Just browsed through some of the talks from the 2015 WCRP Grand Challenge Workshop at Ringberg.
http://www.mpimet.mpg.de/en/science/the-atmosphere-in-the-earth-system/ringberg-workshop/ringberg-2014/talks.html
Does anyone know if there will be a presentation or more of the discussions presented there soon?
Sleepy,
Thank you very much for the link to the 2015 WCRP Grand Challenge Workshop at Ringberg presentations. Based on my initial review it seems to me that the presenters at the workshop were roughly divided into two camps:
(1) Those who choose to continue the AR5 climate sensitivity assumptions that erred on the side of least drama, in order minimize confrontations with policy makers who wish to make positive happy talk; and
(2) Those who believe that the AR5 climate sensitivity assumptions are biased on the low side, and are working towards presenting a consistent paradigm to match the instrumentation record with more accurate physics of the complex Earth Systems.
As AR5 more than adequately represents the position of the first camp, I only summarize three presentations of researchers in the second camp in the following
The Andrews, Webb & Gregory (2015) presentation correlates different SST patterns [most significantly dominated by the ENSO, where greater El Nino frequency/magnitudes (see the first attached image) result in slower global SST rates of increase and much higher ECS values (up to 5C) due to associated changes in cloud cover in the tropics] have a big impact on modeled ECS values (see the second image & the following extract):
Extract: "- Targeted AGCM experiments with various SST patterns – traceable to AOGCM transient behavior and observations – are a valuable tool in understanding the mechanisms and processes related to time varying feedbacks
- Feedbacks are very sensitive to warming patterns: I can get ECS values from 1.3 to 5K just by changing the warming pattern in HadGEM2!
- HadGEM2--‐A results give some insight into why cloud feedback varies with SST patterns, relates to LTS change for low clouds.
- CMIP5 AMIP experiments forced with observed SST variations give feedback and ECS estimates (~1--‐2K) in agreement with observations.
- Perhaps no discrepancy between models and observational estimates of climate sensitivity after all, its just the historical record estimates are biased low because of variability in SST patterns
- Interesting that emergent constraints do not rely on simple linear feedback model, and give higher ECS estimates (e.g. Sherwood et al., Fasullo & Trenberth), unifies models and various observational ECS estimates?
- Much more to understand and do. Detailed results mostly from a single model. Some of these experiments have been proposed for CMIP6 and/or CFMIP3 – please do them, they are cheap runs, early multi--‐model pilot study welcome!"
The Sherwood (2015) presentation focuses on the influence of aerosols on the radiative forcing over the Southern Ocean (which were not previously recognized). The third attached image show how sulfates can have a big impact on radiative forcing associated with cloud cover over the Southern Ocean; and the fourth image shows that aerosols that caused the ozone hole over Antarctica have caused an increase in cloud cover over the Southern Ocean since the late 1970's (when the ozone hole formed). This indicates that as both the ozone hole heals itself and as anthropogenic sulfate emissions are reduced (due to air pollution control), that we can expect the rate of observed global mean surface temperature increase to accelerate as this major masking factor associated with aerosol emissions is reduced.
Extract: "- We should not assume aerosol effects can only be in the northern hemisphere.
- Possible that greenhouse forcing in SH-extratropics has been negated by aerosol (or sea-ice) increases for some time. Deserves further attention?
- Would help to explain both (a) sluggish recent warming and (b) weird SH-NH contrast since 1979.
- Ozone depletion is the most likely culprit for the wind increase—would make this a rapid adjustment to ozone forcing."
The following extract from Fasullo (2015), indicates that the reconstructions of sea level indicate that estimates of ECS based strictly on the instrument records contain a higher degree of uncertainty associated with long-term natural variability than previously recognized, thus indicating a greater risk that ECS may be at the higher than estimated based strictly on the instrument record.:
Extract: "What are the implications?
Larger uncertainty for ECS estimates from the instrumental record? Confirmation of Stevens et al. 2015?
…
- Interpreting climate sensitivity from the instrumental record depends critically on separating forced changes from internal variability - assumptions regarding internal variability are key, model dependent, and challenging to validate.
- The unprecedented observing system in place during the 2000’s hiatus provides a unique opportunity to understand its causes and evaluate the fidelity of simulated internal variability - though challenges remain.
- Strong parallels exist between the Grand Hiatus and the 2000’s (PDO, GMSL). While multiple generations of climate models have reproduced the hiatus mainly as a forced response, sea level reconstructions suggest that the planetary imbalance was persistent during the event.
- TWS cannot account for the sustained increase in GMSL during the Grand Hiatus. Estimation of cryospheric melt using MDD also does not suggest a major cryospheric contribution."
Very best,
ASLR