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Modeling roundup No rest for the laureates: Preparing for round five of IPCC

Less than two years after lead scientists on the Intergovernmental Panel on Climate Change celebrated their sharing of the Nobel Peace Prize with Al Gore, they’re back to heavy lifting once again. The next IPCC assessment report (AR5) is due in 2013. That means participants around the world are hard at work preparing for a new round of massive climate simulations.

At NCAR, the big push has been to prepare CCSM for century- and decadal-scale runs that scientists will undertake from late 2009 through 2010 in support of AR5. The core physical model for version 4.0 of CCSM will be released later this year, along with a host of improvements to various components. The pieces are falling into place a bit more slowly than originally expected, but the primary goal—to have a version of CCSM with interactive carbon cycling ready for the AR5 simulations—remains within sight, says NCAR’s Peter Gent, project lead and head of the CCSM steering committee.

CCSM version 3.5 already features a much-improved depiction of the El Niño/Southern Oscillation, which has bedeviled climate modelers for years. A 2008 Journal of Climate analysis led by Richard Neale (ESSL/CGD) describes how the model’s treatment of showers and thunderstorms across the tropical Pacific has been improved. With the help of this and other boosts, CCSM 3.5 now more accurately pegs the interval between El Niño events, which had been showing up about every two years in CCSM (in nature, it’s every three to seven years).

The atmospheric component of CCSM 4.0 will include a few tweaks beyond 3.5, with several major enhancements on hold until developers have had more time to test their inclusion. Version 4.0 also comes with a newly upgraded set of ocean, land, and sea-ice models, including new code for the interaction between urban areas and the atmosphere. “The component models have really come along,” says William Large, head of NCAR’s Climate and Global Dynamics Division.

Close to 300 people will get a sneak preview of CCSM 4.0 at the 14th Annual CCSM Workshop, to be held in Breckenridge, Colorado, on 15–18 June. Later this year, the interactive carbon-cycle component will be folded into CCSM 4.0. Other permutations, including a version with interactive chemistry, will also be finalized over the next year. The multidecadal runs—one of the most-anticipated parts of the next IPCC assessment—will likely draw on these enhanced versions, says Gent. Scientists will be tackling such questions as how air quality in megacities might evolve by 2030. “People are keen to use the extra components for some of these runs,” he says.


Correlation betweem sea surfact temperatures inside and outside the Nino3 region

These charts analyze the correlation between sea surface temperatures inside and outside the Niño3 region (white box). CCSM 3.5 (middle) does a better job than its predecessor, CCSM 3.0 (bottom), in reproducing patterns observed in nature (top, from the Hadley Centre), including the inverse correlation between Niño3 readings and those near Indonesia. (Illustration courtesy Richard Neale.)

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