## Pielke Sr. and SkS Warming Estimates

#### Posted on 11 October 2011 by dana1981, Albatross

Dr. Roger Pielke Sr. has written a blog post addressing the disagreement between himself and Skeptical Science (SkS) regarding the contribution of CO2 to the net positive anthropogenic radiative forcing. Initially Dr. Pielke cited a presentation he gave in 2006 which said (on slide 12):

"The CO2 contribution to the radiative warming decreases to 26.5% using the IPCC framework given in Slide 9"

This "radiative warming" refers to the human plus natural positive radiative forcings ('natural' being solar). As Dr. Pielke's presentation was given in 2006, before publication of the IPCC Fourth Assessment Report (AR4), his reference to the IPCC is to the Third Assessment Report (TAR) published in 2001. In his new post, Dr. Pielke also references a previous post on his blog on the same subject, which concludes (emphasis added):

"For all of the human-caused warming radiative forcings, which includes the 0.5 Watts per meter squared value for the shortwave albedo change, and estimating tropospheric ozone as 0.3 Watts per meter squared, the aerosol black carbon direct effect as 0.2 Watts per meter squared, the black carbon on snow and ice as 0.3 Watts per meter squared, the semidirect indirect effect as 0.1 Watt per meter squared, and the glaciation indirect effect as 0.1 Watt per meter squared (with the latter two forcings using a nominal value, since these forcings are very poorly known),

the contribution due to CO2 will fall to about 28%."

In this case Dr. Pielke refers to only the human positive radiative forcings, excluding the contribution of solar irradiance.

In short, Dr. Pielke has argued that CO2 contribution to the total positive radiative forcing (since pre-industrial times) is between 26% and 28% (depending on whether solar effects are included), whereas in our previous post, SkS concurred with the AR4 radiative forcing estimates, which put CO2 at approximately 50% of the total positive radiative forcing (nearly twice Dr. Pielke's estimate).

Below we discuss some problems SkS has identified in Dr. Pielke's estimate, and provide a detailed up-to-date estimate of these values. The main underlying problem is that Dr. Pielke is relying on an estimate he made in 2006, failing to account for advances in climate research over the past 5 years, and thus his sources are at least 5 years out of date. Additionally, he appears to have made some mathematical errors in his calculations.

### Methane

Dr. Pielke estimates the radiative forcing from methane at 0.8 Watts per square meter (W/m2), which is significantly larger than the IPCC estimate (both TAR and AR4) of 0.48 W/m2. To support this value, in his 2006 presentation Dr. Pielke references research by "Drew Shindell and colleagues; Keppler et al." (slide 11), and on his blog posts, references Keppler et al. (2006). Keppler et al. do not estimate the methane radiative forcing in their paper - the 0.8 W/m2 figure is Dr. Pielke's estimate based on Keppler et al.'s results.

However, as we noted in our previous post, both the atmospheric methane concentration and radiative forcing are well-known quantities. The IPCC TAR and AR4 best estimates of the methane radiative forcing are 0.48 W/m2, 0.49 W/m2 according to Skeie et al. (2011), and 0.504 W/m2 in 2010 according to the NOAA Annual Greenhouse Gas Index (AGGI). Thus Dr. Pielke's methane forcing estimate appears to be 60% too high.

Additionally, Dr. Pielke appears to have double-counted the methane forcing in his calculations:

"By summing the 0.8 Watts per meter squared for methane and using the total of 2.4 Watts per meter squared of the well-mixed greenhouse gases from the IPCC Report..."

The 0.48 W/m2 methane forcing is included in the 2.43 W/m2 best estimate forcing for well-mixed greenhouse gases in the IPCC TAR (the best estimate is 2.64 W/m2 in the AR4). Thus, summing Pielke's estimated methane forcing (0.8 W/m2) and the IPCC TAR greenhouse gas forcing (2.4 W/m2) double counts the methane forcing.

### Albedo

Dr. Pielke also estimates "*0.5 Watts per meter squared value for the shortwave albedo change*," which is a forcing not included in the TAR or AR4. In his presentation (slide 11), Dr. Pielke claims:

"For the period 2000-2004, a CERES Science Team assessment of the shortwave albedo found a decrease by 0.0015 which corresponds to an extra 0.5 W m−2 of radiative imbalance according to their assessment."

However, there are a number of problems with this estimate. Most importantly, the data in question only cover a period of 4 years. Changes in the Earth's albedo (reflectivity) over a 4-year period tell us little or nothing about changes in albedo over the past century. It's apples and oranges; one is short-term, the other is long-term.

Four years is also simply far too short of a timeframe to ascertain a meaningful trend. From Loeb et al. (2007):

"Commonly used statistical tools applied to the CERES Terra data reveal that in order to detect a statistically significant trend of magnitude 0.3 W m

^{−2}decade^{−1}in global SW TOA flux, approximately 10 to 15 yr of data are needed. "

Additionally, there is significant uncertainty regarding this short-term albedo change (i.e. see Wielicki et al. 2005 and many other papers on the subject). While the CERES data Dr. Pielke references estimated a decrease in the Earth's albedo from 2000 to 2004, albedo change estimates over the exact same timeframe using Project Earthshine data found an even larger ** **** increase** in albedo from 2000 to 2004 than the CERES-estimated decrease.

Loeb et al. (2007) also used a revised version of the CERES data to show that no statistically significant changes in the Earth’s albedo occurred between 2000 and 2005. More recently, Palle et al. (2009) conclude:

"Earthshine and FD [International Satellite Cloud Climatology Project flux data] analyses show contemporaneous and climatologically significant increases in the Earth's reflectance from the outset of our earthshine measurements beginning in late 1998 roughly until mid-2000. After that and to date, all three show a roughly constant terrestrial albedo, except for the FD data in the most recent years"

We should also note that an albedo increase/decrease due to increasing cloud cover would also be accompanied by an increased/decreased greenhouse effect, making the net effect on the climate even more uncertain.

But the bottom line is that in order to incorporate an albedo forcing into these estimates, we must use an estimated albedo change from pre-industrial to Present. We should also investigate the cause of any albedo change to determine if it should be treated as a forcing or as a feedback. If it's a forcing, then it's not anthropogenic, and Dr. Pielke was incorrect to include it in the anthropogenic forcings. If it's a feedback, then it should not be included in the calculation of total forcings at all.

Ultimately, for this calculation, Dr. Pielke's 0.5 W/m2 albedo forcing estimate is unjustified and not supported by more recent observations and scientific literature.

### Black Carbon

Dr. Pielke cites Hansen and Nazarenko (2004) in estimating the albedo effect of soot on snow and ice at 0.3 W/m2, and the net black carbon forcing at 0.5 W/m2. However, as the IPCC AR4 noted three years later, the magnitude of the black carbon radiative forcing remains uncertain. The best estimate of Skeie et al. (2011) of 0.45 W/m2 for the black carbon forcing is in rough agreement with Dr. Pielke's estimate. Ramanathan and Carmichael (2008) give a best estimate for the black carbon forcing at 0.9 W/m2.

In short, the black carbon forcing remains highly uncertain, but Dr. Pielke's estimate is reasonable.

### Tropospheric Ozone

Dr. Pielke's tropospheric ozone forcing estimate is somewhat unclear. He states that the associated forcing is 0.3 W/m2, but the IPCC TAR estimate is 0.35 W/m2, and Dr. Pielke appears to believe the value should be higher:

"Ozone was responsible for one-third to one-half of the observed warming trend in the Arctic during winter and spring [Drew Shindell]"

This release from NASA GISS appears to be the source, from which, if we are interpreting his presentation correctly, Dr. Pielke estimates an additional 0.3 W/m2 on top of the IPCC 0.35 W/m2 tropospheric ozone radiative forcing.

However, there are more recent estimates of this forcing, in addition to the IPCC's 0.35 W/m2 (both TAR and AR4). The best estimate from Skeie et al. (2011) was 0.44 W/m2, and the best estimate from Cionni et al, 2011 (submitted), on which Shindell is a co-author, is 0.23 W/m2. Thus Dr. Pielke's estimate of 0.65 W/m2 appears to be much too high.

### Aerosol Semi-Direct and Indirect Effects

Dr. Pielke also identifies a "glaciation effect" as causing a 0.1 W/m2 forcing, which, in a recent talk, he clarifies as "*An increase in ice nuclei increases the precipitation efficiency*." Lohmann et al. (2007) is a very good paper on this subject, and explains the effect, described as the aerosol indirect effect:

"Global climate model studies suggest that if, in addition to mineral dust, hydrophilic black carbon aerosols are assumed to act as ice nuclei at temperatures between 0 and –35°C, then increases in aerosol concentration from pre-industrial to present times may cause a glaciation indirect effect (Lohmann, 2002a). The glaciation effect refers to an increase in ice nuclei that results in a more frequent glaciation of supercooled stratiform clouds and increases the amount of precipitation via the ice phase. This decreases the global mean cloud cover and allows more solar radiation to be absorbed in the atmosphere. Whether or not the glaciation effect can partly offset the warm indirect aerosol effect depends on the competition between the ice nucleating abilities of the natural and anthropogenic freezing nuclei (Lohmann and Diehl, 2006)."

Lohmann et al. (2007) note that the aerosol indirect glaciation effect is negligible. However, Perlwitz and Mlller (2010) conclude:

"Despite the high complexity and nonlinearity of the microphysical interaction between aerosols and clouds, modeling studies generally indicate that the net effect of this interaction is to reflect more radiation back to outer space [Forster et al., 2007], although recent results show that aerosols acting as ice nuclei could counteract the cooling effect significantly [Storelvmo et al., 2008]. A few observational studies seem to confirm a relation between soil dust aerosols and cloud cover."

In short, the aerosol indirect glaciation effect remains far from clear. Dr. Pielke also identifies the aerosol semi-direct effect, which involves tropospheric aerosols absorbing shortwave radiation, as causing a 0.1 W/m2 forcing. However, the IPCC has not included this as a positive forcing becase

"the semi-direct effect is not strictly considered an RF because of modifications to the hydrological cycle"

Additionally, Lohmann et al. identify the semi-direct effect as most likely causing cooling:

"The semi-direct effect refers to temperature changes due to absorbing aerosols that can cause evaporation of cloud droplets, as was shown in a large eddy model simulation study that used black carbon concentrations measured during the Indian Ocean Experiment (Ackerman et al., 2000). It ranges from 0.1 to –0.5 Wm-2 in global simulations"

The IPCC AR4 also lists the semi-direct effect as "positive or negative" and "small" potential magnitude, and the indirect effect as "positive" and "medium" potential magnitude, where as Dr. Pielke lists both as positive and equal in magnitude (0.1 W/m2). In short, the magnitude and roles of the aerosol semi-direct and indirect glaciation effects in terms of radiative forcings remain far from clear.

### Carbon Dioxide

Dr. Pielke's estimate for the CO2 radiative forcing (1.4 W/m2) is both outdated and not consistent with the value in the IPCC TAR (1.46 W/m2); it appears that he either rounded the value down or eyeballed the IPCC TAR radiative forcing graphic rather than looking up the precise value. However, 1.46 W/m2 was the estimated value in 2001, when the TAR was published. In 2007, when the AR4 was published, the CO2 forcing had already increased to 1.66 W/m2. More recently, the NOAA AGGI estimated the CO2 forcing at 1.79 W/m2 in 2010, and Skeie et al. at 1.82 W/m2.

In other words, the CO2 radiative forcing has increased 25% over the past decade. Some of the other forcing estimates (like tropospheric ozone and black carbon) have changed mainly as a result of new research, but the CO2 forcing has changed as a result of rapidly increasing CO2 emissions and atmospheric concentrations.

As Isaac Held noted,

"I think it is very generally recognized that, for the same global mean forcing, aerosols perturb the mean precipitation field more than do the well-mixed greenhouse gases (WMGGs). So if, up to the present, anthropogenic aerosols and WMGGs have had comparable effects on regional precipitation, say, the WMGG effect will undoubtedly grow and will be essentially irreversible on the time scale of several centuries, in the absence of geoengineering, while the aerosol effect will likely be bounded by its current magnitude, and the WMGGs will dominate."

### Estimated CO2 Contribution

Below we summarize various estimates of the CO2 contribution to the net positive radiative forcing. We believe Dr. Pielke has committed two types of errors: mathematical (double-counting and rounding), and using outdated sources.

We believe the first column is a replication of Dr. Pielke's estimates. The second column corrects Dr. Pielke's math errors by eliminating the double counting of methane, and correcting rounding errors for the CO2 and solar forcings. The third column provides the IPCC TAR estimates which were the basis of Dr. Pielke's estimates, but which, for the most part, we believe are more accurate than Dr. Pielke's suggested values.

The fourth and fifth columns correct for the out-of-date references by using the IPCC AR4 and Skeie et al. (2011) estimates. Bear in mind we have not included the uncertainty ranges - these are all just best estimates of the respective positive radiative forcings (in W/m2).

Forcings | Pielke 2006 | Pielke Math Corrected | IPCC TAR | IPCC AR4 | Skeie 2011 |
---|---|---|---|---|---|

CO2 | 1.40 | 1.46 | 1.46 | 1.66 | 1.82 |

CH4 | 0.80 | 0.80 | 0.48 | 0.48 | 0.49 |

other LLGHGs | 1.00 | 0.49 | 0.49 | 0.50 | 0.51 |

tropospheric ozone | 0.65 | 0.65 | 0.35 | 0.35 | 0.44 |

black carbon | 0.50 | 0.50 | 0.20 | 0.10 | 0.45 |

albedo | 0.50 | 0.50 | 0 | 0 | 0 |

aerosols (semi-direct+indirect) | 0.20 | 0.20 | 0 | 0 | 0 |

stratospheric water vapor | 0 | 0 | 0 | 0.07 | 0.07 |

contrails | 0.02 | 0.02 | 0.02 | 0.01 | 0 |

solar | 0.25 | 0.30 | 0.30 | 0.12 | 0.12 (AR4) |

Total Positive Forcing | 5.32 | 4.92 | 3.30 | 3.29 | 3.90 |

Total Anthropogenic Forcing | 5.07 | 4.62 | 3.00 | 3.17 | 3.78 |

CO2 contribution to Total | 26.3% |
29.7% |
44.2% |
50.5% |
46.7% |

CO2 contribution to Anthropogenic | 27.6% |
31.6% |
48.7% |
52.4% |
48.2% |

If we correct for Pielke's double counting and rounding errors, the CO2 contribution to the total net positive forcing increases to approximately 30%. When we use up-to-date research for all forcings, the CO2 contribution increases to close to 50%, as we originally argued. We again note that this fraction will continue to increase along with continually increasing human CO2 emissions.

### Human Contribution to Global Surface Warming

We are still interested in Dr. Pielke's answer our original question on this subject:

"Approximately what percentage of the global warming (increase in surface, atmosphere, ocean temperatures, etc.) over the past 100 years would you estimate is due to human greenhouse gas emissions and other anthropogenic effects?"

We suggest a back-of-the-envelope answer to this question by applying the probabilistic estimate of transient climate sensitivity by Padilla (2011):

"we find a most-likely present-day estimate of the transient climate sensitivity to be 1.6 K with 90% confidence the response will fall between 1.3–2.6 K"

We can use this range of transient climate sensitivity (alpha = 0.35 to 0.70 K/Wm-2) and scale the transient climate response (we're currently 49% of the way to the radiative forcing associated with CO2 doubling [~1.8 out of 3.7 W/m2]) to estimate the amount of CO2-caused surface warming:

Where F is the radiative forcing. Using the Skeie et al. (2011) CO2 forcing best estimate of 1.82 W/m2 for 2010 and the Padilla (2011) range of transient climate sensitivity parameters, this corresponds to **a CO2 contribution of 0.64 to 1.28°C, with a best estimate of 0.79°C warming of average global surface temperature**.

We can also consider the expected warming for the net anthropogenic forcing, which Skeie et al. estimated at 1.4 W/m2 and the IPCC AR4 estimated it at 1.6 W/m2. Using these two estimates and the Padilla transient sensitivity range yields **a net anthropogenic warming of 0.49 to 1.12°C with a central estimate of 0.65°C warming of average global surface temperature**.

Dr. Pielke, would you concur with these estimated ranges of CO2 and anthropogenic warming?

### Take-Home Message

The main points here are that CO2 is responsible for approximately 50% of the net positive radiative forcing since pre-industrial times (a percentage which will only continue to increase in the future). In the absence of negative forcings, CO2 would have contributed 0.79°C of the 0.8°C observed global surface temperature rise, and hence we would expect the total observed rise to be double that. This tells us that the negative forcings (primarily from human aerosol emissions) have offset approximately 50% of the net positive forcings.

We also found that the net anthropogenic radiative forcing (sum of all positive and negative forcings) accounts for approximately 80% of the observed average surface warming over the past century (~0.65 out of 0.8°C). The other ~20% is a combination of natural forcings (primarily solar), and perhaps a bit of natural variability.

Another key point is that aerosols have a short atmospheric lifetime, unlike long-lived greenhouse gases. Thus their large offsetting of close to 50% of the net positive radiative forcing is only temporary, and will decline rapidly if we reduce aerosol emissions. This is why, as Isaac Held noted in the quote above, we fully expect CO2 and other greenhouse gases to continue as the dominant cause of global warming, and why although we need to address other issues like land use change, CO2 emissions are rightfully the primary target in mitigating climate change.

Tristanat 16:12 PM on 10 October, 2011nealjkingat 19:54 PM on 10 October, 2011Jeffrey Davisat 01:48 AM on 11 October, 2011pielkesrat 02:46 AM on 11 October, 2011KRat 03:24 AM on 11 October, 2011"You also did not discuss that CO2 has been increasing for over a century and some of the CO2 radiative forcing during that period would have been accomodated by the warmer climate. As I wrote, in 2005 V. Ramanthan replied to me (in an estimate) that about 20% of the difference between pre-industrial and current radiative forcing would have been accomodated. Thus the current radiative forcing from added CO2 would need to be reduced by this amount."I would have tostrongly disagree- the radiative forcings discussed here (as in the IPCC AR4, the basis of this discussion) are relative to 1750 pre-industrial forcings,notthe current imbalance (unrealized warming) between temperatures and those forcings. The 20% adjustment you recommend here is an odd (and IMO quite unwarranted) redefinition of well understood terms - shifting the baseline. Unrealized warming and current imbalance are different terms, different values, than forcing changes since 1750.KRat 03:33 AM on 11 October, 2011(rather than the changes since 1750 that are the topic of this thread), it's noteworthy that you cannot just scale the change in CO2 contribution -allradiative imbalances scaled by unrealized warming would be scaled as well, meaning that therelativecontribution of CO2 should not change. Your 20% reduction of relative CO2 contribution is, again, not justified in my view.pielkesrat 03:39 AM on 11 October, 2011pielkesrat 03:42 AM on 11 October, 2011Albatrossat 03:49 AM on 11 October, 2011dana1981at 07:13 AM on 11 October, 2011pielkesrat 09:39 AM on 11 October, 2011Tom Curtisat 09:56 AM on 11 October, 2011dana1981at 10:11 AM on 11 October, 2011Albatrossat 10:13 AM on 11 October, 2011"I calculate that CO2 is ~40% for the anthropogenic positive radiative forcing."First, that value is still significantly higher than the original (and erroneous) claim of 26.5% that he has made on his blog, here and elsewhere in public. Second, Skeie et al. (2011) supersedes Ramanathan and Carmichael (2008), and represents our current level of understanding. Science moves on. Third, from Ramanathan and Carmichael (2008):"The TOA BC forcing implies that BC has a surface warming effect of about 0.5 to 1 °C,So they concede that their method may not be appropriate, or does Dr. Pielke wish us to forget/neglect this important caveat from their paper which he chose to cite?where we have assumed a climate sensitivity of 2 to 4 ºC for a doubling of CO2. Because BC forcing results in a vertical redistribution of the solar forcing, a simple scaling of the forcing with the CO2 doubling climate sensitivity parameter may not be appropriate".NewYorkJat 10:16 AM on 11 October, 2011Philippe Chantreauat 10:54 AM on 11 October, 2011pielkesrat 10:55 AM on 11 October, 2011pielkesrat 10:59 AM on 11 October, 2011pielkesrat 11:01 AM on 11 October, 2011Tom Curtisat 11:43 AM on 11 October, 2011pdtat 12:14 PM on 11 October, 2011pielkesrat 13:40 PM on 11 October, 2011paulhtremblayat 13:43 PM on 11 October, 2011paulhtremblayat 14:12 PM on 11 October, 2011Tom Curtisat 17:53 PM on 11 October, 20111)The IPCC AR4 writes: (My emphasis) Referring back to the IPCC TAR, we find the adjustment to the simple formula was due to the work of Myhre et al, 1998, which in turn depends on intermodel comparisons performed in Myhre and Stordal, 1997 (hereafter, M&S97). In M&S97, Myhre and Stordal perform a detailed series of comparisons between LBL models and a Broad Band Model used at various resolutions. The most detailed resolution used a 2.5^{0}x2.5^{0}grid. The coarsest used a global mean climatology. M&S97 explicitly state that: They go on to describe how the overlap is handled. As the 2.5^{0}x2.5^{0}is global in extent, it necessarily includes the highly humid tropics, and more significantly the very cool polar regions. Later M&S97 compare the 2.5^{0}x2.5^{0}model to a 10^{0}x10^{0}, a 2.5^{0}zonal mean model, a 10^{0}zonal mean model, and a global mean climatology model. The difference in forcing between each of these models is less than 1% in all cases. Further on they explicitly compare CO2 radiative forcing with altitude for Tropical, Mid-Latitude Summer, and Sub-Arctic Winter conditions using both the LBL and Broadband model. The Tropical and Mid-Latitude Summer forcings are scarely distinguishable, with the MLS forcing being slightly stronger. The SAW forcing is considerably weaker than either the TROP or MLS forcing. Of course, as the formula is based on a full global comparison, that is of no consequence to the final figure.2)With regard to whether the IPCC AR4 quotes transient forcings in a given year, or the forcing relative to preindustrial levels, I refer you to this chart: Note the charts heading. For greater clarity, the caption reads: (My emphasis) Lest there be any doubt, based on a pixel count the chart shows a CO2 radiative forcing of 1.67 W/m^2, in agreement with the text. As to what difference this makes, not a great deal. Never-the-less, you brought the question up. You have blogged on the issue at least twice, and have claimed repeatedly that the CO2 radiative forcing is over-estimated when you have in fact been under estimating it. And you have presented your significant underestimate based on your back of an envelope calculation in a talk to a scientific conference. I would have thought that, given the circumstances, professional pride alone would make you wish to correct those errors with alacrity.MA Rodgerat 21:47 PM on 11 October, 2011pielkesrat 23:53 PM on 11 October, 2011pielkesrat 00:01 AM on 12 October, 2011pielkesrat 00:07 AM on 12 October, 2011mdenisonat 00:26 AM on 12 October, 2011critical massat 00:26 AM on 12 October, 2011pielkesrat 00:45 AM on 12 October, 2011Tom Curtisat 01:33 AM on 12 October, 20111)I recommend that you reread my post @25, or better yet, Myhre and Stordal, 1997. As clearly indicated in my post, it was Myhre et al, 1998 who determined the strength of the CO2 radiative forcing by determining the value of the constant in the simple formula for radiative forcing. In doing so they corrected downwards the factor previously used from 6.3 to 5.35. As explained previously, Myrhe et al is built on the detailed model comparisons in Myrhe and Stordal 97, which include a global model run at a 2.5^{o}x 2.5^{o}resolution. That model, because global necessarily included the difference in radiative transfer between tropical and not tropical regions. To further clarify the point,I noted that M&S97 had also run both the broadband model and the LBL model for both tropical and mid-latitude summer conditions, with the latter showing the stronger forcing, clearly showing the effect of increased humidity and cloud cover had been included.To that information, we can add the following quote from the Third Assessment Report: (My emphasis) The Fourth Assessment Report contented itself with saying: (My emphasis) Ramaswamy et al, 2001 is of course, the IPCC TAR. The IPCC do not feel it necessary to spell out details that have been public knowledge for six years (as at the time of the AR4), contenting themselves with a reference to the original discussion. Now, given the detailed analysis by Myhre and Stordal and the explicit statement by the TAR, do you still wish to maintain that the radiative forcing as calculated does not allow for overlap with H2O in the tropics?2)The passage you quoted, it was not a figure caption, did not say otherwise, it just did not specify a fact that was well known. Further, the FAQ plus Fig 2 of the FAQ which I reproduced was not added afterwards. It can be found on page 135 of the PDF reproduction of the original report for anybody interested. What is more, the figure 2.20A on which it is based (page 203) has the same heading. And if that is not enough, we read in the executive summary of Chapter 2: (My emphasis) Seeing you bring up the Summary for Policy Makers, we read there: You will notice the footnote after the introduction of the term "Radiative Forcing". That footnote reads: Should we check the glossary as well, or is my point sufficiently made? This is a very minor, an absolutely trivial point, except for one factor. It is one thing for a Professor of Climatology with, I must add, a very distinguished career, to make a simple mistake on a fact you would expect him to know well. It is quite another to try and save face by making "facts" up. Knowledge is not so often found in this world that it can be thrown away in face saving excercises.pielkesrat 02:45 AM on 12 October, 2011JMurphyat 02:55 AM on 12 October, 2011But when you start with insults because I do not accept your view, I will go off to where more constructive debating occurs.As a matter of interest (and certainly not in a snarky or insulting manner), can you give any examples of where you would get such debating - if you have online sources in mind ? I am genuinely interested.dana1981at 03:00 AM on 12 October, 2011any reasonable calculation based on the agreed-upon inputs will put the CO2 contribution to the net positive forcing at 41% to 50% and rising.You now claim that whether the value is 25% or 50% does not matter, yet you have frequently raised the issue on your blog and in presentations and talks. Ultimately we have identified a number of errors in your calculations, and yet you continue to insist that despite these corrections, somehow your argument must be correct. We have supported our estimate with detailed calculations and references, and have demonstrated that CO2 has thus far accounted for approximately 0.8C surface warming - a calculation which you have not disputed. We are a bit disappointed that this refutation of your reasoning leaves your sense of conviction so unmoved, but at this point, we may as well move on to other issues. Readers can examine our calculations for themselves and decide who is correct.Tom Curtisat 03:35 AM on 12 October, 20111)A LBL (Line By Line) model as used by Myhre et al, 98, and Myhre and Stordal, 97isa one dimensional radiative transfer model, and hence the papers to which I have been referring answer the general point you have been making. They, however, address the practical question of what the radiative forcing is in the real world which includes water vapour. They do not adress the hypothetical question that you ask, ie, what would the radiative forcing of CO2 be in the absence of water vapour. Because the question is purely hypothetical, it is irrelevant to future discussions so I have no interest in doing a literature search in the off chance that somebody has answered this hypothetical. Please note that the radiative forcing of CO2 if there was no overlap with H2O, and the radiative forcing of CO2 in the absence of water vapour are the same, so the slightly different form in which I have expressed the question is of no consequence. The global annual average radiative forcing of CO2 in the presence of H2O with overlaps accounted for in 2005 is the value given by the IPCC in AR4. The value in 2011 is that given by Skeie et al.2)From the glossary of IPCC AR4: (My emphasis) Therefore, according to the glossary, when the IPCC AR4 refers to the radiative forcing for 2005 they mean the change in radiative forcing in 2005 relative to 1750, unless they explicitly state otherwise. That could not be clearer. What is more, the formula for radiative forcing of CO2 is given by the simple formula: ΔF = αln(C/Co), where ΔF is the change in forcing, C is the CO2 concentration in the current year, Co is the CO2 concentration in the inital year, and α = 5.35 (source; also Myhre et al, 98, and various IPCC reports). This is the simple formula referred to in AR4. Clearly from its formula, the radiative forcing requires a baseline year. It is impossible to derive the radiative forcing from this formula for a single year simpliciter for the result would necessarily be 0. Consequently no interpretation of "Radiative Forcing" in AR4 in which it is treated as being the forcing in a single year is consistent with the text which explicitly refers to this simple formula. In other words, not only are you in error in your interpretation of the IPCC AR4, logically your interpretation could not have failed to be in error. Note I say that you are in error because you insist on interpreting the IPCC AR4 as inconsistent whereas in fact you are simply failing to interpret their words in accordance with the glossary.3)You object to what you call my snark. Well I object to the extreme lengths of misrepresentation you are prepared to go to cover up an error. Please note that "misrepresentation" is neither snark nor accusation. It simply notes that you have represented the facts to be one way (the IPCC AR4 was corrected; the IPCC AR4 is inconsistent) when transparently, and as could be discovered by simply reading a glossary, they were another way. You and I are both here trying to reach SkS's audience in order to convince them of what we believe to be the truth about global warming. Fine, I am a great believer in the open market of ideas. But I will not accept a restraint on me that I must not correct your gross errors should they occur (and as has occurred) because such correction will offend our sensibilities. If you cannot debate under the condition that your mistakes will be corrected, then (speaking only for myself), I see little point in debating you.pielkesrat 05:26 AM on 12 October, 2011pielkesrat 05:38 AM on 12 October, 2011pielkesrat 05:55 AM on 12 October, 2011dana1981at 05:57 AM on 12 October, 2011pielkesrat 06:27 AM on 12 October, 2011pielkesrat 06:29 AM on 12 October, 2011paulhtremblayat 06:30 AM on 12 October, 2011paulhtremblayat 06:38 AM on 12 October, 2011KRat 07:04 AM on 12 October, 2011"the radiative forcing requires a baseline year." is not correct. The quote you have states "ΔF is the change in forcing". That does require a base year. The forcing does not and is instantaneous.I will point out that, despite this side-track of current forcing imbalance,the original topic of this threadand the tables that are the basis of the discussionare the numbers for changes in forcing since 1750, as is customary in this field. That is, incidentally, completely clear from the TAR through AR4, as defined in the glossaries, and in labeling of the various tables. In that regard you have repeatedly emphasized a 26.5% relative contribution by CO2 to the forcing deltas, in disagreement with IPCC estimates (here, for example), stating that"The IPCC Has Provided An Inaccurate Narrow Perspective Of The Role Of Humans". At this point in the discussion I believe that dana and Tom Curtis have clearly presented why they disagree. In my opinion you have neither presented either arelevantargument for your factor of ~2x difference with IPCC numbers on total forcing, nor for that matter any numeric estimates ofyoursas to"CO2 ... warming of average global surface temperature over the past century". Perhaps an agreement to disagree on this topic?dana1981at 07:25 AM on 12 October, 2011Conference on the Earth’s Radiative Energy Budget Related to SORCEon September 20-22, 2006, he made the same argument using the same presentation. The presentation has also been featured on several 'skeptic' blogs (i.e. Jennifer Marohasy and JunkScience). And just last month in an interview with a Canadian newspaper (and in our discussions here), Dr. Pielke argued that too much attention is being paid to CO2 - based on our calculations, that's a hard argument to justify. Suddenly claiming that the question is an unimportant one seems like a fairly radical and sudden change, given how frequently Dr. Pielke makes this argument. But as KR suggests, we will probably have to agree to disagree and move on.pielkesrat 09:01 AM on 12 October, 2011MMMat 09:17 AM on 12 October, 2011pdtat 09:29 AM on 12 October, 2011