This post differs from my usual fare as it follows the format of an FAQ of sorts. For me, it is representative of a conversation I have had a number of times now. I have found that the points raised are usually asked of me by people of a right-leaning political persuasion with some background knowledge of climate. But first some brief back-story to explain how this came about...
Recently the TOSCA group posted a series of short videos on YouTube, where they discussed their research in the field of Sun-Earth links for a general audience. They also re-posted my video. This ended with the conclusion that I am 'certain that the hypothesis which states the Sun is responsible for the majority of recent global warming via a link between cosmic radiation and clouds, is false'. (It is interesting to note that I think most researchers would at this point find this conclusion obvious and not at all controversial, while a small number may find it inflammatory.) I also closed by saying that despite this, there are still many open and interesting questions in the field of solar-terrestrial research. After gaining a few views, a comment was posted on the video to which I wrote a reply. There followed a series of questions and replies, which I thought would be useful to write up here.
I should preface this with the disclaimer that due to the nature of a free-flowing conversation large parts of this material stray outside my own area of active research, particularly towards the end. I have also not posted the original questions verbatim (which you can read here), but rather I have simplified and shortened them.
Q: How can you say you are "certain" that cosmic rays aren't the cause of global warming - I thought certainty was unscientific?
It is true that even our most well-tested hypotheses are only technically described as theories, not fact. This is down to the nature of a scientific hypothesis, they can only be disproven or withstand scrutiny, not positively proven. With this in mind, in my video I end by saying I am certain that a specific hypothesis has failed. I refer to the hypothesis that the Sun, via cosmic rays, is a principle driver of climate and a primary cause of recent climate change (see Svensmark's 'Cosmoclimatology' paper here to read this idea in its original form). As the aforementioned hypothesis is making a testable knowledge claim, it is open to exacting scrutiny (it is this very quality that makes it a scientific hypothesis). So, although the scientific method cannot positively prove something, we may test it and perhaps disprove it. Currently, the hypothesis has failed a wide range of independent tests and can be considered thoroughly defunct. So while scientists may not say with definitive certainty they are sure something is true, they may say if specific claims are not true! In the same vein we could say we are certain the Flat-Earth hypothesis has failed.
Q: I thought this cosmic ray-global warming hypothesis was a new idea: how can you dismiss it so readily?
The field of Solar-Climate connections is very old (perhaps first appearing in scientific literature by William Herschel more than 200 years ago). The idea that it is cosmic rays specifically that affect the Earth's weather is younger however, to my knowledge having been first proposed in 1959 by Edward Ney. Some of the first suggestions of a mechanism for this link were along the lines of cosmic-rays induced atmospheric electricity and cloud droplets (R.E. Dickinson, 1975). Sevensmark and Friis-Christensen (1997) first reported that satellite measurements of clouds showed evidence of this, to a sufficient degree to explain large portions of global warming as a natural phenomenon. But, as I discussed in an open-access paper and an earlier post, these observations did not hold weight, and over the last approximately 20 years, many researchers have examined this claim through various independent methods, finding significant problems and null results. I myself have looked primarily at large-scale satellite observations to explore this idea (for example here, and here), which show null results in terms of changes that could be significant to global warming. Cumulatively, this weight of evidence has led mainstream climate scientists to reject the idea of a significant cosmic ray cloud link, as outlined in Chapter 7 Section 4.6 (page 613) of the IPCC fifth assessment report.
Q: What about the politics of the science and scientists: isn't it true that this is some kind of mainstream climate-cult/conspiracy, wherein people who propose new ideas counter to mainstream views are automatically demonised and painted as 'climate deniers'?
I have only made statements regarding ideas, not people. As far as I am concerned original thinking, constrained by reason and evidence, and open discussion should be valued in science. For another perspective on this field and its denizens, read the very interesting article by journalist Paul Voosen. My statement of certainty regarding the falsehood of the cosmic ray--Global warming hypothesis is not a political one: it is purely based on evidence. That is not to say I don't have my own opinions and biases (like everyone), but in this case the hypothesis has failed numerous independent tests. That is the only relevant point, and the only reason for discarding it. The political aspect of this topic is a very different conversation, and for me the interesting question regarding the politics of climate science is actually the inverse of the above: it regards how disproportionate amounts of power, support, and reporting have been given to the minuscule number of so-called 'climate deniers'. It is both angering and motivating that for each clear message from the scientific community the 'deniers' calcified and pushed back, surely contributing to the delay of meaningful international action, as described in the book The Merchants of Doubt. (A fact attested to by politicians apparent acceptance of charlatans and debunked myths as the basis to reject the science of climate change.)
Q: But what about the Little Ice age in Medieval Europe: it correlates to a period of unusually low solar activity called a Grand Minimum. Is this not a big hint the Sun is important to climate?
There may well be solar related mechanisms of regional importance worth investigating, likely related to dynamics. I have even recently done some work on this myself, regarding 200 years of regional weather conditions and solar phase. (This is currently under review, and I will write a blog post on it if/when it is accepted, although you can already view the work as an IPython notebook on figshare.) As I mentioned at the end of my video, there is still much work to be done, and discounting the aforementioned cosmic ray-climate change hypothesis doesn't close the door on many interesting solar-terrestrial pathways which may indeed impact regional climate variability. TOSCA has produced a book, which will be shortly published, summarising the large body of interdisciplinary work in this field which is ongoing. A key point however, is that regional climate variability is most certainly not the same thing as global climate change, for more on this distinction in relation to solar forcing see Benestad 2010. It essentially means that the interest in the role of the Sun is on processes that affect regional-scale variability, not global trends.
Q: Despite what you have said about the Sun not impacting climate change, isn't it true that Scientists don't understand everything about the climate? And if so, how can they be so sure we should make policy changes?
As made crystal clear by the efforts of the IPCC, the science is settled and has been for a long time with regard to having sufficient information for policy makers to go out and make positive changes. (Of course, this itself is a bit exasperating, as the old joke goes, the politician stands up and asks "What if Climate Change is all a hoax and we make a better world for nothing?"). Unfortunately, I would say the clarity of the climate science community, despite earning a Nobel prize, has proved largely irrelevant. Why is this? Well, perhaps you will think this cynical, but I would say that the explanation for this failure can be caricatured thusly: When policy-makers want support for a given action, they call upon an 'expert' to offer scientific rational. But inversely, if particular scientific conclusions are contrary to a desired policy, they will ask their expert source "is everything about this understood?", to which the scientist will diligently and invariably answer "No, of course we don't understand everything". This is just the nature of science, but nuances like that have a habit of leeching out of a public debate. At this point, the trap is sprung and the conclusion is "Well, we simply cant do anything before we can be 100% sure. More research is needed before action can be taken.". Again, this is just a simplification, and is only one of many tactics to take the clarity out of a scientific argument, but it is suitably illustrative to show that scientific findings alone are often lame to drive policy changes. These themes are explored in detail in The Merchants of Doubt, and I would recommend you read it.
Q: But what about climate models: I don't believe they are accurate 100 years into the future, and they seem to be doing a bad job now. How can we base policy on models we can't trust?
Well one thing to keep in mind is the models are statistically projecting future climate states, not predicting future weather. I think many of them don't capture sub-decade time-scale variability well, such as that arising from internal oscillations in complex systems. So it isn't really a big issue to my mind that the model predictions deviate from observations for what seems to us to be relatively long periods. (Although I may well be mistaken here, as climate models are not my field.) They are certainly an imperfect tool, missing, miss-representing, and are even inherently incapable of reproducing some processes. But despite that, they are also still the best tool we have for projecting the future consequences of our emissions. In particular, we should pay attention to where there is clear agreement between the models. For example, all models show the majority of surface will warm significantly over the next century, and experience intense and more frequent heat-waves.
The real message of the models for me anyway, is not the small details a century into the future--which depending on the exact parameter may be quite uncertain--but the message that continued anthropogenic emissions (and the energy imbalance we have already created) will significantly alter the climate system in a way that makes it more hostile for human civilization. This really is bad news for a species that depends on the current status quo of the climate for agriculture and resource management.
I imagine that it is the changing probability of extreme events, and patterns of variability that will be the primary problem for human civilisation: Years of successive extreme events in key areas for people and resources, made more likely by anthropogenic climate forcings, will be far more dangerous to existing global economic social and political systems than the relatively slow change in global mean conditions a century from now. (Although the flooding of coastlines and ocean-acidification will surely take their toll in due course.) The aforementioned human socio-economic systems have already demonstrated their fragility and inter-connectedness for example during the recent global financial crisis: even climatologists studying ENSO must stop and marvel at the teleconnections that cause a property speculation in the USA to be linked to global economic shock waves. To my mind at least, the most immediate global danger of climate change is to add a potentially destabilising wild card to global socio-economic systems. Albeit, a wild card that scientists have been clearly warning society about now for several decades.
As I write the final lines of this post, James Hansen and others have just posted in ACPD a paper that makes a similar point in far more exacting way, so I will close by citing a paragraph from their conclusions:
"Our analysis paints a different picture than IPCC (2013) for how this Hyper-Anthropocene phase is likely to proceed if GHG emissions grow at a rate that continues to pump energy at a high rate into the ocean. We conclude that multi-meter sea level rise would become practically unavoidable. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization."Go Top