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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Comments 27201 to 27250:

Tom Curtis at 17:34 PM on 12 October 2015

CO2 lags temperature

It has now been four days since my challenge to tatelylle @496 that he either justify his apparently absurd claim that ice melt is not a feedback on changes in Global Mean Surface Temperature (GMST), or confirm that his argumentation has been based on equivocating between the cause of changes in GMST (in his earliest post, and by context of the main article) and the cause of initial melt of NH ice sheets. tatelyle has done neither. Apparently he can neither provide evidence for his claim, nor honestly admit to the equivocation that lies at the heart of his rhetoric. He has therefore demonstrated that he is either not interested in, or as MA Rodger suggests @499, not capable of coherent and honest discussion of the issues involved. Consequently I have no further interest in discussing the matter with him.

For readers following the discussion, however, I need to clarrify some issues. Specifically, tatelyle continues to make grossly inflated estimates of the Milankovitch forcing involved both changes in GMST and in the initiation of NH ice sheet melt.

For GMST, global temperatures fluctuate approximately linearly with net global Top Of Atmosphere (TOA) energy flux, subject to a lag based on thermal inertia which is large relative to a single year. It follows the relevant variation in TOA insolation is the globally, and annually averaged value. As a less accurate proxy of GMST, we could estimate regionally averaged temperatures as a function of regionally averaged net TOA flux; and from that estimate a global average temperature. This is less accurate because it ignores the large lateral heat transfers at the Earth's surface due to winds and ocean currents. However, even doing this we must again take a global, annual average. That is, if we assume NH summer temperatures vary with TOA solar flux, then the impact of that variation of GMST must still be averaged over the global surface area to reflect the impact on GMST. Ergo, tatelyle's core argument for higher relevant fluxes is based on the assumption that we are not discussing the effect of Milankovich cycles on GMST (contrary to the clear context in the main post and his initial statement of the issue).

Turning to the relevant forcing for the initiation of glacial melt, tatelyle is quite correct that it should not be globally, or hemispherically averaged. Rather, the value should be considered only over the area of ice melt. Never-the-less, tatelyle's back of the envelope calculations of the value are grossly exagerated. Specifically:

1) tatelyle uses an exagerated estimate of necessary increase in July 65^o N insolation.

tatelyle uses as the baseline of his estimates a 90 W/m^2 change in mean daily insolation in July at 65^o North. He draws that figure from the graph below, but only one of the upswings in summer insolation shown in that graph equals or excedes 90 W/m^2 (and that one did not result in a deglaciation). The mean increase in insolation on that chart, averaged across all upswings, is 60 W/m^2 (or 61 W/m^2 if only the two upswings leading to glaciations are counted). The median is 58 W/m^2 and the 5th percentile is 20 W/m^2. Clearly based on these figures, tatelyle's figure is at least a 50% and potentially a 350% exageration of the July 60^o N insolation necessary for a deglaciation. As the largest insolation upswing did not result in a full deglaciation, it is clear that no value shown on the chart is sufficient for a deglaciation by itself, but that other factors must also be involved.

For what follows, rather than trying to estimate the exact insolation change needed, I have used the deglaciation with the smallest change in insolation, ie, the Holocene deglaciation, as a benchmark. I have calculated the values for the difference in insolation between the inosolation minimum (20 Kya) and respectively, the present, the peak Holocene insolation (9 Kya) and the onset of rapid deglaciation (15 Kya). For insolation figures I have used the data from Berger (1978) as it is considered most accurate for the present (1950) and equivalent to the more recent 1991 calculations out to 800 Kybp. As the data comes by 10 degree latitude band, I have calculated the 65^o N values by taking an area weighted average of the 70^o (75-65^o) and the 60^o (65-55^o) bands. This may result in a small error as an estimate of insolation at 60^o N precisely, but a better estimate of the mean insolation over the band of most significant ice sheet melt. The calculated insolation difference for July at 65oN from the insolation minimum are for 0 Kybp, 9 Kybp and 15 Kybp are respectively, 7.4 W/m^2, 51.5 W/m^2 and 29.2 W/m^2.

2) tatelyle assumes peak montly mean daily insolation over the entire melt season.

As noted, tatelyle's estimate of a 90 W/m2 insolation increase was based on July at 65^o N. The insolation increase in June and August, let alone April and October, is less. As a result the mean daily summer insolation change for 65^o N for LGM to Holocene maximum (20-9 Kybp) is 44.1 W/m^2, 10% less than the July value.

Of course, tatelyle challenges the use of only summer insolation. He considers it obvious that the melt season lasts 40% of the year. That is far from obvious to me. I suspect the melt season depends on latitude, altitude and local conditions. That quibble aside, in Greenland melt occurs between April and October, with the vast majority of the melt occuring in the summer months of June-August. To estimate a melt season, I note that Peter Huybers (2006) notes prior reports that melt is ice ablation correlates with positive degree days, ie, days when the 2 M air temperature rises above 0 degrees. He shows that positive degree days are highly correlated with days when TOA insolation exceeds 275 W/m^2. Using that relationship, I use a melt season consisting of any month in which mean daily insolation averages 275 W/m^2 or more - which turns out to be April-August. So defined, the TOA insolation difference averaged over the melt season at 65^o N turns out to be 2.4 W/m^2 between LGM and present (20-0 Kybp), 32.4 W/m^2 for LGM to Holocene peak (20-9 Kybp), and 25.7 W/m^2 for LGM to onset of rapid deglaciation (20-15 Kybp).

3) tatelyle ignores the effect of albedo.

Being as fair as possible to tatelyle, the 32.4 W/m^2 difference between insolation minimum and maximum is the value he wanted to compute, and is just over his revised estimate of 32 W/m^2. It might appear that his inaccurate calculation has cancelled out the effect of his theoretical errors. This would be the case were it not for his most fundamental error - ignoring albedo.

Solar forcing equals TOA insolation - reflected shortwave radiation at TOA. Therefore, to calculate the equivalent of the CO2 forcing, tatelyle needs to adjust the TOA insolation for albedo. Because in this instance we are examining only the impact over the ice sheets durring the glaciation, and as we are examining the no feedback case (both from tatelyle's hypothesis and because we are examining the regional forcing), the appropriate albedo is ice sheet albedo at the start of the melt season. For Greenland that is 0.835. Adjusting for Albedo then gives us a melt season 65^o N mean daily insolation of 0.4 W/m^2 for the LGM to present (20-0 Kybp), 5.3 W/m^2 for LGM to peak insolation (20-9 Kybp), and 4.2 W/m^2 for LGM to onset of rapid deglaciation (20-15 Kybp). These are overestimates of the relevant values because the calculation does not include the impact of cloud cover, which further reduces the effective mean daily insolation at the top of the ice sheet.

These values (although upper limits) are the best comparitors to tatelyles calculated value of 32 W/m^2. In particular, the difference between the LGM and the onset of rapid deglaciation probably represents the best estimate of the upper limit on the necessary regional insolation forcing change to initiate deglaciation. Based on that, tatelyle overestimates it by 660%.

Note, this is for the change in regional forcing directly impacting on the icesheet. For TOA insolation, his estimate is reasonable, and for global forcing (ie, the most relevant value), the true figure is approximately 1.3 W/m^2 over the melt season and 0.5 W/m^2 averaged over the full years forcing.

PhilippeChantreau at 17:33 PM on 12 October 2015

NASA Retirees Appeal to their Own Lack of Climate Authority

"Character assassination"? Really? Go read WUWT and see how puny we are in that department. Over there, calls for hanging scientists are routine. Posturing is truly better described by rep. Inhoffe bringing a snow ball in the House to argue that climate change isn't happening. That's posturing. So is passing laws that banned public servants from using certain words that pertain to rising sea level because the legislators don't like these words and it's bad for seaside real estate business. Seems you have your scales skewed.

PhilippeChantreau at 17:13 PM on 12 October 2015

NASA Retirees Appeal to their Own Lack of Climate Authority

We are erring on the side of off-topic but since moderators are allowing, I'll follow up. Your humingbird analogy is inappropriate and you qualification of car accident is equally wrong. You don't understand the initial analogy because because you fail to graps the significance of the risk at the scale of an individual vs a population.

You say car accidents are a routine every day occurrence. They are at the level of a population, but not at that of the individual experiencing the accident. For the immense majority of people involved in accidents, they are an extremely rare occurrence. Some find them rare enough that they are confident that it won't happen to them and dispense of insurance. Most people, however do get insurance, not because of the likelihood of the event, but because of dangers involved. For any given person, car accidents are not routine at all. They cause trauma, physical and psychological. They can have very serious consequences, often life changing, and always put a nasty wrench in people's plans.

The initial analogy was about the thought process of an individual assessing his risk and need for an insurance. The probability of the occurrence is low but the implications of it are very significant. Furthermore, the probability is not that low if one looks at the actual numbers, and any individual knows the results of accidents. Therefore, purchasing the insurance is a no-brainer.

At the level of the world population, we need to do the same risk assessment. The people who recently died in floods in the SE US and in France certainly would agree that risk assessment is in order if they could still do so. The fact that most of the New Orleans levees were topped over during Kathrina, the enormous storm surge leading to seawater flooding the NY subway during Sandy, the heat wave in Moscow, the fires in Australia, all these are very real and were either predicted by scientists, or are fully consistent with the theory. We have already reached the level of a continuous background of climate related adverse events. People do die from them and the damages total in the billions.

This makes your hummingbird analogy even more wrong than its sheer absurdity could. We're not talking about a remote risk, dependent on a far fecthed theory at all. We're talking about risk that has already materialized as predicted. We're talking about occurrences happening on a regular basis. How many 1000 years type of events do we need in a decade year for you to understand? How many in a single year?

Your "extreme" mumbo jumbo is completely irrelevant. Responding to future risks identical to some that have already materialized does not constitute extreme risk aversion by any stretch of the imagination. Hence the question about what is extreme, which was in fact entirely justified.

To get back on topic, you still have not come close to demonstrating that the NASA retirees that are the subject of the OP have done a true in-depth examination of the science.

Tom Curtis at 17:08 PM on 12 October 2015

NASA Retirees Appeal to their Own Lack of Climate Authority

zoo58 @62:

"How does one decide whether someone's opinion matters or not?"

1) Your opinion does not matter if you set unrealizable standards for those whose opinion you disagree with. Thus when the letter writers write:

"We, the undersigned, respectfully request that NASA and the Goddard Institute for Space Studies (GISS) refrain from including unproven remarks in public releases and websites."

if by "unproven" they mean lacking deductive proof, they set up an unrealistic standard in that no scientific statement can possibly be proved deductively. Of course, if they are not setting up so unrealistic a standard, NASA already complies with their request in that their public statements on climate are back by comprehensive evidence.

2) Your opinion does not matter if your argument depends essentially on applying a restrictive standard on those you disagree with that you do not accept for yourself. On this count, the NASA contrarian signatories clearly fail. They make numerous claims regarding matters of fact in the letter, and provide not even a single refference in support, let alone "proof". They expect us to take their claim, for example, that NASA's public statements on climate amount to "unbridled advocacy of CO2" on their authority alone. They do not even cite their qualifications to prove their authority, so that we are expected to accept mere interns (Thomas Wysmuller) as authorative simply because they were employed by NASA.

In stark contrast, the public statements by NASA are backed be extensive peer reviewed literature - much of which is available free to the public on the NASA website.

Indeed, it is plain that you also do not accept the standard demanded of NASA. You write, "As distinguished people with related skills and education who have attempted to conduct a non-biased and in-depth examination of the evidence ..." but offer not evidence that all or any have either or both of "related skills and education", that they are "unbiased", or that they have conducted any review of the evidence. Nor will you be able to for such a review is not to be found from most (if not all) of the authors of the letter; and description of NASA's statements as "advocacy" and "extreme" shows without doubt that they are biased.

Tom Curtis at 16:24 PM on 12 October 2015

NASA Retirees Appeal to their Own Lack of Climate Authority

zoo58 @71, in your comment @68 you write:

"The risk analysis involved in something as big as climate change (it truly impacts everything on this planet) is really, truly, extremely complex."

If, as you insist, we shoud interpret your earlier use of "extreme" ("Risk aversion taken to the extreme...") to mean "utter extreme", we must do the same here. Transparently that is not the case, however. Climate, while extremely complex, is not so complex as the action of the brain, the interaction of genes to generate life, or even sociology or psychology. Yet surely your second use emphasises the extremity of the case far more than your first.

We can take home from this that you are mistaken in claiming that your first usage is "...not according to my definition, according to the standard definition of the term...", as your second usage is valid but does not comply with your interpretation of the definition. Your inconsistent usage shows that you do not in fact believe your extremist interpretation of the dictionary definition.

Regardless of your usage, of course, it could simply be pointed out that you have taken one of five senses of the word "extreme" (the fourth sense given) and reified to to be the only usage of the term (at least when it suites your argument). That is, "Risk aversion taken to the extreme" need only mean risk aversion taken to "great or exaggerated lengths" (sense 1b) or risk aversion "exceeding the ordinary, usual, or expected" lengths (sense 1c).

In scientific terms the later woud be glossed as "risk aversion in the upper 5%ile of the population" and the amount of risk aversion needed would be dependent on the distribution of risk aversion in the population. As it is not true that 5% of the population is so risk averse that they never do anything, that also means your original claim is not true.

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