Serendipity

The IPCC schedule impacts nearly all aspects of climate science. At the start of this week’s CCSM workshop, Thomas Stocker from the University of Bern, and co-chair of working group 1 of the IPCC, gave an overview of the road toward the fifth assessment report (AR5), due to be released in 2013

First, Thomas reminded us that the IPCC does not perform science (it’s job is to assess the current state of the science), but increasingly it stimulates science. This causes some tension though, as curiosity-driven research must remain the priority for the scientific community.

The highly politicized environment also poses a huge risk. There are some groups actively seeking to discredit climate science and damage the IPCC, which means that rigor of the IPCC procedures are now particularly important. One important lesson from the last year is that there is no procedure for correcting serious errors in the assessment reports. Minor errors are routine, and are handled by releasing errata. But this process broke down for bigger issues such as the Himalayan glacier error.

Despite the critics, climate science is about as transparent as a scientific field can be. Anyone can download a climate model and see what’s in there. The IPCC process is founded on four key values (thanks to the advocacy of Susan Solomon): Rigor, Robustness, Transparency, and Comprehensiveness. However, there are clearly practical limits to transparency. For example, it’s not possible to open up lead author meetings, because the scientists need to be able to work together in a constructive atmosphere, rather than “having miscellaneous bloggers in the room”!

The structure of the IPCC remain the same: three working groups: WG1 on the physical science basis, WG2 on impacts and adaptation, and WG3 on mitigation, along with a task force on GHG inventories.

The most important principles for the IPCC are in article 2 and 3:

2. “The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.

3. Review is an essential part of the IPCC process. Since the IPCC is an intergovernmental body, review of IPCC documents should involve both peer review by experts and review by governments.

A series of meetings have already occurred in preparation for AR5:

• Mar 2009: An expert meeting on science of alternative greenhouse gas metrics. The met and produced a report.
• Sept 2009: An expert meeting on detection and attribution, which produced a report and a good practice guidance paper [which itself is a great introduction to how attribution studies are done].
• Jan 2010: An expert meeting at NCAR on assessing and combining multi-model projections. The report from this meeting is due in a few weeks, and will also include a good practice guide.
• Jun 2010: A workshop on sea level rise and ice sheet instability, which was needed because of the widespread recognition that AR4 was weak on this issue, perhaps too cautious.
• And in a couple of weeks, in July 2010, a workshop on consistent treatment of uncertainties and risks. This is a cross-Working Group meeting, at which they hope to make progress on getting all three working groups to use the same approach. In the AR4, WG1 developed a standardized language for describing uncertainty, but other working groups have not yet.

Thomas then identified some important emerging questions leading up to AR5.

1. Trends and rates of observed climate change, and in particular, the question of whether climate change has accelerated? Many recent papers and reports indicate that it has; the IPCC needs to figure out how to assess this, especially as there are mixed signals. For example, the decadal trend is accelerating in Arctic sea ice extent, but  the global temperature anomaly has not accelerated over this time period.
2. Stability of the Western and Eastern Antarctic ice sheets (WAIS and EAIS). There has been much more dynamic change at margins of these ice sheets, accelerating mass loss, as observed by GRACE. The assessment needs to look into whether these really are accelerating trends, or if its just an artefact of limited duration of measurements.
3. Irreversibilities and abrupt change: how robust and accurate is our understanding? For example, what long term commitment have been made already in sea level rise. And what about commitments in the hydrological cycle, where some regions (Africa, Europe) might go beyond the range of observed drought within the next couple of decades, and this may be unavoidable.
4. Clouds and Aerosols, which will have their own entire chapter in AR5. There are still big uncertainties here. For example, low level clouds are a positive feedback in the north-east Pacific, yet all but one model are unable to simulate this.
5. Carbon and other biogeochemical cycles. New ice core reconstructions were published just after AR4, and give us more insights into regional carbon cycle footprints caused by abrupt climate change in the past. For example, the ice cores show clear changes in soil moisture and total carbon stored  in the Amazon region.
6. Near-term and long-term projections, for example the question of how reliable the decadal projections are. This is a difficult area. Some people say we already have seamless prediction (from decades to centuries), but not Thomas is not yet convinced. For example, there are alarming new results on number of extreme hot days across southern Europe that need to be assessed – these appear to challenge assumptions about the decadal trends.
7. Regional issues – eg frequency and severity of impacts. Traditionally, the IPCC reports have taken an encyclopedic approach: take each region, and list the impacts in each. Instead, for AR5, the plan is to start with the physical processes, and then say something about sensitivity within each region to these processes.

Here’s an overview of the planned structure of the AR5 WG1 report:

• Intro
• 4 chps on observations and paleoclimate
• 2 chps on process understanding (biogeochemistry and clouds/aerosols)
• 3 chps from forcing to attributions
• 2 chps on future climate change and predictability (near term and long term)
• 2 integration chapters (one on sea level rise, and one on regional issues)

Some changes are evident from AR4. Observations have become more important. They grew to 3 chapters in AR4, and will keep the same in AR5. There will be another crack at paleoclimate, and new chapters on: sea level rise (a serious omission in AR4); clouds and aerosols; the carbon cycle; and regional change. There is also a proposal to produce an atlas which will include a series of maps summarizing the regional issues.

The final draft of the WG1 report is due in May 2013, with a final plenary in Sept 2013. WG2 will finish in March 2014, and WG3 in April 2014. Finally, the IPCC Synthesis Report is to be done no later than 12 months from WG1 report, ie. by September 2014. There has been pressure to create a process that incorporates new science throughout 2014 in to the synthesis report, however Thomas has successfully opposed this, on the basis that it will cause far more controversy if the synthesis report is not consistent with the WG reports.

The deadlines for published research to be included in the assessment is as follows. Papers need to be submitted for publication by 31 July 2012, and must be in press by 15 March 2013. The IPCC has to be very strict about this, because there are people out there who have nothing better to do than to wade through all the references in AR4 and check that all of them appeared before the cutoff date.

Of course, these dates are very relevant to the CCSM workshop audience. Thomas urged everyone not to leave this to the last minute; journal editors and reviewers will be swamped if everyone tries to get their papers published just prior to the deadline [although I suspect this is inevitable?].

Finally, here is a significant challenge in communication coming up. For AR5 we’re expecting to see a much broader model diversity than in previous assessments, partly because there are more models (and more variants), and partly because the models now include a broader range of earth system processes. This will almost certainly mean a bigger model spread,  and hence a likely increase in uncertainty. It will be a significant challenge to communicate the reasons for this to policymakers and a lay audience. Thomas argues that we must not be ashamed to present how science works – that in some cases the uncertainties multiply, during which the spread of projections grows, and then when we get the models more constrained by observations they converge again. But this also poses problems in how we do model elimination and model weighting in ensemble projections. For example, if a particular model shows no sea ice in the year 2000, it probably should be excluded as this is clearly wrong. But how do we set clear criteria for this?