Climate change 101: why is carbon dioxide always the bad guy?
Occasionally it's worth going back to basics on climate change and having a look at why we're concerned about the things we're concerned about. For example, why does carbon dioxide warm up the atmosphere?
I initially thought this was too basic to blog, but a highly unscientific straw poll of friends and acquaintances revealed that only one of those surveyed actually knew the answer. (He also knew why a slice of toast is more calorific per 100g than the bread it was made from, but that's a different story.)
So here goes. The reason is down to the molecular structure of CO2. It doesn't absorb the very short wavelength light emitted from the sun, but it does absorb the longer wavelength thermal infrared radiation (heat, basically) released by the surface of the Earth.
Once it has absorbed this thermal infrared radiation, the carbon dioxide molecule becomes agitated and unstable. It can only achieve a stable state again by emitting this stored radiation, again as heat. Some of this heads outwards to space, but some stays here. So the more CO2 there is in the atmosphere, the greater the warming effect. (Needless to say, this is a massively simplified description that skates over all the tricky stuff like dipole moments and radiative forcing. Apologies to the purists.)
But why focus on carbon dioxide, a trace gas in Earth's atmosphere, rather than, say, methane, which has a much more potent greenhouse effect? (Between 17 and 25 times depending on your source.) Well, basically because there's much less methane and it has a shorter life in the atmosphere - roughly 8.5 years to CO2's roughly 100 years. Carbon dioxide has a much smaller effect, but for a much longer time.
And the biggest greenhouse gas of all, accounting for as much as 85% of the total greenhouse effect? Water vapour, if you count clouds. But before we all stop boiling kettles and breathing out, it's worth bearing in mind that without this effect, Earth would be just another frozen rock floating in space.
As with the climate change debate itself, it's all about balance.
~RS~q~RS~~RS~z~RS~33~RS~)
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and that is the real question - is CO2 the driver of climate change or not. The answer is maybe, but we don't really know. Sensitivity is calculated by various climate scientists as being anything between 0.5C and 6C, depending on whether or not you believe cloud feedback is negative or positive so for a doubling of CO2 ppm we can expect no warming or lots of warming
sceptical scientists calculate low figures, alarmist scientissts calculate high figures. The IPCC choose mis to high figures in their "projections"
it would be good if you guys could expand on CO2's role, perhaps have a sceptical scientists such as Shaviv outline his understanding in laymans terms and an alarmist such as well, any of them really, outline their understanding in laymans terms.
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Hi Richard, great topic as always !
"Well, basically because there's much less methane and it has a shorter life in the atmosphere - roughly 8.5 years to CO2's roughly 100 years. Carbon dioxide has a much smaller effect, but for a much longer time."
I saw this on Wikipedia - thanks for the link.
Can you please find out for us how lasting longer makes its effects worse ?
I just don't follow. In a given day we get X impact from CO2 and Y impact from CH4 (methane).
The X and Y are not affected by what will happen tomorrow or whether the causes of X and Y are still there tomorrow or next week.
Pythons live longer than cobras - but this in itself does not make them more dangerous at any point in time.
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I think the blanket effect of CO2 is in little doubt. As you pointed out water vapour works the same way and you can have two clear nights, one humid and one dry, and the humid night will have a much higher minimum temperature than the dry one - the greenhouse effect clear for all to see.
However what also becomes obvious is that water vapour is thousands of times stronger as a greenhouse gas than CO2 and therefore how can CO2 possibly be a PRIMARY climate driver? A small change in water vapour will completely mask the effect of CO2 so the warmers try to explain this away by introducing feedback, claiming a warmer world will produce more water vapour by evaporation and amplify the heating effect. Unfortunately we seem not have measured that increased humidity and despite continued increases in CO2 concentrations the temperature anomaly is less than half a degree C higher now than at the beginning of the 20th Century. CO2 is also increasing far less quickly than predicted by the IPCC, so even if CO2 was entirely responsible for this rise (unlikely as the Sun's irradiance increased significantly in the 20th Century and only a fool would say that the 15 million degree ball in the sky has no effect on our climate) we are still projecting well below the lower estimate of the IPCC by 2100.
What we also seem to forget is that global warming means just that GLOBAL, the entire system not just the atmosphere and the greatest store of heat on the planet is the oceans. To have global warming the total heat stored in the oceans - measured in Joules as it is energy - should be increasing. Yet since 2003 the total heat content in the top 700m of the ocean seems to have doggedly remained static (http://climatesci.org/2009/05/18/comments-on-a-new-paper-global-ocean-heat-content-1955%e2%80%932008-in-light-of-recently-revealed-instrumentation-problems-by-levitus-et-al-2009/) - this is not global warming and what warming we have seen is not catastrophic.
How long do we have to wait for the global warming scam to unravel and concentrate on alternatives to fossil fuels for the sake of science and development and not the sake of people looking to make a fast buck out of cap and trade?
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The real reason that CO2 is in the firing line is that taxing steam and water would be just too hard.
And they've already had a pop at methane (CH4) and it back-fired:
http://news.bbc.co.uk/2/hi/programmes/from_our_own_correspondent/7646857.stm
Gotta love the farmers' group: Farmers Against Ridiculous Taxes (F.A.R.T.)
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Back to the future?
http://www.telegraph.co.uk/earth/environment/globalwarming/5469353/Global-warming-to-push-London-temperatures-up-to-105F.html
So temperatures in 2080 will be high enough to grow grapes in the UK - just like in Roman times ;)
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Methane certainly shouldn't be ignored, it has a large effect for a brief period (a net lifetime of approx 10 years in the atmosphere), whereas carbon dioxide has a smaller effect for a longer period (over 100 years). The atmospheric life of methane is far shorter than CO2, so in the long run CO2 is more important; atmospheric concentrations of CO2 today will have an effect for a much longer period of time.
Although molecules of methane, CFCs and nitrous oxide absorb and radiate much more infrared per molecule than CO2 (and at different wavelength frequencies) the much larger input of CO2 makes it the more important greenhouse gas produced by human activities.
Since 1750, methane concentrations in the atmosphere have increased by around 145%. So although it's in the atmosphere for a short period, overall concentrations of atmospheric methane have increased.
Interaction with hydroxyl radicals in the atmosphere breaks down CH4 (in combination with oxygen) into CO2 & H2O, carbon dioxide and water. Methane's residence time in the atmosphere (approx 10 yrs) means that one tenth of the methane in the atmosphere is oxidised to CO2 in one year. That means CH4 doesn't entirely leave the atmosphere, but goes on to contribute to the amount of CO2 in it.
To add a comment on the role of water vapour. The absolute humidity of the atmosphere determines the amount of water vapour the atmosphere can hold. Absolute humidity means the atmosphere can only hold an absolute amount of water vapour at any one time. (A definition is: Absolute humidity is the mass of water vapour in a given volume of air. Normally expressed in grams of water vapour per cubic meter of atmosphere at a specific temperature.)
This limit on its ability to hold water vapour is determined by the atmospheres temperature.
The amount of water vapour in the atmosphere cant increase and raise temperatures on its own. It has to be preceded by a rise in the atmosphere's temperature. The airs capacity to hold vapour (absolute humidity) is limited, but increases as the air warms, roughly doubling for each temperature increase of 10 degrees C.
Water vapour has a very short atmospheric lifetime of several days before it falls as precipitation; it is constantly replenished by the earth's water cycle (evaporation > condensation) and so hardly changes in total amount at any time.
Try and add more water vapour to the atmosphere and it wont stay there; it quickly falls as precipitation.
There have been a number of studies looking at whether solar activity is responsible for global warming, including two major recent solar studies.
One by the National Centre for Atmospheric Research et al (Sept. 06): "Scientists have examined various proxies of solar energy output over the past 1,000 years and have found no evidence that they are correlated with todays rising temperatures. Satellite observations over the past 30 years have also turned up nothing."
http://www.ucar.edu/news/releases/2004/wigley.shtml
http://www.sciencedaily.com/releases/2006/09/060914095559.htm
The other is by Heliophysics & the Max Planck Institute for Astrophysics (Sept. 2006) that concluded: "Sunspot-driven changes to the sun's power are simply too small to account for the climatic changes observed in historical data from the 17th century to the present."
http://www.mpa-garching.mpg.de/mpa/research/current_research/hl2006-9b/hl2006-9b-en.html
http://news.nationalgeographic.com/news/2006/09/060913-sunspots.html
Its worth thinking of the charge made by sceptics that scientists produce the results that will increase their funding. In that case the solar observatories would find it in their interest to produce results that pointed towards the sun being the main agent of change, after all they need funding too. But this isnt the case; over and over again they are ruling it out.
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tim
whereas carbon dioxide has a smaller effect for a longer period (over 100 years).
depends who you talk to. Geologists tell us 5 - 20 years, IPCC upto 200 years
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tim
read this from current and ex-members of the American Physical Society:
http://icecap.us/ (scroll down to "they said it"
As physicists who are familiar with the science issues, and as current and past members of the American Physical Society, we the undersigned urge the Council to revise its current statement* on climate change as follows, so as to more accurately represent the current state of the science:
Greenhouse gas emissions, such as carbon dioxide, methane, and nitrous oxide, accompany human industrial and agricultural activity. While substantial concern has been expressed that emissions may cause significant climate change, measured or reconstructed temperature records indicate that 20th - 21st century changes are neither exceptional nor persistent, and the historical and geological records show many periods warmer than today. In addition, there is an extensive scientific literature that examines beneficial effects of increased levels of carbon dioxide for both plants and animals.
Studies of a variety of natural processes, including ocean cycles and solar variability, indicate that they can account for variations in the Earths climate on the time scale of decades and centuries. Current climate models appear insufficiently reliable to properly account for natural and anthropogenic contributions to past climate change, much less project future climate.
The APS supports an objective scientific effort to understand the effects of all processes natural and human -- on the Earths climate and the biospheres response to climate change, and promotes technological options for meeting challenges of future climate changes, regardless of cause.
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#7 "geologists tell us 5 - 20 years" Can you cite some sources for that? All the atmospheric chemistry sources I've seen agree CO2 has a much longer atmospheric life.
#8 I agree with: "objective scientific effort to understand the effects of all processes natural and human - on the Earth's climate and the biospheres response to climate change, and promotes technological options for meeting challenges of future climate changes, regardless of cause."
It comes down to whether or not you believe that GHGs play a major or minor role in climate change: past, present or future. It's an ongoing debate; as many issues are and have been in science and policy.
To save readers the trouble of locating the PDF link on the page you referred me to, below is the current APS policy:
"Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.
The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earths physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now.
Because the complexity of the climate makes accurate prediction difficult, the APS urges an enhanced effort to understand the effects of human activity on the Earths climate, and to provide the technological options for meeting the climate challenge in the near and longer terms. The APS also urges governments, universities, national laboratories and its membership to support policies and actions that will reduce the emission of greenhouse gases."
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Starr, C.: Atmospheric CO2 Residence Time and the Carbon Cycle. Energy Dec 1993
Segalstad, T.: The Distribution of CO2 between Atmosphere, Hydrosphere and Lithosphere; Minimal Influence from Anthropogenic CO2 on the Global Greenhouse Effect in European Science and Environment Forum: "The Global Warming Debate", London 1996
both suggests 5 years
with regards to the current APS policy, the APS is now run by alarmists who only appoint fellow alarmists. Clearly the statement by current and former members of the APS reflects the view of grass roots membership of the APS, not just the ruling body
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Help me with this bit please.
How does the lifespan of a chemical affect what it does - or does not do in a given period ?
It's a red herring.
In a given year we start the year with so much of each gas. They do their stuff during that year. What they do during that year is not affected at all by how long they are going to last after that year.
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We were quite naive to think that emitting 40 billion tons of carbon dioxide into the atmosphere per year would not cause some sort of climate change. When has something like this happened previously in history?
We know its effecting our climate, but what we really need to know is accurately how much and in what way.
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#10. Starr's paper I understand only looked at some C isotopes and ignored others. A similar critique applies to Segalstad's paper.
There's also a question about how CO2 is removed from the atmosphere; unlike methane which is oxidised in the atmosphere, CO2 has to be absorbed by terrestrial sinks. e.g. incorporated into plants, dissolved into the oceans or become bicarbonates through chemical weathering, particularly on contact with silicate rocks.
As CO2 concentrations rise (and it is concentrations that are important) then it takes longer for them to be reabsorbed, the planet isn't becoming larger, and any increase in plant growth due to CO2 is offset by loss of forest, saturation of oceans etc.
The more CO2 there is in the atmosphere the longer it takes earth to reabsorb it; rather like the bigger the meals I give you, the longer it will take you to eat them.
# 11. "In a given year we start the year with so much of each gas. They do their stuff during that year."
Is residency time important? Yes, if you accept increased CO2 concentrations will increase warming that will then have a knock on effect on climate (consequences), then the longer those concentrations remains the longer those consequences will be felt.
OK, back to Segalstad who has a website devoted to his pet ideas. One video caught my eye. An experiment burning a candle under a glass in a bowl of water. (scroll down) http://www.co2web.info/
When the candle goes out Segalstad writes: "The water rises in the glass because the CO2, which replaced the oxygen, is quickly dissolved in the water."
Hmm. There's another explanation, more commonly accepted in chemistry. It's known as Charles' Law and is to do with the relationship between temperature and pressure.
Charles' Law says that volume and temperature are directly proportional to each other. In other words, as the temperature of the air decreased, the volume of the air also decreased.
While the candle goes out because it consumes oxygen (but not all, some is left, but not enough to support a flame), that's not why the water rises, nor because the candle produces CO2 that was being dissolved in the water. The water only rises after the candle goes out.
First, the burning candle significantly increases the temperature of the air in the glass. This caused the air to expand, pushing some of it out the bottom of the glass as it was lowered over the candle. When the candle burns out, the remaining air cools, the rapid decrease in temperature slows the movement of the molecules that make up the air inside the glass, creating lower pressure. The air pressure outside of the glass remains the same. This creates an air pressure differential of greater outside air pressure, which results in the water rising in the glass. In addition, going from a higher temperature to a lower temperature causes water vapour in the air to condense, which also produces lower air pressure in the glass. This experiment can also be done with other liquids that can't absorb CO2.
Note that Segalstad doesn`t even discuss Charles` Law. As a geologist he may know rocks but I'm unconvinced he understands much chemistry.
As for the water he uses (which isn't the same chemistry as seawater) turning white, well, he has added Calcium-hydroxide, aka slaked lime ( Ca(OH)2 ) and yes, it is used to test the presence of any amount of CO2, however large or small.
Its also worth mentioning that tap water already contains some CO2. A 'hard water' also contains calcium. The controls on this 'experiment' are pretty non-existent.
But if water is as effective as he says at absorbing CO2, then the water should absorb it just as quickly directly from the atmosphere. I notice he doesn't try to demonstrate that because he did be there for a much, much longer time.
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Hi Timbo !
Let's go through this again.
The year starts with some CO2 and some CH4 in the atmosphere. During the year each gas has its individual effect. The effect during the year is not changed by what happens after the year.
The gases may carry on in following years or may disappear - but events in a following year cannot affect a previous year.
Gotta go now - it's heli-skiing on Mt Hutt tomorrow ! Climate permitting.
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Re: #6
SheffTim, all these links seem to be variations of the same theme - changes in solar irradiance are too small to account for observed forcings. There is nothing here (unless I missed it) that examined the GCR theory which I'm sure you're familiar with. What makes this interesting is that it does not depend on solar irradience so those previous papers findings would not be relevant here. All the GCR theory requires is that the higher incidence of GCR's can act as cloud condensation nucleii. An attempt was made to refute this using Fuerbusch events, but they missed the point entirely. I believe some physicists at CERN are planning to carry out some experiments as soon as the large Hadron collider becomes available (after they've found the Higg's Bosun?). The results should be interesting.
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it's called the CLOUD experiment and is the subject of the book "The Chilling Stars" by Svensmark and Calder
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