not exist (in fact, they do, see ref #13 below). When Pauling and Corey suggested the triple helix model for DNA in 1953, they were off, but it wasn’t a reason to discard the whole idea of genetics.
- Shaviv, N. J. Using the oceans as a calorimeter to quantify the solar radiative forcing. J. Geophys. Res. (Space Phys.) 113, 11101 (2008) local version (not paywalled)
- Howard, D., Shaviv, N. J., Svensmark, H., The solar and Southern Oscillation components in the satellite altimetry data, J. Geophys. Res. Space Physics, 120, 3297–3306 (2015)
- Ziskin, S., Shaviv, N. J., Quantifying the role of solar radiative forcing over the 20th century, Advances in Space Research 50, 762–776, (2012). local version (not paywalled)
- Svensmark, H., Bondo, T. & Svensmark, J. Cosmic ray decreases affect atmospheric aerosols and clouds. Geophys. Res. Lett. 36, 15101–1510 (2009)
- Svensmark, J., Enghoff, M. B., Shaviv, N. J. & Svensmark, H. The response of clouds and aerosols to cosmic ray decreases. J. Geophys. Res.: Space Phys. 121, 8152–8181 (2016).
- Shaviv, N. J. Cosmic ray diffusion from the galactic spiral arms, iron meteorites, and a possible climatic connection. Phys. Rev. Lett. 89, 051102–05110 (2002)
- Shaviv, N. J. The spiral structure of the Milky Way, cosmic rays, and ice age epochs on Earth. New Astron. 8, 39–77 (2003)
- Shaviv, N. J., Prokoph, A., Veizer, J., Is the Solar System's Galactic Motion Imprinted in the Phanerozoic Climate? Scientific Reports volume 4, Article number: 6150 (2014)
- Svensmark, H. & Friis-Christensen, E. Variation of cosmic ray flux and global cloud coverage—a missing link in solar-climate relationships. J. Atmos. Sol. -Terr. Phys. 59, 1225–1232 (1997).
- Svensmark, H., Pedersen, J. O. P., Marsh, N. D., Enghoff, M. B. & Uggerhøj, U. I. Experimental evidence for the role of ions in particle nucleation under atmospheric conditions. Proc. R. Soc. A 463, 385–396 (2007)
- Kirkby, J. et al. Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature 476, 429–433 (2011).
- Svensmark, H., Enghoff, M. B. & Pedersen, J. O. P. Response of cloud condensation nuclei (>50 nm) to changes in ion-nucleation. Phys. Lett. A 377, 2343–2347 (2013).
- Svensmark, H., Enghoff, M. B., Shaviv, N. J., Svensmark J., Increased ionization supports growth of aerosols into cloud condensation nuclei, Nature Communications 8, Article number: 2199 (2017)