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Tom Curtis at 01:51 AM on 29 July 2011How we know we're causing global warming in a single graphic
Sphaerica, very sorry to hear about your ill health. I hope you are better soon. -
jabba at 01:49 AM on 29 July 2011It's the sun
I am not sure if any of you notice this or not, but the PMOD link goes to a data set that is a little too small of deviation for solar data collected in Earth orbit with daily entries. That is to say, the Earth's orbit is elliptical. For part of the year we are closer and the other half farther away. This results in a difference of about 90 W/m^2 between minimum and maximum. The data on PMOD at most varies by a few W/m^2 in a year. If you are measuring values on 22DEC2009 that are within 1 W/m^2 of values on 22JUN2010, then you have some issues with your data. That difference should be pushing 90 W/m^2. The difference in r value for the intensity calculations is about 5 million km. So, maybe the sources for this article should be revised. -
Tom Curtis at 01:47 AM on 29 July 2011Ocean Cooling Corrected, Again
Berényi Péter @9: From the abstract of Rignot et al, 2011:"In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise."
So how does the sum go if you do not totally misunderstand the paper you are quoting: 2011 Sea Rise 2.3 mm (est) less Ice melt 1.3 mm leaves 1.0 mm. 1.0 mm less the steric sear rise for the upper 700 m of 0.3 mm equals 0.7 mm. 0.7 mm plus the loss of 0.2 mm due to water storage leaves 0.9 mm to be accounted for by steric sea level rise due to warming below 700 m. How quickly do you think Berényi Péter will now find this method so fraught with assumptions as to be worthless, and therefore to be totally ignored? -
Bob Lacatena at 01:42 AM on 29 July 2011How we know we're causing global warming in a single graphic
7, ptbrown31, Apologies if I came off harshly, but your post hit a few of my buttons. I also have not read the long trail of posts that have followed... I am in my second week of the sore-throat-cold-from-hell right now, and sort of faded for a day there. First, for the record, I myself have gotten flack here at SkS for disagreeing with both the DTR and Winter Temperature Range arguments. The bottom line is that any warming or cooling involves strong GHG feedbacks (including H2O and eventually CO2), while even CO2 warming involves strong albedo feedbacks and others. The net result is that any such distinction is going to be very small. The first item of your post that set me off was any requirement that DTR not merely be expected and detected, but that some level of attribution be made. To me, the latter is a ridiculous and unattainable requirement at this point in time, or in the near future. As it is, anthropogenic warming to date is only 0.6C at best (and there are arguments, good and bad, that at least some of that warming may be from other causes). 0.6C of 288.6K is only 0.2%. I don't know what the change in DTR is as a result of that, but it's obviously going to be small. Given all of the spacial, temporal and observational complexities involved, I can't imagine how anyone could ever perform a proper attribution until warming has reached seriously dangerous proportions. As such... your contention, to me, is very similar to that of other posters, by setting an unnecessary requirement (not merely detection, but attribution of a secondary component of warming) that can never be fulfilled. In particular, I was bothered when you said "Not to mention, if it really was a signature of an enhanced greenhouse effect wouldn't that have made it into the report?" AR4 wasn't released until 2007. The three papers merely confirming some observation of the expected DTR change were Braganza 2004, Alexander 2006 (March), Zhou 2009. At best two, and possibly only one, of those three studies were available in time for inclusion in a 3,000 page report that was released in 2007. Any extensive statement in AR4 about DTR would probably have been ripped apart by skeptics. As far as your actual grasp of the factors involved, I was bothered by the "simple model" approach of your logic. This very, very often fails. It fails to include all of the variables, as well as to properly quantify those variables. The latter is very often a problem. Specifically: You state that the earth "should radiate more heat to space during the day," and then conclude that "it does not seem obvious why an enhanced greenhouse effect should cause more warming at night." I see absolutely no tie between these two points, or why they should appear together in an argument. They seem to completely miss the actual reason why a GHE would expand the DTR... the simple fact that during the day, solar radiation dominates temperatures, while at night, only the GHE has an influence. I'm also unsure myself if your initial premise is even correct. When the sun is up, certainly the earth receives more radiation. I've never seen a study that compares sun-side to night-side TOA radiation. But reflected radiation doesn't count, and since outbound radiation (due to GHGs) comes from the TOA, not from the surface or lower troposphere, then the fact that those areas have warmed substantially in the day time, due to solar radiation, does not translate directly to the idea that the earth as a closed system (or, more specifically, the sun-side) will radiate more during that time. One might actually guess (again, using what is probably too simplistic an approach) that the most radiation comes from the evening-night-side quarter of the earth, versus the sun-side half or morning-night-side quarter. Also, I am unsure that your simple tie between TMin and TMax applies. TMax may not depend so much on the starting point (TMin), as it will on the overall level of solar insolation (which in turn is affected by TSI, ground albedo, clouds, aerosols, etc.) and GHG effect. The end result is not that your premise is wrong, but rather that the system is clearly more complex than this, so it is a dangerous premise to make without considering far more factors, and actually running the numbers or doing observations. To me, making this your "main issue" put an exclamation point on the sort of incomplete and shoddy "thought modeling" that I think gets a lot of people into trouble (myself included). -
Albatross at 01:41 AM on 29 July 2011Ocean Cooling Corrected, Again
Welcome back BP, Maybe you are being unclear, but you are not accurately reporting the satellite estimates of GSL rise. The link you provided shows the trend in GSL is 3.2 mm/yr, not 2.3 mm/yr in 2011 as you cited @9. So that error kinda makes your calculations and attendant hypotheses moot. Is this another case of a 'skeptic' showing confirmation bias?
[Source]
Additionally, I'm not sure what you believe qualifies you to question or refute the findings of Von Schuckmann & Le Traon (2011), especially if you cannot get the basics correct.
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DSL at 01:34 AM on 29 July 2011Earth's Climate History: Implications for Tomorrow
Pirate, your attitude is a front. You wouldn't be here at SkS discussing anything with anyone if you didn't share a human concern. You have claimed to be a teacher. Is that attitude proper to your students? Note that the species went through two world wars in the span of thirty years. Are you saying that you could take-or-leave-whatever-shrug another world war? If your attitude is not a front, then you certainly don't have children nor are you a teacher (or, if you are, you must be desperately looking for another occupation, away from bleeding hearts and artists -- maternal and paternal instincts--pshaw!). Take this to the "it's not bad" thread. -
Berényi Péter at 01:15 AM on 29 July 2011Ocean Cooling Corrected, Again
"Clearly much heat is finding it's way down into deeper waters". That can't be the case. Consider Rignot 2011. "Using techniques other than GRACE and MBM, the mass loss of mountain glaciers and ice caps (GIC), including the GIC surrounding Greenland and Antarctica, has been estimated at 402 ± 95 Gt/yr in 2006, with an acceleration of 11.8 ± 6 Gt/yr2 over the last few decades [Kaser et al., 2006; Meier et al., 2007]. Our GRACE estimates and associated errors account for the leakage from the Greenland and Antarctica GIC, and, as discussed earlier, this leakage is small. The MBM estimates completely exclude the GIC. In year 2006, the total ice sheet loss was 475 ± 158 Gt/yr(regression line in Figure 2c), which is comparable or greater than the 402 ± 95 Gt/yr estimate for the GIC. More important, the acceleration in ice sheet loss of 36.3 ± 2 Gt/yr2 is three times larger than that for the GIC. If this trend continues, ice sheets will become the dominant contribution to sea level rise in the next decades, well in advance of model forecasts [Meehl et al., 2007]". I translate it for you. According to Rignot at al. rate of land based ice melt is 877+48.1(t-2006) in gigatons (where t is time in years AD). As it takes about 360 gigatons to raise sea level by 1 mm, in 2011 this rate is 3.1 mm/year. We also have data for rate of sea level rise as measured by satellites. Effect of increasing ocean basin volume due to GIA (Glacial Isostatic Rebound) is already taken into account in these figures (which is about 100 km3/year). We can see there is a slight deceleration (-0.1 mm/yr2) during the satellite era (since the end of 1992). Because of this, rate of sea level rise in 2011 is 2.3 mm/year. That is, sea level rise due to all other factors except melting of land based ice is -0.8 mm/year. Then we can have a look at the NOAA NODC Global Ocean Heat Content site. There we can see current rate of sea level rise due to thermosteric expansion of the upper 700 m of oceans is about 0.3 mm/year. That leaves us with -1.1 mm/year for the rest. There is one more major source contributing to sea level (except abyssal heat storage). It is fluid (not frozen) water storage over land. It can be divided into surface and subsurface waters. On the surface much water is being stored in dams while there is a huge ongoing groundwater depletion. The former process decreases sea level while the latter one increases it. The net result for recent times, according to Llovel 2010 is slightly negative, around -0.2 mm/year. That is, volume of ocean below 700 m is not increasing, but decreasing, by about 0.9 mm/year (320 km3/annum). It means no heat is sequestered there, quite the contrary. The deep ocean is cooling and contracting, it is probably losing more heat than the upper 700 m is gaining. Note that melting ice requires almost two orders of magnitude less heat than thermostreic expansion of water, so talk about recent heat storage in the climate system is inconsistent with claims of accelerating melt of ice sheets and glaciers. -
Rob Honeycutt at 01:15 AM on 29 July 2011Earth's Climate History: Implications for Tomorrow
apiratelooksat50.... You know, that is a very dangerous attitude to take. I hesitate to compare the points throughout history where dismissive comments like this have paved the way for tremendous human misery. When we have the data in front of us that tells us that a humanitarian crisis is looming and we choose to dismiss it... that makes us clearly responsible for the outcome. We stand at a similar precipice in human history now. How we respond today, the level of responsibility we take for future events, will determine the level of misery inflicted upon later generations. -
apiratelooksat50 at 00:52 AM on 29 July 2011Earth's Climate History: Implications for Tomorrow
Muon @ 18 Don't forget about the tens of thousands who die from hypothermia. Whether hypo- or hyperthermia, weather extremes will kill living organisms. And, yes, some will die. Just as some will die from too much or not enough water. Too much or not enough food. That may sound callous, but that is life. Always been like that and always will. -
Rob Painting at 00:28 AM on 29 July 2011Ocean Cooling Corrected, Again
KL - The latest analysis covers 60N to 60S, and is equivalent to 0.38 +/- 0.07 W/m2 globally. Be a lot easier if they all used the same terms of reference - see comment @ 1. So still plenty of missing energy if Dr Trenberth is right, but not so much if Dr Hansen is correct. -
muoncounter at 00:01 AM on 29 July 2011Earth's Climate History: Implications for Tomorrow
Pirate#17: "our direct ancestors survived an Ice Age by technologically adapting. ... That doesn't mean times won't necessarily be difficult" That's starting to sound like discussions on the It's not bad thread, which may be a better spot for continued commentary. Sure, we can adapt, as long as the rate of environmental change is not too fast for our sluggish political, economic and public health systems. What's the downside of this form of forced adaptation? Some parts of the population (those who can't or don't adapt so easily) must fall by the wayside. So the tens of thousands who die each year of heatwave-related causes (chiefly the elderly, infirm, poverty-stricken, etc) are the new Neanderthals. Is this your version of natural selection? Difficult times, indeed. -
apiratelooksat50 at 23:46 PM on 28 July 2011Rising Oceans - Too Late to Turn the Tide?
Tom Curtis @ 13 If I am reading you correctly, the rate of sea level rise from 16K to 8K is well documented and therefor possible. I agree with you and also agree that we may be on the front end of another acceleration. Time will tell. And, I agree with you that even with rates of change in the upper bounds of prediction we can easily adapt. -
apiratelooksat50 at 23:28 PM on 28 July 2011Earth's Climate History: Implications for Tomorrow
Sally at 12 When you look at the bottom portion of the graph what you see is a classic sawtooth graph. It shows business as usual - periodical and predictable changes in climate over a large scale. Neanderthals may have appeared as long ago as 650K years in Europe and Asia. They survived all those alternating periods of warming and cooling. Homo sapiens most likely left Africa 50K to 100K years ago. That means our direct ancestors survived an Ice Age by technologically adapting. Whether we have more warming, or begin to enter another ice age, humans will technologically adapt again. That doesn't mean times won't necessarily be difficult, but we will adapt and survive. That also does not mean the human race should not currently be developing new and more efficient/environmentally sound forms of energy. We definitely should. -
Ken Lambert at 23:12 PM on 28 July 2011Ocean Cooling Corrected, Again
Rob Painting - Original Post and #6 You say that the latest 2011 result is 0.55W/sq.m and that this "warming trend observed is slightly smaller than that seen in Von Schuckmann (2009), where the authors measure down to ocean depths of 2000 metres, and found a warming trend of 0.77 ±0.11 watts per square metre." Does the 0.55W/sq.m number apply to the surface of the oceans or the whole surface of the globe? -
Rob Painting at 22:56 PM on 28 July 2011Ocean Cooling Corrected, Again
JoeRG - it intrigues me how you gloss over the obvious. The oceans down to 1500 metres are warming. It utterly refutes the claims made by Knox & Douglass (2010). They basically insinuate that global warming has stopped. They're wrong - as the continuing sea level rise also confirms. Furthermore, you missed the section in my post discussing the sensitivity of analyses based on using the uncompleted ARGO data (pre November 2007) versus the completed network. Peruse the previous analyses highlighted in Knox & Douglass (2010) - there's only 1 year of data using the completed network, making the result even less robust. If you read Von Schuckmann and Le Traon (2011) you'll gain an understanding of some of the issues involved. -
CBDunkerson at 22:29 PM on 28 July 2011Ocean Cooling Corrected, Again
JoeRG, this is no different than someone pointing to declining temperatures in Cherrypickersville and using this to 'conclude' that 'global temperatures are declining'. Yes, a study which then takes temperature trends from all over the world is certainly 'comparing sandals with boots'... but it can make an actual VALID analysis of global temperature trends. Ditto looking at only the top 700m vs 1500 or 2000m of the ocean to determine whether they are warming or not. A 'conclusion' that 'the oceans are cooling' based on very limited data can very definitely be 'completely refuted' by a more thorough analyses showing warming. -
JoeRG at 21:31 PM on 28 July 2011Ocean Cooling Corrected, Again
I wonder how you can conclude a 'completely refute' if you compare sandals with boots. Apart from the different time scales, Von Schluckmann uses data down to 1500m (2011), resp. 2000m (2009), while Willis, Loehle, Pielke and Knox&Douglas (used in the 'refuted' paper) only use the upper 700m data. Completely different things. -
CBDunkerson at 21:16 PM on 28 July 2011It's Urban Heat Island effect
As EtR said, this seems like a regional study which yields results similar to those found previously. Basically, rapid urbanization around a temperature monitoring station can bias the results of that station. Which is why global temperature anomaly results have always adjusted for this effect. This is thus further confirmation that the adjustments are correct... though the fact that satellite temperature records (which obviously aren't impacted by UHIs), analyses based only on rural stations, and various other studies ALSO match has long made this a moot point. -
Eric the Red at 21:11 PM on 28 July 2011It's Urban Heat Island effect
Fitz, The results are consistent with other measurements of urbanization effects. -
Fitz1309 at 21:05 PM on 28 July 2011It's Urban Heat Island effect
Could I ask how this paper by Yang et al 2011 relates to this post. It's looking at anomalies but shows different trends for different classes of urbanisation in China. Thanks http://www.agu.org/pubs/crossref/2011/2010JD015452.shtml -
CBDunkerson at 20:44 PM on 28 July 2011Ocean Cooling Corrected, Again
1 joule = 1 watt second 1 zettajoule = 1,000,000,000,000,000,000,000 joules Thus, zettajoules are most often used to describe very large energy transfers. For instance, 'all human energy use amounts to about 0.5 ZJ' or 'the Earth absorbs about 3,850 ZJ of sunlight per year'. Watts per square meter would describe an amount of energy in an area (e.g. how much a section of ocean surface has warmed) while joules per square meter would describe the amount of energy transfer per second in the area (e.g. the rate at which a section of ocean surface is being warmed). -
Arkadiusz Semczyszak at 20:44 PM on 28 July 2011Ocean Cooling Corrected, Again
Here's what they write cited skeptics on this real meaning - importance ”systematic errors”: „It is possible that some unknown systematic error in the Argo float system is causing the flattening. Such an error would not explain the non-Argo NODC OHC result, nor the surface cooling.” ... and who here writes “the kibosh”? Definitely not Knox & Douglas and von Schuckmann & Le Traon: “Before the end of 2007, error bars are too large to deliver robust short-term trends of GOIs and thus an interpretation in terms of long-term climate signals ARE STILL QUESTIONABLE ... -
Tom Curtis at 19:27 PM on 28 July 2011How we know we're causing global warming in a single graphic
While the TOA radiative forcing is maximized in the tropics for both CO2 and solar forcings, the relative strength of polar forcings for CO2 is greater than that for solar forcings. From the gisstemp efficacy page we have the following plots: Adjusted forcing for doubled CO2:
Adjusted forcing for 1.02 times solar radiation:
The adjusted forcing is the initial forcing as adjusted after the stratosphere reaches equilibrium, ie, the radiative forcing as per the IPCC definition.
As you can see, for solar forcing the forcing at the tropics is over four times greater than that at the North Pole, and over six times greater than that at the South Pole. In contrast for CO2 forcing of similar strength, the forcing in the tropics is only 1.6 times greater than that at the North Pole, and only 2.4 times greater than that at the South Pole. So even though the greatest forcing is in the tropics for both forcings, the polar forcing is relatively greater for CO2 than for solar forcings as I had deduced.
It still seems likely to me that this difference will result in some temperature differential between poles and tropic after all feedbacks for two types of forcings. Of course, the feedbacks for both forcings are very similar, so the stronger the feedback (and hence the higher the climate sensitivity) the less difference in temperatures will survive. I see that the GISS model E predicts very similar final temperature outcomes:
As you can see, the model shows the CO2 forcing results in the world being 0.4 degrees warmer at the poles than for solar forcing, but 0.2 degrees cooler in the tropics. That 0.6 degree differential in terms of polar amplification set against an increase in mean global temperature of around 2 degrees C, which would surely be detectable. Of course, with the actual forcing todate, the difference may be two small to use polar amplification for attribution purposes (which I guess is what you would argue). You might also argue that model results are, as yet, insufficiently accurate to place much weight on so small a difference for the two forcings.
Never-the-less, it seems to me that:
1) Polar amplification is currently much stronger than expected, which sits more comfortably with a green house rather than a solar primary forcing;
2) Any "skeptic" who denies that there is a substantial difference to the response to CO2 and solar forcings at different latitudes is thereby committed to a large climate sensitivity, and given the known CO2 forcing from anthropogenic sources, is also logically committed to anthropogenic greenhouse gases being the primary agent in the current global warming.
The second point means that the rapid warming in the Arctic is indeed not just evidence of warming, but evidence of anthropogenic warming.
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scaddenp at 18:38 PM on 28 July 2011It's the sun
Um, it's rather a long stretch from quantifying the uncertainties as of 2007 to "it doesnt know whats happening". As that reference points out, solar forcing is extremely well measured for last 25 years (direct measurement by satellite) but is "B" because of reliance on proxies prior to that. For more up to date look at the solar proxy uncertainties see this . Note that all forcings (indeed all scientific measurements) have uncertainties. What's important is the extent to which these can be quantified. -
MA Rodger at 18:02 PM on 28 July 2011Ocean Cooling Corrected, Again
What is the conversion factor between watt/sq metre or joules/sq metre (used here) & zeta joules (used by Levitus & others)? -
davidh5040 at 17:38 PM on 28 July 2011CO2 is not a pollutant
CBDunkerson@23: Here are the definitions from Macquarie. pollution 1. the act of polluting. 2. environmental pollutants, such as motor vehicle emissions, industrial waste, etc. 3. the results of these pollutants, as city smog, etc. pollutant that which pollutes; a polluting agent. pollute 1. to make foul or unclean; dirty. 2. to make morally unclean; defile. 3. to render ceremonially impure; desecrate. Using the second definition of "pollution", we can get CO2 as industrial waste (in the sense of "anything left over or superfluous, as excess material, by-products, etc."), and therefore as an environmental pollutant. (Interestingly, this particular definition doesn't seem to include damage to the environment as a consideration). And so you are correct. I was largely persuaded by Tom Curtis and muoncounter, but this puts the icing on it by applying a more rigorous application of the authority I have proposed, without having to shift to other definitions. Thanks to you all for your contributions to this. I will now feel a little more relaxed about using the term in future (though I will still use it with care). Finally, one last appeal for patience and empathy: I realise the tremendous frustration at the poor quality of much of the discourse around this issue, but I do believe that there are many out there who genuinely hold different views or who genuinely don't know what to think. We need to make it as easy as possible for them to hear what we are saying... Thanks again all! -
Eclipse at 17:13 PM on 28 July 2011It's the sun
Hi all, Do you have a page dedicated to the Denialist claim that the IPCC itself admits it doesn't know what's happening with solar forcings at the following 2007 report page. IPCC 2.9.1 Uncertainties in Radiative Forcing -
Rob Painting at 16:43 PM on 28 July 2011Michaels Mischief #1: Continued Warming and Aerosols
Dana I didn't choose 1998 as a starting point - Michaels did because Kaufmann did. To be fair, Kaufmann chose it because "skeptics" like Michaels did! -
Chris Colose at 14:46 PM on 28 July 2011How we know we're causing global warming in a single graphic
Actually the TOA radiative forcing for both the sun and CO2 (as well as the potency of the water vapor feedback) are maximized in the tropics...note the spatial structure of the radiative forcing has a complex pattern even for a well-mixed gas. So it's not immediately obvious from simple conceptual thoughts of the forcing that any polar amplification should occur at all The climate sensitivity (for the same forcing) would be higher in the poles for a bare blackbody rock, based on the Stefan-Boltzmann law, where the hotter body must respond more sluggishly to the same input of energy. In reality, the polar amplification (for any forcing) depends on complex dynamical transport processes which "export" sensitivity from low to high latitudes, as well as thermodynamics (radiation, ice-albedo feedback, etc) which tends to produce polar amplification for a wide range of idealized cases and forcing. In the upper atmosphere, the tropics are amplified relative to the poles. See for example, Pierrehumbert RT (2007), The Hydrologic Cycle in Deep Time Climate Problems. Nature 419,191-198 Peter L. Langen & Vladimir A. Alexeev (2007), Polar amplification as a preferred response in an idealized aquaplanet GCM, Climate Dynamics DOI 10.1007/s00382-006-0221-x Ming Cai & Jianhua Lu (2007), Dynamical greenhouse-plus feedback and polar warming amplification. Part II: meridional and vertical asymmetries of the global warming, Climate Dynamics DOI : 10.1007/s00382-007-0238-9 Jianhua Lu & Ming Cai (2010), Quantifying contributions to polar warming amplification in an idealized coupled general circulation model, Climate Dynamics DOI 10.1007/s00382-009-0673-x Also the GISS output shows the patterns I described above as well for solar or CO2 forcing http://data.giss.nasa.gov/efficacy/ -
dana1981 at 14:08 PM on 28 July 2011Michaels Mischief #1: Continued Warming and Aerosols
Albatross @74 clarified nicely. I didn't choose 1998 as a starting point - Michaels did because Kaufmann did. I chose GISTEMP simply to illustrate that not all data sets agree on hemispheric trends - it was a contrasting example with easily accessible data. And as Albatross noted, I also showed the data since 1975, unlike Michaels, to show how the hemispheric trends have changed (I didn't plot the Hadley data for this period, but I did discuss it). I'm forced to conclude Eric's cherrypicking accusation is based on the fact that he didn't read the post very carefully. -
Tom Curtis at 12:57 PM on 28 July 2011How we know we're causing global warming in a single graphic
Chris Colose @26, thank you for your response. I notice that @14 you say:" No, a reduction in the pole-to-equator temperature gradient is one of the most robust responses to any global warming situation."
I have a problem with this in that, if you ignore feed backs than in increase in CO2 will decrease the temperature gradient, while an increase in insolation will increase it. That being the case, even if feedbacks result in a reduction of the gradient regardless, there should still be a difference in the change of the gradient in the two cases. Is that difference really not detectable in the models? -
Paul Magnus at 12:49 PM on 28 July 2011Earth's Climate History: Implications for Tomorrow
@15 i 2nd that. -
Chris Colose at 12:40 PM on 28 July 2011How we know we're causing global warming in a single graphic
Tom, If you take a look at the studies I cited, CO2 itself (directly) plays a very minor role relative to cloud cover development, precipitation, water vapor feedback, aerosol effects, albedo, and other factors like irrigation and soil moisture as you approach the regional level (see Engelhart and Douglas, 2005 for a discussion on Mexico's DTR for example). The shortwave component of the energy flux seems to exert a much stronger control through changes in aerosol burden (Wild et al., 2007; Makowski et al 2008). I think I can buy that large increases in sunlight would tend to enhance the DTR itself, in the opposite direction of the long term trend. One thing I haven't seen in many of these DTR studies is a consideration of the top of the atmospheric energy balance, as opposed to just the surface forcing. This seems, to me, to be a very incomplete view and I'm not convinced the authors in some of these works appreciate this. When the atmosphere is well-mixed vertically, radiative forcing at TOA has a greater influence upon the surface air temperature than forcing at the surface, since the atmosphere itself adjusting its OLR is a primary way that equilibrium is re-established in response to forcing. Much of this re-adjustment occurs in the high atmosphere, since the bulk of the boundary layer is optically thick due to CO2 and water vapor. -
scaddenp at 12:39 PM on 28 July 2011How we know we're causing global warming in a single graphic
I would have thought not quite so simple. Any warming invokes feedbacks, including water vapour though CO2 effect should be more prominent in cold, dry air, but at the poles there are other factors (especially Antarctica) to muddy the waters (eg ozone). -
barry1487 at 12:32 PM on 28 July 2011Michaels Mischief #1: Continued Warming and Aerosols
So Eric, you think the trend of each of the past two decades is statistically significant at the 95% confidence level? How did you work that out? -
Albatross at 12:16 PM on 28 July 2011How we know we're causing global warming in a single graphic
Anybody got some thoughts on Chemware's question posed @13? "Would not another signature of anthropogenic warming by greenhouse gases be that high latitudes are warming faster than areas near the equator?" Chris? -
Albatross at 11:52 AM on 28 July 2011Earth's Climate History: Implications for Tomorrow
Dr. Hansen, Thank you for a very clear, succinct and sobering account of a complex and potentially alarming situation. I very much appreciate (and admire and respect) everything that you have done regarding the science behind both natural and anthropogenic climate change. Not to mention the great progress that your dedicated and hard work has fostered in this field. Your efforts are especially noteworthy considering the relentless attempts to undermine your credibility and interfere with your work by 'skeptics' and those in denial about anthropogenic climate change. History will reflect very favourably on your admirable, professional and principled approach to this issue-- the same will not be true for Lindzen, Spencer, McIntyre, Christy, Singer and Michaels and their ilk. -
Tom Curtis at 11:49 AM on 28 July 2011How we know we're causing global warming in a single graphic
Chris Colose @17, are you saying that increased CO2 will not decrease the DTR, or that the decrease is small compared to other factors, ie, changes in aerosol load, and or changes in specific humidity? Further, do you have any comment on my points 1) and 2) @21. Am I getting the nuances right? -
Chris Colose at 11:48 AM on 28 July 2011How we know we're causing global warming in a single graphic
Tenney-- The sun can melt ice too :-) -
Tom Curtis at 11:45 AM on 28 July 2011How we know we're causing global warming in a single graphic
ptbrown @31, I think there is a crucial logical point that is often missed in popular discussion of the fingreprint of the greenhouse effect. That point is that no individual "fingerprint" is unique to the enhanced greenhouse effect. What is unique is the combined pattern of effects. It is also important to realise that the water vapour feedback, being itself an enhanced greenhouse effect will contribute some of the finger print of an enhanced greenhouse effect to any warming. It will, however, do so by counteracting the primary effect of many warmings, so while it means we cannot be simplistic in our analysis, it does not prevent fingerprinting analysis. With that in mind: 1) An increase in albedo due to increased aerosol optical depth will decrease the Diurnal Temperature Range, as will a decrease in Total Solar Irradiance. However, both of these phenomena will also cool the lower troposphere overall. Cooling the lower troposphere will also reduce average specific humidity, which will tend to increase the diurnal temperature range. So, to the extent that increased aerosol optical depth (or reduction in TSI) is responsible for the reduction in DTR, it is only because some other factor is increasing tropospheric temperatures more than they are tending to decrease them. 2) As it happens, global sulfur dioxide emissions have reduced since 1975. Therefore, to the extent that they do influence the Diurnal Temperature range (which is substantial) we would expect the DTR to have increased over that period. The fact that it has not suggests some other factor is causing the DTR to decrease. Thus we could divide the later part of the 20th century into to intervals. During the period 1950 and 1975 the two factors influencing DTR acted in concert to decrease it, while after 1975 one factor continued to decrease it, while the influence of aerosols was to increase it, with no net effect. This is in effect the reverse of the temperature trend. Between 1950 and 1975, increasing aerosols tended to cool the planet, counter acting some other factor that was warming it with a resulting very small change in global temperatures; while after 1975 both the reduction in aerosols and the other factor have tended to warm the troposphere, resulting in a sharp rise in temperatures. This other factor, which both reduces the DTR and warms is therefore an enhanced greenhouse effect. 3) If your argument at this point were valid, then it would also apply to the effect of aerosols. Hence in that you apparently accept the influence of aerosols on DTR, you are contradicting yourself. -
Albatross at 11:43 AM on 28 July 2011How we know we're causing global warming in a single graphic
My two cents worth on the DTR. In my humble opinion (and understanding) the reduction of DTR is theoretically a (subtle) symptom of an enhanced "greenhouse" effect. The problem with the DTR is finding a suitable dataset (and long enough) that has not been affected by other factors that might influence trends in DTR. I think that Braganza is one record saying that because of the myriad of factors that can affect DTR in the real world, it is not the most robust fingerprint of AGW-- note that does not equate to saying that it is not a fingerprint, or that the enhanced "greenhouse" effect has been overturned. If I recall correctly, Braganza considers the seasonal change in warming to be a far better and unambiguous fingerprint of an enhanced "greenhouse" effect. I suggest reading this informative post by Dr. John Nielsen-Gammon, as well as the recent paper by Zhou et al. (2010). At the end of the day, when we consider the body of evidence, a coherent and robust picture of an enhanced "greenhouse" effect on account of an increase of CO2 levels from humans burning fossil fuels emerges. As to which of the many indicators is the best or more robust, well that is open for discussion. -
Tenney Naumer at 11:32 AM on 28 July 2011How we know we're causing global warming in a single graphic
Nothing about retreating glaciers? -
scaddenp at 11:25 AM on 28 July 2011How we know we're causing global warming in a single graphic
I'm not that fond of any single phenomena being called a "fingerprint of anthropogenic warming". I think it would be better to think of the fingerprint as being a set of phenomena observed together. This is much more discriminatory power for comparing anthropogenic warming to natural forcing. Ideally you run the model with anthropogenic forcings, and then same model but with different natural forcings, all of the same strength and compare outputs. There is some data for that here and perhaps in the Hansen et al 2005 paper -
Chris Colose at 11:07 AM on 28 July 2011How we know we're causing global warming in a single graphic
muon-- Hopefully we'll gear future posts away from that meme, or at least clarify the many nuances. ptbrown-- Thanks! I got my B.S. there too, but am doing graduate work elsewhere. Room 1411 will be missed. -
ptbrown31 at 10:59 AM on 28 July 2011How we know we're causing global warming in a single graphic
10, Chris Colose Thanks for the support. By the way, I have seen your posts around the climate blogosphere before and I noticed you are at Wisconsin. I got my undergrad from the AOS dept in '08. Go Badgers! -
muoncounter at 10:58 AM on 28 July 2011How we know we're causing global warming in a single graphic
DTR looked better than a weak fingerprint on this prior thread. We are currently experiencing global warming. If an increased greenhouse effect is a significant part of this warming, we would expect to see nights warming faster than days. There have been a number of studies into this effect, which confirm that this is indeed the case. One study looked at extreme temperatures in night and day. They observed the number of cold nights was decreasing faster than the number of cold days. Similarly, the number of warm nights was increasing faster than the increase in warm days (Alexander 2006). -
Chris Colose at 10:53 AM on 28 July 2011How we know we're causing global warming in a single graphic
ptbrown-- There's a lot of examples of erroneous but popularly held notions that many people have :-) Don't blame the site too much, hopefully that will correct itself. Keep in mind that something not being a 'fingerprint' doesn't necessarily imply it is consistent with everything either. There's no indication that the trends in DTR are consistent with a pure natural forcing. Chemware-- No, a reduction in the pole-to-equator temperature gradient is one of the most robust responses to any global warming situation. -
muoncounter at 10:49 AM on 28 July 2011Earth's Climate History: Implications for Tomorrow
Sally #12: "Are we able to scientifically link the rise in extreme/severe weather events in terms of being attributable to climate change ?" That's a hot button issue. Most people will respond with a cautious 'maybe'; statements like the probability of extreme events has increased due to global warming. See the prior extreme weather thread for cautious discussion of 2010's events. The frequency of extreme warm anomalies increases disproportionately as global temperature rises. "Were global temperature not increasing, the chance of an extreme heat wave such as the one Moscow experienced, though not impossible, would be small" See this recent Scientific American series for this year's version: Increasingly, the answer is yes. Scientists used to say, cautiously, that extreme weather events were "consistent" with the predictions of climate change. No more. "Now we can make the statement that particular events would not have happened the same way without global warming," says Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. Is it a good sign that the language used by the experts is changing? Sorry, didn't mean to give you another reason to lose sleep. -
Chemware at 10:46 AM on 28 July 2011How we know we're causing global warming in a single graphic
Would not another signature of anthropogenic warming by greenhouse gases be that high latitudes are warming faster than areas near the equator ? This is the opposite of what one would expect from increased insolation, and is only explicable by a mechanism that increases the insulating properties of the atmosphere. -
Rob Painting at 10:44 AM on 28 July 2011How we know we're causing global warming in a single graphic
ptbrown31 - let me refine my comment. The DTR is weak evidence for the increased Greenhouse Effect, but insofar as a human 'fingerprint' on climate, that seems to be on far safer ground. This is evident in the 'weekend effect' in heavily industrialized areas for instance. The DTR undergoes change over the weekend when industrial sources of pollution abruptly drop.
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