Saturday, September 28, 2013

IPCC Press release

Here is the yesterday's official press release from the IPCC:

Human influence on climate clear, IPCC report says

STOCKHOLM, 27 September - Human influence on the climate system is clear. This is evident in most regions of the globe, a new assessment by the Intergovernmental Panel on Climate Change (IPCC) concludes. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.

Warming in the climate system is unequivocal and since 1950 many changes have been observed throughout the climate system that are unprecedented over decades to millennia.  Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850, reports the Summary for Policymakers of the IPCC Working Group I assessment report, Climate Change 2013: the Physical Science Basis, approved on Friday by member governments of the IPCC in Stockholm, Sweden. “Observations of changes in the climate system are based on multiple lines of independent evidence. Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased,” said Qin Dahe, Co-Chair of IPCC Working Group I.

Thomas Stocker, the other Co-Chair of Working Group I said: "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."

“Global surface temperature change for the end of the 21st century is projected to be likely to exceed 1.5°C relative to 1850 to 1900 in all but the lowest scenario considered, and likely to exceed 2°C for the two high scenarios,” said Co-Chair Thomas Stocker. “Heat waves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions,” he added.

Projections of climate change are based on a new set of four scenarios of future greenhouse gas concentrations and aerosols, spanning a wide range of possible futures. The Working Group I report assessed global and regional-scale climate change for the early, mid-, and later 21st century. “As the ocean warms, and glaciers and ice sheets reduce, global mean sea level will continue to rise, but at a faster rate than we have experienced over the past 40 years,” said Co-Chair Qin Dahe. 

The report finds with high confidence that ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010.

Co-Chair Thomas Stocker concluded: “As a result of our past, present and expected future emissions of CO2, we are committed to climate change, and effects will persist for many centuries even if emissions of CO2 stop.”

Rajendra Pachauri, Chair of the IPCC, said: “This Working Group I Summary for Policymakers provides important insights into the scientific basis of climate change. It provides a firm foundation for considerations of the impacts of climate change on human and natural systems and ways to meet the challenge of climate change.” 

These are among the aspects assessed in the contributions of Working Group II and Working Group III to be released in March and April 2014. The IPCC Fifth Assessment Report cycle concludes with the publication of its Synthesis Report in October 2014. 

“I would like to thank the Co-Chairs of Working Group I and the hundreds of scientists and experts who served as authors and review editors for producing a comprehensive and scientifically robust summary. I also express my thanks to the more than one thousand expert reviewers worldwide for contributing their expertise in preparation of this assessment,” said IPCC Chair Pachauri.

The Summary for Policymakers of the Working Group I contribution to the IPCC Fifth Assessment Report (WGI AR5) is available at or

Key Findings

See separate Fact Sheet of Headline Statements from the WGI AR5 Summary for Policymakers, available at


Working Group I is co-chaired by Qin Dahe of the China Meteorological Administration, Beijing, China, and Thomas Stocker of the University of Bern, Switzerland. The Technical Support Unit of Working Group I is hosted by the University of Bern and funded by the Government of Switzerland.

At the 28th Session of the IPCC held in April 2008, the members of the IPCC decided to prepare a Fifth Assessment Report (AR5). A Scoping Meeting was convened in July 2009 to develop the scope and outline of the AR5. The resulting outlines for the three Working Group contributions to the AR5 were approved at the 31st Session of the IPCC in October 2009. The Summary for Policymakers of the IPCC WGI AR5 was approved at the Twelfth Session of IPCC Working Group I meeting in Stockholm, Sweden, 23 to 26 September 2013 and was released on 27 September.

The Final Draft of the Working Group I report (version distributed to governments on 7 June 2013), including the Technical Summary, 14 chapters and an Atlas of Global and Regional Climate Projections, will be released online in unedited form on Monday 30 September. Following copyediting, layout, final checks for errors, and adjustments for changes in the Summary for Policymakers, the full report of Working Group I will be published online in January 2014 and in book form by Cambridge University Press a few months later.

The Working Group I assessment comprises some 2,500 pages of text and draws on millions of observations and over 2 million gigabytes of numerical data from climate model simulations. Over 9,200 scientific publications are cited, more than three quarters of which have been published since the last IPCC assessment in 2007. In this IPCC assessment report, specific terms are used to indicate the assessed likelihood of an outcome or a result. For those terms used above: virtually certain means 99–100% probability, extremely likely: 95–100%, very likely: 90–100%, likely: 66–100%. For more information see the IPCC uncertainty guidance note: note.pdf

For more information, contact: IPCC Press Office, Email: Jonathan Lynn, + 41 22 730 8066 or Werani Zabula, + 41 22 730 8120 IPCC Working Group I Media Contact, Email: Pauline Midgley, +41 31 631 5620


@ReinerGrundmann said...

The fifth report uses a different methodology for model calculations compared to AR4, called Representative Concentration Pathways (RCPs). The main difference is that effects from climate policies are included in the estimate of future greenhouse gas emissions. This information is captured in what the IPCC calls scenarios.

Here are the two different ranges for combined equivalent CO2 concentrations in 2100:

'Approximate carbon dioxide equivalent concentrations corresponding to the computed radiative forcing due to anthropogenic greenhouse gases and aerosols in 2100 (see p. 823 of the TAR) for the SRES B1, A1T, B2, A1B, A2 and A1FI illustrative marker scenarios are about 600, 700, 800, 850, 1250 and 1,550 ppm.'

This is a range from 600-1,550 ppm.


'Most of the CMIP5 and Earth System Model (ESM) simulations were performed with prescribed CO2 concentrations reaching 421 ppm (RCP2.6), 538 ppm (RCP4.5), 670 ppm (RCP6.0), and 936 ppm (RCP 8.5) by the year 2100. Including also the prescribed concentrations of CH4 and N2O, the combined CO2-equivalent concentrations are 475 ppm (RCP2.6), 630 ppm (RCP4.5), 800 ppm (RCP6.0), and 1313 ppm (RCP8.5).'

This is a range from 475-1,313ppm.

I wonder if the lower range of projected global average surface temperature increase (1.5°C to 4.5°C compared to 2°C to 4.5°C) is due to this change in methodology.

Also, AR5 states that is 'extremely unlikely [to see] less than 1°C (high confidence), and very unlikely [to see] greater than 6°C (medium confidence)'.

Compare this with the corresponding text in AR4:

'It is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.'

In sum, would this indicate that the IPCC predicts a lower climate sensitivity because it assumes that climate policies will be effective? Or am I missing something?

eduardo said...

@ Reiner,

'In sum, would this indicate that the IPCC predicts a lower climate sensitivity because it assumes that climate policies will be effective? Or am I missing something?#

No, climate sensitivity and climate policies are not related. Consider a spring: the stiffness of the spring is the climate sensitivity. The forced with which you pull is the forcing (CO2) concentrations, etc). The stiffness of the spring is a intrinsic physical property.
However, the attained temperature (deformation of the spring) does depend on both, its stiffness and how strong you pull

Günter Heß said...

Dear Mr. Zorita,

from a scientific point of view you are correct, but
the definition of equilibrium climate sensitivity (ECS) of the IPCC is the analog of your deformation of the spring.

What you call climate sensitivity the IPCC calls climate sensitivity factor.

Best regards
Günter Heß

Günter Heß said...

Sorry, probably climate sensitivity parameter.

eduardo said...

Lieber Herr Hess,

I do not agree, and I am afraid you are not correct in this point. The IPCC defines climate sensitivity as the deformation of the spring for a prescribed pull strength. This is another way to express the stiffness of the spring. If I pull the string with another strength its sensitivity does not change, the deformation of course does.

The climate sensitivity does not depend of how much CO2 we emit (or how strongly we pull the string). It is an intrinsic property of the climate system, and in theory it could be calculated from first principles, without emitting CO2.

Günter Heß said...

Dear Mr. Zorita,

yes, of course, I said you are correct. But you have to look at the IPCC terms and sort it out.
„Climate sensitivity In IPCC reports, equilibrium climate sensitivity refers to the equilibrium change in the annual mean global surface temperature following a doubling of the atmospheric equivalent carbon dioxide concentration. ....
The climate sensitivity parameter (units: °C (W m–2)–1) refers to the equilibrium change in the annual mean global surface temperature following a unit change in radiative forcing.“
This is what the IPCC writes in AR 4 under Climate Sensitivity.
A climate sensitivity should be expressed in units of °C/(W/m2).
Climate sensitivity is sometimes called by the IPCC a climate sensitivity parameter.
What the IPCC calls equilibrium climate sensitivity is in fact a equilibrium climate response.
The IPCC writes indeed in another paragraph:
„Climate Feedback Parameter A way to quantify the radiative response of the climate system to a global surface temperature change induced by a radiative forcing (units: W m–2 °C–1). It varies as the inverse of the effective climate sensitivity.“
So the IPCC jumps around in its definition, which is fine for me, I can check the context.
However, for the sake of clarity I would give another advice.


Günter Heß said...


In AR 5 SPM:

"The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales."

I assumed Reiner Grundmann refered to this equilibrium climate sensitivity, which I would directly call response.

eduardo said...

Lieber Herr Hess,

Let us not discuss about definitions now. The point at discussion now is the sentence by Reiner:

'In sum, would this indicate that the IPCC predicts a lower climate sensitivity because it assumes that climate policies will be effective? Or am I missing something? '

Reiner includes this sentence in the context of climate sensitivity = temperature change under 2xCO2). I think you would agree that Reiner is mistaken here, and that climate policies do no affect climate sensitivity

Günter Heß said...

Dear Mr. Zorita,
Yes, this must be clear,
climate sensitivity in °C/(W/m2) is a intrinsic property of the climate system.
However, different climate policies lead to a different equilibrium response in °C of the climate system, which the IPCC in its wisdom calls "equilibrium climate sensitivity" (ECS) in °C.

Best regards
Günter Heß

Günter Heß said...

My last sentence needs to read:
However, different climate policies lead to a different equilibrium response in °C of the climate system, which the IPCC in its wisdom calls "equilibrium climate sensitivity" (ECS) in °C in the case of doubling CO2.

eduardo said...

lieber Herr Hess,

could you please explain how climate policies can change ECS = temperature change in the case of doubling CO2 ?

Anonymous said...

Reiner you are muddling 2 slightly different things. 1 - the 2100 estimate which depends on the RCP. 2 - the climate sensitivity which is nothing to do with the RCP as Eduardo says.

Anonymous said...

It is unfortunate that the low estimate of these 2 different quantities is 1.5C, hence it is easy to confuse them.

Anonymous said...

Hallo Herr Grundmann

"The fifth report uses a different methodology for model calculations compared to AR4, called Representative Concentration Pathways (RCPs). The main difference is that effects from climate policies are included in the estimate of future greenhouse gas emissions. This information is captured in what the IPCC calls scenarios."

Ich glaube, hier liegen Sie falsch, das hat mit den Effekten von Klimapolitik erst mal gar nichts zu tun.

Wenn ich es richtig verstanden habe, sind die RCPs ein Fortschritt, die Ergebnisse von verschiedenen Klimamodellen besser vergleichen zu können, woraus dann schließlich CMIP5 resultierte.

Das Problem mit den alten Szenarien (SRES) war, dass sie auf gesellschaftlichen und ökonomischen Annahmen beruhend beispielhafte Szenarien für die künftigen anthropogenen CO2-Emissionen entwarfen. Das Problem war, dass verschiedene Modelle damit nicht automatisch dieselben CO2-Emissionspfade besaßen, da der Kohlenstoffzyklus unsicher ist und unterschiedlich in die Modelle implementiert ist.
Gleiche menschliche Emissionen hatten also in den CMIP3 Modellen verschiedene CO2-Konzentrationspfade zur Folge.

Diesen Nachteil hat man mit den RCPs beseitigt, die Vergleichbarkeit steigt.
Umgekehrt gilt aber, dass mit einem RCP nicht automatisch die Mitigationsziele festgelegt sind, ein Beispiel dazu: Wenn in einem Modell mit RCP6.0 die Fähigkeit der Landfläche abnimmt, eine Senke für CO2 zu sein, dann müsste man die CO2-Reduktionen sogar verschärfen, um auf diesem Pfad zu bleiben.

Wenn ich falsch liege, dann würde ich Eduardo bitten, korrigierend einzugreifen.


@ReinerGrundmann said...

Thanks Eduardo, I can see where I went wrong. However, I was baffled by IPCC's (apparently new) approach to include policy interventions into scenarios. This is something they did not do before, hence my question if the IPCC takes successful climate policues into account; not in terms of climate sensitivity (my error) but in terms of future equilibrium temperatures in 2100.

Günter Heß said...

Dear Mr. Zorita,

I didn’t say that. Instead I said, the IPCC calls the the equilibrium climate response to a doubling of CO2, equilibrium climate sensitivity or ECS.
And that in general the response depends of course how much CO2 we put into the air.

Best regards

eduardo said...

@ 14

Ja, Andreas hat im großen und ganzen Recht, obwohl die Details etwas komplizierter sind.
im AR4 hatten sehr wenige Modelle ein eingebautes Kohlenstoffkreislaufmodell. Die Emissionen mussten also von einem anderen Modell, in der Regel, dem Bern Modell, in Konzentrationen umgesetzt werden. Das war so eine Art ad-hoc Lösung. Das Problem, denke ich, lag daran, dass die Ökonomen nur Emissionspfaden vorschreiben konnten. Diesmal ist diese Frage etwas einfacher und das IPCC hat schon Konzentrationen und auch weniger Szenarien, vorgeschrieben. Es machte nicht so viel Sinn, ca 50 Szenarien von der Welt in 2100 sich auszumalen. Ich denke, die jetzigen RCP sind auch als eine Art 'Beispiele' zu verstehen - der Name sagt das ja schon: Representative Concentration Paths

Alex Harvey said...

Hi all,

So what do people actually think of this Summary for Policymakers? It rather reads in a number of places like political advocacy to me.

What on earth is their increased confidence that man caused most of the warming since 1950 based on? In 2001, they said this proposition was "likely" - 66%. And in 2001, it was believed that sulfate aerosol pollution caused the cooling of 1950-1976, and Co2 caused the rapid warming of 1976-1999. Given that we can now see that the warming stalled at 1999, one would think that the proposition is far less likely now than it was in 2001.

Richard Lindzen has said,

" I think that the latest IPCC report has truly sunk to level of hilarious incoherence. They are proclaiming increased confidence in their models as the discrepancies between their models and observations increase.

Their excuse for the absence of warming over the past 17 years is that the heat is hiding in the deep ocean. However, this is simply an admission that the models fail to simulate the exchanges of heat between the surface layers and the deeper oceans. However, it is this heat transport that plays a major role in natural internal variability of climate, and the IPCC assertions that observed warming can be attributed to man depend crucially on their assertion that these models accurately simulate natural internal variability. Thus, they now, somewhat obscurely, admit that their crucial assumption was totally unjustified.

Finally, in attributing warming to man, they fail to point out that the warming has been small, and totally consistent with there being nothing to be alarmed about. It is quite amazing to see the contortions the IPCC has to go through in order to keep the international climate agenda going."

Lindzen's comments sound very reasonable to me?

Alex Harvey said...

Sorry, I mean the first part of Lindzen's statement sound reasonable. I'm not sure I agree with the final paragraph. :)

Pekka Pirilä said...


We know from empirical data that the average surface temperature is about 0.6 C higher in 2010 than in 1951. Over that same period CO2 c0ncentration has risen from 310 ppm to 390 ppm. log(390/310)/log(2)=0.33.

Half of the total warming is 0.3C, dividing that by 0.33 gives 0.9C. Thus the following statements are equivalent:

1) Most ot the warming from 1951 to 2010 is due to increasing CO2 concentration.

2) The transient climate response applicable for the period 1951-2010 is more than 0.9C

The climate response (CR) of 2) is likely to be close to the TCR defined by IPCC, the slightly shorter period lowers the value, but the slower annual rate of increase (0.4% rather than 1%) increases it. Put together the effects largely cancel.

When the increase of other GHGs is added, the required CR is reduced to perhaps 0.8 C.

Several approaches used to estimate TCR have consistently given lower limits of 0.8 C or more, some of them with 95% certainty.

Based on the above the statement of IPCC seems to be technically correct and justified by observational data.

In the same way the other part of their statement that the best estimate of GHG based warming is close to the total warming is also correct based on the analyses available.

Another question is, whether the particular formulation is appropriate. I don't like it, but would rather like to see estimates of TCR replacing it as the primary way of telling about the empirically determinened strength of GHE.

Hans von Storch said...

I think the formulation "Human influence on climate clear" is not very helpful, as it may be read as "the science is settled", and some activists will use this assertion as including the usual scare folklore on, e.g., hurricanes and storm extremes.

What is meant is "the fact that human activity leads to warming and some other changes, is clear"