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Resolved: Climate change is, on balance, anthropogenic in origin

C1) Climate sensitivity is likely high Climate sensitivity is the key argument to this debate. Everyone agrees that CO2 has some direct effect, at least 1 degree C per doubling of CO2 concentration. This is what former climate modeler turned skeptic David Evans argues. “[All] serious skeptical scientists have always agreed with the government climate scientists about the direct effect of CO2. The argument is entirely about the feedbacks.” [1] What are feedbacks? Feedbacks are important because they tell us how much warming we will have in the future. They amplify -- or dampen -- the warming effect of CO2. Changes in albedo, cloud cover, water vapor, and greenage can all affect warming. If sensitivity is 2-3 degrees C, CO2 can explain most of the warming since the late 70s. If it is lower it still causes a significant amount. My opponent needs to pretty much argue that the amplification effects are under one in order to win. Let us assume that climate sensitivity is low. Say, feedbacks are around zero (no positive or negative feedbacks); every doubling of CO2 leads to roughly 1.1 degrees C increase in temperature. Even this unrealistically low climate sensitivity does not harm the AGW hypothesis. Nir Al Shaviv, a skeptical physicist, wrote a paper assuming the feedback effect was 1.1 degrees. He calculated that CO2 actually caused slightly over half of the modern warming trend [2] (about 57%). The famous Lindzen and Choi (and Spencer) results are really the only ones which cast doubt on the fact that CO2 is responsible for the warming. But Nir Al Shaviv told me in an email, “[m]y best estimate is that the sensitivity is higher than Lindzen and Choi, actually closed to no net amplifier, with the 50% of the CO2 doubling, the Anthropogenic contribution is also around 50%.” [3] Essentially, he verified what I sent to him in an email with calculations I had done assuming the amplifier was flat. My data found that it caused about 49.5% of the warming, but I failed to take into account the logarithmic effect of CO2, which makes the effect over 50%. Even then, these assumptions are incorrect. Sensitivity is higher, and if it is, CO2 pretty much causes far more than 50% of the warming, but both estimates are enough to win me the debate. Research by Patrick Michaels, now a libertarian, CATO scholar found the amplifier to be 1.6 degrees C [4]. More than the 1.1 above. This puts the man made contribution to global warming above 50%, and certainly above 57%. This is not even including other gases which amplify the greenhouse effect. The burgeoning evidence suggests that the net amplifier is around 2-3 degrees C. Based on multiple lines of evidence, stemming from volcanic eruptions, instrumental records, paleoclimatology, and more, the mean sensitivity sits firmly at about 3 degrees C. The following picture demonstrates the evidence. As seen, the average never dips below 2 degrees C. The mean is 2 - 4.5 degrees C, all of which are enough for me to win the debate. 2 degrees C probably puts you around 70% of the warming is due to CO2, and 3 at nearly 100%, though I have not done the math (yet…). Some studies find fairly high sensitivity, around 4 degrees C. JD Annan, a leading climatologist, uses a Bayesian statistical technique, the predominant methodology in both the skeptic and realist literature. He found a mean sensitivity of 3 degrees C, with upper estimates at 4 degrees C, though still possible, but very unlikely below 3 degrees C [5]. The following graph [6], which I like because since I have used it pretty much everyone else has stolen it, shows the results from 3 leading studies. Although the results are uncertain, they are certain in that sensitivity is above 2 degrees C. A new paper, published in 2012, actually went against the consensus and found low sensitivity. Despite this, their results concluded that “[h]umanity is . . . responsible for the most recent period of warming from 1976 to 2010.” [7] Sensitivity is high. That means I win the debate. If it is low, I still win the debate because it caused 50% of more of the modern warm period. C2) Evidence from paleoclimatology I love paleoclimatology. I like geology and come from a family of geologists who are also oil entrepenueres (maybe why I still have skeptic leanings). And pretty solid evidence in the paleoclimatological record actually shows a strong CO2 effect. I am just going to c/p my debate with Roy. There is significant evidence from paleoclimate records that CO2 can have an effect on changes in the climate. Climate skeptic and paleoclimatologist Bob Carter emphasizes the importance of paleoclimate data. He compares climate to a piece of string. The current instrumental data (1850 – present) is a very short period of time, according to Carter. And when the ‘string’ is lengthened, we see a lot of climactic variability. Instead of looking at the recent past, we should look at the entire temperature record in order to get an accurate picture of the climate [8]. I will provide evidenc, contrary to what Carter believes, lengthening the string supports AGW theory. Over the Cenozoic Era, which began 66 million years ago, we see clear warming and cooling cycles caused by changes in CO2 concentrations. The sun increased slightly over that time period, whereas temperatures cooled. CO2, however, fell steadily through that time period. Plate tectonics was also accounted for. With natural forcings an unlikely cause, “CO2 was the dominant climate forcing in the Cenozoic” [9]. When you lengthen the ‘string’ over the course of the entire Phanerozoic (500 million years; begins at the Cambrian) there is still evidence of CO2 driving multiple climate changes. The GEOCARB study, published in 2001, is one of the definitive proxy records for CO2 concentrations within the last 500 million years. The study notes that “over the long term there is indeed a correlation between CO2 and paleotemperature” [10]. Evidence from the Vostok ice cores (specifically 240,000 before present), proves that CO2 has had an effect on temperatures. Although the initial forcing was orbital changes in the sun, CO2 “plays . . . a key role in amplifying the initial orbital forcing” and “the CO2 increase clearly precedes the Northern Hemisphere deglaciation”. The study also notes that these forcings “are also at work for the present-day and future climate” [11]. There is also proof that it is warmer now than it has been since the MWP. In fact, it is warmer now than any year since 1400 AD [12]. Newer reconstructions continue to support this finding, and even extends the dataset. It finds that the Roman warm period (RWP) and the MWP as much cooler than today, and claims to have replicated previous ‘hockey stick’ studies [19]. The results are depicted below. Looking into the geologic past, we see strong evidence in favor of the idea that carbon dioxide can increase temperature. It logically follows that if humans continue to emit CO2, and other greenhouse gasses, that human emissions will increase temperatures. C3) Consensus Before I continue, I would like to note this argument in and of itself does not prove that global warming is caused by man. Actual evidence should be the driving force behind this debate. The reason I chose to put this in my argument is simple: the science is not clear because of consensus, but a consensus exists because the evidence is clear. This evidence will be discussed later. A study published in Science reviewed the ISI web of science in order to take a survey of relevant climate literature as to what the causes of climate change are. The study failed to find a single paper which was in opposition to the consensus position, that the main driver of climate change is anthropogenic. 75% of the papers supported the consensus position, whereas 25% had no position (they were focused on things other than forgings, like impacts or paleoclimate) [14]. The study also noted how many organizations have come out supporting the idea of anthropogenic climate change. The IPCC, the American Meteorological Society, American Geophysical Union, and the American Association for the Advancement of Science have all concluded that the evidence for AGW is overwhelming [15]. NASA furthers this argument, noting “most of the leading scientific organizations worldwide have issued public statements endorsing this position”. They also argue “[n]inety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities” [16]. A 196 page report representing 13 governmental agencies, and written by 28 authors from scientific institutions, has stated “[t]he global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases” [17]. 1. https://mises.org... 2. http://www.phys.huji.ac.il... 3. Personal Correspondence. 4. http://www.int-res.com... 5. http://www.jamstec.go.jp... 6. http://www.skepticalscience.com... 7. http://www.scirp.org... 8. Bob Carter. Climate: The Counter Consensus (London: Stacey International, 2011). 9. http://www.columbia.edu... 10. http://earth.geology.yale.edu... 11. http://icebubbles.ucsd.edu... 12. http://www.atmosp.physics.utoronto.ca... 13. http://www.skepticalscience.com... 14. http://www.sciencemag.org... 15. Ibid. 16. http://climate.nasa.gov... 17. http://downloads.globalchange.gov...