Posts Tagged ‘greenhouse effect’

Climate change is real, we are causing it, and it is happening right now

June 14, 2011

A thundering open letter from the Australian scientific community has been published on “The Conversation”, as the start of a two-week series on climate science and “skeptics”:

The overwhelming scientific evidence tells us that human greenhouse gas emissions are resulting in climate changes that cannot be explained by natural causes.

Climate change is real, we are causing it, and it is happening right now.

Like it or not, humanity is facing a problem that is unparalleled in its scale and complexity. The magnitude of the problem was given a chilling focus in the most recent report of the International Energy Agency, which their chief economist characterised as the “worst news on emissions.”

Limiting global warming to 2°C is now beginning to look like a nearly insurmountable challenge.

Like all great challenges, climate change has brought out the best and the worst in people.

A vast number of scientists, engineers, and visionary businessmen are boldly designing a future that is based on low-impact energy pathways and living within safe planetary boundaries; a future in which substantial health gains can be achieved by eliminating fossil-fuel pollution; and a future in which we strive to hand over a liveable planet to posterity.

At the other extreme, understandable economic insecurity and fear of radical change have been exploited by ideologues and vested interests to whip up ill-informed, populist rage, and climate scientists have become the punching bag of shock jocks and tabloid scribes.

Aided by a pervasive media culture that often considers peer-reviewed scientific evidence to be in need of “balance” by internet bloggers, this has enabled so-called “sceptics” to find a captive audience while largely escaping scrutiny.

Australians have been exposed to a phony public debate which is not remotely reflected in the scientific literature and community of experts.

Beginning today, The Conversation will bring much-needed and long-overdue accountability to the climate “sceptics.”

For the next two weeks, our series of daily analyses will show how they can side-step the scientific literature and how they subvert normal peer review. They invariably ignore clear refutations of their arguments and continue to promote demonstrably false critiques.

We will show that “sceptics” often show little regard for truth and the critical procedures of the ethical conduct of science on which real skepticism is based.

The individuals who deny the balance of scientific evidence on climate change will impose a heavy future burden on Australians if their unsupported opinions are given undue credence.

And don’t miss this excellent article by Karl Braganza who describes in as few words as realistically possible how we know that we are warming up the earth:

fundamental understanding of the physics of radiation, combined with our understanding of climate change from the geological record, clearly demonstrates that increasing greenhouse gas concentrations will inevitably drive global warming. (…)

It’s now practically certain that increasing greenhouse gases have already warmed the climate system.

That continued rapid increases in greenhouse gases will cause rapid future warming is irrefutable.

Venus battle resolved?

June 7, 2011

Jeff Id took issue with Chris Colose for bringing up the high surface temperature at Venus in his SkS post

CO2 is a strong greenhouse gas, and it is important in impeding how efficiently our planet loses radiative heat to space.  We don’t often think of CO2 as a “pollutant” on Venus, yet it still allows the planet to support temperatures well above the melting point of lead or tin.

Jeff replied at his blog:

Venus does have a more reflective atmosphere but it is also closer to the sun than the Earth.  For the thinking mind, it is difficult to ignore that the atmosphere is a ridiculous 90 times more dense. (…) In fact, if you just used Nitrogen alone at the same mass you would get a ton of heat just by the insulating properties of a gas.

On a subsequent post he reiterates his thought that

the reason for Venus surface temeprature being so high was the pressure and that any gas would create a huge warming effect 

However, during the discussion he seems to be backpedaling:

#15, Chris, (…)

My reply was that it was the pressure and amount of gas which caused the temperature more than the specific greenhouse effect of some particularly powerful gas. I pointed out that even N2 would cause a ton of warming with wording that clearly recognized there would be less warming and a paper was referenced where even the 96.5 percent N2 atmosphere had 80C of warming. I was also careful not to claim that all gasses would definitely cause a hot Venus and intentionally phrased even that as a question. In other words, you are making assumptions of a point I didn’t state.

To be fair, I admit that a pure nitrogen atmosphere had less warming than I would have (but did not) guess.

Is it just me, or does that indeed sound like he agrees that the majority of the >500 degrees greenhouse effect on Venus stems from the radiative properties of its atmosphere (~96% CO2) rather than from its density/pressure? The impression I got from his post was that the opposite though. Makes me wonder what the argument is really about. So I asked:

Jeff, 

It seems that you agree that the high temperature on Venus is due primarily to a strong CO2 greenhouse effect (few hundred deg) and secondarily (?) to the high surface pressure (the ~80 deg number that was mentioned upthread).

If so, then I don’t understand the beef you have with Chris’ take, where he uses Venus as an example that shows that CO2 is a greenhouse gas.  

Jeff replied:

Bart,

I object to its comparison to Earth as a scare tactic in general. That’s all.

Argument resolved. Both agree that the greenhouse properties of Venus’ atmosphere are primarily responsible for its high surface temperature, and they disagree as to whether or how this could be mentioned in a discussion about Earth’s climate.

Quick rundown on Venus’ climate:

Venus is closer to the sun than the Earth, but its higher reflectivity more than compensates for that. Without a greenhouse effect Venus would actually be colder than the Earth would be without a greenhouse effect. In reality Venus is about 500 degrees warmer than this so called black body temperature (the greenhouse effect on the Earth is about 33 degrees). This is primarily due to the inception of infrared radiation by its thick atmosphere of almost pure CO2. The high density also helps, but is of secondary importance.

More reading:

Realclimate on Venus

SoD’s Venusian Mysteries

Brian Angliss at S&R

Eric Wolff on areas of agreement and on the public debate about climate science

May 25, 2011

Dr. Eric Wolff is spot on (see also further below): 

as an outsider to the blogosphere, it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

A peculiar line-up of speakers assembled recently at the Conference on the Science and Economics of Climate Change in Cambridge: Phil Jones, Andrew Watson, John Mitchell, Michael Lockwood, Henrik Svensmark, Nils-Axel Morner, Ian Plimer, Vaclav Klaus and Nigel Lawson. Bishop Hill reports that

Dr Eric Wolff of the British Antarctic Survey tried valiantly to find a measure of agreement between the two sides.

This proved an interesting exercise and resulted in a useful list (also reproduced by Judith Curry) on what we can all agree on (perhaps excluding those too far out on the fringes; links added by me):

  1. CO2 does absorb infrared radiation
  2. The greenhouse effect (however badly named) does occur in practice: our planet and the others with an atmosphere are warmer than they would be because of the presence of water vapour and CO2.
  3. The greenhouse effect does not saturate with increasing CO2
  4. The CO2 concentration in the atmosphere has risen significantly over the last 200 years
  5. This is because of anthropogenic emissions (fossil fuels, cement production, forest clearance). [Ian Plimer disagreed, but as Curry stated: “the anthropogenic contribution is (should be) undisputed”]
  6. If we agree all these statements above, we must expect at least some warming. [Bishop Hill noted “broad agreement” with this point]
  7. The climate has warmed over the last 50 years, [as is evident from] land atmospheric temperature, marine atmospheric temperature, sea surface temperature, and (from Prof Svensmark) ocean heat content, all with a rising trend.
  8. We probably don’t agree on what has caused the warming up to now, but it seemed that Prof Lockwood and Svensmark actually agreed it was not due to solar changes, because although they disagreed on how much of the variability in the climate records is solar, they both showed solar records without a rising trend in the late 20th century. [Excellent point and ironically hitting Svensmark with a stick of his own making. Note the distinction between variability and trend.]
  9. On sea level, I said that I had a problem in the context of the day, because this was the first time I had ever been in a room where someone had claimed (as Prof Morner did) that sea level has not been rising in recent decades at all.  I therefore can’t claim we agreed, only that this was a very unusual room.  However, I suggested that we can agree that, IF it warms, sea level will rise, since ice definitely melts on warming, and the density of seawater definitely drops as you warm it.
  10. Finally we come to where the real uncertainties between scientists lie, about the strength of the feedbacks on warming induced by CO2 [i.e. climate sensitivity]

Eric Wolff also chimed in with a substantial comment over at Bishop Hill’s, rebutting some commonly heard arguments and making some very spot-on remarks:

(…)

I should first state the rationale for the summary I made at the Downing event. The meeting was about the science and economics of climate change, and I was asked to lead a discussion that came between the science talks and the two economics talks. I therefore felt the most useful thing I could do was to try to summarise what we had heard, as a basis for the discussion of whether society should do anything in response to that, and if so what. In particular I did hear a surprising number of things on which almost everyone in the room could agree, and it seemed worth emphasising that, rather than rehearsing old arguments.

I notice in the thread here several comments about who sets the “terms of the debate”, and about the “context of the debate”. While such phrasings may make sense in discussing energy policy, it is a strange way to discuss the science. Our context is the laws of physics and our observations of the Earth in action; our aim as scientists is to find out how the Earth works: this is not a matter of debate but of evidence. I think some of the comments on this blog come dangerously close to suggesting that we should first decide our energy policy, and then tell the Earth how to behave in response to it.

Regarding Plimer’s proposal that volcanic emissions were more important than we thought, (…) if volcanoes were “causing” the recent increase, then around 1800 their emissions would have had to rise above their stable long-term rate, and then stayed high. This is however a rather hypothetical discussion because the change in the isotopic composition of CO2 in the atmosphere over the industrial period is not consistent with an increased volcanic source anyway.

Regarding the idea that the “temperature increase stopped in 2000”: my point is that we know there are natural variations (due eg to El Nino) that cause runs of a few years of temperature colder than the average or a few years warmer. Look on the record at the decade around 1910 for example when there was a long run of cold years on a flat background.

Such a period superimposed on a trend would look like the last decade (but more so). The point of my analogy is that you can’t determine the trend over several months by measuring the gradient in a run of a few days. Similarly, you simply can’t determine a multidecadal trend by measuring the gradient over a few years because all you get is the “noise” of natural variability.

Professor Morner claims that globally sea level has not risen at all; he dismisses the evidence, from both satellites and the global tide gauge network, that it has. (…) There are numerous reasons why a single site can show a sea level signal, either real or apparent, that departs from the global mean.

I am not the best person to discuss models and feedbacks in detail (see comment on expertise below). However, I could not let two issues pass. Firstly, when models are run out for a century into the future, they do indeed show runs of years with flat temperatures amidst a trend (…) (because of El Nino and other natural factors). I am therefore not clear why this is evidence that something is missing. Regarding positive feedbacks: a positive feedback implies amplification, but not a system out of control; this is only the case if the sum of the gain factors is greater than 1.

Finally, a few specific issues that interested or worried me.

(…) CO2 emits infrared as well as absorbing it. (…) indeed, this property is precisely why its effects do not saturate (but fall logarithmically), because it allows the height from which the emitted radiation finally escapes to rise into regions with less and less air.

Geckko accidentally made an important point. S/he did not like the statement: “We can agree that if it warms the sea level will rise”, because it was too simplistic. Well, as a scientist I always like to boil things down to a statement that my brain can grasp, but that contains the essential explanation of an observation or process. And this one does, for example being demonstrably what was observed in going from a cold ice age world, with sea level 120 metres below the present level, to the present. However, you are right: there are factors that could make this statement false, such as increased snowfall when it warms, adding more ice into ice sheets. As soon as several such competing processes have to be taken into account, our brains cannot predict the outcome, and so we have to resort to putting all the “millions of assumptions” into a numerical model and seeing which of them “win”. An argument for models?

Coldish made a good point about expertise, and this is where I am going to go into a slightly more challenging area. I freely admit that I am not an expert on all, or even most, aspects of climate. When I reach a topic that I have not previously studied, I go to those who are experts, either in person or by reading their work. I maintain scepticism about some of their conclusions, but my working assumption is that they are intelligent and that they have probably thought of most of the issues that I will come up with. Can I observe as an outsider to the blogosphere, that it surprises me that so many people, presumably mostly with even less knowledge and training than me, seem absolutely convinced they have mastered every area of climate science.

and more so, convinced that they are right and almost all of the experts are wrong. That must be the height of hubris.

However, Coldish specifically mentioned IPCC, and I think there is also an interesting point to make about that. At the Downing event, there seemed to be two IPCCs in the room. To some it was a huge plot, masterminded by some mysterious power that manipulates troublesome scientists. To me and the scientists in the room, it is (at least in WG1) simply a set of well-researched review papers, describing the present state of the peer-reviewed literature. I mention this only because I think the former view is a type of groupthink where, because people form an extreme opinion in their private space, they think it is widely held, or even true.

Alas, Wolff’s forray into the blogosphere was short, as is evident from a short comment a while later:

Just in case anyone thinks they are addressing me with their remarks:

I thought this might indeed be a chance for a civilised discussion, and some of the respondents seem happy to have that. However there are also a lot of remarks on here that are frankly rude and aggressive, and I won’t be returning. Now I remember why I hate the blogosphere.


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