One-trick-ponies point over-and-over again to the modern observational record that is dominated by the faux hiatus period from say 1999 to say 2013 to promote low values of climate sensitivity. Clearly this record is not long enough to get a clear (low noise) climate sensitivity signal that accounts for such factors as the PDO cycle (we have just entered a positive phase of this cycle & thus do not yet have the benefit of data from the full positive phase of this cycle, while the faux hiatus period does include a full negative phase of the PDO cycle), anthropogenic aerosols, ocean heat uptake & ocean thermal inertia, volcanoes, incomplete instrument coverage (particularly in the polar regions as indicated by Cowtan & Way). This is why since the beginning of this thread I have recommended focusing on improving state-of-the-art ESMs in order to get an appropriately inclusive estimate of climate sensitivity (note that the AR5 Carbon Budget does not use climate sensitivity values based on the CMIP5 projections (with a mean ECS of 3.4C) but rather uses its "process" that is subject to manipulation by one-trick-ponies to reduce this down into ECS values in the 3 to 3.2C range).
In this light while Goddard Space Center (headed by Gavin Schmidt) was heavily involved in the CMIP5 modeling effort, and thus one would expect Gavin Schmidt to support the likely 2.1 to 4.7C ECS range reported for the CMIP5 projections; nevertheless, after the Ringberg workshop at the linked RealClimate web article below; after considering all of the extant evidence Schmidt increased this likely range for ECS to 2 to 5C (with a mean value of 3.5C). I note that Gavin Schmidt's increased likely ECS range includes his evaluation of recent input from Sherwood, Fasullo, Marvel, Geoffroy, Stevens, Lewis, etc; but many not have included consideration of the Trenbreth et al (2015) finding as Trenbreth & his co-authors did not present at the Ringberg workshop. Furthermore, one-trick-ponies too frequently hide behind the uncertainties remaining about the impact of aerosols, while Shindell & others are working to cut this uncertainty in half by 2030.
http://www.realclimate.org/index.php/archives/2015/04/reflections-on-ringberg/Turning to the weather related positive feedback vapor signal identified by Trenberth et al (2015) no CMIP5 model had a sufficiently fine model mesh resolution to appropriately account for the impact of this weather related vapor signal positive feedback (that is likely connected to tropical deep atmospheric convection that can only be properly modeled by use of a high resolution mesh); which is why I suspect that the ACME program (with higher resolution) will demonstrate a still higher climate sensitivity than that emergent from the CMIP5 projections. In this regard, I remind the readers that while the ACME program runs 10-days, the company Kitware has been hired by the DOE to focus, in the first 3-year phase, on three key goals [focused on water cycle, biochemistry, and cryosphere systems].
http://www.prweb.com/releases/2015/02/prweb12539509.htmExtract: "For each science driver, a question was selected to be answered in a three-year time range. Further questions will be answered over the course of the 10-year project. Questions to be answered in the next three years include: How will more realistic portrayals of features important to the water cycle (resolution, clouds, aerosols, snowpack, river routing, and land use) affect river flow and associated freshwater supplies at the watershed scale? How do carbon, nitrogen, and phosphorus cycles regulate climate system feedback, and how sensitive are these feedback to model structural uncertainty? Could a dynamical instability in the Antarctic Ice Sheet be triggered within the next 40 years?
In regards to the water cycle, ACME’s Project Strategy and Initial Implementation Plan states that changes in river flow over the last 40 years have been dominated primarily by land management, water management, and climate change associated with aerosol forcing. During the next 40 years, greenhouse gas (GHG) emissions in a business-as-usual scenario will produce changes to river flow.
As the plan states, a goal of ACME is to simulate the changes in the hydrological cycle, with a specific focus on precipitation and surface water in orographically complex regions such as the western United States and the headwaters of the Amazon.
To address biogeochemistry, ACME researchers will examine how more complete treatments of nutrient cycles affect carbon-climate system feedback, with a focus on tropical systems, and investigate the influence of alternative model structures for below-ground reaction networks on global-scale biogeochemistry-climate feedback.
For cyrosphere, the team will examine the near-term risks of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice sheet grounding lines.
The experiment would be the first fully-coupled global simulation to include dynamic ice shelf-ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica."