A very interesting paper was published recently by Klaus-Peter Schroeder and colleagues (Astronomy & Astrophysics, 540, A130, 2012). A link to this paper is:http://www.aanda.org/articles/aa/pdf/2012/04/aa18363-11.pdfIn this paper, the authors examine the latest solar minimum in 2009 compared to the chromospheric flux of a sample of solar-type stars, a measure of stellar activity comparable to the solar sunspot index. To be precise, they used the Mt. Wilson S-index, which is a measure of excess (chromospheric flux) in the 3933 A line of ionized calcium. This quantity can be measured in other stars (unlike the sunspot index) and provides a suitable proxy of stellar activity. It turns out that the scatterplot of S-index vs. stellar temperature (in terms of color index B-V -- just a way of measuring stellar surface temperature) has a minimum locus (Fig 3 of the Schroeder et al. paper). No star with a chromospheric flux (or stellar activity) below this locus are observed. These are Maunder minimum stars in a very low state of activity.The authors also monitored the Sun during the recent 2008-2009 solar minimum, when the solar S-index was very low by historical standards. It turns out that on several occasions during early 2009, the solar S-index actually touched the Maunder minimum locus (which is S=0.150 for the Sun, for those interested). One such date was on Feb 6, 2009 when the Sun looked like this in the light of the hydrogen Balmer-alpha (H-alpha) line at 6563 A (a good diagnostic of chromospheric activity).ftp://ftp.ct.astro.it/Sole02/2009/Chromosphere2009/oact_halp...A completely featureless solar disk is seen, which is very unusual. For comparison, take a look at today's Sun in H-alpha:http://web.ct.astro.it/sun/solec.jpgWhat this result means is that for the first time we *know* what the Sun looked like during the Maunder minimum -- it looked like the Sun on Feb 6, 2009 (and other days around then). We also know what the MM total solar irradiance is -- it's the 1360 W/m^2 observed in Feb 2009.There has been a whole industry of recent trying to reconstruct past solar TSI (total solar irradiance -- the total solar flux reaching the Earth). The results obtained depended critically upon the assumed state of the Maunder-minimum (MM) Sun. For example, Shapiro et al. (2011) assumed *all* magnetic activity vanished during the MM and predicted a TSI some 6 W/m^2 lower than present. The reality, as shown by Schroeder et al. is that a small amount of small-scale magnetic field remains even during MM times, and the TSI is not nearly so reduced. Instead it only drops by about 1.0 W/m^2 from mean solar TSI values, for a total range of about 2.0 W/m^2 due to activity variability. This is a much smaller effect than claimed for some previous TSI reconstructions.One important consequence of this is with regard to the climate sensitivity -- it must be fairly high because we observe substantial effects on global temperature (about 0.5 C peak to peak) due to small changes in TSI. Compare this to expected changes in global surface temperature for a simple planet with no other feedbacks. Then the expected change in surface temperature due to radiative equilibrium considerations would be T_surf*(delta_TSI/TSI)/4 = 0.11 C [where T_surf= 288 K, TSI= 1360 W/M^2, delta_TSI= 2.0 W/m^2]. This is just 20% of the actual temperature response, which suggests a high climate sensitivity.Phil
Thanks for the interesting links and discussion, Phil. Establishing a TSI value for Maunder Minimum type states of the sun is a big deal!You lost me though, here:"One important consequence of this is with regard to the climate sensitivity -- it must be fairly high because we observe substantial effects on global temperature (about 0.5 C peak to peak) due to small changes in TSI."Do you mean peak to trough of a typical solar cycle? I thought that the observed change in global temperature over the cycle was about .1 C.
There were also changes in albedo and emissitivity between now and the MM. And difference in the degree of pertubation.
Thanks, Astrophool!Let's see if I understand what you are saying.First, we suppose that the observed change in global mean temperature due to changes in total solar irradiance (measured in watts per square meter) is about 0.5 K, when comparing trough TSI to peak TSI. This includes all feedbacks (positive or negative) that act over time scales measured in, um, let us say months or less.Second, we suppose that the theoretical change in global mean temperature would be, in this particular case, just 0.11 K, if there were no feedbacks in the system.The ratio of these two numbers, 0.5/0.11 = 4.55, gives the total multiplicative effect of *ALL* short-term feedbacks together. These include the water vapor feedback, the ice-albedo feedback, the cloud feedback, the lapse rate feedback, and perhaps other feedbacks that we may know nothing about.Third, we can apply this same multiplier to the climate's sensitivity to changes in atmospheric carbon dioxide, because the same set of feedbacks would be at work, in the same way. However, climate sensitivity is defined as the response of temperature to a *doubling* of atmospheric CO2, not to a unit change in CO2. Another way to say this is that climate sensitivity is the response of temperature to a unit change in the logarithm (base 2) of CO2.If the effect of feedbacks in the climate system is equivalent to multiplying the CO2 by a factor of 4.55, then the feedbacks are contributing log2(4.55) = 2.19 to climate sensitivity. Without any feedbacks the sensitivity would be exactly 1.0, according to Wikipedia. If all of the foregoing is correct, then we should conclude that our estimate of short-term climate sensitivity from this study of total solar irradiance is 1.0+2.19 = 3.19.Are there any flaws in that line of reasoning? I seldom do this kind of physics, so I am not completely confident that I got it right.A statistical note for Astrophool: Rather than use peak-to-trough guesstimation, I would use all the data in a regression model and estimate the effect of TSI from its regression coefficient. This is very likely to give you smaller error bars for your estimate. I can do this for you if you like.And a note for Ajax: I hope you notice that what happened a thousand years ago during the Medieval Warming Period is completely irrelevant to this estimate of climate sensitivity. All we needed were a couple of decades of TSI and temperature data, and some good theory.Loren
One important consequence of this is with regard to the climate sensitivity -- it must be fairly high because we observe substantial effects on global temperature (about 0.5 C peak to peak) due to small changes in TSI. Is this correct?
First, we suppose that the observed change in global mean temperature due to changes in total solar irradiance (measured in watts per square meter) is about 0.5 K, when comparing trough TSI to peak TSI. This includes all feedbacks (positive or negative) that act over time scales measured in, um, let us say months or less.Do you have a reference for this 0.5 you supposed? I checked out one of my favorite websites and they called it 0.15.http://www.skepticalscience.com/solar-activity-sunspots-glob...And this article calls it 0.1, and I believe that is what the IPCC approximates to.http://www.agci.org/docs/lean.pdfPerhaps the term TSI is being misused by someone.I recalculated sensitivity using 0.15 and your method and I got 1.5.
Do you have a reference for this 0.5 you supposed?I merely copied the value given by AstroPhool in his post at the top of the thread. I have no independent source. I do have access to the latest TSI data, so I am thinking of using that data to come up with my own estimate. The only problem is that the data are daily, so it will involve some tedious mucking about with spreadsheets -- not my favorite activity.Loren
However, climate sensitivity is defined as the response of temperature to a *doubling* of atmospheric CO2, not to a unit change in CO2This is where the concept of radiative forcing becomes useful. It allows one to compare different climate forcings. All perturbations, co2, methane, changes in TSI, are quantified in terms of their impact on the incoming energy of the climate sytem. The response of the globally annually averaged surface temperature is assumed to respond equally to equal radiative forcings, regardless of the source. This is the basic idea beyond energy balance modeling. Of course it is an approximation.The ratio of the change of temperature to the radiative forcing is one way to measure the climate sensitivity. This is easily converted to the sensitivity to doubling co2 once you know the radiative forcing for doubling co2.The radiative forcing for doubled co2 is about 3.7 = 5.35 ln(2) W/m2.http://www.grida.no/publications/other/ipcc%5Ftar/?src=/clim...
And a note for Ajax: I hope you notice that what happened a thousand years ago during the Medieval Warming Period is completely irrelevant to this estimate of climate sensitivity.That said, it is completely relevant to the political discourse, which of course will define what (or whether) action is taken.How?The alarmists keep insisting that this time is different and we have never had this situation and we are in new territory and the sky is falling and ...In fact, temperature has been at this level within recorded history. It has perhaps even been warmer. Civilization did not end. In fact it has flourished.Adaptation is likely the most cost-effective response to global warming, regardless of whether it is man-made. This is something the alarmists do not want to consider.But we've apparently done it before.
The alarmists keep insisting that this time is different and we have never had this situation and we are in new territory and the sky is falling and ...In fact, temperature has been at this level within recorded history. It has perhaps even been warmer.Civilization did not end. In fact it has flourished.When WE assert "this time it is different" the description is of the CO2 and Methane levels... THIS graph... http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html...and when a warm climate allowed our "civilization to flourish" we were many many billions of humans fewer, organized in agrarian societies. The civilizations that "flourished" were the northernmost, the "western" civilizations, others not so much affected. The production of distant lands was largely irrelevant, and the civilizations and related economies were NOT dependent on complex transport webs. You are proclaiming it an easily adaptable event based on half a degree of the two degrees (at least) we've quite certainly forced (or the more likely 3+ degrees that the scientists for the most part expect now, barring tipping points). Such an assertion on your part is not to be relied on, being based on the zero experience any of our civilizations have had with abrupt transitions to new temperature regimes and the related changes, and the vastly greater vulnerabilities built into our food production and delivery systems, and the intricate interrelationships of our economies ( One problem with a "global economy" is that a collapse becomes something that has global effects). You wish to bet our children's lives that adaption is going to be most cost effective. The science doesn't support that bet. Not at all. Nor do you or anyone else, have the moral right to make it. Yet it is being made, even as we argue... has been ever since the "masters of the universe" decided to ignore Kyoto. Loren is EXACTLY right, the MWP is entirely irrelevant.
Let me first explain a little more clearly what I'm trying to do by means of this bit of analysis, and then I'll try and and address some particular concerns.First and foremost, I am trying to understand the temperature record of the previous millennium or so prior to the Industrial Revolution, a period which still saw substantial global surface temperature variability, but for which atmospheric CO2 was nearly constant (at 275 ppm). That constancy removes the effect of variable emissivity of the Earth + atmosphere (i.e., global warming considerations) from the equation. I do this because we now understand the magnitudes of all the other possible radiative forcings, and so we should be able to use this information to "calibrate" the response of the climate system to these known effects (thereby establishing the climate sensitivity).My assumptions are this: (1) the Earth is in radiative equilibrium with solar insolation, at least on decadal or longer timescales, and (2) the Earth's climate is stable (in the strict physical sense that a small change in external conditions leads to a small change in climate outcomes, and not to a climate runaway). This means that the observed decadal temperature variability was *caused* by some change in radiative forcings -- these temperature changes didn't just occur without cause.There are only a few ways that external forcings can result in variations in radiation absorbed by the Earth: (1) intrinsic solar variability, (2) variations in the Earth's orbit, (3) variable transmission of the Earth's atmosphere (due to aerosols), (4) variable albedo of the Earth's atmosphere + surface, and finally (5) variable emissivity of the Earth + atmosphere due to greenhouse gases. The latter is constant for this period. Volcanoes put aerosols into the atmosphere but these are flushed out after about 2-3 years, resulting in a short-term effect only. The strongest example in the past 1000 years was probably the Tambora eruption of 1815. In this analysis, I only consider effect lasting a decade or longer, so the impact of volcanic activity can be ignored.I assume that albedo variations are unimportant, except as part of feedbacks due to other effects. So, e.g., an increase in snow cover due to solar cooling would be viewed as a feedback to solar forcing and not an albedo effect. The climate trend since the Holocene Climatic Optimum around 7000 BC has been that of a slow cooling trend but with substantial decadal variability superimposed. I assume that the slow trend is due to orbital forcing -- the timescale and direction are correct. That leaves only intrinsic solar variability to explain the shorter, decadal variations, so I explicitly assume that these are of solar origin. There does seem to be correlation (but the data are limited) of historical global temperature with sunspot activity, and longer term temperature reconstructions correlate with Be^10 isotope ratios (a measure of cosmic ray flux, which anticorrelates with solar activity).The Schroeder et al. paper establishes the Maunder minimum (MM) TSI at about 1360 W/m^2, and therefore the range of peak-to-peak (or more accurately, peak-to-trough) TSI at about 2 W/m^2. Interestingly, the short 11-yr solar cycle does not appear to leave its imprint in the climate record (although, it has been speculated for many years that this cycle drives the ENSO cycle -- mostly because no-one really understands ENSO and the period is similar to that of the solar cycle). Instead, it is the longer 90-yr grand solar cycle that shows up in the climate record. SO I examined the 1000 years of temperature data from 800 to about 1850, and here I used the reconstruction of Mann et al. (2008), which has the drawback of being only northern hemisphere data, and so probably slightly overestimates the actual global effect. Fig 3 of Mann et al. is here:http://www.ncdc.noaa.gov/paleo/pubs/mann2008/fig3.jpgThe mean of the reconstructed temperatures range from a minimum of about -0.6 C in the depths of the LIA around 1700 AD to about maximum of about -0.1 C in the MWP around 1000 AD (with a lot of scatter between the reconstructions), where the zero point is the temperature in 1950. [Sorry, Loren, I do actually make use of the LIA/MWP here!]. That gives me the peak-to-trough range of 0.5 C. This actually isn't that different from the 0.1-0.15 C effect others mentioned. Dividing the peak-to-trough range by two to get an amplitude yields 0.25 C. If a standard deviation was used instead of a peak amplitude that would further reduce the value to about 0.15 C. Finally, allowing for global instead of northern hemisphere temperatures might further reduce this value to 0.10-0.12 C. I don't do this here because I don't readily have these figures available -- the Pages 2K temperature reconstruction (Nature Geoscience, 6, 339: May 2013) does include the southern hemisphere (but not the oceans yet) but you still need to combine these data to get an overall land effect. Loren is also correct in that, properly, a regression analysis should be carried out instead of simply comparing peak-to-trough quantities, as I have done. The reason I didn't do this regression of TSI vs global temperature (or, at least, vs northern hemisphere temperature) is because this requires a TSI reconstruction. (Directly measured TSI data only go back about 3 decades, and even compiling a consistent dataset from the different satellites has been the subject of much controversy). I don't trust the available reconstructions fully,although many look reasonable, because none make use of the Schroeder et al. Maunder minimum TSI result. But I now know the TSI range (2 W/m^2), which allows me to carry out the present peak-to-trough analysis, but then I need to use comparable peak-to-trough temperatures from the Mann et al. reconstruction (the 0.5 C range). As Loren points out, the ratio of the observed 0.5 C range to that calculated from radiative equilibrium from the TSI range (0.11 C) gives an estimate of the total multiplicative (short-term) feedback ratio: 0.5/0.11= 4.55. This is probably an overestimate because of the use of only northern hemisphere temperature data. If I had to estimate, I would say that the overall global temperature response would probably be about 2/3 of that of the northern hemisphere, or about 0.35 C peak-to-trough over the 800-1800 AD period. That gives a smaller feedback ratio of 0.35/0.11= 3.2. One simple way of comparing to the standard CO2 climate sensitivities is to assume that the forcing due to CO2 affects the climate system in a similar way to the other forcings. The direct effect on global temperature due to doubling CO2 alone (from radiative transfer models) is about 1.1 C. Multiplying this direct CO2 sensitivity by the above feedback ratio of 3.2 gives a total climate sensitivity (including all the short-term feedbacks) of about 1.1*3.2= 3.5 C for doubling CO2. So the climate sensitivity derived assuming the short-term, pre-industrial decadal temperature variability was of solar origin agrees with the IPCC climate sensitivity of 2 to 4.5 C. The overall consistency of this result provides confirmation that the pre-industrial decadal temperature variability was mostly due to intrinsic solar variability.Sorry for the lengthy post, but I think this is an interesting result.Phil
And a note for Ajax: I hope you notice that what happened a thousand years ago during the Medieval Warming Period is completely irrelevant to this estimate of climate sensitivity. All we needed were a couple of decades of TSI and temperature data, and some good theory.Loren How did you arrive to this conclusion that the Medieval Warming Period is completely irrelevant - based on what? How about the Roman Warm Period and the Minoan Warm Period - are these naturally occurring global warming periods irrelevant too - because you want to blame the current, very mild by comparison, warm period on CO2?Besides, the Vostok ice-core data (covering over 400,000 years) show that CO2 lags temperature by about 800 years - which means that CO2 is a consequence of global warming and not the cause.You are in effect asking us to ignore these real data and processes and accept your baseless assertion that CO2 drives temperature and causes global warming. The exact opposite of what is happening all around us.In the end, since:1. Global warming is a natural event that does not require CO2 and 2. CO2 is a consequence of global warming and not the cause thenClimate Sensitivity is a very small number close to zero and might even be negative.I am sorry but what you are proposing is not science but nonsense.-=Ajax=-
I hope you notice that what happened a thousand years ago during the Medieval Warming Period is completely irrelevant to this estimate of climate sensitivity.And what happened when Galileo dropped the different weights off the Tower of Pisa 424 years ago is completely irrelevant to the law of gravity today. Back then, different weights fell at the same rate. Today, heavier things fall faster. I know this because Mann and Gore told me.--fleg
Interesting thread. Thank you.
1. Global warming is a natural event that does not require CO2 andYep. Everyone agrees on that. Global warming can happen naturally, with or without CO2. 2. CO2 is a consequence of global warming and not the cause thenCO2 is definitely not the consequence of global warming this time around, given that we know we caused the CO2 increase - we've dug up and burned about 2x as much CO2 as the atmospheric concentration has increased. (The rest has gone into the biosphere, oceans, etc.)Climate Sensitivity is a very small number close to zero and might even be negative.Nope. If that's the case, the climate wouldn't change so much with small changes in solar input. We wouldn't have ice ages and interglacial periods. If the climate sensitivity is zero, then how come a TSI change that should cause 1 degree increase actually causes a 3 degree increase instead?
Back then, different weights fell at the same rate. Today, heavier things fall faster.For chrissake, Fleg, we are trying to understand some difficult physics in this thread (difficult for me, anyway). I'm putting you and Ajax temporarily in the p-box so that I can concentrate on thinking this through.Loren
How did you arrive to this conclusion that the Medieval Warming Period is completely irrelevant - based on what? Lets see.... There is the fact that climate sensitivity CAN be worked out from the latest "quiet sun" giving a "calibration" for what the insolation value actually is for a Maunder Minimum event... which is what Loren was talking about. You quoted him. Did you bother to read what you copied?There is the fact that CO2 as feedback AND forcing has been explained to you many times. http://www.skepticalscience.com/co2-lags-temperature-interme...There is the fact that there has never been a claim by any climate scientist that all warming is due to CO2, a necessary assumption if you are to claim AS YOU ARE CLAIMING, that any instance of warming NOT caused by CO2 proves it was not the CO2. Your logic in this is not merely faulty... it is wilfully so because YOU HAVE BEEN TOLD OF THE PROBLEM MANY TIMES!!!1. Global warming is a natural event that does not require CO2 and 2. CO2 is a consequence of global warming and not the cause Lets try saying it right. We can't have mistakes like this lying about for people who don't know what you are doing (which would include you), to get a misapprehension. 1. Global warming is a natural event that may be initiated by many different physical conditions. 2. CO2 may be a feedback OR a forcing depending on the source of the CO2. 3. The source of the CO2 at this time is US, and therefore it IS a forcing. ...and there isn't a bit of that that allows you to claim to know what climate sensitivity is. Has to be measured separately. Your claim is rubbish, you are spewing nonsense and you are definitely one of the sorriest people I've ever encountered.
If there were a prize for WORST posts on the fool this could be a contender. Bye
I hope you notice that what happened a thousand years ago during the Medieval Warming Period is completely irrelevant to this estimate of climate sensitivity.Except that is where Astrophool got his 0.5C...
SO I examined the 1000 years of temperature data from 800 to about 1850, and here I used the reconstruction of Mann et al. (2008), which has the drawback of being only northern hemisphere data, and so probably slightly overestimates the actual global effect. Fig 3 of Mann et al. is here:http://www.ncdc.noaa.gov/paleo/pubs/mann2008/fig3.jpgThe mean of the reconstructed temperatures range from a minimum of about -0.6 C in the depths of the LIA around 1700 AD to about maximum of about -0.1 C in the MWP around 1000 AD (with a lot of scatter between the reconstructions), where the zero point is the temperature in 1950. [Sorry, Loren, I do actually make use of the LIA/MWP here!]. That gives me the peak-to-trough range of 0.5 C. This seems like a not great way to do it since if you pick another study you can easily move your range 50%, maybe more, change the years, you can do the same, plus the uncertainties are most likely underestimated.
If there were a prize for WORST posts on the fool this could be a contender. ByeActually your post may be the worst post, since I have no idea what post you're actually talking about- you didn't bother to quote it.There isn't really a need to tell people when you put them in the frown face mode.
<<<Back then, different weights fell at the same rate. Today, heavier things fall faster.>>>For chrissake, Fleg, we are trying to understand some difficult physics in this thread (difficult for me, anyway). I'm putting you and Ajax temporarily in the p-box so that I can concentrate on thinking this through.Loren Hear that Fleg?? The Climate man is thinking! He's going through the extra motion and energy of P-Boxing you so he will have the extra time to think! Your postin interferes with his thinking!What a quite fitting response. The historical parallels are apt. Fleg has now been placed into a "Penalty BoX" by Loren because Fleg committed climatological heresy. Fleg refers to Galileo in the inertial properties of mass and falling object in gravitational field, who served time before the Catholic Church because of religious heresy. Galileo also was placed into the "penalty box".Fleg, you are now a grayling on the board. I heard that Galileo became gray after some time....served.
>So I examined the 1000 years of temperature data from 800 to about 1850, and here I used the reconstruction of Mann et al. (2008), which has the drawback of being only northern hemisphere data...Whoa! Danger, Will Robinson! Phil, I can't believe you used Mann 2008. That study used some proxies upside down, was overly dependent upon bristlecone pines which have numerous problems and, IIRC, the study was statistically shown to be invalid before about 1400. Pick another reconstruction; almost any would be better.DB2
jck101: [referring to my approach to determining the temperature range] This seems like a not great way to do it since if you pick another study you can easily move your range 50%, maybe more, change the years, you can do the same, plus the uncertainties are most likely underestimated. This is just a first pass, with the goal of seeing whether or not the pre-industrial temperature fluctuations are consistent with intrinsic solar variability as their source (and I conclude hey are). It is, as you (and Loren) say, not the best approach. Ideally you want to regress temperature reconstructions and TSI reconstructions for the period in question (800-1850 AD) in order to get a more robust climate sensitivity. The problem is that there are no good reconstructions of either quantity available at present. The Mann study (aside from DB2's objections) is only a northern hemisphere reconstruction, so it is limited. Although the study does include a global land + ocean reconstruction in the appendix, it only goes back to about 1400 AD. I plan to do the full analysis when the PAGES 2k ocean temps reconstruction is completed, and I've had the chance to come up with the best TSI reconstruction. So regard the present analysis as a "back-of-the-envelope" first pass.DB2: Phil, I can't believe you used Mann 2008. That study used some proxies upside down, was overly dependent upon bristlecone pines which have numerous problems and, IIRC, the study was statistically shown to be invalid before about 1400. Pick another reconstruction; almost any would be better. I used Mann et al. (2008) because they present (in their Fig. 3) an ensemble of (at least 16 different) reconstructions and historical data. The spread among the various reconstructions gives one a good sense of the uncertainties involved in each of the individual reconstructions. Even if any one particular reconstruction is problematic, the overall mean or, better, median value for any year should be reasonably robust. I didn't actually use the Mann et al. reconstructions presented in the appendix. Rather I just "eyeballed" the median of the ensemble of reconstructions presented in their Fig 3. Again, my goal was merely to see if interpreting pre-industrial temperature fluctations as being due to solar variability made sense. And it really does seem to.I expected to get flak over the use of Mann data. The fact remains that this work is a major compilation of climate reconstructions, published in the PNAS (Proceedings of the National Academy of Science), and linked to from the NOAA site. I trust the NAS and NOAA. As a working scientist, I don't have time to second-guess every published result, especially one as distant from my own research field as this. You simply have to trust published material from credible sources (unless you have particular reason to suspect otherwise), or you'd never get anything done. That doesn't mean I uncritically accept every claim made. But generally I will accept the results of a paper published in a major journal, especially after several years in press, and if it's outside my particular area of expertise. If something is really wrong, you would definitely know about it by then. That's not to say that journals don't get it wrong sometimes. I remember a major paper in Nature a few years back that nearly made the cover (it ended up being a runner-up). It was basically a good paper, but there were some blatantly incorrect assertions made in the paper. Over time, these have been mostly addressed elsewhere in the literature. And that's typical of the game -- science is mostly a self-correcting enterprise because there is a lot of personal prestige and reputation wrapped up in ensuring that this is the case.Phil
Adaptation is likely the most cost-effective response to global warmingWhat is your evidence for this claim?Economists generally agree, from what I've seen, that the most effective way to deal with market externalities like pollution is to attach the cost of damage that the pollution imposes on society to the purchase price of the goods that cause the pollution and damage.This acts as mitigation, reducing demand for those goods and reducing pollution, and it provides an income stream that can be used for adaptation.Mitigation and adaptation are required.In the absence of mitigation we can look forward to increasing 'adaptation' in the form of massive human suffering as global temperatures soar past the 2°C warming threshold established as dangerous, and head on to 4°C warming where catastrophic impacts become increasingly likely.
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