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Bill McKibben: 350 The Most Important Number in the World

Australian Broadcasting Corporation
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deepsleep Avatar
deepsleep
Posts: 2
Posted: 06.01.09, 08:12 AM
It's Mr. Anderson!
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deepsleep Avatar
deepsleep
Posts: 2
Posted: 06.01.09, 08:18 AM
Oops, I meant agent Smith.
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sactownjudge Avatar
sactownjudge
Posts: 40
Posted: 06.01.09, 10:34 AM
The argument that manmade CO2 emissions will lead to a catastrophe is based on a three step argument.

1. CO2 has a first order effect that warms the planet
2. The planet is dominated by net positive feedback effects that multiply this first order effect 3 or more times.
3. These higher temperatures will lead to and already are causing catastrophic effects.

You are dead right on #1, and skeptics who fight this are truly swimming against the science. The IPCC has an equation that results in a temperature sensitivity of about 1.2C per doubling of CO2 as a first order effect, and I have found little reason to quibble with this. Most science-based skeptics accept this as well, or a number within a few tenths.

The grand weakness of the alarmist case comes in #2. It is the rare long-term stable natural physical process that is dominated by positive feedback, and the evidence that Earth’s climate is dominated by feedbacks so high as to triple (in the IPCC report) or more (e.g. per Joe Romm) the climate sensitivity is weak or in great dispute. To say this point is “settled science” is absurd.

So thus we get to the heart of the dispute. Catastrophists posit enormous temperature increases, deflecting criticism by saying that CO2 as a greenhouse gas is settled. Though half right, they gloss over the fact that 2/3 or more of their projected temperature increase is based on a theory of Earth’s climate being dominated by strong positive feedbacks, a theory that is most certainly not settled, and in fact is probably wrong. Temperature increases over the last 100 years are consistent with neutral to negative, not positive feedback, and the long-term history of temperatures and CO2 are utterly inconsistent with the proposition there is positive feedback or a tipping point hidden around 350ppm CO2.

So stop repeating “settled science” like it was garlic in front of a vampire. Deal with the best arguments of skeptics, not their worst.
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Invictus_88 Avatar
Invictus_88
Posts: 78
Posted: 06.04.09, 06:42 PM
Judge,

Could the positive feedback not be tied to the atmosphere, but to the shrinking polar ice-caps and thus greater storage of heat from the sun - fuelling the release of gas from lakes, defrosting tundra...etc?

I sympathise with your frustration, and accept that I'm no authority on this matter, but there does seem to be a certain intuitive plausibility to the notion of a tipping point of CO2 beyond which an unstoppable slide begins, especially if it arises from some tangible physical phenomenon such as gas bubbling from lakes and tundra rather than some impalpable assessment of atmosphere.

Why is positive feedback "in fact...probably wrong"?
__________________
Francis J.L. Osborn.

Philosophy Undergraduate, St David's College Lampeter.
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eglasgow Avatar
eglasgow
Posts: 9
Posted: 06.05.09, 02:26 PM
McKibben makes a good point in Will Dwindling Fossil Fuels Strengthen Community Ties? - whether or not you believe climate change will have catastrophic effects on the planet, going without fossil fuels will lead to a higher quality of life.
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urbieta Avatar
urbieta
Posts: 1
Posted: 06.06.09, 09:05 PM
Traducido al español (Translated to spanish)

http://www.youtube.com/watch?v=kKcg2jg4q_I
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Rdallas1 Avatar
Rdallas1
Posts: 44
Posted: 06.10.09, 11:19 AM
Eglasgow, I totally agree with you that going without fossil fuels will lead to a higher quality of life. I think it is inevitable that climate change will have catastrophic effects on the planet and although we are making some progress with the environment, at this point we would have to make huge changes in the way we live in order to make enough difference in preventing this.
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quimson Avatar
quimson
Posts: 1
Posted: 06.13.09, 01:35 PM
i totally agree
i dont understand why oil company's are not investing on other sources of fuel
investing in hydrogen fuel cells or something eco friendly something that does not emit carbon
if they do they will be the richest company because, everyone is trying to find a better fuel source. investing is something other that oil will be the greatest economical and environmental decision yet!
i hope they see this soon
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RevolutionTav Avatar
RevolutionTav
Posts: 1
Posted: 06.18.09, 08:21 PM
i thought the same thing...the likeness is amazing.
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mszlazak Avatar
mszlazak
Posts: 18
Posted: 10.24.09, 11:44 AM
sactownjudge and Invictus, here is a link to the CO2 sensitivity and feedback issues which I'll reproduce below:

http://www-personal.buseco.monash.ed...#_Toc240972836

--------------------------------------
From "Responses to Questions & Objections
on Climate Change" By Dr. Brett Parris



14. CO2 is a weak greenhouse gas. Doubling of CO2 from its pre-industrial levels of 280 ppm to 560 ppm would only bring warming of about 1ºC.



False - twice. The warming effect of CO2 in the atmosphere diminishes logarithmically as its concentration increases, as Svante Arrhenius confirmed in 1896.[96] It has been claimed by some who accept this logarithmic relationship, that a doubling of CO2 would only bring warming of around 1ºC and that since we have already experienced about 0.76°C of warming there is only a very small amount of benign warming still to come. But this claim is false in two different ways:



Firstly, basic radiation calculations show that for a doubling of CO2, surface temperatures would warm by around 1.2ºC (not 1ºC) if, and only if, the structure of the atmosphere and all other factors remained fixed.[97] So the assertion that doubling CO2 would bring warming of only 1ºC is already about 0.2 ºC wide of the mark in this purely theoretical calculation.



Far more serious is the second way in which this assertion is false, namely that in the real world, the structure of the atmosphere and a host of other factors are not fixed at all. There are a large number of feedbacks in the climate system which reinforce the warming. If the logarithmic relation between CO2 concentration increases and temperature increases is accepted, and it is accepted that the 35% increase in CO2 concentrations from 280 to 379 ppm up to 2005 led to the approximately 0.76°C warming we have already experienced since pre-industrial times, then it is easily shown that a doubling of CO2 from pre-industrial levels would likely lead to at least about 1.74ºC of warming.[98]



This calculation however, presumes that we have already experienced the full effects of the increase in CO2 concentrations to 379 ppm. We haven’t. We have experienced some of the feedbacks from this increase, but by no means all. The climate system has momentum and delayed feedbacks, due to factors such as the immense volume of the oceans which take a long time to warm up. So there would have been a further ‘committed warming’ already guaranteed from the increase to 379 ppm even if all emissions had ceased in 2005. In other words, the 1.74ºC figure applies only if we ignore the committed warming we will get from past emissions and their feedbacks on the climate system – or if we presume (on the basis of a climate model?) that the feedbacks cancel out. Once those feedbacks are properly taken into account however, the temperature increase resulting from a doubling of pre-industrial CO2 levels (referred to as the ‘climate sensitivity’) is “likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C.”[99]



The most recent assessment of climate sensitivity by James Hansen and his team, based on empirical geological evidence, is even more disturbing.[100] Hansen argues that the figure of 3°C for the sensitivity of the climate to a doubling of CO2 used in most climate models only accounts for ‘fast’ feedback effects, such as cloud formation, water vapour, and sea ice. Once ‘slow’ feedback effects are accounted for (on timescales of centuries or less), such as ice sheet disintegration, vegetation changes, and CO2 and methane releases from soils, tundra and ocean sediments, the climate sensitivity for a doubling of CO2 above pre-industrial levels is likely to be more like 6°C. This higher climate sensitivity suggests that a 300-325 ppm CO2 target is what we need for a safe climate with sea ice restored to its area of 25 years ago.[101] Since CO2 levels are now approaching 390 ppm, this implies not only drastically reduced emissions but an extended period of actually removing CO2 from the atmosphere.



Furthermore, even ignoring these feedback effects, emissions projections at current trajectories are likely to see CO2 levels of 1000 ppm by 2100, leading in turn to temperatures well over 3°C.[102] What is the highest level of CO2 that those who are opposed to strong emissions reductions would consider safe? Is there any level of CO2 concentration they would agree is too high?



Let’s allow for the moment the argument that human greenhouse gas emissions have not contributed much at all to warming so far, and that the warming we’ve seen (which is not in dispute) is mostly of natural origin: What then is the policy implication? Well, the evidence from both theoretical physics and empirical data collected over more than 100 years show that these gases do contribute to warming, so if we’re already being subjected to natural warming, does that in any way lessen the case for reducing our emissions? Hardly. That argument only follows if, for sound theoretical reasons, we believe that the greenhouse gases we emit will have no significant impact on the climate. But such a judgement has no sound basis in science and could only be arrived at by use of a climate model, none of which show negligible impact from rising greenhouse gases.



It should be remembered then, that when critics spurn climate models as ‘voodoo science’, asserting that the sensitivity of the climate to a doubling of CO2 is just 1ºC or less, they must be implicitly adopting a climate model which either ignores all feedback effects, or which presumes that the feedbacks cancel out. To say anything about the effects of greenhouse gases on climate, there is no alternative but to use some kind of model – and any model that arbitrarily assumes either that there are no feedback effects or that they all cancel out, is scientifically unjustifiable. As Reto Knutti from the Institute for Atmospheric and Climate Science in Zurich wrote recently in his evaluation of climate model projections,



No credible model has been produced that questions the strong anthropogenic influence on climate in the past and future. I, therefore, argue that the large-scale model projections are very likely robust and accurate within the stated uncertainties.[103]
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