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The Big Picture (2010 version)

Posted on 24 September 2010 by dana1981

Note: this is the initial version of our Big Picture article published in 2010. As part of our Rebuttal Update Project, the article has been updated and republished with more current data in February 2023. You can access the current version here.

Oftentimes we get bogged down discussing one of the many pieces of evidence behind man-made global warming, and in the process we can't see the forest for the trees. It's important to every so often take a step back and see how all of those trees comprise the forest as a whole. Skeptical Science provides an invaluable resource for examining each individual piece of climate evidence, so let's make use of these individual pieces to see how they form the big picture.

The Earth is Warming

We know the planet is warming from surface temperature stations and satellites measuring the temperature of the Earth's surface and lower atmosphere. We also have various tools which have measured the warming of the Earth's oceans. Satellites have measured an energy imbalance at the top of the Earth's atmosphere. Glaciers, sea ice, and ice sheets are all receding. Sea levels are rising. Spring is arriving sooner each year.  There's simply no doubt - the planet is warming (Figure 1).

warming world

Figure 1: Indicators of a warming world

Global Warming Continues

And yes, the warming is continuing. The 2000s were hotter than the 1990s, which were hotter than the 1980s, which were hotter than the 1970s. 2010 tied for the hottest year on record.  The 12-month running average global temperature broke the record three times in 2010, according to NASA Goddard Institute for Space Studies (GISS) data.  Sea levels are still rising, ice is still receding, spring is still coming earlier, there's still a planetary energy imbalance, etc. etc.

Contrary to what some would like us to believe, the planet has not magically stopped warming.  Those who argue otherwise are confusing short-term noise with long-term global warming (Figure 2).


Figure 2: The data (green) are the average of the NASA GISS, NOAA NCDC, and HadCRUT4 monthly global surface temperature anomaly datasets from January 1970 through November 2012, with linear trends for the short time periods Jan 1970 to Oct 1977, Apr 1977 to Dec 1986, Sep 1987 to Nov 1996, Jun 1997 to Dec 2002, and Nov 2002 to Nov 2012 (blue), and also showing the far more reliable linear trend for the full time period (red).

Foster and Rahmstorf (2011) showed that when we filter out the short-term effects of the sun, volcanoes, and El Niño cycles, the underlying man-made global warming trend becomes even more clear (Figure 3).

before/after filtering

Figure 3: Temperature data (with a 12-month running average) before and after the short-term factor removal

For as much as atmospheric temperatures are rising, the amount of energy being absorbed by the planet is even more striking when one looks into the deep oceans  and the change in the global heat content (Figure 4).

global heat content

Figure 4: Total global heat content. Data from Nuccitelli et al. (2012)

Over 90% of global warming goes into heating the oceans.  When taking the heating of the entire climate system into account, the planet has warmed at a rate equivalent to 4 Hiroshima atomic bomb detonations per second over the past 15 years.

Humans are Increasing Atmospheric Greenhouse Gases

The amount of greenhouse gases in the atmosphere - particularly carbon dioxide (CO2) - has been rising steadily over the past 150 years.  There are a number of lines of evidence which clearly demonstrate that this increase is due to human activities, primarily burning fossil fuels.

The most direct of evidence involves simple accounting. Humans are currently emitting approximately 30 billion tons of CO2 per year, and the amount in the atmosphere is increasing by about 15 billion tons per year.  Our emissions have to go somewhere - half goes into the atmosphere, while the other half is absorbed by the oceans (which is causing another major problem - ocean acidification). 

We also know the atmospheric increase is from burning fossil fuels because of the isotopic signature of the carbon in the atmosphere.  Carbon comes in three different isotopes, and plants have a preference for the lighter isotopes.  So if the fraction of lighter carbon isotopes in the atmosphere is increasing, we know the increase is due to burning plants and fossil fuels, and that is what scientists observe. 

The fact that humans are responsible for the increase in atmospheric CO2 is settled science.  The evidence is clear-cut.

Human Greenhouse Gases are Causing Global Warming

There is overwhelming evidence that humans are the dominant cause of the recent global warming, mainly due to our greenhouse gas emissions. Based on fundamental physics and math, we can quantify the amount of warming human activity is causing, and verify that we're responsible for essentially all of the global warming over the past 3 decades.  The aforementioned Foster and Rahmstorf (2011) found a 0.16°C per decade warming trend since 1979 after filtering out the short-term noise. 

In fact we expect human greenhouse gas emissions to cause more warming than we've thus far seen, due to the thermal inertia of the oceans (the time it takes to heat them).  Human aerosol emissions are also offsetting a significant amount of the warming by causing global dimming.  Huber and Knutti (2011) found that human greenhouse gas emissions have caused 66% more global warming  than has been observed since the 1950s, because the cooling effect of human aerosol emissions have offset about 44% of that warming.  They found that overall, human effects are responsible for approximately 100% of the observed global warming over the past 60 years (Figure 5).

knutti breakdown

Figure 5: Contributions of individual forcing agents to the total change in the decadal average temperature for three time periods. Error bars denote the 5–95% uncertainty range. The grey shading shows the estimated 5–95% range for internal variability based on the CMIP3 climate models. Observations are shown as dashed lines.

There are also numerous 'fingerprints' which we would expect to see from an increased greenhouse effect (i.e. more warming at night, at higher latitudes, upper atmosphere cooling) that we have indeed observed (Figure 6).


Figure 6: Observed 'fingperprints' of man-made global warming

Climate models have projected the ensuing global warming to a high level of accuracy, verifying that we have a good understanding of the fundamental physics behind climate change.

Sometimes people ask "what would it take to falsify the man-made global warming theory?". Well, basically it would require that our fundamental understanding of physics be wrong, because that's what the theory is based on.  This fundamental physics has been scrutinized through scientific experiments for decades to centuries.

The Warming will Continue

We also know that if we continue to emit large amounts of greenhouse gases, the planet will continue to warm. We know that the climate sensitivity to a doubling of atmospheric CO2 from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv (we're currently at 390 ppmv) will cause 2–4.5°C of warming. And we're headed for 560 ppmv in the mid-to-late 21st century if we continue business-as-usual emissions.

The precise sensitivity of the climate to increasing CO2 is still fairly uncertain: 2–4.5°C is a fairly wide range of likely values.  However, even if we're lucky and the climate sensitivity is just 2°C for doubled atmospheric CO2, if we continue on our current emissions path, we will commit ourselves to that amount of warming (2°C above pre-industrial levels) within the next 75 years.

The Net Result will be Bad

There will be some positive results of this continued warming. For example, an open Northwest Passage, enhanced growth for some plants and improved agriculture at high latitudes (though this will require use of more fertilizers), etc. However, the negatives will almost certainly outweigh the positives, by a long shot. We're talking decreased biodiversity, water shortages, increasing heat waves (both in frequency and intensity), decreased crop yields due to these impacts, damage to infrastructure, displacement of millions of people, etc.

Arguments to the contrary are superficial

One thing I've found in reading skeptic criticisms of climate science is that they're consistently superficial. For example, the criticisms of James Hansen's 1988 global warming projections never go beyond "he was wrong," when in reality it's important to evaluate what caused the discrepancy between his projections and actual climate changes, and what we can learn from this. And those who argue that "it's the Sun" fail to comprehend that we understand the major mechanisms by which the Sun influences the global climate, and that they cannot explain the current global warming trend. And those who argue "it's just a natural cycle" can never seem to identify exactly which natural cycle can explain the current warming, nor can they explain how our understanding of the fundamental climate physics is wrong.

There are legitimate unresolved questions

Much ado is made out of the expression "the science is settled."  The science is settled in terms of knowing that the planet is warming rapidly, and that humans are the dominant cause.

There are certainly unresolved issues.  As noted above, there's a big difference between a 2°C and a 4.5°C warming for a doubling of atmospheric CO2, and it's an important question to resolve, because we need to know how fast the planet will warm in order to know how fast we need to reduce our greenhouse gas emissions. There are significant uncertainties in some feedbacks which play into this question. For example, will clouds act as a net positive feedback (by trapping more heat, causing more warming) or negative feedback (by reflecting more sunlight, causing a cooling effect) as the planet continues to warm?  And exactly how much global warming is being offset by human aerosol emissions?

These are the sorts of questions we should be debating, and the issues that many climate scientists are investigating. Unfortunately there is a very vocal contingent of people determined to continue arguing the resolved questions for which the science has already been settled. And when climate scientists are forced to respond to the constant propagation of misinformation on these settled issues, it just detracts from our investigation of the legitimate, unresolved, important questions.

Smart Risk Management Means Taking Action

People are usually very conservative when it comes to risk management.  Some of us buy fire insurance for our homes when the risk of a house fire is less than 1%, for example.  When it comes to important objects like cars and homes, we would rather be safe than sorry.

But there is arguably no more important object than the global climate.  We rely on the climate for our basic requirements, like having enough accessible food and water.  Prudent risk management in this case is clear.  The scientific evidence discussed above shows indisputably that there is a risk that we are headed towards very harmful climate change.  There are uncertainties as to how harmful the consequences will be, but uncertainty is not a valid reason for inaction.  There's very high uncertainty whether I'll ever be in a car accident, but it would be foolish of me not to prepare for that possibility by purchasing auto insurance.  Moreover, uncertainty cuts both ways, and it's just as likely that the consequences will be worse than we expect as it is that the consequences won't be very bad.

We Can Solve the Problem

The good news is that we have the tools we need to mitigate the risk posed by climate change.  A number of plans have been put forth to achieve the necessary greenhouse gas emissions cuts (i.e. here and here and here).  We already have all the technology we need.

Opponents often argue that mitigating global warming will hurt the economy, but the opposite is true.  Those who argue that reducing emissions will be too expensive ignore the costs of climate change - economic studies have consistently shown that mitigation is several times less costly than trying to adapt to climate change (Figure 7). 

Figure 7:  Approximate costs of climate action (green) and inaction (red) in 2100 and 2200. Sources: German Institute for Economic Research and Watkiss et al. 2005

This is why there is a consensus among economists with expertise in climate that we should put a price on carbon emissions (Figure 8).

should US reduce emissions


Figure 8: New York University survey results of economists with climate expertise when asked under what circumstances the USA should reduce its emissions

The Big Picture

The big picture is that we know the planet is warming, humans are causing it, there is a substantial risk to continuing on our current path, but we don't know exactly how large the risk is. However, uncertainty regarding the magnitude of the risk is not an excuse to ignore it. We also know that if we continue on a business-as-usual path, the risk of catastrophic consequences is very high.  In fact, the larger the uncertainty, the greater the potential for the exceptionally high risk scenario to become reality. We need to continue to decrease the uncertainty, but it's also critical to acknowledge what we know and what questions have been resolved, and that taking no action is not an option.  Th good news is that we know how to solve the problem, and that doing so will minimize the impact not only on the climate, but also on the economy.

The bottom line is that from every perspective - scientific, risk management, economic, etc. - there is no reason not to immeditately take serious action to mitigate climate change, and failing to do so would be exceptionally foolish.

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Comments 101 to 150 out of 221:

  1. "A strong, credible body of scientific evidence shows that climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems…. Some scientific conclusions or theories have been so thoroughly examined and tested, and supported by so many independent observations and results, that their likelihood of subsequently being found to be wrong is vanishingly small. Such conclusions and theories are then regarded as settled facts. This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities." I like how they covered their you know what here. "This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities." Very likely, but they are not certain. No doubt.
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  2. cruzn246, you are incorrect in stating that "correlation does not mean causation." Correlation is necessary but not sufficient as evidence of causation. There are empirically-backed theoretical reasons for our prediction that CO2 levels will correlate with temperature. Those predictions were made long before it was even possible to adequately measure the global levels of either of those variables for sufficiently long to confidently detect that correlation. The correlation later was discovered to exist, thereby supporting the other empirical evidence and theory
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  3. Daniel Bailey at 13:50 PM, your quick synopsis was a little bit too quick. Before you can use points 1-3 to arrive at 4, you have to decide one more condition as proffered in point 1, that being "all else being equal" Where is the evidence that all else is indeed equal? Or has ever been equal for that matter.
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  4. Daniel Bailey #56 "So, essentially a global average temp of -2 degrees F, or about -18 degrees C. Thus, no liquid water anywhere and no life. All very well understood for over a hundred years." ...and since life did appear, one must assume there has always been some CO2. Not too much (mind you) lest it get too hot to support life. No, just the right amount to where life can get its start, and then reach the current equilibrium... ...the point at which creationist models almost begin to seem more attractive.
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  5. RSVP #104 "One must assume there has always been some CO2. Not too much (mind you) lest it get too hot to support life." Wrong. Early life was anaerobic. this may be of interest to you. Particularly: "Three and a half billion years ago, Earth's atmosphere contained almost no free oxygen. Instead, it consisted mainly of carbon dioxide, perhaps as much as 100 times more carbon dioxide than contained in today's atmosphere. During this time, Earth's only life forms were aquatic, one-celled organisms -- primitive forms of bacteria -- that extracted energy from a variety of sources." Sounds like the perfect environment for civilisation to thrive!
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  6. and when cyanobacteria started producing highly poisonous (for the time) oxygen it was a massacre. RSVP's history of life would need a thorough rewrite the whole earth history as well.
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  7. I have a question for cruzn246. Why is it so difficult to trust what the experts in the field of climate have to say?
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  8. kdkd Thanks for the link. While what all is said there may have all kinds of merit, given no better theories etc., I cant see this as more than just a theory, since it all supposedly happened "3.5 billion years ago". The presentation however couches all this stylistically as indisputable fact, which I find a little bothersome, and no less dangerous than dogmatic aspects of myth cultures it may attempt to topple. For instance, are they sure it wasnt 3 billion years and not 3.5 billion years? And if you think I am making a bit too much of this, just wait until "they" come up with a genetically engineered anaerobic bacteria that is going to save us from global warming (if they havent done so already).
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  9. Re: johnd (103)
    "Before you can use points 1-3 to arrive at 4, you have to decide one more condition as proffered in point 1, that being "all else being equal" Where is the evidence that all else is indeed equal? Or has ever been equal for that matter."
    Thanks for pointing that out. The missing step, of course, is the tie that links the rising CO2 to that emitted through fossil fuel use. The extra/increasing concentrations of CO2 in the atmosphere can be shown by isotopical analysis to come from fossil fuel emissions. So, all else being equal, unless skeptics can come up with a physical mechanism that explains why fossil-fuel derived CO2 emissions do not act as greenhouse gases, we our causing the temperatures to rise, and the Arctic Ice cap (the Northern Hemisphere's refrigeration equipment) to dwindle. The Yooper
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  10. Daniel Bailey #109 The normal dose of aspirin for a headache is usually one or two pills max. If that takes care of it, you are in luck, while for some, the headache remains...(sorry). The dose of course depends on your weight, but my point here is that there is a minimal dose that works, and taking more has no extra benefit. Such things do occur in nature, and I suspect that while CO2 can act as a greenhouse gas, the effect is relative to many factors and therefore its significance as well. For example, I can imagine a planet like the Earth (all things being exactly equal) with an atmosphere that has double or half the volume. I assume you would allow that those conditions, would influence the overall impact of a greenhouse gas. I am not espousing David Hume's philosophy (the king of skeptics), but I would recommend checking out what he had to say about causation, simply to temper anyone's sense of sureness in anything. Taking empiricism to the extreme, he would say that "effect" is only a human expectation projected onto "reality". All you can truely observe is a succession of ordered events. This to me sounds closer to "science" than I feel comfortable with, however, this thinking is logical, and supposedly truer to a "detatched" spirit.
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  11. Re: RSVP (110) Thanks for the thoughtful reply. I will check out David Hume when I get a chance (all I know is the reference to him from the Monty Python's Flying Circus sketch back in the '70's...about him outconsuming Hegerle in alcohol). ;) If I understand your pain reliever analogy correctly (and please do correct me if I'm interpreting what you said incorrectly), you have reservations about "extra" CO2 being added to the carbon cycle having any significant negative impact. Would that be a fair interpretation?
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  12. RSVP - I suspect your aspirin analogy about CO2 would be more appropriate on the "Is the CO2 effect saturated". The numbers, however, don't support a saturation effect. Really really off topic - Hume's "Problem of Causation", while a fascinating philosophical exercise, is essentially an overuse of reductionism based upon the observer - a fun topic at parties, especially after a few drinks [ :) ], but not really a relevant view of the world we understand through the view of actual physics, chemistry, and quantum mechanical interactions. We actually do understand the cause-effect relationships with greenhouse gases - it's a challenge to the skeptical viewpoint to simultaneously (a) show some other cause for the various measurements (temp rise, ice melt, seasonal advance) and (b) demonstrate why CO2 increases do not follow what we know of physics, and hence cause the warming.
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  13. Posted by dana1981 on Friday, 24 September, 2010 at 09:19 AM And those who argue it's just a natural cycle" can never seem to identify exactly which natural cycle can explain the current warming, nor can they explain how our understanding of the fundamental climate physics is wrong. Well, heat capacity of oceans is enormous. If all ocean circulation stopped it would take about five millennia to heat them up by 1°C for the geothermal heat flux through oceanic crust. It also implies if there was a long term 0.8 W/m2 radiative imbalance at TOA (Top of Atmosphere) indeed as it is assumed by some based on model calculations (and neither contradicted nor confirmed by measurements), average ocean temperature would go up by 0.13°C in a century (provided 80% of the excess heat is absorbed by the ocean). That's negligible. Therefore the atmosphere can only warm up by 2-4.5°C on a century scale if a substantial imbalance develops in distribution of heat between hydrosphere and atmosphere. If for any reason a major redistribution of this excess energy occurs during this period, average atmospheric temperature change becomes absolutely indeterminate. This occasional redistribution is what's provided by so called natural cycles. It can also be explained easily how your understanding of the fundamental climate physics is wrong. If overall IR opacity of the atmosphere is increased while everything else is kept constant, surface temperature should go up indeed, that much is true. However, if you keep adding IR opacity to the system, entropy production is decreasing. As the climate system has a huge number of degrees of freedom and it is very far from thermodynamic equilibrium (but has a steady flow of energy going through it), it tends to reconfigure itself to maximize entropy production. In order to do that, it has to both reconfigure circulation patterns and decrease overall IR opacity by making water vapor distribution a bit more uneven on all scales. But on this level the exact mechanisms are not important, the system has enough degrees of freedom to achieve maximum entropy production somehow under any circumstances. And while it is possible to keep overall IR opacity constant by redistributing some GHGs, it will always be one of the major avenues leading to this kind state. Anyway, with the radiation flux output kept constant the lower the radiation temperature gets the higher radiation entropy becomes. Therefore the MEP tends to keep temperature as low as possible (it serves as a strong "negative feedback"). That's fundamental physics (providing a genuine big picture as well).
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  14. BP, assuming that adjustments in radiative pathways from Earth must be made in order for the planet to continue shedding energy in a way that does not ultimately result in a significant increase in surface temperature, will those changes be invisible to us? Energy is conserved and if systems must adjust themselves to dispose of energy in ways other than a previously more efficient particular IR distribution while leaving surface temperatures largely unaffectdd, how will these adjustments manifest themselves?
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  15. Obviously the climate has changed radically in the past. The glacial/interglacial cycle is almost entirely driven by Milankovich geometry, which doesn't actually change the mean insolation at all, just its spatial/seasonal distribution. Yet changes to this spatial/seasonal distribution of insolation are sufficient to increase or decrease the global mean temperature by something like 8 degrees C. In other words, the real world doesn't have these "strong negative feedbacks" that BP speculates about. Temperature, precipitation, and circulation can and do change dramatically in response to radiative forcings. Our civilization arose during a time (the Holocene) when conditions have been relatively stable. Relatively minor changes in climate (the Medieval Warm Period, the Little Ice Age) were sufficient to have large impacts on societies that experienced them. The probable outcome of projected 21st century carbon emissions would be a much larger forcing than anything we've experienced since the last deglaciation. The "Principle of Maximum Entropy" didn't prevent the Earth's climate from changing in the past, so I see no reason to assume that it will do so in the future.
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  16. #114 doug_bostrom at 01:30 AM on 28 September, 2010 how will these adjustments manifest themselves? Atmospheric distribution of moisture is pretty fractal-like along a scale of many orders of magnitude from global down to micron sized droplets. Opacity for electromagnetic radiation depends not only on average moisture contents of air, but also on finer details of its distribution. While MEP does not give any direct answer to the question what kind of atmospheric state maximizes entropy production, it strongly suggests the lowest possible average temperature provided there are ways to maintain radiative energy balance other than increasing temperature. Therefore since the same level of atmospheric moisture can give a wide range of IR opacities depending on its distribution, I guess it is enough to adjust its fractal dimension slightly. Not even large scale rearrangement of flows is required, so no radical climate change is expected for moderate increase in well mixed IR opacity. It is not easy to measure these properties, but there is a literature about it well worth studying, for example: WATER RESOURCES RESEARCH, VOL. 35, NO. 6, PAGES 1853­1867, JUNE 1999 Multifractal modeling of anomalous scaling laws in rainfall Roberto Deidda, Roberto Benzi & Franco Siccardi WATER RESOURCES RESEARCH, VOL. 32. No 9. PAGES 2825-2839, SEPTEMBER 1996 A deterministic geometric representation of temporal raifall: Results for a storm in Boston Carlos E. Puente and Nelson Obregón It is also impossible to include these effects properly in gridded models (due to their multi-scale behavior), but one can always try to use other representations (like Puente 1996). If we accept the science is very far from being settled, a wealth of exciting directions open up immediately. It is really hard to understand why one would stick to a worn-out paradigm.
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  17. Berényi Péter what you describe is a feedback mechanism, not a cycle. As for "the same level of atmospheric moisture can give a wide range of IR opacities depending on its distribution", in the wavelength range of interest it's not so. Absorption coefficient depends on the total water column, not on the size of the particles. Scattering, which in general depends on particle size, is irrelevant given the longer wavelength of the EM wave with respect to particle size.
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  18. Berényi - You seem to be claiming that the distribution of water vapor will change to increase IR radiation, providing a strong negative feedback. As has been pointed out, modelled and empirical evidence indicates that the actual climate sensitivity is ~3°C for a doubling of CO2 or an equivalent radiological forcing. That indicates that your negative feedback does not exist, certainly not at the level you seem to be suggesting. As Riccardo points out, atmospheric absorption/emission in these IR bands depends on the integrated total water column. Finally - it seems to me that increased inhomogeneity (which would be required to emit more IR) represents a local increase of order. A global higher IR emission won't have any influence on local order - global IR is an emergent phenomena, the sum of local events. The mechanisms are important; your increased inhomogeneity means lower local entropy, and is not a natural direction for the system to move in.
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  19. #115 Ned at 02:08 AM on 28 September, 2010 Obviously the climate has changed radically in the past. Yes, it did. However, the ice albedo feedback is really a strong positive one, you don't need rocket science to see this. If ice cover reached 30° latitude somehow (and there are hints it could during the next glacial cycle), Earth would enter a "permanent" icehouse state ("snowball Earth") even with the present insolation & CO2. As sea ice extent grows tremendously, evaporation diminishes and the so called "arctic window" (IR wavelengths above the 14 μm CO2 absorption line) opens up. With decreased SW absorption and increased LW outbound losses, the cold state is stabilized beyond repair for tens of million years. Due to the present configuration of continents the climate system is a bistable one with a considerable hysteresis between the two possible (cold vs. warm) states. As you can see during the last several million years the amplitude of glacial cycle keeps increasing while its frequency is decreasing, which is a sure sign of a would-be phase change in chaotic systems. As long as sea ice extent does not grow too large, the process is self-limiting, because as soon as elevation of ice sheet surfaces above continental masses become too high, they cease to be effective radiators, for while their surface temperature is very low, potential temperature of air masses above them is still relatively high. It means as air is cooled above the surface and descends along the slope (so called katabatic wind) it is heated adiabatically, along a 3 km high slope by as much as 30°C (because this air is very dry). It means on the plateau radiative losses relative to sea level temperature of the air parcel are 40-50% lower. On the other hand if even the sea surface at mid latitudes freezes over, radiative losses are not limited this way while most of the incoming short wave radiation is reflected back to space. The extreme cold coming out of the Antarctic region during southern winter (like the recent cold spell above South America) is generated this way, above floating ice, not the elevated ice sheet. Come the next glaciation, sea ice can easily extend to the tropics, as it has happened several times in the deep past. It would be a true disaster for both humanity and nature. During the present epoch ice albedo effect is asymmetric. The extent of low lying snow covered surface is limited and it can only decrease so much, while it has considerably more room to increase. Insolation on lower latitudes is also higher on average, so it has a more pronounced effect should it get reflected. Still, anything that decreases snow albedo (like soot pollution) has an immediate warming effect right at the surface, even if the sky is covered by low clouds. Clean snow is a special stuff. It is white in the visible portion of the spectrum, but pitch "black" in IR (hence an effective radiator at low temperatures due to Kirchhoff's law of thermal radiation). Winter snow cover on the vast low lying continental areas of the Northern Hemisphere can act the same way. As soon as anthropogenic soot pollution gets limited, the multidecadal growing trend of NH December/January snow cover would extend well into springtime, bringing severe cooling into the region.
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  20. #117 Riccardo at 06:22 AM on 28 September, 2010 Absorption coefficient depends on the total water column, not on the size of the particles It is not so. It may not depend on size of droplets and ice crystals much (SW absorption does), but plain water vapor distribution is also very uneven as it depends on history of individual air parcels, not just local parameters. The distribution is uneven both along lateral and vertical directions and as temperature is not uniform either, outgoing radiation depends on the fine details of it, not only the column integrated value.
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  21. BP - "even with the present insolation & CO2" care to back that up please? It doesnt match the opinion I heard from Tom Crowley on the subject and with CO2 heading to pliocene levels, it doesnt match paleoclimate indication. Why did we enter the ice age cycle in first place? Milankovitch cycles still happened in Miocene/pliocene. The total solar output has been steadily (if slowly) increasing? Changes in the atmosphere due to steady low of CO2 is best bet. A reset to pliocene means all bets are off. However, somewhat beside the point for humanity for the next 10,000 years.
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  22. Berényi Péter short wavenlegth does that because they are more similar in size to the droplets (hundreds of nm). At long wavengths you loose the dependence on size. The vertical distribution of clouds does matter, but it's another story. Water vapour concentration rapidly falls with altitude anyway.
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  23. BP, that's all more or less totally irrelevant to anything in this discussion. You've suggested that a "Principle of Maximum Entropy" means the climate must have "strong negative feedbacks" that would presumably prevent anthropogenic climate change. That claim is incompatible with the numerous episodes of climate change that have occurred during the past couple of million years. I take it that your new comment means that the previous one is no longer operational ...
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  24. #118 KR at 06:32 AM on 28 September, 2010 modelled and empirical evidence indicates that the actual climate sensitivity is ~3°C for a doubling of CO2 It would be so if models would handle atmospheric water and turbulence properly (they don't) and if all the warming measured during the last several decades would be due to GHGs and none to soot on snow, UHI or ocean heat redistribution cycles. your increased inhomogeneity means lower local entropy, and is not a natural direction for the system to move in. Look again. It is not a closed system, but an open one, meaning there is a steady flow of energy through it. In such systems maximum entropy production is equivalent to minimum entropy contents under a wide range of conditions. Just consider the human body. You'll notice inhomogeneity in it on all scales, still, it is quite natural. At least as long as there is a steady flow of free energy through the system coupled to a high entropy production rate. Should the guy be starved to death or get suffocated though, homogenization of both body temperature and structure kicks in immediately.
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  25. @BP, you have not presented a convincing case that climate sensitivity is lower than 3C. There is no strong indication that soot on snow, the UHI effect or ocean redistribution cycles are responsible for a significant temperature change (in fact, the UHI effect has tended to introduce a *cold* bias, not a warm one). Furthermore, you have repeatedly failed to address the criticism regarding your statistical analysis on a different thread. Until you at least attempt to clear your name, I cannot take anything you say at face value - if you can't admit making a mistake, then we can't assume that *any* of your analyses are correct.
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  26. #122 Riccardo at 08:18 AM on 28 September, 2010 The vertical distribution of clouds does matter, but it's another story. Water vapour concentration rapidly falls with altitude anyway. It's the same story. General shape of clouds is a fractal right because distribution of water vapor was like this in the first place before condensation started. It is this way in both lateral and vertical directions. If opacity is distributed unevenly in a medium, in most cases transparency is increased. You can see through a lattice, but can't do the same with a plate.
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  27. Berényi Péter, the fractal structure (if any) is irrelevant as far as absorption and scattering are concerned. The different scattering properties of a uniform vs an unven distribution of particles is due to a concentration effect which, at some point, starts to produce multiple scattering. Even an uniform distribution may produce multiple scattering if concetrated enough. So, although it is indeed relevant for clouds (fractal or not), it's not for water vapour. Unless you call water vapour micron size water droplets.
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  28. #127 Riccardo at 16:44 PM on 28 September, 2010 So, although it is indeed relevant for clouds (fractal or not), it's not for water vapour. In case of water vapor radiative properties in the thermal IR range it is not scattering, but absorption and emission. Let's consider a thin horizontal slab of air loaded with a fixed quantity of some "greenhouse gas" (one which has a nonzero absorptivity in thermal IR). For the sake of simplicity let's suppose absorptivity is independent of frequency in this long wave range (the stuff is "grey" here). Let molar density of this GHG along the surface of slab be d(x) where x is any point on the surface of the slab, expressed in mole/m2 units. Integral of d for the entire surface is clearly the total quantity of stuff, so it is constant as it is said before. However, otherwise d is allowed to vary along the surface. Opacity at point x is clearly 1-e-c·d(x) with some positive constant c. If |c·d(x)| is small everywhere (absorptivity of stuff is not too high and/or the slab is thin), second order approximation of it is c·d(x)-1/2·c2·d2(x). Overall specific opacity of the slab can be calculated by integrating this expression along the entire surface and dividing by area. Integral of first term being proportional to average molar density, as long as the second term is negligible, you are right, only the quantity of stuff counts, not fine details of its distribution. However, as soon as second moment of d gets significant (distribution is "rough"), it is no longer true. You can also see that integral of the second term is always positive, therefore if it's got subtracted from integral of the first one, specific opacity is always decreasing. It's also possible that second order approximation is not good enough. In this case higher moments of distribution also come into play. Specific opacity is a nonlinear (concave) function of molar density, so departures from uniform distribution tend to decrease opacity. For well mixed GHGs it is not an issue, but water vapor is not one of them.
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  29. archiesteel #125 Ned and I did some forensics on BP's failed statistical analysis (i.e. would get him a fail grade as a first year university assignment) in this thread. We determined that the analysis suggested that if his estimate of the urban heat island effect was reasonable (and it's far more likely to be an overestimate - but we can't say if it is or by how much because he hasn't released his methodology) then his estimate for climate sensitivity is bang-on 3 degrees Celsius once corrected for the urban heat island effect. Which is entirely consistent with the mainstream climate science estimate. BP's current tangent appears to be a variant of the 'models are inaccurate' argument. It seems to me to be without merit as it uses the "if we can't know everything then we know nothing fallacy.
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  30. Berényi Péter you treatment assume a condensed phase behaviour. As I said before, unless you call water vapour micron size liquid droplets it does not apply. Probably it's just a misunderstanding, you include clouds under the term water vapour. In this case, I agree with you, distribution does matter. By the way, it's included in any model.
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  31. Berényi Péter, to add to my previous comment, absorption coefficient of water is relatively high throughout the infrared and all light is fully absorbed in a few tens of microns. Just a few droplets in the water column will suffice to block all the outgoing radiation.
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  32. #130 Riccardo at 20:33 PM on 28 September, 2010 you treatment assume a condensed phase behaviour No, it does not. Water vapor is a gas, transparent in the visible portion of the spectrum (with some absorption lines in the near IR though) and lots of absorption in thermal IR, even in the so called "atmospheric window" between 8 and 14 μm (see the slightly mysterious "water vapor continuum"). In its gas (a.k.a. "vapor") phase water is a perfectly legitimate GHG quite independent of its condensed phase ("cloud" or "fog") behavior. It is its atmospheric distribution which is not independent of the fact it can have multiple (gas, fluid, solid) phases under ordinary meteorologic conditions. As soon as a parcel of air gets saturated (due to adiabatic cooling) and precipitation is formed, the air exiting at cloud top is left with very low specific humidity (and high potential temperature). As it enters a cloud free region, it starts to cool radiatively to space, descending slowly. In this process it can get turbulently mixed with other air parcels with different specific humidities, but due to multi-scale properties of turbulent 3D flows this mixing seldom have the chance to complete its job, that is, before homogenization could get down to the molecular level, another saturation episode occurs, resetting the clock once again. Therefore water vapor (gas phase) distribution is very far from being uniform most of the time and under most meteorologic conditions, even under clear skies. So average specific humidity alone can never tell the whole story of its radiative properties, much less column integrated water content. Humidity distribution above the boundary layer is pretty much decoupled from surface temperatures below, reflecting history of air masses involved.
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  33. Berényi Péter, did I say that WV is not a gas? Did I say it does not absorb IR? Did I say that its distribution is not related to the possible phase changes in the atmosphere? No, obvisously, I was pointing out the opposite. I also warned to treat the various phase separately and that the liquid easily absorbs thermal IR throughout the relevant frequency range. The liquid phase, I'm sure you'll agree, is one the larger uncertainty in many respects and needs a much larger point of view. Finally, no one I'm aware of has calculated the WV effect as a well mixed gas. That local inhomogeneities significantly affect the estimates has yet to be proven.
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  34. Berényi - You missed half of my statement, and a very important half: I wrote: "Modeled and empirical evidence indicates that the actual climate sensitivity is ~3°C for a doubling of CO2 or an equivalent radiological forcing." - see How sensitive is our climate? Not just models, but multiple sets of paleo data and analyses indicate about 3°C climate sensitivity. The empirical evidence shows it quite clearly; we don't have the large negative feedback you are postulating. And as I have stated before, if the evidence contradicts your hypothesis, you need a new hypothesis. Claiming "we can't know, so what about this theory!" is a variation of the Appeal To Complexity; a bad argument.
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  35. BP, Riccardo, KR Excellent discussion gentlemen. This WV-Cloud-CO2 interaction is the nub of the whole AGW hypothesis. I have followed BP's arguments through many months and many threads, and a constant theme is that the WV and ice albedo feedbacks are not as positive as claimed and therefore the 'greenhouse' insulating effect of the atmospheric column is lower. Dr Trenberth puts the WV and ice albedo feedback at about +2.1W/sq.m - would anyone like to update this figure? I don't profess to fully understand how this energy flux number relates to temperature differential across the column or how the 'fractal' nature of clouds as seen from space affects the average IR emitting temperature of the Earth which is quoted at about 255degK. BP's response on the paleo data argument would also be very interesting.
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  36. #134 I wrote: "Modeled and empirical evidence indicates that the actual climate sensitivity is ~3°C for a doubling of CO2 or an equivalent radiological forcing." - see How sensitive is our climate? I see. Climate sensitivity is at leas 3°C (Lorius 1990), but not more than 2.3°C (Tung 2007). Fine. The science is settled. Seriously. As I have already mentioned multiple times, not all "forcings" are created equal. They act at different parts of the climate system (soot: snow covered surface, CO2: upper troposphere to stratosphere) and influence different processes (SW absorption vs. LW emission). Sensitivity of average surface temperature can be radically different for such agents, even if their magnitude converted to the common currency of energy flux anomaly happens to be the same. Also, regional distribution of climate response also varies widely depending on the particular kind of forcing applied. With paleoclimatic studies it is a bit more difficult. It is quite easy to see that general climate sensitivity should be higher in a world where permanent continental ice caps reach down to 40N than in our present day setup. Therefore "climate sensitivity" does not only depend on the kind of forcing but also on structural aspects of the climate system, changing themselves slowly over geologic times (as mountain ranges, configuration of continents, oceanic currents, presence or lack of ice sheets, etc.)
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  37. You can see climate variability during glacial times is huge compared to its present day value. This variability also implies a much higher sensitivity. Therefore paleo climate sensitivity values derived from glacial epochs have to be scaled down considerably to be applicable today.
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  38. Given that the various empirical climate sensitivity estimates include volcanic aerosols, Milankovitch redistributions, seasonal irradiation, and the 11 year solar cycle, I think there's plenty of data there on different kinds of forcings. Water vapor and clouds act as feedbacks on other forcings; if the temperature of the atmosphere changes, we should see regional feedbacks in a matter of days at most. In fact, given the speed of water vapor feedback, we should see your postulated large negative feedback on a seasonal basis (summer/winter) - and we don't. Unless you have evidence/papers indicating fractal vapor distribution changes over the seasons that induce large negative feedback on seasonal temperature changes??? Regarding glacial estimates and uncertainties, I am much more interested in papers such as Tung 2007; calculating 2.3 to 4.1°C based on the 11-year solar cycle (i.e., what happens when deviating from current conditions), Hoffert 1992, who looked at reconstructions for both colder and warmer periods, est. 2.3 +/- 0.9 °C, and Bender 2010, response to Mount Pinatubo aerosols, 1.7 to 4.1°C. I agree that glacial ice coverage introduces additional effects - hence my preference for estimates that don't include glacial periods. And again, your postulated large negative feedback is not seen.
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  39. Perhaps we should move this discussion to How sensitive is our climate? We're well off topic here...
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    Moderator Response: Yes, everybody, please do.
  40. The IPCC state in 'Climate Change 2007 - The Physical Science Basis'(p21) that there is still an incomplete physical understanding of many components of the climate system. They say 'Key uncertainties include aspects of the roles played by clouds, the cryosphere, the oceans, land use and couplings between climate and geochemical cycles.' Since 1958, CO2 has increased by 75 molecules per million of dry air. Now take a look at P38 of 'Climate Change 2007'. Four graphs show surface, trophospheric and stratospheric observed air temperatures since measuring began at Mauna Loa. Portends of CO2 induced doom? I don't think so.
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  41. So the lower atmosphere and surface temperature are increasing, and the lower stratosphere temperature is decreasing. That's what one would expect with an enhanced (increased) Greenhouse Effect. You have a problem with that? Or is yours one of linear extrapolation? Hopefully I'm not responding to another Doug Cotton sockpuppet.
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  42. Carbon500 @140 refers to this graph: As noted by Rob Painting @141 notes, the record shows rising tropospheric and surface temperatures, and declining stratospheric temperatures as is predicted by the models for an increased greenhouse forcing. The rate of rise of temperature at the surface is consistent with that predicted by the models, which same models predict large, and potentially disastrous rises in temperature in the 21st Century with ongoing emissions of greenhouse gases. So, having conveniently referred us to solid evidence ongoing, and dangerous global warming, Carbon500 presents us with the full body of "skeptic" counter evidence:
    "I don't think so."
    I must admit, I had never considered the full weight of that evidence before. I will alert the IPCC of this astonishing evidence so that it can be included in the AR5 - anonymous internet guy doesn't think so. With evidence that incontrovertible, it is no wonder "skeptics" have not been convinced by actual physical evidence for the case for global warming.
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  43. You haven't explained why you think these temperatures represent any kind of dangerous threat, apart from reference to models. What I see in these graphs is a 50 year record, with undulating trophospheric anomalies of plus or minus half a degree at the most - tiny variations, with a recent downturn. I suggest that these graphs show that the Earth is in fact regulating its temperature rather well.
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  44. Carbon500 - Doug is that you? Yes the Earth is regulating it's temperature so well it keeps going up. Not sure what your point is here. We expect it to go up according to the increased Greenhouse Effect - and it is! No one expects El Nino/La Nina, volcanoes, and other naturally variable factors to suddenly vanish. So a wiggly upward trend isn't exactly shocking news.
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  45. Carbon500, this is an overview post and thus does not include all the details. If you don't understand why rising temperatures are bad (beyond a false belief that this is only because 'models say so') please see positives and negatives of global warming. The links in the list of common climate myths in the upper left portion of the page might also be useful in correcting some of the false information you have apparently absorbed. That said, the flaws in your belief that temperatures show, "tiny variations, with a recent downturn" are amply explained in the article above and directly disproven by figures 2, 3, and 4. That you would repeat a false belief in 'response' to a posting which disproves it is not a particularly good sign.
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  46. #143 carbon500: your post is a great example of somebody not understanding the small range of mean temperatures that have been present for all of human agriculture (the Holocene), thus the significance of a degree Celsius warming. Just four degrees or so is a glacial-interglacial transition. Similarly, you don't understand the exceptionally rapid rate of warming we're experiencing in comparison to any other known period in recent, Quaternary or geological history, much faster than animals, plants and particularly soils can adapt. Fancy growing wheat on what is now tundra? How long do you reckon it might take to get fertile soils in the tundra?
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  47. CB Dunkerson and Skywatcher: my comment was about the numerical data presented in the four graphs shown; it's not a matter of belief - of course the temperature changes shown are minimal - just look at it! As regards the lack of understanding on my part that you suggest, I assure you that I've done plenty of reading around the subject, from the IPCC's 'Climate Change 2007' and numerous research papers plus books by so-called 'sceptical' scientists. As a result,I don't consider the idea of AGW to be a fact. Who's right? We'll see over the years ahead, won't we?
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  48. Carbon500 writes: "'s not a matter of belief - of course the temperature changes shown are minimal - just look at it!" The word "minimal" is subjective, and thus inherently is a "matter of belief". That 'minimal' rate of change is more than an order of magnitude greater than that which ended the last glaciation. Personally, I do not find a temperature shift sufficient to cover half the planet in ice over a mile thick 'minimal'... but that's just my own subjective belief. As to seeing who is right about AGW over the years ahead, that would have been a somewhat reasonable statement... in 1900. Since then 'the years ahead' have transpired and AGW is now observed reality. Humans have caused atmospheric CO2 levels to increase. That, perforce, will cause (indeed, has caused) global temperatures to rise. Observed reality. If you can't see reality now there seems little reason to assume that you will be able to do so at some time in the future.
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  49. Carbon5003147:"of course the temperature changes shown are minimal - just look at it!" This kind of statement reveals you have some continued reading to do. Do you have any idea how much additional energy it takes to raise global temperatures by one degree C? We know where this energy comes from; the 'minimal temperature change' you dismiss is a symptom that something is very out of balance. Start by working your way through the Alley video and the most used climate myths. Then see if your so-called 'sceptical' scientists (and who might they be, by the way?) answer those arguments.
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  50. A good place to discuss whether the observed warming has been 'minimal' or 'rapid', for example, would be A Big Picture Look at Global Warming, where we examined a subjective, unsupported claim by a certain blogger, very similar to Carbon500's assertions.
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