Chris C
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To Chris C
I don't think Lomborg ever said that we should do nothing to better manage climate change.
He is more against the ridiculous and 'heroic' measures that some idiots are advocating. What is needed to better manage climate change is a blend of new technology (eg. Hydrogen fuel cell cars. New generation nuclear power), better environmental management (stop Indonesia chopping down forest and converting peat bogs to CO2), and a degree of adaptation on our own part to the inevitable climate change that will remain after taking reasonable steps.
The world is currently warming at an average rate of 0.15 to 0.2 Celsius per decade. An increase of 3 Celsius is unlikely in the near future. We have time to implement sensible measures - not idiotic measures that will drastically reduce the standard of living of all people and drive the poorest into starvation.
Actually, a 3 C rise is the most likely scenario keeping the way we do things. And if we don't do things, "by 2100" will be worse than "2x pre-ind CO2." Obviously sensible application from economic and scientific angles is required, but Lomberg doesn't really have AGW scenarios in perspective.
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Lomborg doesn't really seem to know what would happen in the world got 3 C hotter...his expertise in "economics" and "cost-benefit" is cute, and a lot of expertise in this area is needed, but the view that there is little benefit to stopping climate change is wrong.
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Arguments aside, thank you all for the data. That is what I was wanting to see. As for water vapor I've never heard anyone support the claim that it causes warming. If anything shouldn't it act as a sort of cooling agent? Maybe I'm all off base there, so I apologize.
Not too long ago I had also heard that the Sun has been producing excess "solar activity." Now what that means I'm not entirely sure. However it seems to me that extra solar activity would surely be a cause of global warming (since it's what makes us warm in the first place). Has there been any data to suggest this?
I will try to be as simple as I can, but emphasize some points for all readers. For water vapor (H20 as a gas), it is a greenhouse gas, and a bit more abundant than CO2. Without either gas though, we'd be in an uninhabitable cold planet, even neglecting the "cooling" ice-albedo feedback such a planet would have. Atmospheric motions have a drying effect which keeps the atmosphere from reaching saturation and can almost be seen by keeping the relative humidity fixed at some sub saturated value as the climate warms or cools... in other words, water vapor content in the atmosphere increases roughly exponentially as a function of temperature (warmer air holds more WV and so this produces a positive feedback which further amplify temperatures, opposite if you move the climate to a cooler state. So WV is very influential at the tropics, and much less as you move poleward. Note that without CO2, the atmosphere would be too cold to have much WV in it, so you lose much of the WV greenhouse effect as well.
A common skeptic claim is that since water vapor may be "more abundant or more powerful or what have you" that the CO2 effect is negligible. Skeptics with a bit more savvy and partially educated in radiative physics will tell you that since the outgoing longwave radiation (OLR) is mostly "delayed to space" by water vapor, the absorption bands of CO2 don't matter much. As an analogy, they say that you put on a pair of sunglasses, and then one of those welding face shields over that, you roughly get how much influence CO2 has (CO2 comparable to the glasses). It is a cute claim, and fooled most physicists early in the century- a bit of history on this at http://www.aip.org/history/climate/co2.htm or http://www.aip.org/history/climate/Radmath.htm . As that touched upon, CO2 is the powerful mechanism for *change in* temperature, and is the suspect today.
It comes with its share of problems, one of which I emphasized. Water Vapor is a feedback, not a forcing mechanism, so if you see an increase in global temperatures it cannot be caused by changing WV content, WV content changes with the temperature and that change amplifies initial warming. Another problem with the claim is that the layer at the top of the atmosphere where radiation escapes to space is what determines our heat balance, and up here it is cold and dry; CO2 is well-mixed throughout the atmosphere, while WV has a stronger vertical gradient being concentrated a bit more lower down. Finally, there are windows of "absorption" that are dominated by CO2, but little influence from water vapor (e.g. at the 15 micron area). It is the ability of greenhouse gases to absorb and emit infrared radiation which makes the effect work, and is indeed the concern at all. Much better to say CO2 and water vapor compliment each other, rather than say "one dominates the other."
The "attribution" issue with Global Warming (and I define this here as the increase in temperature from pre-industrial state) is what caused it. At first glance, CO2 is a suspect, a brighter sun is a suspect, and some other ones, but water vapor is not. I hope you picked this up- see http://www.nature.com/nature/journal/v419/n6903/full/nature01087.html;jsessionid=91DFE859DBCA925B3F060EE2B72A3274 for further discussion (I apologize if you need subscription). Water Vapor is of concern though because it will provide a feedback. With basic physics you get 1.2 C per doubling of CO2 without feedbacks (except the negative T^4 feedback from radiative flux). Projections, however, are ~3 C per doubling of CO2. The difference is made up by indirect impacts of CO2 (the feedbacks to a warmer climate) which include positive water vapor (which dominates the feedback discussion), ice feedback, and others (there is a thread here at http://www.scienceforums.net/forum/showthread.php?t=29932 where I posted a few posts down)
The role of the sun has been more clearly spoken of in the threads in ecology and environment section. I did post #6 at http://www.scienceforums.net/forum/showthread.php?t=28554 for instance. Some in other threads here on global warming, but you should go to the scientific literature and IPCC on the subject. More references in those posts, but as a summary: the sun played a more significant role in some of the early-century warming. During the middle of the last millennia, a decline in solar activity helped result in what you may Google as the "little ice age." Changes in the solar output and in the distribution of radiation on the globe (astronomical cycles alter this which helps move us in and out of ice ages) play a large part in paleoclimates. Since 1950 or so, there is minimal change in the sun- in fact, the changes in the sun and other natural factors should probably be giving us a very slight cooling trend now. CO2 and other greenhouse gases have dominated. -- Chris
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It isn't too difficult to look it up yourself but ok.
http://en.wikipedia.org/wiki/Global_warming
There are plenty of historical graphs for both CO2 and temperature there. Note, for the references please see the bottom of the page as the IPCC is listed several times since that is the holy grail for environmentalist I'm sure that is necessary or the data is just make-believe.
it is just a conglomeration of thousands of scientific papers into the current state of knowledge. No biggy. But, yes, I remember about the conspiracy theories. The IPCC 2007 report is ~1,000 pages in length. Have you read it? Or even the 20+ page summary? We can discuss its errors if you have.
Further the first paragraph of the link explains the 100 year warming trend we have had 1.33 +- .32 degrees.
Ok...Quite a big rise in 100 years
The main "idea" to take away from the articles is that the CO2 concentration plots DO NOT follow the temperature trends, which is my point.
They do, actually. Obviously CO2 is not the only factor, but is the *primary* factor since mid-century. It has also been a big factor over long-term scales (millions of years). Aerosols did contribute a bit in the mid-century during the cooling trend (to answer Mr. Skeptic, the 0 line on the graph refers to 1750 conditions). So the positive and negative forcing are relative to pre-industrial conditions, with little from natural since 1950 (see http://www.pnas.org/cgi/reprint/104/10/3713.pdf for instance)
I find it difficult to say "CO2 doesn't follow the temperature rise" when you look on a graph of CO2 concentration with temperature with time. For one thing, you are looking at two different Y axis- degrees and ppm. Not really supposed to overlap and every bump and curve. Second, more is going on than just CO2. Not sure why you expect all these graphs to follow perfectly, but there is a clear correlation between the two, and simple radiative physics allows for attribution.
Right.
Ok, before things get too off tilt:
I didn't say water vapor was causing the INCREASE in global temperature. I said it is the MAJORITY contributor to GW. Something I have noticed is that the definition of GW is different for some people. GW is the process by which a planet/celestial body is warmed due to the atmosphere. The "natural" fluctuation of our planets temperature is DUE mostly too how much water vapor is in the atmosphere, however YES the current additional average temperature isn't due to water vapor but other extra greenhouse gases such as CO2. Of course, increases in water vapor in the atmosphere can add to increased average temperature as well (the feedback you are referring too).
In summary, i'm not saying water vapor is why we have experienced a 1 degree temperature increase the past century. I'm saying that the greenhouse gas that is most abundant and facilitates GW the most is water vapor. After all GW is a natural process.
You are using an odd definition of GW which would never be used in technical papers or such, but this seems to be a jump from your origninal argument, so I'll let it go
Perhaps you are reading it wrong. I'll attempt to rephrase.
Without the existence of humans the planet earth would not have a flat line average global temperature over time correct?
No. Maybe ch. 6 on paleoclimatology in the IPCC report WAS an illusion. However, past climate changes do have caused, it just doesn't change because the Earth presses a button. Siberian traps, asteroids, milankovitch cycles, biological impacts, or what have you. It is why we both detect and "attribute" climate change, not just detect.
My point was that the natural fluctuation that earth experienced before industrialization had a specific magnitude (imagine a sine wave). The past century warming that has occurred if plotted would closely fit the trends over time.
Unlike of course if you observe the natural CO2 fluctuations and current increases. The only point I have been trying to make is that the focus and emphasis is always put on CO2 concentrations, why? Because it makes the global situation seem much more dire. The problem is that they are not 1 to 1 trends.
Emphasis is given because of CO2's strong role in changing global temperature. This graph represents CO2 concentration with time over the glacial-interglacial cycles
The one thing that stands out is the magnitude of CO2 rise compared to previous interglacials. But also note the *rate of* change in both CO2 and temperature. You'll need better industrial-time resoultion for the latter, but there is something else clearly at work, not apparent in the previous cycles. In both magnitude and rate, we are washing out natural variation. If not humans, what? If even "business-as-usual" projections by 2100 are correct, than we will be far outside even the 120k event where sea levels were much higher. Things do not adapt well to such fast change, and the climate change we are experiencing is much different than previous trends. If you read nothing else by me, I think http://geosci.uchicago.edu/~rtp1/papers/LawReviewCatastrophe.pdf by Dr. Pierrehumbert puts some things in perspective geologically speaking.
In closing I just want to make a few points I guess.
As with most things, being too idealistic or extreme on either end of a spectrum is not a good thing.
I hope scientists are alarming, but not alarmist. I actually think people don't really get what is going on, especially when people say something like "we have only went up by a degree in 100 years" and are unerestimating projections. I tend more toward the geology side of things, so looking at the greenhouse forcings of previous extinction events, the idea of doubling or tripling atmospheric CO2 is scary. Mark Lynas' book really would be a good pickup, or working group 2 report on impacts from http://www.ipcc.ch
Outright denying that humans effect greenhouse gas levels and thus global climate is ridiculous and extreme.
However, exaggerating or misleadingly using data to "scare" people is extreme and wrong too. I agree, but I don't feel the need to exaggerate to call for action, and to emphasize the problems
The damage to the environment does need to be mitigated, but idealistic ideas or attempts at returning earth to how it was prior to industrialization is absurd.
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theCPE,
For one thing, water vapor has nothing to do with the increase of global temperature. It is a feedback, not a forcing agent in the climate system (so one could say it has contributed to a bit of the warming but indirectly from anthropogenic anyway). A reading of Kump (2002) in Nature would clear up your confusion on its role. Secondly, CO2 is the primary driver of climate change from about 1950 to present. This is said with high confidence from lack of solar and cosmic-ray trends, heat going in the ocean not going out, the stratosphere cooling, the energy imbalance at the top-of-atmosphere, etc CO2 is not 100% of the warming, but most of it is CO2, and anthropogenic dominates the temperature rise in the second half of the century.
Note Water Vapor doesn't appear on the graph because it is not a climate forcing agent. Secondly, there is no "zero point" to which climate always returns, so the statement "Over the past century we have had temperature increases in line with prior century temperature increases before the industrial age" is indefensible, unless I am really reading this wrong. Temperatures have been stable since the last ice age (not going outside of a +/- 1 degree change) and are now highest (probably) since 120,000 years ago, and will be hotter by 2100 than if we go back millions of years. You don't seem to understand the significance of "one degree" from a climatology perspective. Mark Lynas' book "Six Degrees" would be a good read for this, but 1-2 degrees is significant but not drastic- some benefits, some harm at first. Agiruclture may flourish in some places, more heat waves and droughts in others. 2 C is getting pretty severe, and will have a lot of harmful impacts. Most scientists say 2 C is the thereshold for "dangerous." 3-4 C will cause mass hardships for countless people and ecosystems, lots of extinctions, severe impacts. Past 4-5 C you are almost in an uncrecognizable world from today. For perspective, if you lower the temperature about 3.5 to 4 C, you have an ice age.
As for the OP, I'm not sure if you mean "CO2 on Earth" or "CO2 in the atmosphere." The Earth has about as much CO2 as Venus, the only difference being that on Venus most of it is up in the atmosphere, wheras on Earth it is locked up in the ground with (relatively) little in the atmosphere- just enough to keep us from freezing over
So, much different in terms of the greenhouse power. If you're referring to in the atmosphere, CO2 is pretty well-mixed so you will get about the same reading of atmospheric CO2 concentration if you take measurements in Antarctica, Hawaii, or any other place (so if you're wondering if there is an "ideal" place to take measurements of atmospheric concentration, or if it builds up in some places vs. others, the answer is no). I am assuming you were speaking of "CO2 in the atmosphere" from your Q 2 and 3. I don't have expertise in the current technologies emerging, and I have heard of ideas to "take away" CO2 from the atmosphere. (Maybe return it back to pre-industrial conditions). They remain ideas for now at best, and I can think of theoretical problems in changing the composition of the atmosphere back at a faster rate than we already did. Climate isn't just something that you bounce back and forth from state 1 to state 2, and have a linear response from initial to final to initial conditions. For example, in the non-linear world of sea ice if the Arctic were to melt more (or totally), if you returned the climate back to pre-industrial conditions it would still be lost, and it would take a much colder climate and millenia to get it back. Of course, if you did stop CO2 emissions the warming trend would stop after a while (not immeditately, because of the lag time between forcing and response). Probably would be more immediate if "removed" the CO2 because it is no longer absorbing infrared radiation (which is the problem).
I can say with good confidence the idea is not being worked out now, and is not really on lists for a top 3 "stop global warming" solution. More like what you hear about- reduce fossil fuel emissions, altenative energies, capture and storage, cap and trade, all the good stuff
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For those who don't know what a 'feedback' is, it is basically a reaction to a change in the Earth's climate system which either amplifies or dampens the initial warming. Note that unlike, say, CO2 feedbacks don't "force" initial climate change, they respond to it, and the response either makes it worse (positive feedback) or brings the system back closer to initial conditions (negative feedback). Right now, the net feedback is overall positive, The basic physics says doubling CO2 gives about 1.2 C of warming without feedbacks (except the negative T^4 feedback from radiated thermal flux). Right now, however, with feedback we should get ~3 C per 2x CO2 (IPCC 2007), especially with water vapor contribution (warmer air holds more water vapor which is a greenhouse gas and amplifies warming).
A summary of our understanding is as follows:
Temperature (Planck) feedback: The major negative feedback on climate change (as Earth warms it radiates more according to Planck's law), and completely understood.
Water vapor feedback: Strongly positive, but still some uncertainty in its magnitude due primarily to the upper troposphere contribution
Lapse rate feedback: A major negative feedback that offsets part of the water vapor feedback; well understood conceptually (lapse rate change follows the moist adiabatic lapse rate approximately, so for a given warming at the emission to space altitude there's less warming at the surface) but magnitude depends on other feedbacks
Sea ice feedback: Less ice, more open ocean with less albedo. More solar radiation absorbed than reflected. Positive, but magnitude is uncertain
Cloud feedback(s): There are many cloud feedbacks, on amount, height, optical thickness, etc., and different for different cloud types and at different latitudes. Overall, today's models produce cloud feedbacks ranging from approximately neutral to positive.
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To Chris
You obviously just jumped in onto this thread. To get you up to date, my argument has been that greenhouse gases have been the dominant driver of global warming since about 1976, but earlier than that, the correlation gets shaky. In fact, before 1976, sunspot activity correlates much better and has done for at least 1000 years into the past.
I believe that there is a real confusion between solar irradiance and sunspot activity, which has other effects above and beyond simple irradiance changes.
More references
http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/sunspots.html
A quote from this paper.
"Using a global climate model based on energy conservation, Lane et al (3) constructed a profile of atmospheric climate "forcing" due to combined changes in solar irradiance and emissions of greenhouse gases between 1880 and 1993. They found that the temperature variations predicted by their model accounted for up to 92% of the temperature changes actually observed over the period -- an excellent match for that period. Their results also suggest that the sensitivity of climate to the effects of solar irradiance is about 27% higher than its sensitivity to forcing by greenhouse gases. "
The next reference contains an error that was later corrected. The authors overstated the number of sunspots since 1960, but their earlier estimates were pretty much correct. I am not sure why the error occurred. I doubt it was scientific dishonesty - more likely a human mistake.
http://www.oar.noaa.gov/spotlite/archive/spot_sunclimate.html
The level of solar activity is related with several aspects, such as solar magnetism, solar wind, solar UV levels, solar 10.7 cm emission, and total solar irradiance (TSI; due to the appearance of dark sunspots and faculae). Changes in solar activity tend to involve changes in all of these aspects.
The sunspots themselves play a minor role - they are usually only taken as an indicator of the solar state. There are 3 proposed main mechanisms whereby changes in the sun affect our climate:
1 - change in TSI
2 - change in solar UV, which alters the absorption of energy in the stratosphere and the temperature of the upper atmosphere. May affect circulation and distribution of heat.
3 - change in galactic cosmic rays (GCR). Svensmark & co reckon the GCR affects the cloudiness. Others, such as Tinsley, think it affects the atmospheric fairweather electric field, which again may have an effect on the cloud micro-physics.
Then, you have feedbacks which can amplify or dampen impacts, etc- a lot of details on the subject- Rasmus Benestad has a whole book on the subject:
Benestad, R.E. (2002, 2005) Solar Activity and Earth's Climate,
Praxis-Springer, Berlin and Heidelberg, 287pp, ISBN: 3-540-43302-3
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Skeptic, the sources are fine but they don't have much to say about today. We know solar activity has influenced temperature over the Holocene and throughout paleoenvironments. I'm famaliar with most of those authors (and have contact with them) and can tell you none of them think there is a solar forcing predominant over the last 50 years (many guys in the third one are from realclimate as well). The sun is obviously an important part of global temperature but no real trend (or negative) since mid century, and we know CO2 reduces the infrared loss to space- actually if you think about it if you got more solar activity you get more incoming and less outgoing (because of CO2) and you just get worse-- Chris
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Creato, try the graph from the AR4:
From about 1940 to 1970, starting with increased industrial production during WW2, output of sulfate aerosols and other particulates did in fact increase dramatically. After regulations caused a decrease, and CO2 rose higher, the positive forcing overwhelmed the negative forcings. Interesting to note that some parts of the southern hemisphere may have been warming during this time (Stanhill and gunn, 1975). We do know though that aerosols are doing a good job of masking a lot of warming today, as you can see. This can be significant becuase if we reduce this pollution we might actually get more warming, and if it were to increase you get cooling but other problems like smog, acid rain, etc. The effects aren't perfect opposites so you get different places reacting differently.
Chris
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I Just e-mailed Tung himself, here is his response:
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Dear Chris,
Thank you for your inquery. The solar cycle signal goes up and down on a
11-year periodicity. So there should not be a secular trend in the global
mean temperature if the beginning and end years are at the same phase of the solar cycle, i.e. from solar max to solar max, or from solar min to solar
min. If you see a secular trend, then it must be attributed to something
else, possibly CO2. The solar-cycle signal is on top of any CO2 secular
trend, so it adds or subtracts 0.2 C depending on the period. For the next
5 years it will add 0.2 C on top of any CO2 warming.
--KK Tung
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I really hadn't seen what the point of referencing this study was- I had thought it was clear that Tung showed how CO2 sensitivity will match IPCC projections and even eliminate low-end sensitivity. I hope this ends this discussion here regarding Tung and Camp (2007) since we know what it really means (ie http://environment.newscientist.com/channel/earth/climate-change/mg19526164.800).
It has been extremely well documented now that solar changes since about 1950 have a very minimal forcing, and maybe even negative (solar irradiance also declined from 1960 to about 1990 from Gilgen et al 1998; Stanhill and Cohen, 2001) and I have already supplied a great deal of references on this subject.
http://www.pnas.org/cgi/reprint/104/10/3713
http://www.nature.com/nature/journal/v443/n7108/abs/nature05072.html
http://www.ucar.edu/news/releases/2006/brightness.shtml#
http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf
These two go over the temperature profiles of the layers of the atmosphere which I've gone over as being indicative of a greenhouse warmed planet and not a solar warmed planet:
http://www.climatescience.gov/Library/sap/sap1-1/finalreport/default.htm
http://www.sciencemag.org/cgi/content/summary/314/5803/1253
As we know though, if a strong natural forcing is to become apparent we will get just more forcing on top of CO2 as we know the physics behind CO2 increase. There are still countless other journals on the impacts of higher CO2, and what kind of forcing we get from that, and the explanatory and preditive power of the greenhouse warmed planet
Wrote this earlier in another forum so I will reproduce it here:
Remember, Earth's climate system is based on a radiative balance between absorbed visible radiation "A" and longwave radiation emitted at the Top-Of-Atmosphere "B"...so A≈ B. . At all times, globally averaged, A and B equal each other. As more solar radiation goes in than IR goes out, you get warming; if more IR goes out, than solar radiation comes in, you get cooling. This equilibrium isn't the case regionally-there is more solar radiation than outgoing IR at the equator, and more outgoing radiation than solar incoming at the poles. The only reason the two areas don't contine to warm (equator) and cool (poles) toward infinity is because of oceanic and atmospheric currents which transport heat from the equator to the poles keeping a stable temperature profile. Globally averaged, the radiative balance is in equilibrium and so temperature remains stable. So, the heat content of the climate system is something like dH/dt = A−B. However, when we speak of "global warming" we refer to some "forcing" which disrupts one side of the equation. As is well documented in the scientific literature, the increase in greenhouse gases have allowed more solar radiation going in than infrared going out (A > B) on a GLOBAL scale (which is the problem), but we know we aren't getting more solar radiation but we're delaying the IR out, and we know primary radiative forcing driving the increase in surface temperature is an increase of downward sky infrared from the atmosphere to the surface- sun is not forcing, and the temperature trends in the portions of the atmosphere (cooling in the stratosphere and above, and warming in the troposphere and below) are what we expect from more greenhouse gases and not more solar radiation) or the fact night temperatures are increasing faster than day temperature indicative of greenhouse gases and not the sun, so the explanatory and predictive power is there.To achieve a new radiative balance, the Earth must warm. Greenhouse gases work on the "energy loss" side of the equation: IR loss to space, not absorption of solar radiation. The CO2 forcing is simple physics- I think you do something like dT = 6.3 ln (C/Cx) where C and Cx are your final and initial CO2 levels, where the IPCC gets the ~1.6 W/m^2 radiative forcing from. Doesn't matter if "something else" will go positive, because we know what happens if you put in more CO2- if anything, it just gives more cause for alarm if we have stronger natural forcings because temperatures should increase even more.
From this point, I hope intelligent conversation is possible on the subject, but right now the scientific data shows clearly that the anthropogenic signal has dominated the second half of this century in its warming trends, and not just because of lack of other forcings but because we know how CO2 works as well and what forcing we will get with a given addition. The IPCC 2007 report gives greater justice to all these topics as well, and from pgs 188-192 goes over the solar variability very well, with an enormous load of other references which readers can review for additional insight on the topic- http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch02.pdf
I cannot possibly do justice to all of the literature and knowledge on both solar variation and the physics of more CO2, paleoclimate consistency, etc but I can try my best to lay out an overview of what we know. I am not trained as an astrophysicist, and I can get a bit more technical but not too much- I strongly encourage people to read the relevant literature and avoid secondary sources from blogs and other wingnut sites, full of misdirected claims which can easily be refuted
Chris
But doesn't current sunspot activity imply that global temperatures should presently be decreasing, which it's not?Pretty much. We keep rising becuase of the greenhouse dominance, and it looks like we will get ~3 C per 2x CO2; I think Camp and Tung just show we might get more as we head toward solar maxima coming up.
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See my graph above from the AR4...sun is in a "positive forcing" but not that significant in relation to greenhouse gases, and not much in relation to the peaks vs. drops in the 11-year cycle. I want to point out that the change in the mean is ~ 0.05% or about 0.5 W/m^2, much less than the variation within a cycle.
If the ACRIM data changes in the mean insolation are correct, then the inferred increase in solar radiance would account for ~10% of the temperature anomaly over 1990-2000 compared to previous decades:
The highest attribution of warming to the 1950-2000 period to solar activity I've seen is about 25% (http://www.agu.org/pubs/crossref/2005.../2005GL023849.shtml). this is very likely a high end figure, but even still, it leaves 75% left to other forcings. But if new and updated TSI data are used, then the trends they calculate vanish. The Foukal et al. paper (http://www.nature.com/nature/journal/v443/n7108/abs/nature05072.html) also show there is no positive evidence for a longer term forcing larger than seen over the 11 year cycle, as we also see in the Lockwood and Frohlich 2007 paper- http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf. Trends over the past few decades not doing what it should to explain warming, or even coming close to the magnitude of warming, as has been shown by countless studies all demonstrating the vast majority of post-1950 warming due to anthropogenic forcing. This still brings into question the stuff like stratospheric cooling which I brought up in my last post.
Chris
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Hi Chris C, nice to have you around. Given the sheer abundance of confusion that surrounds climate change (even around here), it's always great to see someone who's well-informed.
A couple other points of note:
Early 20th century warming can be partially attributed to a decrease in volcanic activity (due to reasons Chris C outlined above)
Anthropogenic CO2 emissions are over two orders of magnitude greater than natural ones, including volcanoes
Thanks for the welcome, I look forward to posting here. I've not heard of that argument in point 1 before (do you have a link I can look at?), but it looks like that warming from ~1900-1950 can be attributed largely to solar activity and some human forcing (but minimal) whereas the human forcing from about 1950 onwards is very strong.
The Lockwood and Frohlich paper (http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf) and Ammann et al. paper (http://www.pnas.org/cgi/reprint/104/10/3713) go over some of this, but personally I think that the trends are indicative of external forcing rather than internal stability; in other words, decrease of eruptions may partially explan why there is no cooling, but not why there is warming. If the lack of volcanic activity hypothesis held, than the 1950 baseline would be the temperature which the Earth was "supposed to" return to, which seems odd. Does look like an increase in volcanic activity, along with decrease in solar forcing was largely responsible for the maunder minimum though (time of our little ice age), so if volcanic activity declined, temperatures would have flattended out a bit but not raised abruptly.
I went over more on solar trends and why they are highly unlikely to have caused a large part of warming from about 1950 on in the "sunspot" thread in the ecology and environment forum.
An addition I want to make to my response of the OP- Actually, the 1940-1970 cooling in the graph above (which skeptics often use to show that CO2 does not cause temperature increase) was caused by increased aerosol usage which have a strong net negative forcing (and actually have partially mitigated warming trends today). The volcanic effects are similar to the large aerosol output in the more "dirtier" times of the industrial revolution- emissions go in the atmosphere and deflect solar radiation and cause surface cooling. This is what global dimming is all about.
With point 2, remember that the oceans and biomass are still a primary release of CO2 (in the sense that more CO2 is released naturally than by anthropogenic sources), but they are irrelevant in the CHANGE of CO2. The carbon cycle sequesters about as much is emitted by natural sources. When a skeptic hits you with the argument that natural sources far outweigh the human sources, tell them to remember the carbon cycle. CO2 cycles between the oceans, biosphere, atmosphere, etc so that what is released is removed at the same rate. What humans have done is change one side othe equation- which is why we call it an EXTERNAL forcing. Just for random numbers mathematically, it would look something like
100 from natural
4 from humans
but, the 100 from humans obviously doesn't keep acumulating otherwise the CO2 line would keep going to infinity, the same 100 units are removed via photosynthesis, oceanic uptake, etc...so
100 - 100 = 0 (so all you have is what is already in the atmosphere, or the pre-industral value which was stable over the entire Holocene from the last ice age)
Now add humans-
100 -100 + 4 = 4 (so now you have a rise in the line)
year 2- 104 -100 + 4 = 108
keep doing this on a yearly basis and it accumulates. I'm sure there is a lot of flaws in that simple set of equations, but that's the idea- humans are responsible largely for the variables, not the constants. Atmospheric CO2 concentrations began to exceed the narrow, naturally maintained range of atmospheric CO2 concentrations near the onset of the industrial revolution. See these graphs-
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if I was not clear on a particular point I will try to rephrase
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here is a more up to date graph on relative radiative forcings (Collins et al 2006; IPCC, 2007)
From Foukal et al (2006)Here is the abstract:
Variations in the Sun's total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century.Looks like Solar irradiance has decreased over the past few decades and is poorly correlated with temperature trends over the last 100 years, and the trends are too small to have outweighed the anthropogenic signal especially from 1950 onwards (early century warming can be associated with higher magnitudes of solar forcing) . (Gilgen et al., 1998; Crowley, 2000; Stanhill and Cohen, 2001; Max Plank Institute, 2004; Foukal et al., 2006; Lockwood and Frohlich 2007; IPCC, 2007)
Moreover, we know from the IPCC TAR that night temperatures are increasing at a faster rate than daytime temperatures, which is inconsistent with a primary external influence from the sun and consistent with increase in greenhouse gases. Moreover, the troposphere is warming while higher layers (Stratosphere, mesosphere, theremosphere) are cooling, which again, is not consistent with the primary influence from the sun.
In short, The decrease in lower stratospheric temperatures is the result of decreased ozone concentrations at the tropopause and greater insulation by greenhouse gases in the troposphere. The lower stratosphere has cooled primarily due to ozone depletion, while the troposphere has warmed from the enhanced greenhouse effect.
The thermal profile of the stratosphere is the result of a balance between radiative heating and cooling rates due to greenhouse gases(ie CO2, O3, water vapor). The reason the stratosphere cools with increase of CO2 is the balance in the stratosphere is between absorption of solar radiation by O3 and cooling by infrared emission. As you increase CO2, there is radiative cooling, therefore, the stratosphere cools to come back into balance. Increase of greenhouse gases at the troposphere creates an increased temperature gradient so that anything below will generaly warm, while anything above will cool. This is also consistent with temperature trends at the mesosphere and thermosphere (see Lastovicka et al., 2006) and a comparison made by the study-
"The increase in global surface air temperature during the 20th century has been attributed mainly to the increasing atmospheric concentrations of greenhouse gases. In the upper atmosphere, the radiative effects of greenhouse gases, particularly CO2, become more pronounced and produce a cooling rather than a warming effect. This effect is demonstrated by the CO2-dominated atmosphere of Venus, where the troposphere is more than twice as warm as Earth's and the thermosphere is 4 to 5 times as cold "Addition as well- numerous studies now demonstrate that over the last 60 years or so the anthropogenic signal is strongly detectable and overwhelms "natural" external forcings (Ammann et al 2007) and that if there was a strong solar forcing to come it would only be of more concern as the radiative physics behind more CO2 in the atmosphere is well known.
Much is known about the physics of climate change, and this paradigm, developed from many parts of science over the decades, has repeatedly proven to be successfully predictive as well as explanatory with high confidence. Much work remains to fully understand paleoclimatic templates (such as "tipping points" or abrupt climate change), feedbacks, and to assess possible implications for the future, but the foundations for this work are remarkably solid.
Chris
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They do release a fair amount of CO2 but the abopve users are quite wrong in the conclusions (normally). Volcanic eruptions actually cause global cooling. CO2 is released as above users have pointed out, however, the carbon cycle quickly removes this CO2 and returns to equilibrium rather quickly. Humans release more CO2 per year and it accumulates year to year to year which is why you see a steady rise, but no abrupt jumps even at volcanic eruptions.
So why do they cause cooling? Volcanos typically emit large quantities of sulfate ejecta, which deflect incoming solar radiation, which causes a decrease in insolation (and temperatures) on the earth. This is not the same as "dust" which may have less significant impacts (ie Mt. St. Helens). The Mt. Pinatubo eruption in '91 caused a ~0.5 C degree cooling for a couple of years, but the cooling agents are also quickly removed in the atmosphere and significant climatic effects shouldn't be seen many years later.
I recommend this site for Volcanic relations to climate change
http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html
Volcanic eruptions can be asociated with global warming especially in paleoenvironments with more intense and frequent volcano activity. A particular event was the Paleocene-Eocene thermal maximum (PETM) he massive outpouring of Siberian Trap Volcanoes at the Permian-Triassic boundary. However, what you say is generally the case in relation to smaller scale and individual eruptions
fatty,
your explanation of the greenhouse effect is wrong. For one thing, you are confusing "greenhouse gases" with "ozone." Ozone can act as a greenhouse gas (primarily in the troposphere) but the ozone layer is contained in the stratosphere and plays minimal role in global warming. Its main role, for our purposes, is to block UV radiation which causes sunburn, skin cancer etc. Without it, life on land and shallow water would not be possible. The depletion of the ozone layer is a separate topic, and is kind of fading away as it is actually in recovery and CFC's have largely been regulated since the Montreal Protocol.
In contrast, solar radiation (which peaks at the visible spectrum, not UV, which is why we see it) enters the atmosphere and goes though unblocked (almost) by the atmosphere. The Earth reflects some of it back out via clouds or other reflecting objects, and absorbs much of it. The visible radiation absorbed is emitted as infrared radiation (the wavelength of peak emission is inversely proportional to temperature by Wein's law and the Earth is much cooler than the sun so it emits in a different wavelength) and greenhouse gases in the troposphere (not the stratosphere where ozone resides) absorbs and re-radiates that infrared radiation. I don't want to get technical from here, because some can re-radiate upwards and sideways, but also downwards. Generally speaking, layers below will warm, and it is this effect that keeps the planet warm enough for life. So...
1) The ozone layer is in another layer of the atmosphere and regulated harmful UV emission, it plays little role in global warming
2) Greenhouse gases in the troposphere are what absorb and re-radiate infared radiation. You can say that the sun does not heat the atmosphere but rather it heats the surface which heats the atmosphere, so the suns effect is indirect. The problem is not depleted ozone but the increase of greenhouse gases which absorb more infrared radiation delaying its return to space.
Chris
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Storms
in Other Sciences
Posted
For *thunderstorms* it is mainly vigorous convection that extends high up into the troposphere (maybe even into the stratosphere). Frontal or orographic lifting, converging surface winds, solar heating produces forced convection and you might get a thunderstorm.