We often get requests to provide an easy-to-understand explanation for why increasing CO2 is a significant problem without relying on climate models and we are generally happy to oblige. The explanation has a number of separate steps which tend to sometimes get confused and so we will try to break it down carefully.
Step 1: There is a natural greenhouse effect.
The fact that there is a natural greenhouse effect (that the atmosphere restricts the passage of long wave (LW) radiation from the Earth’s surface to space) is easily deducible from i) the mean temperature of the surface (around 15ºC) and ii) knowing that the planet is roughly in radiative equilibrium. This means that there is an upward surface flux of LW around 
(~390 W/m2), while the outward flux at the top of the atmosphere (TOA) is roughly equivalent to the net solar radiation coming in (1-a)S/4 (~240 W/m2). Thus there is a large amount of LW absorbed by the atmosphere (around 150 W/m2) – a number that would be zero in the absence of any greenhouse substances.
Step 2: Trace gases contribute to the natural greenhouse effect.
The fact that different absorbers contribute to the net LW absorption is clear from IR spectra taken from space which show characteristic gaps associated with water vapour, CO2, CH4, O3 etc (Harries et al, 2001; HITRAN). The only question is how much energy is blocked by each. This cannot be calculated by hand (the number of absorption lines and the effects of pressure broadening etc. preclude that), but it can be calculated using line-by-line radiative transfer codes. The earliest calculations (reviewed by Ramanathan and Coakley, 1979) give very similar results to more modern calculations (Clough and Iacono, 1995), and demonstrate that removing the effect of CO2 reduces the net LW absorbed by ~14%, or around 30 W/m2. For some parts of the spectrum, IR can be either absorbed by CO2 or by water vapour, and so simply removing the CO2 gives only a minimum effect. Thus CO2 on its own would cause an even larger absorption. In either case however, the trace gases are a significant part of what gets absorbed.
Step 3: The trace greenhouse gases have increased markedly due to human emissions
CO2 is up more than 30%, CH4 has more than doubled, N2O is up 15%, tropospheric O3 has also increased. New compounds such as halocarbons (CFCs, HFCs) did not exist in the pre-industrial atmosphere. All of these increases contribute to an enhanced greenhouse effect.
Step 4: Radiative forcing is a useful diagnostic and can easily be calculated
Lessons from simple toy models and experience with more sophisticated GCMs suggests that any perturbation to the TOA radiation budget from whatever source is a pretty good predictor of eventual surface temperature change. Thus if the sun were to become stronger by about 2%, the TOA radiation balance would change by 0.02*1366*0.7/4 = 4.8 W/m2 (taking albedo and geometry into account) and this would be the radiative forcing (RF). An increase in greenhouse absorbers or a change in the albedo have analogous impacts on the TOA balance. However, calculation of the radiative forcing is again a job for the line-by-line codes that take into account atmospheric profiles of temperature, water vapour and aerosols. The most up-to-date calculations for the trace gases are by Myhre et al (1998) and those are the ones used in IPCC TAR and AR4.
These calculations can be condensed into simplified fits to the data, such as the oft-used formula for CO2: RF = 5.35 ln(CO2/CO2_orig) (see Table 6.2 in IPCC TAR for the others). The logarithmic form comes from the fact that some particular lines are already saturated and that the increase in forcing depends on the ‘wings’ (see this post for more details). Forcings for lower concentration gases (such as CFCs) are linear in concentration. The calculations in Myhre et al use representative profiles for different latitudes, but different assumptions about clouds, their properties and the spatial heterogeneity mean that the global mean forcing is uncertain by about 10%. Thus the RF for a doubling of CO2 is likely 3.7±0.4 W/m2 – the same order of magnitude as an increase of solar forcing by 2%.
There are a couple of small twists on the radiative forcing concept. One is that CO2 has an important role in the stratospheric radiation balance. The stratosphere reacts very quickly to changes in that balance and that changes the TOA forcing by a small but non-negligible amount. The surface response, which is much slower, therefore reacts more proportionately to the ‘adjusted’ forcing and this is generally what is used in lieu of the instantaneous forcing. The other wrinkle is depending slightly on the spatial distribution of forcing agents, different feedbacks and processes might come into play and thus an equivalent forcing from two different sources might not give the same response. The factor that quantifies this effect is called the ‘efficacy’ of the forcing, which for the most part is reasonably close to one, and so doesn’t change the zeroth-order picture (Hansen et al, 2005). This means that climate forcings can be simply added to approximate the net effect.
The total forcing from the trace greenhouse gases mentioned in Step 3, is currently about 2.5 W/m2, and the net forcing (including cooling impacts of aerosols and natural changes) is 1.6±1.0 W/m2 since the pre-industrial. Most of the uncertainty is related to aerosol effects. Current growth in forcings is dominated by increasing CO2, with potentially a small role for decreases in reflective aerosols (sulphates, particularly in the US and EU) and increases in absorbing aerosols (like soot, particularly from India and China and from biomass burning).
Step 5: Climate sensitivity is around 3ºC for a doubling of CO2
The climate sensitivity classically defined is the response of global mean temperature to a forcing once all the ‘fast feedbacks’ have occurred (atmospheric temperatures, clouds, water vapour, winds, snow, sea ice etc.), but before any of the ‘slow’ feedbacks have kicked in (ice sheets, vegetation, carbon cycle etc.). Given that it doesn’t matter much which forcing is changing, sensitivity can be assessed from any particular period in the past where the changes in forcing are known and the corresponding equilibrium temperature change can be estimated. As we have discussed previously, the last glacial period is a good example of a large forcing (~7 W/m2 from ice sheets, greenhouse gases, dust and vegetation) giving a large temperature response (~5 ºC) and implying a sensitivity of about 3ºC (with substantial error bars). More formally, you can combine this estimate with others taken from the 20th century, the response to volcanoes, the last millennium, remote sensing etc. to get pretty good constraints on what the number should be. This was done by Annan and Hargreaves (2006), and they come up with, you guessed it, 3ºC.
Converting the estimate for doubled CO2 to a more useful factor gives ~0.75 ºC/(W/m2).
Step 6: Radiative forcing x climate sensitivity is a significant number
Current forcings (1.6 W/m2) x 0.75 ºC/(W/m2) imply 1.2 ºC that would occur at equilibrium. Because the oceans take time to warm up, we are not yet there (so far we have experienced 0.7ºC), and so the remaining 0.5 ºC is ‘in the pipeline’. We can estimate this independently using the changes in ocean heat content over the last decade or so (roughly equal to the current radiative imbalance) of ~0.7 W/m2, implying that this ‘unrealised’ forcing will lead to another 0.7×0.75 ºC – i.e. 0.5 ºC.
Additional forcings in business-as-usual scenarios range roughly from 3 to 7 W/m2 and therefore additional warming (at equilibrium) would be 2 to 5 ºC. That is significant.
Q.E.D.?
Maybe I missed it but I didn’t see anything in this post about water vapor or clouds.
I know it was a post about CO2 but isn’t much the green house effect an enhancement of effect of CO2 caused by water wapor?
An interesting “toy model” was published by Svante Arrehenius in 1896 and his conclusions about the “carbonic gases” has proven to be one of the most prescient papers ever written.
Re # 91 Marc,
With all due respect, I’m afraid I (a biologist) don’t understand how you (an astronomer) can state, with respect to the emission spectrum of solar radiation that “just under half is pretty close to most.” And yes, the peak emission is in the so-called wavelengths, but so what? Integrating (even crudely, by eyeball) the area under the energy emission spectrum (and I was referring to energy flux, Watts per cm^2 per sec – not photon flux)reveals that visible wavelenths make up about as much as IR and UV combined. Stating this fact shouldn’t complicate explanations of the “greenhouse effect.”
My experience teaching science to non-science major college students (mostly freshman and sophomores) for over two decades hasn’t been quite as exasperating as it apparently has for others who have posted here. But, I’ve usually found it better to simplify complex topics by withholding information rather than simplifying to the point of being incorrect, or relying on flawed analogies (unless I state clearly why a particular analogy is just that, and not a scientific explanation). Students come to class with enough misconceptions – I don’t want to introduce more by telling them things that aren’t true (Funny how obviously flawed analogies seem to sink in much more readily than correct scientific explanations).
Are you able to point me to resources that set out how the net cooling affect of aerosols has been calculated? Also, are you able to tell me what the accepted estimate of the degree of uncertainty associated with net cooling affect of aerosols?
“We often get requests to provide an easy-to-understand explanation for why increasing CO2 is a significant problem without relying on climate models and we are generally happy to oblige.”
Yet you did NOT. You rely on climate models for the key numeric values for the strenghts of different forcings and sensitivities.
[Response: Not so. LBL codes are not climate models, and the sensitivity is from observational constraints. Please read the relevant papers. – gavin]
And I noticed GiSS have adjusted their estimations for average annual temperatures in the United States due to the great work done by Watts, McIntyre and initially Pielke. As a result the hockey stick won’t have a blade soon, and 4 of the warmest years on record are from 1930’s now. 1998 has lost it’s place as the warmest year on record, and 1934 now holds that position. And soon you will be trying to get the models to simulate trends for 0.xx degrees less warming. Shouldn’t you be thankful to them (people you have derailed in the past in realclimate articles), that the science is getting more accurate? Or are you disappointed with these developments?
[Response: All improvements are of course welcome. However, this had nothing to do Watts or Pielke, and the global mean temperatures are basically unaffected (since the problem was only with US temperatures which cover less than 2% of the globe). No changes in the models will happen because of this. – gavin]
Comparing your communication of your research to the likes of Pielke, is like comparind a night to a day. You are so certain, so convinced and showing next to no doubt, while e.g. Pielke comes across as open minded, uncertain and full of doubt. Which of the two is the more scientific approach?
[edit]
I’m seriously concerned that we will spend thousands of billions on something that isn’t necessarily a problem to begin with, while as a result neglegting many real concerns because our resources are limited. These include bio-diversity loss, ocean depletion and water shortage.
It’s not a win win situation. If unimaginable amounts are used to combat “global warming” and in the end it is proven that there wasn’t a serious initial problem to start with, people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind. I hope you then won’t have any explaining to do about the sincerity, openness and scientific integrity of your research.
Step 5 may be facing some challenges here:
http://earth.myfastforum.org/about56.html
[Response: Not really. – gavin]
I think this article is important, in terms of the motivation for this particular post and the site as a whole: What matters most in politics – facts and logic, or stories and feelings?
I see a lot of facts and figures in the “easy-to-understand” explanation. I’m also not sure of the necessity of the steps 4-6 in such an explanation.
There has to be a simpler way of making these arguments.
One interesting thing I came across is the idea of “lies-to-children”*. I think it was in the Pratchett, Stewart and Cohen book about “science” where they said that much of science education consisted of a series of “lies-to-children” in which they were not told the complete truth. When students got to the next level of education they would then be told “You were taught x, but, actually, it’s more complicated than that…”
One thing we have to understand is that we are never going to convince the tiny, but loud, minority of nutjob denialists. calmly pointing out their dishonesty is important, but not if it comes at the expense of talking to the not particularly interested majority. They’ll get bored by the details, and use incessant arguing about them to justify not giving a damn.
* A “lie-to-children” is the sort of thing you tell a small child who asks lots of questions about the world. It isn’t possible to tell them the whole truth, because they won’t understand it, but you can tell them something that approximates the truth.
RE: 104
A recent theory has proposed that the Younger Dryas may be associated with a comet impact striking the North American ice sheets.
http://www.newswise.com/articles/view/530208/
[[The planet is NOT in dire straits; it is the state and content biosphere we depend upon for our existence. The planet and life in general will continue on quite nicely with or without us, thank you very much, though as a member of an interested species, I would prefer the former to the latter.]]
This isn’t really correct. We’re in the middle of a mass extinction that human technology has essentially caused and global warming will make much worse. Global warming is not just a problem for humans.
Hi all
Any comment on the latest revelations at climateaudit.org on the revelations regarding the USHCN Data Set.
Regards
Peter Bickle
[Response: McIntyre noticed that there was an odd offset in the GISTEMP analysis in 2000 which turned out to be related to the transition between USHCN data to the GHCN data. The offset occurred because the USHCN corrections (for Time of Observation bias mainly) affect the more recent values in USHCN but not GHCN (as opposed to only affecting earlier values). Once notified of the problem, GISS investigated immediately, found the error, and added an extra step to the analysis to remove any jump at the transition. This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn’t effect the global temperatures. Note that this wasn’t a problem with the USHCN data – rather in how the different data sources are melded. It also had nothing to do with any micro-site issues. – gavin]
“This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn’t effect the global temperatures.”
You make it sound like, it was no big deal. What’s 0.15C between friends, eh? And how do you know such problems are only restricted to the USA? Perhaps there are worse problems elsewhere?
After the adjustments 1934 is now the hottest year on record after a 3/4 century of CO2 emissions. Now what did you say was the climate sensitivity for a doubling of CO2? a) 3.0C b) Perhaps 2.5C or c) To be honest, you don’t know exactly?
[Response: 1934 is the warmest US year. Globally 2005 was the warmest year in GISS and NCDC, 1998 in the CRU analysis. And you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity ‘exactly’. – gavin]
This only affected the US temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but since the US is such a small part of the world, it doesn’t effect the global temperatures. Note that this wasn’t a problem with the USHCN data – rather in how the different data sources are melded. It also had nothing to do with any micro-site issues. – gavin]
That’s a big conclusion that isn’t justified.
One of the largest sets of data is the US.
With this error, it isn’t a small percentage of the world’s temperature that is the issue. It is that the US data is a large percentage of the data available.
Nick
[Response: But the global average isn’t simply an average of all the stations divided by the number of stations. You need to adjust for area so that a high concentration of stations in one spot doesn’t bias the mean. If the US is 2% of the area, then a 0.15 ºC correction there implies only a 0.15*0.02=0.003 ºC correction to the global mean (though it’s actually a little higher because of incomplete global coverage). These things should obviously be fixed, but the implications need to be kept in perspective. – gavin]
“Not so.”
What is this then:
“experience with more sophisticated GCMs suggests that…”
I don’t think you are saying that you count the actual forcings and sensitivies independently of the hugely complex mechanisms of the atmosphere / climate? For an example, different AGM’s cited by the IPCC offer everything between 1.4C and 6.4C for the climate sensitivity of doubling of CO2. What is the worth of a value that is theoretized with no consideration for the huge complexity and countless mechanisms that affect the climate? And when you consider them, you have to model it to the best of your ability, to make some sense of it, isn’t that right? Or alternatively just hold your hands up.
I don’t think anyone denies that CO2 affects the climate. The question is how much. I’m sure the so called “denialists” would basically agree with everything else here except “3.0C”.
The northern hemisphere should have warmed more than the southern (e.g. New Zealand observed no warming during the 20th century), this is how the theory goes. Now you do little adjustments, and you find out it was even a bit warmer in 1930’s than in the first decade of the 21st century. And don’t say it is just 2%. The US is bit more than just 2% of the land area in the Northern hemisphere, and representative of an even larger area.
No noticeable increase in temperature in 75+ years of CO2 emissions. And who knows if the current mean temperatures will come down a little bit more, when the sites have been surveyed.
Then there’s Pielke and dozens of his colleagues who say that land use change is a major climate forcing, which they say have been neglected by the IPCC and the AGM modellers. Then there are another dozen or more uncertainty factors.
You cannot possibly confidently state an accurate number for the doubling of atmospheric CO2. That makes no sense. It is far beyond our current capacity.
Re #111 [[After the adjustments 1934 is now the hottest year on record after a 3/4 century of CO2 emissions. Now what did you say was the climate sensitivity for a doubling of CO2? a) 3.0C b) Perhaps 2.5C or c) To be honest, you don’t know exactly?
[Response: 1934 is the warmest US year. Globally 2005 was the warmest year in GISS and NCDC, 1998 in the CRU analysis. And you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity ‘exactly’. – gavin]]]
Gavin, I’m afraid you’re forgetting, here and in your responses to #110 and #112, that nothing outside the USA really counts :-)
“you appear to be mistaking me for someone else if you think I ever claimed to know the climate sensitivity ‘exactly’.”
Didn’t you just say:
“Climate sensitivity is around 3ºC for a doubling of CO2”
?? What am I missing here?
[Response: A dictionary? – gavin]
re 109
[[The planet is NOT in dire straits; it is the state and content biosphere we depend upon for our existence. The planet and life in general will continue on quite nicely with or without us, thank you very much, though as a member of an interested species, I would prefer the former to the latter.]]
This isn’t really correct. We’re in the middle of a mass extinction that human technology has essentially caused and global warming will make much worse. Global warming is not just a problem for humans.
You’ll forgive me if I disagree.
While I have no arguement re the effects of global warming, my point was the biosphere has survived five mass extinctions so far and will likely survive the current one, if that is what it turns out to be (and I believe it is, for what it is worth).
Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere – and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.
Re: #113, “You cannot possibly confidently state an accurate number for the doubling of atmospheric CO2. That makes no sense. It is far beyond our current capacity.”
CAGW skeptic, yes, you can. As atmospheric CO2 concentrations were roughly 275-280 ppm prior to 1850 (when we started to industrialise), we can say that a doubling of CO2 would lead to concentrations around 550-560 ppm. Simple mathematics.
Re: #105, “It’s not a win win situation. If unimaginable amounts are used to combat “global warming” and in the end it is proven that there wasn’t a serious initial problem to start with, people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind.”
CAGW skeptic, have you heard of the Stern Review on the Economics of Climate Change? It says investment in fighting the worst effects of climate change is necessary to prevent an economic disaster as a result of climate change.
http://www.hm-treasury.gov.uk/independent_reviews/stern_review_economics_climate_change/sternreview_index.cfm
A nice summary is here:
http://en.wikipedia.org/wiki/Stern_Review
#67 Barton, A little idea, cloud albedo may reflect energy to space, but we often forget that clouds are rich in water vapour, which is a source of energy through latent heat of evaporation, I think that these clouds may have been underestimated as a source of heat, or rather the heat loss through cloud albedo (reflection of sunlight)is not the correct calculation of net heat loss since clouds themselves are a latent heat source.
Re: # 105 CAGW skeptic
“If unimaginable amounts are used to combat “global warming” – Who is suggesting that this is necessary?
“people will ask questions about how those thousands of billions could have been spent more productively for the good of mankind” – Such questions are always asked about potentially expensive policy decisions, such as going to war.
Off-topic, and I apologize in advance. Just following up on an earlier commenter’s detour.
#87– I recognize the humor in your comment, but you’d do well not to alienate the religious people who take interest in reading the comments on climate blogs. There are more religious people who believe in gravity, evolution, thermodynamics, relativity, the green house effect and the sun-god who traverses the sky by day and visits wrath upon the underworld by night than you seem to think there are.
———-
[[One thing I’ve found over the years of dealing directly and indirectly with high school students is that the direct scientist-student route is not very productive (very different assumptions about what an explanation entails!). However, the scientist-teacher then teacher-student route is much more so. Teachers get the scientific points much faster and are also in a much better position (and have more patience) to lead the students to understanding. Therefore, maybe we could help each other out here.]]
I think this is a terribly interesting piece of the puzzle to ponder–how best to bridge the gap between Scientist and lay person? It seems not so different from the problem of bridging the gap between Pope and lay person in some ways. (The biggest difference is, of course, that the Scientist is actually qualified to tell people about the errors of their ways, and how then to live in order to be saved!)
And religion has a history of causing people to actually change their ways. (Granted, its not always a nice, pleasant story about some non-violent Mahatma starving himself to liberate his people from imperial tyranny or a Messiah choosing death on a cross in favor of attempting a coup.)
The educational process is not getting the job done in the USA, and I think a grassroots movement is what is needed to actually change America’s behavior on CO2. And if there’s one group that in America today that can spark a grassroots movement, isn’t it the evangelical? Read this.
The emerging rapprochement is regarded by some as a sign of how dramatically U.S. public sentiment has shifted on global warming in recent years. It also has begun, in modest ways, to transform how the two groups define themselves.
“I did sense this is one of these issues where the church could take leadership, like with civil rights,” said Northland’s senior pastor, Joel C. Hunter. “It’s a matter of who speaks for evangelicals: Is it a broad range of voices on a broad range of issues, or a narrow range of voices?”
Hunter has emerged among evangelicals as a pivotal advocate for cutting greenhouse gas emissions that scientists say are warming Earth’s climate.
#119 Make that latent heat of condensation, A cloud 100 meter thick probably reflects just as much energy as a cloud 1000 meters thick. The difference is that one has more energy than the other…
RE #111, The Dust Bowl was caused by global warming! I knew it! :)
Re #113, #115 and possibly others here regarding CO2 sensitivity.
You might like to read Camp and Tung (submitted to JGR)
Seems the CO2 sensitivity is quantifiable and its value is being refined.
No matter how you look at it, it seems to me, whether the actual value is skewed left, right, or not at all wrt the wide range arising from different model runs or Camp and Tung’s constrained range (95% confidence level, independent of models) for CO2 sensitivity (based on actual measurement data), the value is ~3°C for a doubling of CO2. Of course, this might change after peer review of the Camp and Tung paper has been completed. Think it unlikely though.
And you might like to read Camp and Tung’s analysis of solar attribution of temperature variation and the 11 year cycle at GRL or here.
Wayne, a cloud is droplets of liquid H20 that have lost some heat to the surrounding atmosphere. Water vapor is H20 in gas form, molecules that have enough energy that they don’t stick together as droplets. Not sure where you’re going with the notion of clouds having energy, but it’s all just bouncing around in the lower atmosphere at that level; only when the heat gets up to the top of the atmosphere can it radiate away.
#121, I can vouch that my church has not been much help re global warming (though some evangelicals & others (e.g., Green Lights Episcopalians) are doing things). I know Pope John Paul II told us in 1990 that it’s everyone’s responsibility to mitigate GW, and the U.S. Bishops in 2001 (what took ’em so long?) said that prudence requires us to do so, but these statements haven’t translated into action or even change of heart in my parish. One “very religious” person even said the bishops might be wrong; another said, “we all have to die sometime” (to which I responded, yes, but we don’t have to kill); and the priest seriously considers Limbaugh’s views on GW & said he’s worried about what the Limbaugh Catholics in the parish might think if he broaches the GW topic. As with the government and media, churches are also tied into anti-environmental forces & evil money; for instance when our parish’s environmental committee was to put on an “eat low on the food chain” program, the beef guys on the parish council sent a message via the nun in charge to can it (we disobeyed, since the program was already set). And educational institutions are just as bad; my friend worked up a vegetarian day during Earth Week some years back at an Illinois community college, and the beef guys on the school board disallowed her from explaining how the veggie food the students were eating that day related to environmental issues.
What that leaves us with, I’ve recently come to conclude, is Hollywood as our only hope against the corrupt institutions of our society :) They’re only into titilating and and luring the money-paying public, and their relationship with the public is more direct, not deflected by evil as much as the church-state-education-business-(non movie)media. And if Hollywood hasn’t provided us with enough GW movies and documentaries to effect significant GHG reductions, that’s only because the public has already been corrupted to a large extent by the other societal institutions. So that’s my latest macro-sociological analysis of the global warming situation :)
“the value is ~3°C for a doubling of CO2”
In laboratory, in theory, or in complex reality?
If we accept this value 3 degrees, then today it should be approx. a degree warmer than it was in 1930`s with all the CO2 we have put in the atmosphere. But it isn`t and the theoretical value breaks down there and then. There`s no decline in solar activity to compensate, aerosol effects are mostly local, and the atmosphere e.g. in USA has been getting clearer. You look at this data, and if you don`t doubt the 3C, then how do you explain that?
[Response: Climate sensitivity is an equilibrium concept. Right now we are not at equilibrium (as evidenced by the increasing temperature rises and ongoing increases in ocean heat content). The oceans have a huge inertia and take time to warm up. As in Step 6, the warming seen so far is completely consistent with a sensitivity of about 3 ºC and a net heat imbalance (going mostly into the ocean) of about 0.6 W/m2. Think of that imbalance as the ‘unrealised’ forcing. So of the 1.6 W/m2 we think we’ve added to the system, only 1 W/m2 has been realised, and so we expect a warming of about 0.7 to 0.8 degrees. Pretty consistent, no? – gavin]
“we expect a warming of about 0.7 to 0.8”
That`s fine, except that current global temperatures are only around 0.2-0.3 warmer than in 1930`s if even that considering UHI effect and sudden 0.15C adjustments.
Much/Most of the warming occurred in early 20th century.
[Response: That’s simply not true. Do the analysis yourself: http://www.giss.nasa.gov/gistemp – gavin]
re 126 and the Catholic Church, I have to wonder at how credible the C Church is regarding doing anything about GW so long as they maintain an anti-contraceptive stance.
That said, nice analysis….
Re#114:
This is nonsense. Over the 20th century NZ warmed by at least 0.7C. Go here and scroll down to Fig 6.
Your claim is eerily similar to one made by a local sceptic who claimed on the basis that a hot summer in Christchurch in the early 1900s was similar to a very cold summer in 2006 that there was no warming taking place. Complete bollocks, if you’ll pardon my anglo-saxon.
And – sorry to go off topic, but could I suggest RC solicit an urgent post from a sea ice expert?
From Cryosphere Today:
[[Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere – and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.]]
I sincerely doubt it. The next step after the habitable Earth is the runaway greenhouse Earth, about 0.6-1.4 billion years from now. Since life as we know it requires liquid water, that pretty much rules out life continuing on the Earth — unless, of course, we alter the climate at that time artificially.
[[You might like to read Camp and Tung (submitted to JGR)]]
Good paper overall, but in their estimation of the effect of changing solar constant, they seem to neglect the Earth’s albedo.
Gareth, New Zealand experienced glacial advances between 1980`s and early 2000`s.
GiSS and CRU disagree so much with each other, and often the samples are wholly inadequate, and then as a rule the derived mean temperatures are always high on the scale, that it`s very difficult to take them at a face value, if you are a rational person.
These are presumably teams of highly skilled professionals, and then a single person like Steve McIntyre can spot a basic error which makes them adjust their mean temperatures by 0.15C and they pretend it`s nothing [edit]. I doubt these errors are restricted to the USA, because the sample data is less adequate in the rest of the world, and the modellers seem to have a fetish for deriving as high mean temperatures as possible. The less data you have, the higher the mean temperatures will be.
They try to make fun of the surface station survey, but Anthony Watts has already proven how unreliable many of these stations are. The attitudes are more political than they are scientific. A scientist would be happy that someone is doing this job, so that we can have more accurate data, but these people seem to be genuinely afraid and annoyed that they will have to adjust the mean temperatures another 0.1C soon. And down on the scale of course, as everyone could have predicted.
#130 Garreth. Yep its bad, never quite seen anything like this…
#125 Hank, I’ve been looking for temperature variation reasons, knowing full well that 2007 started really warm, yet there was a recent small bit of cooling which I’ve detected independently from other more known temperature records which confirm the same thing (GissTemp, NOAA etc…), been trying to find where the energy has gone to, I have reasoned that its in the clouds, which are a mixture of vapour and droplets. Of which there is 600 Calories per gram of water vapour, no small figure considering the size Earth’s cloud areas. This greater cloud extent may have been indirectly proven by strong rain showers all over the world…….
Re:#133:
Wayne, re that recent plateau in temperature, New Scientist just published an article that mentions it; it turned up as one of the results of a new model using the Argo (sea temp) instrument data; I quoted an excerpt and gave a cite here.
The original article is in the current Science: http://www.sciencemag.org/cgi/content/abstract/317/5839/796
Excerpt I quoted from NS in the other topic is here:
https://www.realclimate.org/index.php/archives/2007/07/green-and-armstrongs-scientific-forecast/langswitch_lang/sk#comment-45973
Thanks for the links Hank, variability is always there, it doesn’t mean we can’t explain it. There is also
a certain planetary wave offset stemming from the all time low Polar ice as cited above, immediate consequences just been explored since the North Pole looks soo different now, its a new landscape.
Re #133,
The cyclical behavior of New Zealand’s glaciers on a decades timescale is nothing new. What matters is the long-term behavior. For example, see Figure 6 in this USGS reference:
http://pubs.usgs.gov/pp/p1386h/nzealand/nzealand.html
The short-term advances aren’t very impressive when superimposed on the long-term trend.
#111 response: Globally 2005 was the warmest year in GISS
Interesting that it appears that the year to July 2007 is the equal warmest year in GISS. One year is not statistically significant, of course.
Re # 134 “… [specific heat of] 600 Calories per gram of water vapour”
Wayne, You should be aware that your spelling of calorie with a capital C may be lead to confusion – nutritionists, dieticians, food manufacturers et al use Calorie (capital C) to represent kilocalorie. Of course, the SI unit is joule, rather than calorie, but that is another matter.
Re: [[Life WILL go on, most likely, until that day in the far future…]
All well and good, I suppose, but you seem not understand that it’s ME going on, in reasonable comfort and so on, that I’m worried about :-) And to a somewhat lesser extent my friends and putative descendants.
Regarding New Zealand glacial advances:
According to Chinn et al (2005) the cause of the advance in glaciers in New Zealand’s southern alps is primarily from changes in the global circulation, causing a strengthening of westerly circulation at those latitudes. This results in increasing precipitation over the glaciers and a decrease in ablation temperatures due to the increasing wind velocities.
Much of the changes observed in the global circulation are thought (although the research is by no means conclusive) to be coincident with the currently observed climate change, which has anthropogenic factors as one of its driving sources.
Meanwhile, there has been an overwhelming glacial retreat observed in the last decade. The retreat of the Greenland ice sheet has accelerated from 21.33 m (70 ft) per day to 33.5 m (110 ft) per day in the period from 2001 to 2005 (Howat et al. 2006).
It would help if people would, before bringing these points out in a debate, to read the literature and get a rudimentary grasp of the topic at hand. You can be far more convincing this way.
[[These are presumably teams of highly skilled professionals, and then a single person like Steve McIntyre can spot a basic error which makes them adjust their mean temperatures by 0.15C and they pretend it`s nothing [edit]. I doubt these errors are restricted to the USA, because the sample data is less adequate in the rest of the world, and the modellers seem to have a fetish for deriving as high mean temperatures as possible. The less data you have, the higher the mean temperatures will be.]]
Global warming has also been detected in sea surface temperatures — are there urban heat islands on the ocean? It has been detected in boreholes — are there poorly sited temperature stations underground? It has been detected from balloon radiosonde data, satellite observations, melting glaciers, rising sea levels, tree lines moving toward the poles, animals migrating toward the poles, and on and on and on. Are you familiar with any of this evidence? What makes you think global warming will go away if you discredit the surface record?
Re #98
My problem with the link I found, http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch01.pdf is that it represents the IPCC position now. There are two important features, it includes evaporated heat tranfers an convection, neither of which are included in here. Further the IPCC diagram shows the atmosphere radiating 324W to the earth, in general the troposphere is colder than the surface, thus, as anyone knows, energy just doesn’t go this way.
To #6 onstantin
The surest thing about climate change is that it will change precipitation patterns. Some parts will be drier and some wetter. Hydro power is ridiculous without water and dam(n) dangerous with too much water. Riverside nuclear power stations are very dangerous if flooded or unsufficiently cooled.
Agriculture, in rich or poor countries, can on average and over long time possibly adapt to climate change. But it can’t adapt to transients: if you’ve potatoes are rotting it is not much of a comfort that it would have been a great rice harvest.
Both more and less water will mean a shorter life for buildings, as ground water table falls or rises. Kind of global Tower of Pisa, but not much of a tourist attraction if it happens pretty simultaneously in several millions of buildings, some of them skyscrapers. This last (buildings, water-tables) is however my own speculation -would be most grateful if anybody could find reviewed studies to confirm it.
CAGW skeptic,
According to an article I read recently, it appears that it is the older temperature records that have exagerated the temperatures higher than they really were. Apparently due to insufficient shielding from the sun.
This is directly inverse from the line of resoning from folks like yourself who deny AGW.
Anyone capable of observing reality, truely objectively, without distorting it via their desired reality, can see how dramatically the climate is warming.
I have noticed that there is a story circulating that 1934 has now been given the record hottest US year. I am skeptical that would be the case, I doubt that a place as large as the US could be so far outside the warming trend that I observe in Australia. How long was the ice fishing season in 1934? How long in the last 5 winters? Does anyone have any concrete information regarding this story?
re 131 –
[[Life WILL go on, most likely, until that day in the far future when the sun boils off our atmosphere – and like even then it will find a way within the crust and mantle. Not life as we recognize it in the here and now, perhaps, but it will go on.]]
You wrote: “I sincerely doubt it. The next step after the habitable Earth is the runaway greenhouse Earth, about 0.6-1.4 billion years from now. Since life as we know it requires liquid water, that pretty much rules out life continuing on the Earth — unless, of course, we alter the climate at that time artificially.”
Not to nitpick (even though that’s exactly what I’m doing), but I was more or less saying that when I noted the sun would boil away our atmosphere, the assumption being a runaway greenhouse effect was a given. Of course, this does not mean life won’t survive in a runaway greenhouse world – we have no proof one way or the other and comments in that direction are at best speculation (but as I recall, if life exists withing the crust and mantle, it would still exist, tough obviously we’re not talking about complex life).
My real point in my original and follow-up is that life in the biosphere will go on WITHOUT US – at least in the geologically measured short-term, in relation to the original comment regarding the planet being in trouble. It isn’t.
“…unless, of course, we alter the climate at that time artificially.”
Ah, but isn’t that the problem being discussed here? *grin*
Seriously, I grew up in the age where we dreamed of expanding outward into the solar system and, somehow, some way, into the galaxy. As time has gone by I’ve become pessimistic of our odds of doing so. At the same time, it is becoming ever so much more apparent to me that, in the end, we may be faced with leaving the planet as the only hope of our continued existence. (particularly if we ever manage the feat of surviving that 0.6 billion years to where it becomes absolutely imperative that we do.)
Regardless of who or what survives, we certainly have found ourselves in one heck of a pickle, as my dear, departed Grandmother was fond of saying.
Have a happy Friday.
Re: [[Life WILL go on, most likely, until that day in the far future…]
All well and good, I suppose, but you seem not understand that it’s ME going on, in reasonable comfort and so on, that I’m worried about And to a somewhat lesser extent my friends and putative descendants.
================
Ah, but I do. I’ve a daughter and nieces and nephews that I wonder about constantly. It’s then when I find myself the most depressed about the outlook.
Put another way, I think we’ve just passed what are, in many ways, some of the best years to be a human alive on this planet (if you are in the the right country and a decent economic situation, of course). Things may never be quite so good, particularly in terms of the environment and climate.
One can’t help but feel the generations that follow aren’t being cheated.
Gavin,
I was wondering about your numbers in Step 2. You stated that removing CO2 reduces the LW absorbed by 14% or 30 W/m2. Is this a result from the referenced papers? From the 150 W/m2 LW absorbed in Step 1, it would appear that 14% should be 21 W/m2. Thanks!
[Response: Going back over the papers, you get around 30 W/m2 for clear sky profiles (i.e. the situation without clouds) (Kiehl and Trenberth, 1997). Ramanathan and Coakley (1979) have 12% decrease in all sky conditions, and Hansen et al 1988 (using a LBL model) have 14% – again in all sky conditions. In radiative forcing calculations, the instantaneous value is around 22 W/m2, while the adjusted value is closer to 30 W/m2. Some of these variations are related to the particular configuration or metric, while some is real uncertainty. For the sake of this argument, those details aren’t particularly important and so a looser statement, such as ‘between 20 and 30 W/m2’ is probably fine. Thanks for pointing out the inconsistency. – gavin]
Thanks Gavin. I appreciate your website and use it as a jumping off point to find references on many topics concerning climate science. It’s nice to see a discussion of the science without all of the political rhetoric (at least in the original posts!).