Lack of Environment

A blog on the politics and psychology underlying the denial of all our environmental problems

Archive for the ‘junk science’ Category

Occam’s Razor works for me!

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‘The Hockey Stick and the Climate Wars: Dispatches From The Front Line’ by Dr Michael Mann, Professor of Meteorology at Pennsylvania State University, was recently published in paperback.  I decided to purchase a copy.  Here is my review of the book, as published on amazon.com.

In the opening chapters of this book, Michael Mann repeatedly makes it clear that, as a physicist, his interest in palaeoclimatology was entirely natural.  That is to say, he did not approach the evidence for climate change with any prejudicial notion of what he wanted to find, least of all to prove that ongoing climate change is predominantly human-caused.  

Those who are suspicious of Michael Mann’s motives will no doubt respond:
“Well, he would say that, wouldn’t he!

However, all readers of this book will, sooner or later, have to decide where they stand on the question of the validity of ‘Occam’s Razor’.  This is the logical supposition that, among competing hypotheses, the hypothesis with the fewest assumptions should be selected.  With regard to climate science, I have to say, it works for me:  Either this book is an unashamed piece of propaganda and, from the very start, is deeply disingenuous; or it is the honest account of a very humble physicist who, completely unwittingly, became the focus of the biggest industry-funded misinformation campaign of modern times.

Having read both this book and Andrew Montford’s ‘Hockey Stick Illusion’, I should like to propose that, even if you have not done so, you have the following choice:  Do you put your trust in an authoritative argument from a genuine expert (Mann) or do you want to believe the conspiracy theory put forward by a non-expert (Montford)?

Put it another way, are you going to believe that climate scientists are over-stating a problem in order to perpetuate the funding of their research; or are you willing to accept that business leaders are down-playing a problem in order to perpetuate the viability of their business?

If you are undecided, the following facts may help you:
(1)  There is no significant precedent for research scientists over-stating environmental problems – nor any evidence (that has not been examined and found to be groundless) that climate scientists are doing this or have done this at any time in the last twenty years.
(2) There is a very significant precedent for business leaders (in the tobacco industry) down-playing environmental problems – and a great deal of evidence that this is exactly what fossil fuel executives have been doing for at least the last 20 to 50 years.

In the opening chapters of this book I was particularly impressed by the following argument (attributed to Stephen Schneider): We do not buy home insurance because we think our house may burn down. We buy it because that very unlikely event will be catastrophic… Applied to the issue of anthropogenic climate disruption, humanity’s continuing failure to take out insurance against an increasing probable catastrophic outcome does indeed seem “crazy”…  Unless of course, you prefer to believe the ideologically prejudiced opinions of other genuine non-experts like Senator James Inhoffe, who would have us all believe that anthropogenic climate disruption (ACD) is a false alarm.

If, after reading this book, you still think ACD is a false alarm, I suggest you cancel your fire insurance – you’re wasting your money – it’s never going to happen.

The imprudence of being earnestly Oakwood

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As for the flat Earth, the debate is over.

I concluded yesterday’s post, entitled ‘The importance of being earnestly wrong’, by quoting a wonderfully circular argument from Oakwood.  This was the assertion that “…you cannot show any one of these [opinions] to be inaccurate, except by appealing to ‘the consensus’…”   In reality, the scientific consensus regarding climate science is no more the subject of legitimate debate than the consensus views that: the Universe and the Earth were not created in six days little more than 6000 years ago; the Sun does not orbit the Earth; humans did not co-exist with dinosaurs; and the Earth is not flat.

There are therefore some things about which we humans are no longer wrong (with the exception of those whose approach to science is prejudiced by their ideology or theology).

Yesterday’s post also contained a TED video of a March 2011 talk, entitled ‘On Being Wrong’, given by Kathryn Schulz.  This is so good – and so fundamental to appreciating the predicament that Oakwood is in – that I have embedded it here once again.

Schulz warns against automatically assuming that people with opposing views are either ignorant of all the relevant facts, intellectually incapable of processing the information, or deliberately stating things they know to be false.  However, she also makes the fundamental point that most people don’t know they are wrong – they are just as convinced that they are not wrong as those who are actually right.  This makes it critically important that everyone be willing to accept that they may be wrong.  I have done this a lot; and I still do it regularly.  However, with regard to climate science, I repeatedly find myself coming back to the logical proposition that:

Doubting the science can only be justified by asserting that the consensus is unreal, unreliable or unreasonable.  This does not require all scientists to be liars; but it does require the vast majority of genuine experts to be either stupid, mistaken or mendacious.

Not only would such (implausible, improbable, or insidious) things be without precedent (and require an awful lot of people to be wrong or corrupt), there is also a clear precedent – in the tobacco industry – for the business-funded disputation of highly inconvenient science (which only required a few people to be corrupt in order to fool an awful lot of people).

So, then, because I think it highly instructive – and since it is impossible to breach the confidentiality of someone who chooses to remain anonymous – Oakwood’s email to me is reproduced below (entirely without permission) with rebuttals included in bold text:

“You are entitled to your own opinions but not your own facts.”  Yes, that applies to everyone.  Here are a few facts:

IPCC models did not predict the current temperature pause.  If the IPCC has [now] said ‘because of what we know about the ocean’s massive heat capacity compared to the atmosphere, and the potential for aerosols from growing economies such as India and China, a 15 to 20 year pause is possible’. Of course, they didn’t say that [before], and only come up with the theory after the event.  The IPCC do not do the modelling; they merely synthesise the results and summarise the implications.  This is therefore statement of belief in either widespread scientific incompetence or political conspiracy.  Furthermore, since (1) ice continues to melt (at sea and on land); (2) sea level continues to rise; and (3) ocean pH continues to decline, warming has clearly not stopped.  See also ‘How reliable are climate models’ and ‘Global Warming Has Stopped’ on SkepticalScience (SkS).  

Proxy temperature data studies cannot reproduce instrumental data for recent decades – when temperatures are at their highest. Therefore, we cannot rely on them to say anything about previous ‘high temperature’ episodes, such as the MWP.  This is a complicated issue but this argument has been comprehensively and repeatedly discredited.  For example, see ‘Response by Marcott et al’ on Real Climate (with links to other sources of info).  As for the MWP, see ‘How does the Medieval Warm Period compare to current global temperatures?’ on SkS.

While so much is made of the Arctic’s ‘record’ low, little is said about the Antarctic’s ‘record’ high, except ‘well that’s different’.  Antarctica is geographically isolated and affected by the hole in the ozone layer but, despite this, the West Antarctic and the Antarctic Peninsula are warming as fast as the Arctic.  See also ‘Antarctica is gaining ice’ on SkS.

The IPCC finds NO convincing link between extreme weather events (floods, drought, hurricanes) and global warming. Their best is ‘medium confidence’ (for heavy precipitation). (More warm days and fewer cold days is not ‘extreme weather’, but simply a logical outcome of the fact temperatures rose over the 20th C). The IPCC has been repeatedly shown to understate all kinds of risk.  Historical analysis of weather in the Northern Hemisphere has shown that extreme weather is becoming more frequent.  Multi-decadal change like this cannot be explained without reference to human activity.

IPCC and climate scientists have no idea when the pause will come to an end. Their ‘accurate’ models cannot tell them. This does not matter.  Arguing that warming has stopped requires falsification of the evidence that increased atmospheric CO2 is the dominant factor.  See ‘It’s not us’ on SkS.

The 97% consensus includes most AGW-sceptics, including me. That is: CO2 is a greenhouse gas; its concentration has increased over the 20th C; it has very likely made some contribution to warming.   This myth has been repeatedly debunked.  This piece on the RealSceptic blog is the best source of information I have yet seen on how and why this argument is entirely bogus.

There is general agreement amongst climate scientists that a doubling of CO2 on its own will create about a 1dgC rise.  CO2 is not acting alone and it is the totality of change that is causing problems.  Apart from that facet of reality, this is a very misleading argument, as explained by Michael Mann himself on the LiveScience blog

Anything more relies on the belief/assumption that positive feedbacks will significantly outweigh negative feedbacks. Ongoing change despite a pause in surface warming implies warming effects are outweighing cooling effects.

But, we’ve had all these discussions before. But you cannot show any one of these facts to be inaccurate, except by appealing to ‘the consensus’ and making nonsensical statements about ‘believing all scientists to be liars’. No, Martin, the practice of science is not about saying: ‘If you disagree with me, you’re calling me a liar’. I have not called Oakwood a liar but, I must admit, he/she does seem to be remarkably incapable of accepting that he may be wrong.

It’s about proper open debate.  The fact that the vast majority of ‘sceptics’ are libertarians and/or free-market ideologues proves that the ongoing ‘debate’ is driven by policy implications not any residual uncertainty regarding science. See this excellent essay by Stephan Lewandowsky on The Conversation blog.

While still a minority, there are plenty of climate scientists and experts who do not believe AGW is a major threat.  For this to be valid the pool of “climate scientists and experts” would have to be broadened to include all kinds of scientists whose expertise is not relevant.  Since we do not generally allow this when discussing evolution or cosmology, why should we do it for climate science? 

Of course the answer to that final question is that, as with evolution and cosmology, some people are ideologically opposed to accepting the nature of reality.

The hypocrisy of willful blindness

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Activity levels in the deniosphere have been very high this week, following the publication of the usual nonsense from David Rose in the Mail on Sunday on 8 September 2013.  Whilst I cannot be bothered to even try and engage with people on that blog, I did attempt to do so with readers on Mike Adams’ Natural News (NN) blog (see my previous post on this blog).  Sadly, even on that very ill-judged republication, the levels of selective deafness amongst Mike Adams’ readers would appear to be very high.

As anyone who has attempted to reason with those who believe climate science is a Communist conspiracy will tell you, circular arguments are very common. However, I think the example below is an absolute classic.

Swindon’s so-called ‘Magic Roundabout’ (Image credit: Van Rhijn Aerial Photography)

The same blogger who drew my attention to the NN article also pointed me in the direction of a rebuttal on the WordPress blog of the UK’s Meteorological Office.  In response to a number of comments on that blog, I have posted a number of replies (all of which are currently awaiting moderation). However, in a style reminiscent of ‘Denier Comment of the Day’ on uknowispeaksense, I would like to draw attention to one comment in particular (and my response to it):

Judge Fudge (@jdey123) (16:27:20) 13/09/2013
Records of arctic sea ice extent starting only in 1979 are way too recent to make meaningful conclusions. Antarctic sea ice extent is in any case increasing. How come this is continually ignored? We are told that global surface temperature pause is due to the ocean absorbing more heat, yet this year, arctic [sea ice] extent has increased more than 50% from that recorded last year and Antarctic sea ice extent is above average. The myth has unravelled. Why are taxpayers paying for the Met Office to promote Marxist ideology hidden as environmental concerns? It’s time for the Coalition government to stop funding these people.

Martin Lack (10:37:46) 14/09/2013
So, what you’re saying is this: You cannot draw any firm conclusions from a 34-year accelerating loss of sea ice but you want the World to do just that on the basis of a 15-year pause in a multi-decadal warming trend.

For the record, the above was actually my second reply to Judge Fudge. This was my first:

Martin Lack (20:50:30) 13/09/2013
The Antarctic is colder than it would otherwise be because of the hole in the ozone layer above it (another example of how humans can affect the environment). Antarctica is also completely surrounded by a huge expanse of uninterrupted, cold ocean. Despite all of this, however, the Antarctic Peninsula is the fastest-warming place in the southern hemisphere. The only myth that is unravelling is the 50-year-out-of-date paranoia that everything you don’t like the sound of must be part of a Communist (or Zionist) plot for World domination.

Written by Martin Lack

14 September 2013 at 12:00

Nice website, shame about the ideological blindness

with 20 comments

Masthead-v6

A  blogger friend of mine who subscribes to NaturalNews.com sent me the a link to an article on it, entitled ‘Global warming computer models collapse; Arctic ice sheets rapidly expand as planet plunges into global cooling’ , challenging me to find the scientific flaws in it.

Sadly, this was very easy:  There is no valid science in the article, which is written by Mike Adams, who… “is an award-winning journalist and holistic nutritionist with a passion for sharing empowering information to help improve personal and planetary health…” (i.e. he is not a scientist).

Indeed, upon reading the article and doing some investigation of its sources (etc), it quickly became apparent that the article is, in fact, just a regurgitation of misinformation posted by scientifically-illiterate journalists in the Mail on Sunday (David Rose) and Sunday Telegraph (Hayley Dixon).  ***Update – Apparently ‘Hayley Dixon’ IS David Rose (see first comment posted below)***

Dana Nuccitelli, author of a number of peer-reviewed articles on the scientific basis for concern about human-caused climate change, has done two good demolition jobs on these articles: (1) briefly (on both) on the Guardian website; and (2) in more detail (on David Rose) on the SkepticalScience website:

(1) - Arctic sea ice delusions strike the Mail on Sunday and Telegraph

(2) - Arctic sea-ice ‘growth’, a manufactured IPCC ‘crisis’ and more: David Rose is at it again

However, for the record, this is my response to the (un)original article by Mike Adams:

The flaw in the article is that it is full of statements of opinion dressed up as fact; and that those opinions can only be justified by dismissing the consensus view of our predicament as a political and/or scientific conspiracy. Indeed, this article is quite remarkable in that it manages to include just about every ‘sceptical’ argument I have ever heard. All of which are answered on sites like SkepticalScience/Arguments.

The problem, of course, is that if you are a conspiracy theorist, any source of information that conflicts with your beliefs is automatically rejected as being part of the conspiracy. If so, how do I know that it is not me that is the conspiracy theorist? That is simple: My beliefs are not just my beliefs; they reflect the settled view of the vast majority of relevant experts based on an examination of all of the evidence.

Therefore, unlike the erroneous consensus that the Earth is flat that was overturned by the weight of conflicting evidence, the consensus that humans are the primary cause of climate change will never be overturned by people like Mike Adams who cherry-pick the only data capable of justifying an alternative view.

To dismiss the vast majority of experts as stupid, mistaken, or deceitful, is not just conspiracy theory; it is also highly improbable. As I have now said many times, it is more likely that the Moon Landings were faked and/or that 9/11 was an inside job.  

Clearly, people like Mike Adams (who has chosen very unwisely to live in Tuscon, AZ – one of the World’s most unsustainable cities) are perfectly at liberty to choose to believe conspiracy theories rather than accept science. However, in doing so, the vast majority of the evidence suggests that they are being ideologically blinded to the intellectual dishonesty required to make that decision: The decision not to follow the evidence to the fully justifiable conclusion that humans are primarily responsible for what is happening to our planet and need to modify their behaviour accordingly.

Resources are not infinite, and perpetual growth in consumption of any resource is therefore ultimately impossible. Fossil fuels will run out one day and we therefore need to plan for a World without them. However, now that we know burning them is endangering the climatic stability that made all life on Earth possible (i.e. the settled view of the vast majority of scientists), we need to phase out fossil fuel use wherever possible; and as fast as possible.

If we do not plan for this transition (to a fossil fuel-free future), it will happen anyway (and be a lot more abrupt, costly, and unpleasant). Therefore, as someone once said, “Failing to plan is tantamount to planning to fail!”

Written by Martin Lack

11 September 2013 at 16:00

To mark Australia’s return to the anti-science wilderness!

with 35 comments

It looks like Australia is just about to elect the most anti-science government outside of North America:  ‘Tony Abbott to win Australian election, final polls show’ (i.e. on UK’s Telegraph website).

To mark this latest ‘victory’ for those duped by conspiracy theory explanations for climate science in particular (and the stupidity of libertarian ideological blindness in general), I have decided to reproduce below my response to my most recent reality-challenged follower, called ‘freedomfan’, who has suggested that Richard Lindzen’s beliefs are a good reason to think humanity is not sleepwalking into an environmental catastrophe.

Richard Lindzen may be a meteorologist but he is not well-respected. He shredded his scientific credibility a long time ago as a result of being willing to appear as an expert witness for tobacco companies trying to dispute the reality of inconvenient science. Sadly, he learnt nothing from doing this and has repeated his mistake with the fossil fuel industry.

For someone who is gambling the future habitability on low climate sensitivity (when every time the issue is revisited the consensus view is that Lindzen is wrong), you seem remarkably confident in your own wishful thinking. This seems even more ill-judged when you consider that the International Monetary Fund, the International Energy Agency and the US Department of Defense all agree that anthropogenic climate disruption is happening; and that it is significant, bad, and worth preventing. Are they all in on the conspiracy to perpetuate scientific research funding; and/or justify higher taxes and authoritarian government? Quite frankly, it is more likely that the Moon Landings were faked (e.g. that flag was blowing in a breeze after all, right?).

If there is no positive feedback mechanism (and/or massive inertia in the climate system), why have the glaciers, ice caps, ice shelves and sea ice all continued to melt? If there is no positive feedback mechanism, why is the Keeling Curve a curve (rather than a straight line)? Positive feedback mechanisms are everywhere in Nature (very few things are linear); because Nature is biological – and we are part of it.

Here are 10 positive feedback mechanisms, which Guy McPherson has identified, that all need to be “disappeared” before your ambivalence towards the veracity of climate science becomes anywhere near being anything other than ideological blindness:
- Methane hydrates are bubbling out the Arctic Ocean.
- Warm Atlantic water is defrosting the Arctic Ocean.
- Siberian methane vents are increasing in size.
- Amazonian drought/fires released more CO2 than USA in 2010.
- Peat decomposition in boreal forests is accelerating.
- Methane is now being released from seabed in the Antarctic.
- Wildfires are increasing in frequency and scale.
- Increased CO2 is accelerating glacier disintegration.
- Exposure to sunlight is accelerating the thawing of the permafrost.
- Arctic drilling is being fast-tracked by Western governments.

For links to data sources, see: What on Earth are we doing (19 February 2013).

Anyone in any doubt about Lindzen, should read the large number of posts on this blog in the ‘Lindzengate’ category.  However, anyone in a hurry should start with:  Lindzen is either negligent, incompetent, or deceitful (6 July 2012).

How NOT to be sceptical

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In the process of compiling my previous post, I was reminded of this one; and decided it warranted being re-posted in its own right…  Originally posted on 7 September 2011, as How to be a climate change “sceptic”, this is probably (even if I do say so myself) one of the best things I have ever written here (because it neatly summarises the raison d’etre of this blog).

———-

Washington and Cook - Climate Change DenialIf I have not said it before, the reason sceptic is inside quotation marks is because I take the view, as do Clive Hamilton, Peter Jacques, and David MacKay, that those who deny anthropogenic climate disruption (ACD) are not sceptics at all.

As a consequence of this, my (MA in Environmental Politics) dissertation (researching climate change scepticism in the UK) included a threefold theoretical background, as summarised (on my old blog) as follows:
1. The philosophical roots of scepticism;
2. The political misuse of scepticism; and
3. The psychology of denial.

All of this leads me to offer readers this easy-to-use guide on “How to be a climate change ‘sceptic’”, as follows:
1. Assume everything you have been told by authority figures is a lie.
2. Assume, even though you are not an expert, that you know best.
3. Allow confirmation bias to prevent you from considering any information that might alert you to the fact that you are suffering from cognitive dissonance (i.e. “It is hard to convey just how selective you have to be to dismiss the evidence for climate change. You must climb over a mountain of evidence to pick up a crumb: a crumb which then disintegrates in your palm. You must ignore an entire canon of science, the statements of the world’s most eminent scientific institutions, and thousands of papers published in the foremost scientific journals…”George Monbiot, 10 May 2005).
4. Continue asserting your individual human rights whilst simultaneously ignoring your collective human responsibilities.
5. Maintain a utilitarian attitude to the environment (i.e. “use it up and wear it out”) despite mounting evidence to indicate that the ecological carrying capacity of planet Earth (w.r.t. humans at least) has already been exceeded.
6. Accuse anyone who asserts that there is cause for concern and/or an urgent need for radical action to mitigate humanity’s impact on the planet as being any or all of the following:- anti-human, anti-libertarian, anti-progress, anti-Western, and/or in favour of a new global socialist world government (“which is what the UN is all about, init!”).

In his book, ”Bad Science”, Ben Goldacre says that proponents of pseudoscience have succeeded in making people think science is impenetrable. However, the truth may be even more insidious because, by awakening people to the fact that they are regularly being lied to, these peddlers of pseudoscience have in fact contributed to – if not caused – a much more widespread distrust of science and all scientific authority.

Therefore, I would humlby suggest that claiming that humanity is not the cause of climate change is even more stupid – and even more dangerous – than claiming (as did Thabo Mbeki for a long time) that HIV is not the cause of AIDS.

My final word on Oakwood?

with 8 comments

Over on Learning from Dogs this week, Paul Handover has (i.e. across Monday and Tuesday) re-posted a lengthy juxtaposition of arguments for (Oakwood) rejecting and (me) accepting the reality of anthropogenic climate disruption (ACD) – along with (today) his response to it all.  Since all 3 posts are in danger of feeding the myth that it is still reasonable to question the reality of ACD, this is my response to Paul (also posted as a comment [awaiting moderation] on Learning from Dogs):

——-

Your acceptance of people with all kinds of weird and wonderful beliefs is indeed admirable, Paul. Furthermore, since you are entirely capable of reaching an informed decision of your own, I would not be so stupid as to thank you for agreeing with me on any of this. However, for the record:

With regard to the NYT article, Justin Gillis is quite simply wrong. The current hiatus in surface warming is not a mystery. This is because scientists have quantified the radiative energy imbalance caused by so-called greenhouse gases trapped in our atmosphere – 0.6 Watts per square metre (i.e. equivalent to the detonation of 400 thousand Hiroshima bombs per day). Sadly, we do not have the technology to measure the ‘missing’ heat that must, since we cannot find it anywhere else, therefore be collecting in the deep ocean.

With regard to [Paul's old friend] Dan Gomez, I am fairly certain that he is no climate scientist and claiming that global warming is a new religion is just another ‘zombie argument’ (i.e. one that refuses to die no matter how many times it is refuted). Indeed, a quick Google search reveals that it is one favoured by the right-wing media (e.g. Fox News and Forbes magazine). This is also just another way of saying ‘Sceptics are like Galileo’, which is one of many illogical arguments put forward by people who appear unwilling to accept the nature of reality. For example, on theScholars and Rogues website, Brian Angliss has started a good series of posts on this subject here. In a nutshell, climate sceptics are like the medieval Catholic Church – they are the ones rejecting all the evidence that conflicts with their beliefs.

With regard to Oakwood’s assertion (yesterday) that the label ‘climate change denier’ is offensive because it suggests equivalence with Holocaust denial… Upon reflection, I think this too is an illegitimate line of argument. This is because, as the tagline for my blog “on the politics and psychology underlying the denial of all our environmental problems” suggests, the only point being made is that such denial is not consistent with all the available evidence. Prof. Michael E. Mann puts it this way (emphasis mine):

The trouble is that the hockey stick graph become [sic] an icon and deniers reckoned if they could smash the icon, the whole concept of global warming would be destroyed with it. Bring down Mike Mann and we can bring down the IPCC, they reckoned. It is a classic technique for the deniers’ movement, I have discovered, and I don’t mean only those who reject the idea of global warming but those who insist that smoking doesn’t cause cancer or that industrial pollution isn’t linked to acid rain.
http://www.guardian.co.uk/science/2012/mar/03/michael-mann-climate-change-deniers

Personally-speaking, I wish the Earth were at the centre of the Universe and that everything (including our Sun) revolved around it. Sadly, such fanciful beliefs belong only to childhood or back in the Dark Ages. Therefore, although you may choose to insist that ACD is not a certainty, I can only respond by saying: (1) it is as near to being a certainty as anything in science ever is; and (2) those with a vested interest in perpetuating the status quo have turned residual uncertainty into unreasonable doubt.

Therefore – since it is almost certainly unreasonable to believe that ACD is a scientific hoax, a political scam, or a false alarm – I hope that anyone who is still undecided will at least read this excellent summary (on the Guardian website) of Chapter 4 of Michael Mann’s book, The Hockey Stick and the Climate Wars. For the benefit of those who will not, here is the bit I like the most:

A little more than a year after we had published our millennial hockey stick reconstruction, paleoclimatologist Thomas Crowley of Texas A&M University (and coauthor of the Crowley and Lowery reconstruction discussed earlier) published findings based on the use of a theoretical climate model simulation designed to investigate causes of past temperature change. Crowley subjected the model to estimated changes in natural factors over the past thousand years, using indirect measures of changes in solar output and explosive volcanic activity, information on both of which can be recovered from atmospheric deposits in polar ice cores.

These simulations revealed that the natural factors could explain the extent of medieval warmth in our reconstruction; in the model, this warmth arose from a relative lack of cooling volcanic eruptions combined with relatively high levels of solar output. The natural factors could also explain the cooler conditions of the ensuing Little Ice Age, which resulted from relatively low levels of solar output and more frequent explosive volcanic eruptions.

Fed the natural factors only, the model could not, however, reproduce the abrupt twentieth century warming. In fact, the model predicted that the climate should have cooled in recent decades, rather than warmed, if only natural factors had been at play. It was only when Crowley added the modern human influences – increasing greenhouse gas concentrations primarily from fossil fuel burning and the regional cooling effect of industrial sulphate aerosols emissions – to the model simulation, that it was able to track the hockey stick all the way through to the present.

The conclusion was clear: Natural factors could explain the temperature changes of the past millennium through the dawn of the industrial revolution, but only human influences could explain the unusual recent warming.

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