A Climate Change / Global Warming Spectrum

In politics, most people’s views can be placed on a spectrum, when it comes to climate change / global warming there is no such perspectives. The views are often polarized, particularly by those who believe in a future climate catastrophe. This is an initial attempt at a grid aimed at clarifying the issues. Your constructive advice is sought on how this might be improved.

When there are contentious or politicized issues, a spectrum of opinions emerge where there is free discussion of ideas. This is true in politics and the Christian religion. In both, there is not just a one-dimensional spectrum of ideas, but multi-dimensional perspectives. For instance, in politics it has been argued that the left-right spectrum should be split into economic and moral issues. The United States Libertarian Party has had a simple survey running since 1995. A more comprehensive (but still American-orientated) survey is the Political Spectrum Quiz.

Another idea comes from Greg Craven, who did a series of zany You-Tube videos on Climate Change, particularly such as The Most Terrifying Video You’ll Ever See” and “How it all ends“. He claimed that for the mass of non-scientists it was best to take a risk-based approach, grading the science on the credibility of those who made the claims. One objection with his analysis was it was based on polar extremes. That is either the worst climate catastrophe imaginable, or it is all a hoax. I proposed that there was a spectrum of possible outcomes, with the apocalyptic catastrophe at one extreme and the null outcome at the other. Basically there is a spectrum of views.

For this spectrum, the possible scenarios are from the null outcome on the left, rising to a huge climate catastrophe on the right.

Craven’s argument was to consider either 0 or 1000, whereas I claimed that the UNIPCC scenarios (representing the “consensus” of climate scientists), allowed for a fair range of outcomes. I have provided a log scale, as this puts clear distance between someone who believes in a low risk of catastrophe of extreme catastrophe to someone who says there is no risk at all. For instance, if someone believes that there is a 1% chance of the worst case, a 9% chance of loss of 100 and a 90% chance of a loss of 10, then their score would be 0.01*1000 + 0.09*100 + 0.90*10 = 28. In other words, for that person, especially if they are risk averse, there is still a very significant issue that should justify serious consideration of some type of global policy action.

But this measure of the prospective level of climate catastrophe needs to be based upon something. That something is scientific evidence, not people’s intuitions or gut feelings. If we imagine that the uncertainties can be measured as risks (as neoclassical economists do) then then the worst case scenario can only be attained if there is near certain, unambiguous scientific evidence in support of that prediction. If the evidence is weak statistically, gives highly variables results depending on methodology or data sets, or only tangential to the prediction, then a lower risk weighting lower than 1 will need to be ascribed. For an overall picture, we need to ascribe a weighting to the body of evidence. I propose a traffic light system. In outline green is for an overwhelming body of evidence, red is for no proper evidence whatsoever, and amber is for some weak evidence. Something along the following lines:-

Basically, an unambiguous case for impending global catastrophe must have a substantial body of strong scientific evidence to substantiate that case, with little or no contrary evidence. I will develop on another day the analogy with evidence presented to a criminal court by the prosecution. However, for the present, an analogy that is relevant is that this conclusion is only reached once the evidence fails to fall over under independent cross-examination.

This gives us a grid with the magnitude of the climate catastrophe on the X axis, and the scientific case on the Y axis. The grid, with my first opinion of where people various groups are placed, is given below. I know it is controversial – the whole aim is to get people to start thinking constructively about their views.

Alarmist Blogs (for instance Skeptical Science and Desmogblog) have an extreme black-and-white one world where they are always right, and anyone who disagrees is the polar opposite . “Deniers” is a bogeyman construct of their making.

If one reads the detail of UNIPCC AR4 report, the “Consensus” of climate scientists allow for some uncertainties, and for scenarios which are not so catastrophic.

The more Sceptical Scientists, such as Richard Lindzen, Roger Pielke Snr and Roy Spencer, view increasing greenhouse gases as a serious issue for study. However, they view the evidence as being both much weaker than the “consensus” and pointing to a much less alarming future.

The most popular Sceptic Blogs, such as Wattsupwiththat, Climate Audit and Bishop Hill I characterise as having a position of “The stronger the evidence, the weaker the relevance“. That is they allow for a considerable spread of views, but neither dismiss rise in CO2 as of no consequence, nor claim that the available evidence is strong.

Finally, the Climate Realists such as Joanne Nova and the British Climate Realists website. They occupy a similar position as the “deniers”, but from a much more substantial position. They can see little or no evidence of catastrophe, but huge amounts of exaggeration dressed up as science.

What are your opinions? What position do you think you lie on the grid? Is there an alternative (and more informative) way of characterizing the different positions?

Heartland Leak – The Implications

The stolen documents from the Heartland Institute have caused a lot of comment on the blogs. There are a number of things that will come out of this.

1. The consensus climate scientists and their cohorts cannot deal with numbers. Just as they have no sense of proportion with financial values (see Jo Nova on this), they likewise have no sense of proportion with sea level rise, temperature rise, or extreme weather events.

2. A better antonym of “sceptical” than “undoubting” or “believer” is “gullible”. Seems DeSmogBlog did not think to check out the authenticity of the damming 2012 strategy document, neither do they accept the Heartland rebuttal. It fitted the narrative, so they published within an hour of receiving the mail. Similarly The Guardian posted a number of one-sided reports (here, here, here), as did Roger Black of the BBC, without waiting to verify the facts. The most alarming 2012 strategy document is a fax (Judith Curry has other references)

3. A number of people, like me, will visit Heartland.org for the first time. They will find they have 7 policy areas employing 20 people, of which “Environment & Energy” employs 3. They specialise in providing cogent summaries of these issues to policy-makers. Whatever you think of their political stance, they are hardly the secretive, rabid backwoodsmen right-wingers that the alarmists project.

4. This support for spreading information in a concise, intelligible form also comes out in the sceptic-funding “exposes”. There is one-off support for Antony Watts who

proposes to create a new Web site devoted to accessing the new temperature data from NOAA’s web site and converting them into easy-to-understand graphs that can be easily found and understood by weathermen and the general interested public.” 

The, alleged, biggest recipient by far of monthly funding is Craig D Idso, who founded the co2science.org website. This provides summaries of climate science papers, collating their results to help give an overall picture of such as the medieval warm period, ocean acidification and the effect of CO2 on plant growth. For instance, I like this graphic summarising the proxy studies of the MWP showing that the Mannian Hockey Stick studies need to at least reconcile their claim that average global temperatures are warmer than in the last 1000 years.

5. It illustrates the upside-down nature of climatology, compared with conventional science. Conventional science is based on making bold statements and predictions that are substantiated by the evidence, with very clear and replicable methods. Over time it refines its techniques, strengthens its methods of analysis and sees its predictions confirmed. It does not need to denigrate, or attempt to silence its detractors. Like the historians of the holocaust, conventional science just points to the evidence and enlightens those who seek the truth. The real deniers of truth in history have been those who silence their opponents and fabricate distortions.

Overall, the leak exposes why the little Heartland Institute is so evil and dangerous to many. They threaten the jobs and reputations of tens of thousands of climate scientists, “policy-makers”, regulators, and powerful business interests in the alternatives to reliable energy. On the other hand, they are on the side of those made hungry by fuel crops competing with food, and of future generations globally, who will be worse-off by growth-sapping mitigation policies.

Joseph Stiglitz on the causes of the current crisis

Roger Pielke Jr. takes a critical look (here and here) at a novel theory of the recession from Nobel Laureate Joseph Stiglitz in Vanity Fair, the eminent economics journal. This is an extended version of the comment that I made on the second posting.

The Stiglitz theory would make a bit of sense if it were not for what he misses.

  • Your evidence that other countries, like, Germany, have similar increases in productivity but not the endemic problems.
  • That output per capita is identical in National Income Accounting with income per capita. Therefore, the long term rise in per capita income is a result of increased productivity per capita.
  • Since the start of the industrial revolution, real per capita output has risen (in the wealthy economies) more than 200 times. If there has been no corresponding increase in per capita income, unemployment would be greater than 99%.
  • Stiglitz quite rightly points to the rise in personal debt. He makes no mention of public sector debt. In the USA and in Britain in the period 2000 to 2007 government finances swung from a small structural surplus to significant structural deficit. If deficit-financed investment is expansionary, it was not just the low interest rates that kept the boom going but the fiscal stimuli. Similar structural deficits were present in many European countries like Greece, Portugal and Italy.
  • In the 1990 Japan entered a prolonged slump. In the following decade the economy stagnated despite huge public works investment like Stiglitz advocates. The Japanese national debt spiralled to 300% of GDP, with nothing to show for it, except a lot of fantastic roads to nowhere.
  • Japan was fortunate in that its borrowings are at near zero interest rates. The European economies are not so fortunate. Those European economies with large deficits reached a crisis tipping point when interest rates exceeded 7%. To save the economy, radical contractionary policies have been implemented.

I would therefore contend that Keynesian fiscal expansion in the USA or elsewhere would not only be ineffective (coming on top of other fiscal expansion), but carries a huge risk of making matters dramatically worse. Morally I believe that economic policy-making has a powerful analogy to medical practice. It is not just a matter of diagnosing properly the type and extent of the ailment. It is providing, at a minimum, a remedy for which there is a reasonable expectation that the patient will be better off being treated than not. Like with a GP, an economist has a duty of care in what they advocate, particularly when there are very clear and evident risks. Joseph Stiglitz seems to take no such care.

Economic v Climate Models

Luboš Motl has a polemical look at the supposed refutation of a sceptics arguments. This is an extended version of my comment.

Might I offer an alternative view of item 30 – economic v climate models?

Economic models are different from climate models. They try to model empirical generalisations and (with a bit of theory & a lot of opinion) try to forecast future trends. They tend to be best over the short term when things are pretty much the same from one year to the next. The consensus of forecasts are pretty useless at predicting discontinuities in trends, such as the credit crunch. At there best their forecasts at little better than the dumb forecast that next period will be the same as last period. In general the accuracy of economic forecasts is inversely proportional to their utility.

Climate models are somewhat different according to Dr MacCracken.

“In physical systems, we do have a theory—make a change and there will be a response in largely understandable and calculatable ways. Models don’t replace theory; their very structure is based on our theoretical understanding, which is why they are called theoretical models. All that the computers do is to very rapidly make the calculations in accord with their theoretical underpinnings, doing so much, much faster than scientists could with pencil and paper.”

The good doctor omits to mention some other factors. It might be the case that climate scientists have all the major components of the climate system (though clouds are a significant problems), but he omits to include measurements. The interplay of complex factors can cause unpredictable outcomes depending on timing and extent, as well as the theory. The climate models, though they have a similarity of theory and extent, come up with widely different forecasts. Even this variation is probably limited by sense-checking the outcomes and making ad hoc adjustments. If the models are basically correct then major turning points should capable of being predicted. The post 1998 stasis in temperatures, the post 2003 stability in sea temperatures and the decline in hurricanes post Katrina are all indicators that models are overly sensitive. The novelty that the models do predict tend not to be there, but the novelties that do exist are not predicted.

If it is the case that climate models are still boldly proclaiming a divergency from trend, whilst economic models have much more modest in their claims, is this not an indicator of climate model’s superiority? It would be if one could discount the various economic incentives. Economic models are funded by competing in institutions. Some are private sector, and some are public sector. For most figures there is forecast verification monthly (e.g. inflation, jobs) or quarterly (growth). If a model were consistently an outlier if would lose standing, as the forecasts are evaluated against each other. If it was more accurate then the press would quote it, being good name placement for the organisation. In the global warming forecasts, there is not even an annual variation. The incentive is either to conform, or to provide more extreme (it is worse than we thought) prognostications. If the model projected basically said “chill-out, it ain’t that bad man”, they authors would be ostracized and called deniers. At a minimum the academics would lose status and ultimately lose out on the bigger research grants.

(A more extreme example is of a major earthquake forecast. “There will not be one today” is a very accurate prediction. In the case of Tokyo area over the last 100 years that would have been wrong only twice, an accuracy of greater than 1 in 10,000).

Al Gore’s faulty case for CAGW

Wattsupwiththat have an estimate of Al Gore’s Climate Reality online viewing figures. I posted at the follow-up article

manicbeancounter says:

September 22, 2011 at 12:17 pm

I was one of those who stayed for over 5 minutes.

A video they had justified the case for global warming by re-doing the CO2 in a jar experiment – very nicely as well. Only they did not say what the concentrations were compared to the atmosphere (probably >1000 times the 0.04% at the moment).

Then in the space of a sentence mentioned feedbacks amplifying the effect.

So of the predicted warming up to 6 degrees centigrade this century predicted by the most extreme alarmists, Al Gore’s little video had a flawed experiment to justify the insignificant first 20%, and a “trust the computer models” for the alarming bit.

Don’t take my word for it – I am just a (slightly) manic beancounter. Check out for yourself at http://climaterealityproject.org/video/climate-101/

By the way – don’t worry about the stats – Alexa currently ranks this site at 16,989 and Climate Reality at 64,734.

REPLY: I have a post coming up on this video, which is online here also, without the need to visit Gore’s site: http://vimeo.com/28991442
-Anthony


Feedbacks in Climate Science and Keynesian Economics

Warren Meyer posts of a parallel between Climate Science and Keynesian Economics. I posted about a subject close to his heart, and central to Keynesianism – Feedbacks. I have also attempted to update on the current debate on feedbacks.

Warren

There is a parallel between Keynes and the CAGW that is close to your heart – feedbacks. Pure Keynesianism is that an increase in government expenditure at less than full employment would have a positive feedback response. Keynes called the feedback measure the multiplier. (The multiplier is the reciprocal of the proportion of Government expenditure to GDP. So if government expenditure was 20% of GDP, then a $1bn fiscal boost would increase output by $5bn.)

By the 1950’s the leading sceptic was Milton Friedman who, in his 1962 book “Capitalism and Freedom”, estimated empirically that the multiplier was about 1 – that is it did not have any impact. Friedman was denounced as a denier and a dinosaur. (At the same time, mainstream economics adapted his verificationist methodology.) Indeed by the end of the 1960s it was generally agreed that the long-term feedback impact of government demand management was negative, as increased government expenditure crowded out the private sector, caused escalating inflation (as economic actors ceased to be fooled by the false signals 0f increased expenditure), slowed economic growth and generally undermined the very structures of the capitalist system. (see Friedman’s Nobel Prize lecture “Inflation and Unemployment“)

Keynesian thinking is that the capitalist economic system is inherently unstable. Stability is only achieved through the guiding hand of government. Keynes contrasted this with a caricature of neoclassical economics, with the macroeconomic system would rapidly come back into equilibrium. Similarly, the climate models assumption of chronic instability is contrasted by an extreme caricature of those who disagree with them. That is the “deniers” are saying that the climate is incredibly stable, with human beings having no influence. In both cases the consequence of this caricaturing is to automatically claim any extreme occurrence as vindification of their perspective.

IPCC & Greenpeace

The Shub Niggurath (Hattip BishopHill) arguments against the IPCC’s SSREN growth figures are complex. The Greenpeace model on which they were based basically took a baseline projection and backcast from there. A cursory look at the figure GDP figures shows that the economic models point to knife-edge scenario. The economic models indicate that the wrong combination of policies, but successfully applied, could cause a global depression for a nigh-on a generation and lead to 330 million less people in 2050 than the do-nothing scenario. But successful combination of policies will have absolutely no economic impact.

Shub examines this table :-

Table 10.3, page 1187, chapter 10 IPCC SRREN

(Page 32 of 106 in Chapter 10. Download available from here)

I have looked at the GDP per capita and population figures.


To see whether the per capita GDP projections are realistic, I have first estimated the implied annual growth rates. The IEA calculates a baseline of around 2% growth to 2030. The German Aerospace Centre then believes growth rates will fall to 1.7% in the following 20 years. Why, I am not sure, but it certainly gives a lower target to aim at. Projecting the 2030 to 2050 growth rate forward to the end of the century gives a GDP per capita (in 2005 constant values) of $56,000. That is a greater than five-fold increase in 93 years.

On a similar basis there are two scenarios examined for climate change policies. In the Category III+IV case, growth rates drop to 0.5% until 2030. It then picks up to 2% per annum. Why a policy that reduces global growth by 75% for 23 years should then cause a rebound is beyond me. However, the impact on living standards is profound. Almost 30% lower by 2030. Even if the higher growth is extrapolated to the end of the century, future generations are still 12% worse off than if nothing was done.

But the Category I+II case makes this global policy disaster seem mild by comparison. Here the assume is that global output per capita will fall year-on-year by 0.5% for nearly a generation. That is falling living standards for 23 years, ending up at little over half what they were in 2007. This scenario will be little changed in 2050 or 2100. Falling living standards mean lower life expectancy and a reduction in population growth. The model reflects this by projecting that these climate change policies will lead to 330 million less people than a do-nothing scenario.

Let us be clear what this table is saying. If the world gets together and successfully implements a set of policies to contain CO2 levels at 440ppm, the global output in 2050 will be 40% lower. There is a downside risk here as well – that this cost will not contain the growth in CO2, or that the alternative power supplies will mean power outages, or that large-scale, long-term government projects tend to massively overrun on costs and under perform on benefits.

Let us hark back to the Stern Review, published in 2006. From the Summary of Conclusions

“Using the results from formal economic models, the Review estimates that if we don’t

act, the overall costs and risks of climate change will be equivalent to losing at least

5% of global GDP each year, now and forever. If a wider range of risks and impacts

is taken into account, the estimates of damage could rise to 20% of GDP or more.

In contrast, the costs of action – reducing greenhouse gas emissions to avoid the

worst impacts of climate change – can be limited to around 1% of global GDP each

year.”

Stern looked at the costs, but not at the impact on economic growth. So even if you accept his alarmist prediction costs of 5% or more of GDP, would you bequeath that to your great grandchildren, or a 40% or more reduction lowering of their living standards along with the risk of the policies being ineffective? Add into the mix that The Stern Review took the more alarming estimates, rather a balanced perspective(1) then the IPCC case for reducing CO2 by more solar panels and wind farms is looking highly irresponsible.

From my own perspective, I would not have thought that the impact of climate mitigation policies could be so harmful to economic growth. If the models are correct that the wrong policies are hugely harmful to economic growth, then due diligence should be applied to any policy proposals. If the economic models from the IPCC are too sensitive to minor changes, then we must ask if their climate models suffer from the same failings.

  1. See for instance Tol & Yohe (WORLD ECONOMICS • Vol. 7 • No. 4• October–December 2006)

Update 27th July.

Have just read through Steve McIntyre’s posting on the report. Unusually for him, he concentrates on the provenance of the report and not on analysing the data.

Comparing Politicians to Global Warming Deniers

At CafeHayek, Don Bordeaux has a post that requires careful reading. It is an attack on politicians and overbearing government, couched in a metaphor of global warming deniers.

My comment was

Using the metaphor of global warming is apt, but like any metaphor breaks down once examined closely. I would claim that a global warming “denier” has a more tenable position once the evidence is examined in detail and from different perspectives. Conversely, a denier of the unintended consequences of interventionism, like a holocaust denier, has a less tenable position once the alternative evidence is examined.

This brings me onto a second point. Politicians are selling themselves to get elected, which implies building up coalitions of diverse interest groups. Early Public Choice theory called this Pork-Barrel politics. A more successful approach in the television era is one based on image. That is projecting personality over policy substance. It goes against the notions of weighing up the pros and cons, learning from error in one’s past judgments, and recognizing limitations in one’s abilities and knowledge. Good government requires questioning skeptics, but has a propensity to elect the smooth-talking deniers.

An early example of image-based politics – indeed the forerunner in modern times – is JF Kennedy. A more recent example in Britain is New Labour. The image-based politics justified building up a structural deficit in the boom years. The need to save face, and the political ambitions of the key player, meant that the political business cycle did not operate after the 2005 general election. That is, according to Public Choice Theory, to boost the economy to get re-elected and then take the necessary measures to reduce the deficit immediately after.

Biofuels – a policy that is killing the poor

The GWPF reports on a new paper by Indur M. Goklany, Ph.D. that estimates the biofuels policy may be causing 200,000 additional deaths a year. This is compared to the 141,000 deaths (on a like by like basis) that WHO claims may be attributable to climate change.

This paper understates the comparison as the biofuels estimates are many times more robust than the climate change deaths estimates.

The biofuels element is a direct relationship. As real income increases above $1.25 per day, the quantity of food that people can buy increases. From mostly a subsistence existence people can trade. Variety and calorific value of food increase. Also constancy of food supply is assured as a rapidly shrinking portion is reliant on the local harvest. Push up the real cost of food rapidly and this virtuous growth cycle is reversed.

The aspect of Global Warming comes from page 72 of the WHO World Health Report 2002.

“Climate change was estimated to be responsible in 2000 for approximately 2.4% of

worldwide diarrhoea, 6% of malaria in some middle income countries and 7% of dengue

fever in some industrialized countries. In total, the attributable mortality was 154 000 (0.3%)

deaths and the attributable burden was 5.5 million (0.4%) DALYs. About 46% this burden

occurred in SEAR-D, 23% in AFR-E and a further 14% in EMR-D.”

The global warming element comes from

  1. Looking at other elements and relating the impacts to temperature and climate volatility empirically.
  2. Measuring accurately recent temperature record to show increases in temperature. The warming in recent years may have been overstated due to failure to adjust for the urban heat island effect and possible biases in the calculation.
  3. Correctly relating this a proportion of this warming to anthropogenic factors. If it is overstated, then so is the justification for policy to mitigate the climatic effects of that warming.
  4. Accurately measuring the impacts of warming on the climate factors such as floods, droughts, sea level rise, extreme heat waves etc.

If any of these issues are overstated individually, then they can significantly reduce the relationship. But compound and they make the global warming deaths insignificantly different from Zero. For instance the relationship between temperature and malaria is highly controversial and has been dismissed. This might be 10% of the deaths. If the recent rise is only 0.3 degrees, rather than 0.4 degrees, then the mortality impact will reduce more than proportionately. If half the temperature rise due to anthropogenic factors, then it more than halves the impact. Most importantly there is the influence on climate variability. If extreme weather has not increased due to global warming – for instance the hurricane impacts were based on insurance claims rather than increasing frequency and intensity of storms (they may be decreasing), then some of the factors are decreased. Let us give a minimal impact of each of these impacts. Linking each of the elements to climate change could reduce of the attribution by 10% to >90% (say 60%). Measurement actual AGW reduces by 20% to 60% (say 40%). Weather variability due to AGW is highly suspect due to separation from the highly variable natural variability, so the will reduce the attribution by 50% to >100%. Take this as an 80% reduction. The compound effect on attributable deaths is 154,000(100%-60%)(100%-40%)(100%-80%) equals around 7,400. In other words, it is statistically insignificant.

On the other hand there is no mention of the most direct and beneficial impact of increasing greenhouse gases on the health and well-being of the poorest. Higher CO2 levels are directly related to increased plant growth rates and biomass. That means increased agricultural productivity for free.

The later 2003 WHO report “Climate Change and Human Health – Risks and Responses” used this report’s findings, but had plenty of hidden warnings. For instance the final conclusion was

“The increasing trend in natural disasters is partly due to better reporting, partly due to increasing population vulnerability, and may include a contribution from ongoing global climate change.”

Finally, one must consider that if the global warming estimate is accurate, it is not an either/or comparison. Current climate change policies will not achieve a significant reduction in CO2 levels. So the poor will be hit with extra deaths from both sources.

 

The Economist on Corn Production over 30 degrees

The Economist gives a positive spin to the article ““Nonlinear heat effects on African maize (corn) as evidenced by historical yield trials”, Lobell et al.” in Nature : Climate Change. I posted the following comment:-

Experimental conditions must be controlled to get comparable results. But this is not real world conditions. In the real world farmers will seek to optimize output given the constraints. When temperature, or rainfall changes, farmers will adapt. It is part of the human condition to adapt, which is why there is agriculture to be found in Southern Sweden and the blazing heat of Minas Gerais. Corn production is to be found in Edinburg, Texas with 136 days a year above 30 degrees. This is achieved through both planting and harvesting earlier in the year than further north.

As well as looking to the negatives of warming, we should look to the positives. More temperate climates should, ceteris paribus, see increasing yields as temperatures get warmer. For instance, Northern Europe, the Steppes of Central Asia and the Canadian plains should benefit from higher temperatures. Also higher temperatures will be caused by higher CO2 levels. Experimental studies have shown a doubling of CO2 will increase maize biomass by around a third. Finally, according to Al Gore, precipitation increased by 20% in the last century, mostly in above mentioned areas, Southern South America and SE Australia.

One of the biggest risks for climate change is supposedly to the stability world food supplies, with possible famines. But, as Amartya Sen has shown, the biggest famines are made serious not by natural factors but by adverse terms of trade. The Bengal famine of 1943, in which more than 3 million died, was exacerbated by a ban on exports between provinces in India, at the same time as extra demand was present from those supplying the troops fighting in Burma.

 

http://wattsupwiththat.com/2011/03/14/which-group-is-smarter/

 

http://www.co2science.org/data/plant_growth/dry/z/zeam.php

Al Gore : An Inconvenient Truth pages 114-115

http://www.economist.com/node/4293198