Chapter 6. What have we done?

6.1 Into the fray It was April 11, 2014 and the McGill press release went online at 1:30 in the

afternoon. Although I’d published over two hundred papers, they were on fundamental areas of geoscience and the release summarized my first paper that had significant social and political consequences. Its title: “Scaling fluctuation analysis and statistical hypothesis testing of anthropogenic warming”1a, was arcane, but the release was clear enough: “Statistical analysis rules out natural-warming hypothesis with more than 99% certainty”.

It had been 15 months since the paper was submitted for peer review, but now the sedate pace picked up dramatically. Within hours, the tone was set by the skeptic majordomo Viscount Christopher Monckton of Brenchely who displayed his Oxbridge classics erudition by deliciously qualifying the paper as a “mephitically ectoplasmic emanation from the Forces of Darkness” b. Three days later, with the release getting 12,000 hits per day, the "Friends of Science" sent an aggressive missive to the McGill chancellor asking that it be removed from McGill’s sitec. The Calgary based group with its Orwellian name, was set up in 2002 (?) to promote the theory that the warming is caused by the sun: "Not CO2. Not us", see fig. 6.1. One could understand their thunder: rather than trying to prove that the warming was anthropogenic - something that is impossible to do "beyond reasonable doubt" - the new paper closed the debate2 by doing something far simpler - disproving the giant natural fluctuation (GNF) hypothesis, that the warming is natural. Excluding divine or extraterrestrial intervention, there is no viable third explanation: the warming is either natural or human, so the skeptics were stuck. To add insult to injury, their prepackaged sermons on the inadequacies of computer models or their speculations about the sun were irrelevant.

Provoked by the media attention and several op-Edsd, in the hours, days and weeks that followed, in email, blogs and twitter, I was treated to a deluge of abuse: “atheist”, “Marxist”, “hippy name” etc.: everything it seemed, short of death threats. Reminiscing later with my colleague Gavin Schmitt – who had been on the firing line for years - I realized that I had only received the standard treatment from the well fundede and organized climate

aFor the press release: http://www.physics.mcgill.ca/~gang/Society/McGill.Press.release.27.4.14.pdf. By the end of the year, in terms of media attention, it had attained the status of the most "mentioned" of over 750 papers in 2014 in the journal Climate Dynamics.b On the “The Watts Up with That” (WUWT) web site run by Anthony Watts. The site touts itself as “the world’s most viewed site on global warming and climate change”.c McGill ignored the request, but this was only the beginning of hostilities with this group composed largely of retired petroleum engineers. d

Live Science, April 18, 2014: Is Global Warming a Giant Natural Fluctuation?, http://www.livescience.com/44950-global-warming-natural-fluctuation.html and in The Gazette, June 10, pA17: "Research Shows that global warming isn't natural", http://www.physics.mcgill.ca/~gang/popular.articles/Gazette.7.14/Gazette.2.op.ed.orignial.10.6.14.jpg.e In 2014, groups sharing climate skeptic ideologies received over $900 million, see: 3 Brulle, R. J. Institutionalizing delay: foundation funding and the creation of U.S. climate change counter-movement organizations. Climatic Change 122, 681-694 (2014).

skepticf community. Schmidt summed up his own experience: “You’re road kill. It’s like having a spotlight trained on you until they move on to their next victim…”.

But Monckton was mistaken not only about the science substance but also about the science process. In the very first sentence of his blog, he railed: “It i s time to be angry at the gruesome failure of peer review that allows publication of papers, such as the recent effusion of Professor Lovejoy of McGill University…”. The comment was ironic, not least because the paper had been rejected successively from three different journals - each time on spurious grounds - and that very morning, a follow-up paperg had been dismissed by Nature Climate Change without even being sent to reviewh. One might have thought that the climate skeptics would be pleased with this 75% rejection rate: no system is perfect and this one was apparently doing its best to keep out the new approach!

To understand this unnatural convergence of skeptic and mainstream views, recall that for decades, the primary approach to climate science has been through huge numerical climate models (Global Circulation Models, GCM’s). Since the 1970's and 80's, they have so heavily dominated the field that scientists and skeptics alike find it difficult to imagine solving fundamental climate problems without them. Caricaturing this blinkered mindset, one irate reviewer had even claimed that the goal of statistical testing of natural warming can’t be achieved without GCM’s and told me to "go get your own GCM!” i. The reception by both scientists and skeptics thus revealed as much about the sociology of science as about it's content, in particular, the disjunction that had grown between climate science and my own area of nonlinear geophysics.

I was not much surprised by this initial rejection. When it comes to genuinely new ideas, science is no different than other areas of life: acceptance requires protracted struggle. In the real world, one expects the rejection of the unfamiliar. This is nothing like the skeptics’ fantasy world, where climate scientists conspire to foist their pet theories (including anthropogenic warming) on an unsuspecting public. In order to make this fairy tale seem plausible, the fantasy scientists are portrayed as little more than money driven businessmen seeking fat research grants. When the skeptics accused me of “wasting tax payer money”, it was therefore little more than a ritualistic incantation. The disclaimer j at

fI use the term "climate skeptic" to denote those who dispute the theory of anthropogenic global warming. But

today, the term "climate denier" is more accurate. Yet the term "denier" has an unnecessary emotional charge so that for example "denialist" has been proposed instead. I find this new proposal awkward and will stick with "climate skeptic", see however: 4 Gillis, J. in New York Times (New York, 2015). g Published a few months later in the more specialist journal, it made front page news: 5 Lovejoy, S. Return periods of global climate fluctuations and the pause. Geophys. Res. Lett. 41, 4704-4710, doi:doi: 10.1002/2014GL060478 (2014)..h Rejection without review is a common practice for the high-end publications such as Science or Nature. It sent a clear signal that they didn’t find my approach to climate variability of much interest. i Unfortunately for the reviewer, at present, the natural warming hypothesis can only be disproved by using empirical data with the help of some nonlinear science. As discussed in ch. 5, GCM's cannot do this since their relevant pre-industrial centennial scale natural variability isn't sufficiently realistic, see also: 6 Lovejoy, S., Schertzer, D. & Varon, D. Do GCM’s predict the climate…. or macroweather? Earth Syst. Dynam. 4, 1–16, doi:10.5194/esd-4-1-2013 (2013).j See: 7 Oreskes, N., Carlat, D., Mann, M. E., Thacker, P. D. & vom Saal, F. S. Viewpoint: Why Disclosure Matters. Environ. Sci. Technol. 49, 7527−7528, doi:DOI: 10.1021/acs.est.5b02726 ( 2015).

the bottom of the paper: “this work was unfunded, there were no conflicts of interest” k was irrelevant.

The accusation of being financially motivated with insinuations of misconduct was particularly rich. Back in 1998, in order to publically demonstrate their commitment to the Kyoto accords that they had just ratified, the Canadian federal government re-earmarked $150 million of environment and other funds to create the three year Canadian Climate Action Fund (CCAF)l. In March 2000, taking advantage of this opportunity, I submitted a proposal to perform a hypothesis testing study virtually identical to the one that had just been publishedm. Curiously, the proposal was not rejected on scientific grounds – it was admitted that the proposal would indeed fill “a knowledge gap” - rather it was rejected because the agency doubted that “the deliverables” (techno-speak for the results of the test) would be ready on time (one year later). This reasoning was bizarre since - depending on the result of the research - filling the “knowledge gap” could potentially save the government $150 million, yet they were not ready to spend the requested $28,000 for an assistant to help me find out if the warming was no more than a giant natural fluctuation. At the time, I only had a few climate publications – the rest concerned atmospheric variability at shorter weather time scales - and this rejection with its unscientific justification only confirmed my suspicions that climate research was too political to be worth pursuing. A few years later, in 2006, following the election of the climate skeptic Conservative party in the federal elections, the Canadian Fund for Climate and Atmospheric Science (CFCAS, the successor organization to the CCAF) was shut down. Since this was the only public body that specifically funded academic research into the environment and climate, when the research was finally performed in 2013, there were no longer any funding possibilities in Canada, I had no choice but to do the research in my spare time.

k At the time, I had a very small National Sciences and Engineering Research Council (NSERC) grant, but it was earmarked for a different project (“Multifractal Geophysics”) and in any case it barely covered my publication costs.l The fund was set up to “increase the understanding of impacts, costs and benefits of Kyoto implementation”. 93% of the fund was in the form of tax breaks to corporations who claimed to be mitigating and adapting to climate change, only 7% was for research. But even this meager offering could only provide matching funds: a minimum of 50% of the research had to be funded from other sources, in my case I could only offer an "in kind" contribution, a donation of a percentage of my time (and hence salary). mThe proposal, submitted in March 2000 to the CCAF had two deliverables: a) a new analysis of climate extremes, (“especially with regard to the possible existence of long-range statistical correlations which give rise to spurious trends, and to fat tailed probability distributions which give rise to spurious transitions”- i.e. to “black swans” although the term had yet to be coined) and b) the development of “appropriate statistical tests capable of rejecting the (nonclassical) null hypothesis at various confidence levels”. Fourteen years later, the Climate Dynamics paper addressed both issues.

Fig. 6.1: The billboard war on science waged by the “Friends of Science”, and defended (upper left) by Quebec’s association of scientific communicators “Association des Communicateurs Scientifiques”, November 2014. The top show Montreal billboards, the bottom, Toronto (left) and Ottawa (right). The English version of the top left is: “The sun is the main driver of climate change. Not you. Not CO2”; the translation of the upper right is “What Science really says: the climate is changing. Because of us.” In March 2015, as a result of many complaints – including one by the author – the Advertising Standards Canada determined that the Friends of Science billboards contravened articles 1(e) and 8 of their coden.

6.2 What have we done?We have seen that the atmosphere is a turbulent fluid whose temperature, humidity

and wind vary from tiny millimeter sized eddies to huge planetary weather systems, from milliseconds to the age of the earth. In ch. 1 we showed quantitative proxy temperatures confirming with the help of fluctuation analysis (fig. ?), its (unstable) variability out to megaclimate scales. Although (section 5.?) the interpretation of the proxies is not always straightforward, qualitatively different evidence confirms the basic conclusions. For example, sixty five million years ago, the temperature was five or even ten degrees warmer than it is today and dinosaurs roamed an ice-free south pole. As little as fourteen thousand years ago, the earth was still in the throes of an ice age with ice sheets several kilometers thick and with global temperatures 2- 4 degrees cooler than today. More recently, in the middle ages, records of wine making show that England was warm, yet only a few centuries later in the “little ice age” it was much cooler.

There are thus converging lines of evidence that the temperature varies considerably over geological epochs. While the quantitative amounts of warmings and coolings are debated, there is no doubt that without human intervention, and over sufficiently long periods, that the temperature of the earth can readily change by several degrees. But what about this: since the end of the 19th century, instrumental records show that the earth has

n Article 1e says « …Both in principle and practice, all advertising claims and representations must be supportable….” And article 8 says « … Advertising claims must not imply that they have a scientific basis that they do not truly possess….”.

warmed by about one degree centigrade. The evidence of a warming is all around us: from the melting of polar sea ice – including the summer opening of the Northwest passage – to rising sea levels to deadly heat waves. But what is the cause? Is it simply another natural fluctuation, or is it something different, something artificial, something that only we could have done? More precisely, is a one degreeo warming of the whole planet in only a single century an ordinary - even common - event in the history of the earth, or is it so exceptional as to demand a non natural explanation?

Fig. 6.2: An updated version of Mann’s Hockey stick using the three post-2003 multiproxies in fig. 5.12? (black, with a thirty year smoother, from 1500 – 1900 only) and the annual resolution globally averaged temperatures since 1880-2013 (Green, the same NASA-GISS series as in fig. 6.3?). The brown is the Moburg multiproxy at annual resolution from 1000 AD (taken from fig. 1.4d bottom, it is the same one whose 30 year smoothed data from 1500-1900 data was used in fig. 5.13.

The legendary hockeystick has been superposed showing slightly cooling preindustrial temperatures followed by a sharp increase in the industrial period.

The modern answer to this question emerged well before the warming itself was felt or even before human emissions had significantly changed the composition or temperature of the atmosphere. In 1896, in an attempt to understand the causes of the ice ages, the Swedish chemist Svante Arrhenius (1859-1927) estimated that if the concentration of carbon dioxide (CO2) in the atmosphere was doubled, that global temperatures would rise by 5 – 6o C, a result revised a little later by Guy Stewart Callander8 (1897 - 1964) to 2oCp. From a scientific point of view, the basic action of CO2 is straightforward: CO2 is a “Greenhouse Gas”: it lets visible light from the sun through to the surface while absorbing part of the earth’s outgoing heat radiationq.

That the earth’s temperature is significantly higher due to its atmosphere trapping infra red (“heat”) radiation was known since Joseph Fourier (1768 - 1830), and John Tyndall (1820 - 1893). The basic effect is the same as for a Greenhouse: visible radiation can come through the glass roof, but the glass traps the infra red radiation, leading to a

o This is the average over the earth’s surface: many regions - especially the arctic - have warmed significantly more. pThis is close to the modern value of 1.5- 4.5oC, IPCC5. Interestingly, Arrhenius himself later revised his own estimate downwards by about 1oC: 9 Arrhenius, S. Die vermutliche Ursache der Klimaschwanungen, (The probable cause of climate fluctuations). Meddelanden fran K. Vetenskapsakademiens Nobelinstitut Band 1, no. 2. (1906).q This explanation is more or less correct for the earth in thermodynamic equilibrium. But the consequences of adding CO2 are not so obvious, see below.

higher equilibrium temperature. Arrhenius and Callender’s problem is a little different: what is the change in the equilibrium temperature when the concentration of Greenhouse gases is increased? Thinking in terms of a real greenhouse immediately shows the limits of the analogy: if the glass roof was so thin that a significant fraction of the inside infra red radiation could escape, then doubling its thickness would indeed increase the trapped radiation and increase the temperature inside. However, the glass needn’t be very thick so as to trap all (or almost all) of this heat radiation: on a real greenhouse, doubling the thickness of the glass would hardly make any difference.

When it comes to atmosphericr CO2, the situation is like the real greenhouse with its thick glass roof: even small (pre-industrial) amounts of CO2 make the atmosphere opaque over a range of wavelengths: how does increasing these already “saturated” CO 2 bands lead to a rise in temperature? To understand this, consider the upper part of the atmosphere where there’s only a little CO2, so that the bands are only beginning to saturate. It is the temperature at this (high altitude) that the earth's infra red (heat) radiation is effectively emitted to outer space. By increasing the concentration of CO2, this effective emission altitude increases and at higher altitudes, the temperatures are lowers. The net result is that the infra red radiation is now emitted at a lower temperature and is hence diminished. Since the incoming solar radiation is unaffected, the earth must heat up in order to return to thermodynamic equilibrium. Returning to the Greenhouse analogy, increasing the concentration of Greenhouse gases has the effect of raising the altitude of the roof of the Greenhouse so that its ambient temperature is lower (fig. 6.3). Therefore, the roof emits less radiation to outer space – and since the incoming (visible) solar radiation is unaffected, the heats up, thereby emitting more radiation than before and (over time) it regains equilibrium.

Although we will follow convention and continue to use the term “Greenhouse effect”, when it is applied to the atmosphere, it stretches our picture of a real backyard Greenhouse in another important way. It is often (correctly) pointed out - often by climate skeptics, as though they have noticed something that the scientists had missed - that water vapour is a much more potent “Greenhouse gas” than CO2 and any of the other common “Greenhouse gases” (primarily methane). In addition, water in the form of clouds also has a huge effect on the earth’s radiative equilibrium, so why worry about a much smaller CO2 contribution?

The point is that we must make a distinction between a gas such as water vapour that traps infra red radiation, and long lived Green House Gases (GHGs). GHGs stay in the atmosphere for decades (e.g. methane) or millennia (e.g. CO2) and aside from their radiative properties, they don’t otherwise interfere with the usual weather dynamics. In contrast, both water vapour and clouds are highly variable in space and in time with a typical water molecule staying in the atmosphere only over weather, not climate scales. Whereas the highly variable distribution of water (vapour and clouds) is modelled explicitly in GCMs (and is one of their most uncertain components), in contrast, the GHGs are fairly uniformly mixed by the weather and are quite rapidly spread around the whole atmosphere; when their concentrations are increased, the result is a kind of uniform “background” increase in surface heating. The complication discussed below is that different parts of the earth react either more or less to an increase in heating, their “climate sensitivities” are different (see below).

r Absorption and emission occur in a large number of frequency bands and at the earth’s surface, these are almost all “saturated”.s In the atmosphere, the average temperature falls off exponentially with increasing altitude; this is the explanation for the logarithmic variation of GHG radiation with concentration.

Fig. 6.3 The atmospheric Greenhouse effect showing how an increase in Greenhouse gas concentrations effectively increase the altitude of the Greenhouse roof. Since the atmosphere is colder at higher altitudes, the earth emits less heat radiation and thus must warm up to regain thermodynamic equilibrium.

Arrhenius’s theory signalled the beginning of modern attempts to prove the anthropogenic provenance of a warming that only became strongly apparent in the 1980’s. From a purely scientific point of view, the main difficulty is that there are complicated feedbacks between CO2, water vapour and clouds: these are the main effects responsible for the uncertainty. Arrhenius spent the best part of a year with pencil and paper grappling with these complications; today, it is handled by supercomputers.

Is the warming mostly man-made, through changes in land use, the emission of CO2

and other Greenhouse gases and aerosols (pollution) or is it is mostly natural? Today, the theory of anthropogenic warming is entering a mature phase in which continued efforts to prove it even more convincingly, are suffering from diminishing returns. Take for example the IPCC’s Fifth Assessment Report (AR5, 2013): not withstanding massive improvements in computers and algorithms, it cited exactly the same range of temperature increase for a doubling of CO2 as did the US National Academy of Science report in 1979: 1.5 to 4.5oC. Whereas the fourth report (AR4, 2007) stated that it is “likely that human influence has been the dominant cause of the observed warming since the mid-20th century”, six years later, the AR5 only upgraded this to “extremely likely”t.

In spite of the strong evidence in favour of the anthropogenic theory, it still faces a chorus of denial with entire organizations – such as Canada’s “Friends of Science” - dedicated to the proposition that the “The sun is the main driver of climate change. Not CO2. Not you” (fig. 6.1). In the US there are currently 91 different organizations with combined funding of over $900 million (think tanks, advocacy groups, and trade associations) that collectively comprise a "climate change counter-movement." u Significantly, these groups spend no money on scientific research attempting to prove that their theories are correct,

t In IPCC parlance, “extremely likely” refers to a 95–100% probability level.u According to a recent study in the US there are currently 91 different organizations with combined funding of over $900 million (think tanks, advocacy groups, and trade associations) that collectively comprise a "climate change counter-movement.": 3 Brulle, R. J. Institutionalizing delay: foundation funding and the creation of U.S. climate change counter-movement organizations. Climatic Change 122, 681-694 (2014).

instead they invoke solar, volcanic and internal climate system variability as plausible – or even proven – alternatives to the anthropogenic theory. So who is right?

In order to break through the impasse, to “close” the debate2 it is helpful to recall that science progresses not only from attempting to prove certain theories to be true, but also by rejecting theories that are false. In this, it benefits from a fundamental asymmetry in scientific methodology: while no theory can ever be proven true “beyond reasonable doubt”, even a single decisive experiment can disprove one that is otherwise highly seductive. In their day-to-day work, scientists constantly reject ideas and theories that are incompatible either with observations or with more powerful theories that are known to be true.

To fully appreciate the ability of the scientific method to reject false theories, consider a common medical situation. The human body is a highly complex system and in order to come up with a new drug or treatment, biologists focus on only one or two fundamental components (or “pathways”): they develop a theory explaining how a particular drug would be effective. But no matter how beautiful or promising the idea, no one would take the drug without clinical trials: one performs experiments capable of rejecting them if they are ineffective. It is important to appreciate that these ineffective treatments can be rejected even when there is no understanding of the underlying biology . The converse is also true: treatments may turn out to be effective even in the absence of a theory - until recent decades almost all new drugs were in fact discovered by accident and many are still not understood.

Sometimes theories such as “young earth”v can be confidently rejected because they would contradict of a huge body of evidence, in other cases, the degree of confidence of the rejection must itself be quantified using statistics. Medicine again provides a typical example. Properly designed experiments try both new treatments and placebos on an ensemble (collection, “population”) of patients with similar afflictions. In order to avoid bias, both the patients and the scientists themselves are unaware of who gets what: the experiment is “double blind”. Even with an effective drug, due to various difficult to control or simply unknown factors (notably including the placebo effect!), some of the placebo patients typically show a positive response and some of the medicated patients show none. The outcome of drug trials therefore requires statistical comparisons of the results on the two populations. A possible experimental outcome might be a statement such as “the hypothesis that the medication is clinically effective can be rejected at the 99% level”. In this case, we are effectively admitting that there is a small residual chance (1%) that the medication is in fact effective, but common sense and tradition has it that when the probability that the medication is effective is too low that the medication should not get approval for use in the general population.

This example illustrates yet another feature of hypothesis testing: subjective elements can never be totally eliminated. Few people would take a medication if it only had a 1% chance of workingw. But what if the experiment found that the medication worked in 30% rather than 1% of the patients? In this case, the conventional conclusion is that the confidence is not high enough and the issue would be have to be resolved by changing the experimental protocols and/or by increasing the size of the population being tested. The traditional threshold for rejecting a hypothesis is 95% confidence, but one can easily imagine situations - such global warming - where the implications of rejecting a hypothesis are so important that the bar would be set much higherx. If scientists could only reject the

v Bishop Usher's interpretation of the Bible that the earth was created in 4004 BC currently embraced by many religious fundamentalists including a large fraction of US congressmen. w One could easily imagine exceptions!x For a discussion, see:

hypothesis that an asteroid was on a collision course with earth at the 95% level, one would not feel serene about the future and one would strive for higher levels of certitude. Obviously, when the stakes are high enough – and with global warming it is potentially the fate of civilizations and ecosystems – then exceptionally high levels of confidence are required.

The human body and the climate are both complex systems with many strongly interacting components. Why not apply standard scientific methodology to attempt to reject false theories of warming? For the warming, hypothesis testing is particularly seductive since - unless one entertains a third theory such as divine or extraterrestrial intervention - there are only two options: anthropogenic or natural. Whereas in most cases of statistical testing, the rejection of one theory still leaves several possibilities open, in the case of global warming, the elimination of one virtually forces us to accept the other.

6.3 The Giant Natural Fluctuation (GNF) hypothesis We have explained that basic physics predicts that increasing GHG concentrations will

cause the earth to emit less infra red (“heat”) radiation, and hence to no longer be in radiative equilibrium, and warm up to re-establish equilibrium. Imagine that tomorrow the CO2 concentration was doubled everywhere in the atmosphere. This is a common GCM scenario so that we can use the GCM notion of a climate state as the long term state to which control runs will converge (see section 5.?). The doubling will change the long term temperature around which the natural variability occurs, the difference in the temperatures of the climate states before and after the doubling is called the “Equilibrium Climate Sensitivity” (ECS), and since the scenario cannot be realized in practice, although it may be a useful idealization, it is nevertheless a somewhat academic model concept.

So what will happen? When comparing the atmosphere before and after the doubling, there are two separate issues: what happens to the climate and what happens to the macroweather? For the climate - as with the convergence to any climate state - we expect that it will take a long time for the temperature to adjust to its new state. In the statistical terms of ultra slow converge discussed earlier, there is a memory in the system so that past temperature history is only slowly forgotten. Equivalently, it can be understood in physical terms: since much of the forcing (increased heating) goes into the oceans, including some into deep, slow ocean currents, and it also takes time for this ocean heat to be transferred to the atmosphere, the response is not expected to be immediate. Although the climate state changes, what about the “internal variability”, the deviations about this state: the statistics of the new anomalies? In our language, does the new macroweather continue to have the same type of statistical variation as the old macroweather only varying around a different mean value at each point in space?

Although the atmosphere is highly nonlinear, here we are only considering small changes to the boundary conditions, and the effect of these changes can be linear. For example over the industrial epoch, the anthropogenic forcing (increase of heating) is only about 2 W/m2, about 1% of the average energy delivered by the sun (see section 4.?). It is still only a relatively small perturbation and classically, the effect of small perturbations on boundary conditions is lineary. This means that if we double the forcing then we double the temperature response. On the other hand - inasmuch as this approximation is valid - it is tantamount to assuming that there are no strongly nonlinear consequences of the increased

10 Oreskes, N. in New York Times Vol. January 4, 2015 SR2 (New York edition,, 2015).y This is confusing since the atmosphere is still “sensitively dependent on initial conditions” (the “butterfly effect”), but this only implies that the detailed weather will change. The question here is how does the long term climate state change with the small change in forcing and does the type of macroweather variaotins about the new state change.

forcing. The existence of such “tipping points” - whereby a small cause such as a small rise in Arctic temperatures – might cause a massive release of permafrost-trapped methane initiating a catastrophic feedback cycle of increases in warming followed by increases in temperatures. It should also be clear that if we consider the global temperature response to the GHG forcings (which are by nature global) that any notion of a linear response can only be meaningful at time scales long enough for the atmosphere ocean to act as a single coupled system. Analysis has recently shown that for time scales below the ocean weather – ocean macroweather transition at 1- 2 year scales, that of the correlation of atmospheric and oceanic temperature fluctuations is very small whereas as scales larger than this, they become very large11. This means that at monthly scales, the atmosphere as whole may increase its temperature while over the same month, the average ocean (surface) temperature could easily display a decrease. However, for fluctuations longer than this coupling scale (one to two years), on the contrary, they both tend to vary together.

For the moment, we have not triggered such a tipping point and in ch. 7, we confirm that the responses of GCMs are indeed highly linear to industrial epoch forcings. But if we are to reject the GNF hypothesis without using GCMs, we need to investigate this from the empirical point of view using the temperature and forcing data over the industrial epoch. Fig. 6.4 compares the globally averaged temperatures at annual resolution, and the CO 2

concentrationz measured in terms of the number of concentration doublings when compared to a conventional reference value of 277 parts per million (ppm), the rough value that pertained at the beginning of the industrial epochaa. Recall that due to feedbacks with clouds and water vapour, the exact efficacy of CO2 in increasing the heating is uncertain, that it will nevertheless, not on the CO2 concentration directly, but rather on the number of doublingsbb. Without sophisticated analysis, we see that the shapes are very similar.

This suggests that rather than plot the temperature as a function of the data, that we should plot it as a function of the number of CO2 doublings. The result, is the impressively linear graph shown in fig. 6.5a; its slope: 2.33±0.22 oC per CO2 doubling is called the “effective climate sensitivity” (EffCS), it is the actual sensitivity of the climate to the historical increase in CO2. The interpretation that the straight regression represents the total anthropogenic forcing is reinforced in figs. 6.5b, c. In the former, we simply overlaid the straight relationship of fig. 6.5a onto the plot that it implies of temperature as a function of calendar date since 1880; we see that it does an excellent job of reproducing the overall trend. Finally the difference between the anthropogenic (climate) change and the observed temperature is the macroweather (internal) variability (fig. 6.5c). The fact that the amplitude of the fluctuations is reasonably bounded to within about 0.2o C of the average with no obvious systematic difference between the beginning and end of the series supports this interpretation.

Yet at first sight, this interpretation is too good to be true. It would seem to imply that the warming depends only on the CO2 concentrations whereas there are other anthropogenic factors that are known to be important, the main ones being changing land use, methane emissions and aerosols (particulate pollution). Indeed, such a graph had not been previously published presumably because it was too simplistic to attribute all the warming to CO2 alone. For example Judith Lean12 had also empirically investigated the linearity of the temperature response to forcings, but had simultaneously examined the z The concentrations were smoothed somewhat since only scales longer than the 2 year atmosphere-ocean coupling scale are pertinent.aa Extrapolating fig. 6.5a back to 0 doublings, we see that this implicitly defines the beginning of the industrial epoch to be about 1750: half way between Newcomen’s “atmospheric engine” (1713) and Watt’s rotative steam engines (1780’s).bbThe relationship with the concentration is logarithmic.

temperature response to CO2 and to several additional forcings (including solar and volcanic eruptionscc). Another criticism is that it relates the temperature at a given year to the CO2 over the previous five years (a 5 year smoothing was used). While this is (appropriately) longer the atmosphere-ocean coupling time, as discussed above, we expect that there is a longer time lag/ memory in the system.

But before dismissing fig. 6.5a, consider the other anthropogenic forcings. Since 1880 the global mean CO2 concentrations have been fairly well estimated first from the analysis of air bubbles trapped in ice, then – famously (since 1957) at Charles Keeling’s Mauna Loa and Antarctic observatoriesdd. However, the other main forcings; methane and aerosols – particulate atmospheric pollution - are much more poorly estimated. Even with today’s technology and understanding, the overall radiative effect of aerosols is particularly problematic. To start with – unless launched high into the stratosphere by volcanic eruptions or by high flying military aircraft – their residence time – the typical time that they stay in the atmosphere before falling to earth or being washed out by rain – is of the order of weather, not macroweather scales. They therefore tend to stay near their points of emission, so that their impact is regional not global famously being responsible for a brownish atmospheric tint over India and China and visible from outer space. The main difficulty however is that they have nontrivial impacts. For example in the “direct” aerosol effect, black carbon aerosols absorb sunlight and cause heating whereas the more prevalent (brownish) sulphate particles reflect light back into space and have a cooling influence (a negative forcing). However, aerosols also have an indirect effect on the radiation: by seeding clouds, they increase cloudiness and this in turn reflects more solar radiation and increases the cooling effect. Even in 2017 quantifying all of this is hard enough, but trying to “reconstruct” its effects since 1880 – even as only a global average - is very difficult, see ch. 7.

But the increase in CO2 is not fortuitous; it is due to the burning of fossil fuels that today account for 80% of all energy used. Human emissions of CO2 are thus excellent surrogates for economic activity (which itself depends directly on energy consumption). To a good approximation, double the economic activity, double the CO2 forcing, double the methane forcing, double the aerosol forcing, double the land use forcing; fig. 6.6 shows that this is indeed compatible with our knowledge of the global economy and with sulphate production, itself a surrogate for sulphate aerosols. Fig. 6.5a can therefore be interpreted in a quite different way, one that that largely transforms a vice into a virtue and the apparently simplistic into the simple: simply consider the CO2 forcing to be a surrogate for all the anthropogenic effects. In this way, it even indirectly takes into the difficult to determine effects of aerosols: as long as the radiative effects of the aerosols - whatever they may be – remain a fixed fraction of the total, then they are indeed taken into account in the plot. As we will see in the next chapter, knowledge of the CO2 concentration and past temperature data is enough to make highly accurate predictions of future temperatures, see fig. 6.7ee.

cc She used a multiple regression technique.dd It is often thought that before 1957 that there had been few direct atmospheric CO 2 measurements, but this is not true. The difficulty was that before Keeling’s spectroscopic method, that measuring its concentration required time consuming chemical procedures. In addition, the measurements were typically near the ground and near urban areas and were very badly corrupted by local and highly variable turbulence. ee This figure was tweeted in response to Scott Pruitt who had just been sworn in as US secretary of the environment (March 2017). On the occasion, he was famously quoted as denying that there was any relationship between the levels of CO2 and the earth’s temperature.

Fig. 6.4: Top: The fraction of a CO2 doubling that has occurred using the preindustrial reference of 277 parts per million (ppm); a value of 0.5; half a doubling was exceeded in 2014 (the dot at the upper right). According to radiation physics, the extra energy reaching the earth’s surface (the “radiative forcing”) is proportional to the number of doublings.

Bottom: The globally averaged temperature (NASA-GISS), since 1880. Notice that the two graphs have nearly the same shape.

Fig. 6.5a: The globally averaged annual temperatures of fig. 6.4 plotted as a function of the number of CO2 doublings instead of time. The slope is the effective climate sensitivity (EffCS); 2.33±0.22 oC per CO2 doubling. Adapted from ref.1

Fig. 6.5b

Fig. 6.5c

Fig. 6.6a

Fig. 6.6b

Fig. 6.7: If in 1909, one had advance knowledge of the future CO 2 emissions, and one knew the globally, annual averaged temperature back to 1880, then the global temperature could be predicted (the smooth middle line) to within 0.22 oC with 95% certainty, see the dashed lines. This figure is an adaption of one that appeared in ref.13

6.4 Why the warming can’t be naturalFig. 6.5b shows that since 1880, we’ve had about 1oC of warming; this is close to the

IPCC AR5 estiatme of 0.85o±? What is the probability that a warming this amount of in roughly 125 years? Since we suspect that the recent period is not at all representative of the natural (pre-industrial) variability, the only way to answer this question is to use pre-industrial data to deduce the probability distribution of centennial length temperature changes, to use the multiproxies discussed in section 5.?.

Fig. 6.8 shows the result when three multiproxies were used to estimate the northern hemisphere temperature from 1500- 1875. The series was broken into three segments each 125 years long and the mean was removed. The graph thus shows three typical pre-industrial centennial length periods, the typical variation of 0.2 oC is also indicated for reference. Above the three, at the top, is industrial epoch global temperature since 1880 with the original 125 year length slightly extended to bring it up to date. We can see that it

is totally different than the pre-industrial segments showing an overall change of about 1 oC over the same period of time. What is the probability that it is just a GNF? Also shown below it are the residuals obtained by removing the CO2 contribution, taken from fig 6.5c; as expected these appear (visually) to be very similar to the pre-industrial multiproxies.

Fig. 6.8:

From the figure, one can obtain the conventional estimate the 1 oC change is a GNF; one simply measures the standard deviation of the preindustrial variability for differences of temperature over 125 years (about 0.2oC), so that 1oC is 1/(0.2)=5 standard deviations. The probability of this is about 1 in 3 million. If this was particle physics, we have just discovered the Higgsff!

The assumption that temperature fluctuations follow the bell curve is actually quite usual, but is it warranted? According to our previous discussion, a generic consequence of scaling is the existence of power law probability distributions, associated with “black swan” extreme events (box?). What about the distribution of 125 year temperature fluctuations? Using three multiproxies, we determined the cumulative histograms shown in fig. 6.9.

ff The convention in particle physics is that an experiment purporting to discover a new particle is not statistically significant unless it occurs at this ridiculously high level of confidence. Usually the level is set at 2 standard deviations i.e. 95% confidence.

Fig. 6.9

6.3 The pauseShortly after the Climate Dynamics paper appeared, the follow-up paper "Return

periods of global climate fluctuations and the pause"gg was published, and it shed a somewhat different light on the prevailing sociology and politics of science. The new paper used the same basic approach as the April paper and provided the first estimates of how long one would expect to have to wait in order to observe natural global temperature fluctuations of various amplitudes over various time periods. It concluded that the "pause", "hiatus" or "slowdown" in the warming since 1998 was simply a fairly common natural cooling event that largely masked the ongoing anthropogenic temperature increase. By showing that the pause was natural, the remaining skeptic argument the warming had stopped in 1998 was demolished. The paper achieved media prominence and was notably featured on the front page of "The Gazette", Montreal's daily paper with the headline: "Global Warming slowdown just a 'pause'"hh.

At this point in July 2014, I was trying to promote some of my simpler graphs (see ch. ?) as educational tools to help convince remaining skeptics of the reality of anthropogenic warming. In many countries - notably, Canada, the US, Britain and Australia - the skeptics still included substantial proportions of the general public and I considered that battling them was an important priority. I contacted colleagues particularly familiar with this kind of hand-to-hand combat, especially the feisty Michael Mann. In 1998 Mann and colleagues had pioneered the technique of reconstructing past climates with the technique of "multiproxies" that enlisted every available natural indicator of past climate

gg 5 Lovejoy, S. Return periods of global climate fluctuations and the pause. Geophys. Res. Lett. 41, 4704-

4710, doi:doi: 10.1002/2014GL060478 (2014). The McGill press release was entitled: "Global warming ‘pause’ reflects natural fluctuation": https://www.mcgill.ca/newsroom/channels/news/global-warming-pause-reflects-natural-fluctuation-237538. hhThe Gazette, July 24, 2014, p1: http://www.physics.mcgill.ca/~gang/popular.articles/Gazette.7.14/Gazette.pause.all.final.jpg. This was followed by an op-Ed in the Gazette in August by "The Friends" exposing their theory of solar causation and attacking me personally: (The Gazette, August 28, 2014: http://montrealgazette.com/opinion/editorials/opinion-global-warming-pause-is-more-than-temporary-scientific-evidence-shows). It was signed: " Len Maier is an engineer and president of the Friends of Science Society in Calgary. "

change (tree rings, ice cores, lake sediments etc.) into a year by year estimate of global scale temperaturesii. The resulting temperature estimates since 1000 A.D. (fig. 2c?) resembled a hockey stick - with its long handle corresponding the slowly varying (mostly decreasing) temperatures from 1000 until about 1900 - after which the record displayed the characteristic sharp anthropogenic rise. The "hockey stick" had become the poster figure of the scientific community (playing prominently in the International Panel on Climate Change's (IPCC) third assessment report (AR3, 2002?), and consequently had become a primary skeptic targetjj. Mann himself was not shy of a fight and had quickly become the main skeptic whipping boykk.

Mann was both helpful and encouraging and put me in contact with NGO's that were committed to bringing media attention to that was science deemed important in the fight against anthropogenic warming. Here I was in for a disappointment. Following Mann's advice, I forwarded the paper, press release and supporting material to a US-based NGO hoping to get help in spreading the word. At first, I received a polite response saying that they would consider it. After a few weeks, when I hadn't heard any answer, I prodded them with another email. This time, I received a laconic reply that in their view it was best to ignore the pause: any mention of it - even to show that it was no more than a natural fluctuation - would give it undue publicity and make it appear that there was a debate where - according to them - there wasn't any. By this time (summer 2014) the environmentalists had become supremely confident - in my opinion, overconfident - and believed that the skeptics were better ignored than confronted.

One could understand their attitude: by any usual scientific standard, the debate was over. The last serious scientific difficulty for the anthropogenic warming hypothesis originated back in 1996 when satellite measurements of atmospheric temperatures since 1980 - in contradiction with the surface measurements - had failed to show the expected warmingll. But by 2006, the last of four flaws in this work had finally been laid bare: with the correct treatment of errors and biases (several of them were subtle), the satellite data ended up fully supporting the warming evident in the surface measurements. It was at this time that Michael Shermer, the influential editor of the Skeptical Inquirer, changed his position saying that due to the advances in climate science, that continuing to oppose anthropogenic warming on the grounds of skepticism would be antiscientific.

But this end of the scientific debate had played out in an academic literature largely impervious to the layperson. It had barely diminished the strength of the skeptics who continued to tout variants of their own giant natural fluctuation theory, nor had it done much to change public perceptions. To paraphrase Carl Sagan: claims with extraordinary consequences require extraordinary evidencemm. For global warming, the stakes for the economy and for the future of humanity were so extraordinary that the usual levels of scientific proof were simply inadequate. It seemed to me that the strongest possible ii 14 Mann, M. E., Bradley, R. S. & Hughes, M. Northern Hemisphere Temperatures During the past Millenium: Inferences, Uncertainties, and Limitations . Geophys. Res. Lett. 26, 759-762 (1999)..jj Skeptics ritually refer to it as "the discredited hockey stick".kk See his own compelling account, 15 Mann, M. E. The Hockey Stick and the Climate Wars: Dispatches from the Front Lines. 448 (Columbia University Press, 2012).ll The chief protagonists in this affair were Christy and R. Spencer who collaborated in the analysis. Both were upfront about their religion with the latter publically justifying his scripture-based skepticism: "Earth and its ecosystems – created by God's intelligent design and infinite power and sustained by His faithful providence – are robust, resilient, self-regulating, and self-correcting".mmThe expression "Extraordinary claims require extraordinary evidence" was popularized by Carl Sagan and attributed to Mario Truzzi, it referred to claims of paranormal events.

arguments had to be brought to bear and that the intellectual debate was not totally "closed" until the only competing theory - that of a giant natural fluctuation - could be convincingly discarded.

This book explains in simple terms the science behind the rejection of the giant natural fluctuation hypothesis. By necessity it also describes some nonlinear science on atmospheric variability including new answers to the question: "what is climate?", and it explains in a new way how to conceptualize and quantify atmospheric variability over huge ranges of time and space scales ranging from milliseconds to the age of the plant, from millimeters to its size. Many of these ways of viewing the atmosphere originated in nonlinear science - in particular in my own field of nonlinear geoscience - and they may be unfamiliar even to those with an otherwise solid grounding in climate science.

Science is a very human activity, and in many respects anthropogenic warming involves more social, political, moral and ethical issues than any other challenge facing humanity today. Although my focus is on the science, I will attempt to put these developments into their social, political, economic context: the reader will be taken through some of its more interesting, amusing - and sometimes disturbing - ramifications.

This book is the story of how, starting in the 1980’s, advances in nonlinear geophysics have finally allowed us to reject the natural warming theory with more than 99% confidence. Whereas the scientific theory of anthropogenic causation is difficult for nonspecialists to follow, a bonus of this disproof is that it is more accessible. Whereas proving anthropogenic warming can easily get one embroiled in arcane arguments about the corrections and biases of thermometer and satellite measurements, about what is the best way to parameterize the “sub-grid” properties of clouds or aerosols (pollution) or as to what are exactly the ocean-atmosphere interactions or what is the ocean uptake of CO 2? In comparison, the disproof cuts to the chase requiring only some relatively straightforward notions of probability and of space and time scales that are explained below.

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