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The Fourth IPCC Assessment Report

by nanne Thu Feb 15th, 2007 at 07:49:56 AM EST

On the second of January, the Intergovernmental Panel on Climate Change (IPCC), a large body of scientists established by two United Nations agencies, released the first details of its fourth assessment report.

The IPCC's fourth assessment report will come in three main parts. One part will deal with the scientific basis, another with vulnerabilities, and yet another with options for curbing climate change. What we have now is the summary for policymakers of the report on the scientific basis. This is an 18-page summary of what will eventually become a 400 page document. Obviously, it does not contain all the scientific information that is relevant for policy-making.

Following the publication of the summary for policymakers, a debate has ensued on whether or not the fourth assessment report is more or less alarmist than the third. This debate is premature, as the estimates of the damages climate change will cause are contained in the second part of the report, which is expected to be released in early April. It's also a silly debate to have.

Bumped/promoted by DoDo & whataboutbob

Nonetheless, a short side-by-side comparison of the findings of the two reports can be instructive for understanding what the IPCC really says. At the core of the third assessment report's predictions on the range of future surface warming are six scenarios, taken from the IPCC's special report on emissions scenarios. These scenarios are crucial for understanding what the report actually states, so with that in mind here is a brief out-take from that report:

By 2100 the world will have changed in ways that are difficult to imagine - as difficult as it would have been at the end of the 19th century to imagine the changes of the 100 years since. Each storyline assumes a distinctly different direction for future developments, such that the four storylines differ in increasingly irreversible ways. Together they describe divergent futures that encompass a significant portion of the underlying uncertainties in the main driving forces. They cover a wide range of key "future" characteristics such as demographic change, economic development, and technological change. For this reason, their plausibility or feasibility should not be considered solely on the basis of an extrapolation of current economic, technological, and social trends.

  • The A1 storyline and scenario family describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building, and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income. The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis: fossil intensive (A1FI), non-fossil energy sources (A1T), or a balance across all sources (A1B).
  • The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in continuously increasing global population. Economic development is primarily regionally oriented and per capita economic growth and technological change are more fragmented and slower than in other storylines.
  • The B1 storyline and scenario family describes a convergent world with the same global population that peaks in midcentury and declines thereafter, as in the A1 storyline, but with rapid changes in economic structures toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, but without additional climate initiatives.
  • The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social, and environmental sustainability. It is a world with continuously increasing global population at a rate lower than A2, intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines. While the scenario is also oriented toward environmental protection and social equity, it focuses on local and regional levels.

The estimation in the third assessment report (TAR) contains a range of estimates of the average level of wordlwide surface temperature change in the year 2100 on these scenarios that runs from 1.4 to 5.8 degrees celsius, depending on different models. The range of estimates in the fourth assessment report (AR4) runs from 1.1 to 6.4 degrees celsius in the 2090-2099 period, including estimates of 'likely' scenarios. Such probabilistic estimates were not available in the third assessment report, so these numbers represent different methodologies.

I'll hazard the guess that the "best estimates" for the scenarios in AR4 can be compared to the harmonised estimates in TAR. The numbers:


This represents something of a minor downward adjustment. On the other hand, the generalised range of "likely" temperature changes according to the summary for policy makers is 2 to 4.5 degrees, which is the exact same range as that for the harmonised estimates for the scenarios in the TAR.

Other issues.

It has been noted here that the IPCC uses optimistic estimates of the world's fossil fuel resources and therefore would project temperature changes that are unrealistic. However, I think that these estimates will only really be relevant for the A1FI scenario.

There is a notable lag between the emission of carbon dioxide and the effect it has on surface temperatures and carbon dioxide is not the only relevant greenhouse gas (it is expected to account for about 55% of total current warming, the other gases account for about 30%). The IPCC report also has a "best estimate" of the temperature change for a scenario where the athmospheric concentrations of all greenhouse gases remain equal to 2000 levels, and that is 0.6 degrees celsius. This reflects the lag between the level of atmospheric concentration and the associated warming, and also the degree to which the process of global warming has become self-driving.

The degree to which climate change is self-driving increases with the expected temperature increase, for the A2 scenario the IPCC estimates that feedbacks in the carbon cycle alone will cause more than 1 degree of  the warming. In order to stabilise at a given level of warming in 200 to 300 years, disproportionate cuts in emissions are necessary and this imbalance will increase the longer we postpone these cuts.

Another controversy has been raised over the expected degree of sea level rise (see this post by Roger Pielke Jr.). Near as I can tell, the estimate has decreased from a maximum of 0.88 meters rise to 0.79 meters assuming a linear increase of the degree of melting with the degree of temperature change. It seems that the TARs numbers used that method. So-called "dynamic effects" like "changes due to changes in ice streams, calving, grounding line movement" are not included in either of these numbers, but these effects are now thought to be potentially significant. At the time of the third assessment report, they were largely judged to be negligable. Dynamic effects are not included because the science on the topic is not yet fully established.

Because of changed methodologies, a more precise characterisation of the fourth assessment report is only possible once the first part of the report has been released. A complete discussion of the desired policy responses can be had once we have the second and third parts of the report.

AR4 Summary for Policymakers (.pdf)

IPCC Reports page

Adapted from this comment.
by nanne (zwaerdenmaecker@gmail.com) on Sun Feb 11th, 2007 at 05:12:22 PM EST
Just dropping off stuff...

At Roger Pielke Sr.'s blog entry:

As discussed on Climate Science, when climate metrics are investigated in detail, the reality of the real world often conflicts with the pronouncements of the climate assessments. With respect to glaciers, this mismatch between reality and the assessments has been presented before (see and see).

The weblog for today provides yet another example of the incomplete information that is being communicated to policymakers and others.

An article in the November-December 2006 issue of the Earth Observer entitled “The GLIMS Glacier Inventory of the Antarctic Peninsula” by Frank Rau,  Jeffrey S. Kargel,  and Bruce H. Raup provides an update on the recent behavior of glaciers in the northern Antarctica peninsula (see the November-December pdf on pages 9-11). This is a region where significant regional surface temperature warming has been recorded.

An excerpt from their article, however, shows that the response of the glaciers is more complex in response to this reported regional warming. They write,

“Analysis of high resolution ASTER data co-registered to Landsat Thematic Mapper ™ and Enhanced Thematic Mapper Plus (ETM+) data provide information on glacier front variations between the years 1986 and 2002. In regional case studies, more than 300 glaciers were examined, covering a variety of glacial systems distributed over the northern Antarctic Peninsula. Of these, only 40 (12.8%) displayed advancing glacier fronts accounting for a gain of 7.1 km², while 171 (54.6%) showed retreating ice fronts accounting for a loss of 146.1 km². In addition, 102 (32.6%) were found to be in invariant conditions. The glaciers examined displayed no indications of dynamic flow instabilities. The observed glacial variations are therefore interpreted as direct consequences of the rapidly changing climatic conditions in the region that are affecting accumulation and ablation.

Beyond the overall trend toward retreating ice fronts, observations dating from the mid 1980s to 2001 reveal different patterns of glacier variation across the Antarctic Peninsula. An area of significant retreat is concentrated on the northeastern sectors of the peninsula-- eastern coast of Trinity Peninsula and James Ross Island. Similarly, a consistent distribution of predominant glacial recession is also identifiable along the southwestern coasts of the study area--Graham Coast, Loubet Coast and Marguerite Bay. Thisis in sharp contrast with glacier frontal positions recorded in northwestern parts of the Antarctic Peninsula adjacent to Bellingshausen Sea, where only slight recessions and minor advances were recorded--western coast of Trinity Peninsula and Danco Coast. These observations from the northwest, which are presumed to be in the natural range of frontal fluctuations of tidewater glaciers, suggest relative dynamic stability of the glacial systems in this sector.”

This article indicates that 45.4% of the glacier fronts are either advancing or are invariant over the period from the 1980s to 2001. While the retreating glaciers have lost more area than has been gained by the advancing glaciers, this also need to be placed in context of the total area of the glaciers in this region (which was not done in this article).

Nonetheless, even without that information, the general message that glaciers are receding almost everywhere is clearly not accurate when the data is evaluated in detail.

by Nomad (Bjinse) on Mon Feb 12th, 2007 at 04:16:10 AM EST
To compare & contrast, this is what the IPCC's summary for policy makers says on the topic:
Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea level rise (ice caps do not include contributions from the Greenland and Antarctic ice sheets)

New data since the TAR now show that losses from the ice sheets of Greenland and Antarctica have very likely contributed to sea level rise over 1993 to 2003 (see Table SPM-1). Flow speed has increased for some Greenland and Antarctic outlet glaciers, which drain ice from the interior of the ice sheets. The corresponding increased ice sheet mass loss has often followed thinning, reduction or loss of ice shelves or loss of floating glacier tongues. Such dynamical ice loss is sufficient to explain most of the Antarctic net mass loss and approximately half of the Greenland net mass loss. The remainder of the ice loss from Greenland has occurred because losses due to melting have exceeded accumulation due to snowfall.

I see no 'mismatch' here. The report clearly states that glaciers are retreating 'on average' and notes the relative balance between the melting of ice and increased precipitation in Antartica and Greenland. Clearly, the glaciers on the Antartic peninsula are also retreating on average.

A map of the peninsula can be found here. Note that the 300 glaciers represented in the study are all 'case studies' that do not necessarily represent more than a sample of the total glacier area (the question by Pielke Sr. about the significance of the loss in the context of the total glacier area would otherwise probably have to be answered with 'miniscule').

by nanne (zwaerdenmaecker@gmail.com) on Mon Feb 12th, 2007 at 02:11:36 PM EST
[ Parent ]
  1. Beyond what nanne says about the supposed claim of all glaciers receding, I don't understand why Roger Pielke Sr. didn't further consider the stark regional differences. Could it be that local geologic features ensure a 'heat insulation' for glaciers there? Say, shielding by the South Shetland Islands?

  2. Why does the ratio of glacier surface loss to total glacier area matter? The way I understand it, the mass loss of a glacier is in significant part thinning, not just shortening.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Feb 14th, 2007 at 09:12:14 AM EST
[ Parent ]
Alex Steffen takes stock of the IPCC reception and consequences on WorldChanging.

Some outtakes and comments:

Climate commitment -- the fact that the actions we've already taken have doomed us to a very serious set of changes to our planet's climate, with disastrous results -- will require us, in some ways, to keep two contradictory ideas in mind at the same time: on the one hand, we need to fight like hell to reduce our carbon emissions to prevent disastrous climate change from turning into an unprecedented catastrophe for human civilization; on the other hand, we have to acknowledge that disaster is upon us, and start preparing our systems to be rugged enough for a world of rising seas, droughts and floods, ecological instability and mass migrations of refugees.

For example, planners in the Bay Area have begun to worry about the costs of dealing with rising sea levels; engineers in Seattle are running studies to anticipate the degree to which this city's water supply (which comes mostly from meltwater from the nearby, snowy Cascade mountains) will be impacted by drier, hotter summers; while in British Columbia, the Royal Canadian Mounted Police is bracing itself for possible Katrina-like chaos and floods of climate refugees.

This discussion is right and true on the main issue: mitigation and adaptation are two things that both need to be undertaken to a much greater extent. Seeing the strategies as being competitive is a grave strategic error and the main reason why environmentalists (with whom I sort of identify) dislike advocates of adaptation like many conservative pundits, neoclassical economists, Lomborg, Pielke jr., etcetera. Of course it also holds that some environmentalists view the strategies as being competitive, which is as much of an error.

However, Alex skirts the main issue of adaptation, which is the extent to which and the way in which rich countries (who are responsible for climate change) provide assistance to poor countries (who will experience the brunt of the impacts).

What's more, while we're heartened by the media's generally good reporting on the severity and unanimity of the IPCC's conclusions, we're a bit disappointed that more reporters haven't picked up on the fact that the IPCC's conclusions are baselines, conservative findings they were sure they could scientifically defend (and in some cases, even less bold than that) and (as Gil wrote yesterday), many serious scientists believe that the most accurate climate models suggest we can expect to see much more dramatic effects, much more quickly, particularly as regards how quickly the seas will rise. Worse, there has been little acknowledgment that some of the major wildcards, like the possible release of massive amounts of methane from melting permafrost, or a huge change in the climate functions of the ocean due to acidification leads to (as Andy Revkin puts it) "a more than a 1-in-10 chance of much greater warming, a risk that many experts say is far too high to ignore.

The IPCC report only assesses "likely" climate change, which in its high emissions (A1FI) scenario goes up to 6.4 degrees (worst case). Generalised, the "likely" climate change goes up to 4.5 degrees celcius. Likely climate change, I think, is climate change which has a >2 out of 3 chance of happening under a single scenario. (This I would guess based upon the use of the word "likely" in the context of current warming). That unlikely warming isn't assessed in the policy makers summary is justifiable IMO. What is to be done about unlikely warming depends upon your views on the precautionary principle. As a green, you'd see it pertaining mainly to the earth and its creatures (our symbiotic planet, gaia, whatever floats yr boat), as a conservative/neoliberal you'd see it pertaining mainly to the market economy.
Carbon blindness should be a constant concern as well: climate change is dire, but it is far from the only problem we face, and if we attempt to tackle it abstractly apart from the myriad of interconnected challenges which face us, we will fail. If nothing else, the climate crisis should teach us that ignoring the big picture and the long term is ruinous to any society. What we need now is not only action, but action with an eye to holistic connections and long-term results. We have a sustainability crisis, of which our destabilization of the climate is but one symptom. We need not just a climate solution, but a bright green future.

Hear, hear!
by nanne (zwaerdenmaecker@gmail.com) on Fri Feb 16th, 2007 at 06:44:53 AM EST

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