A few notes before I lose track of today’s event.
Stephen Schwartz’ presentation was essentially a re-statement of recent publicized JGR paper with some interesting additional commentary. Schwartz’ recent paper attempted to unpack the almost definitional equation:
He then showed the IPCC diagram summarizing forcings, observing the change from IPCC TAR in forcing estimates in which aerosols were estimated at -1.2 (range -2.4 to -0.6) wm-2, resulting in total forcings having a range of 0.6 to 2.4 wm-2, observing that the range was a factor of 4. He then showed the IPCC ensemble which had a very narrow range, wondering how the range in model output could be less than the range of forcings.
HE then discussed Kiehl 2007 (recently discussed here at CA) which observed an anticorrelation between climate sensitivity and aerosol forcing history, observing that the forcings and sensitivities should cover the full range.
HE then discussed the estimate of forcing sensitivity based on his article, noting that the sensitivity depended on the heat capaciy of the ocean and the response time.
One of the puzzles for climate models has been that temperature increases in the 20th century have been less than GHG models indicate – the discrepancy is usually blamed on aerosols or said to be “in the pipeline”. The “pipeline” in this case is ocean heat capacity which SChwartz estimated in ballpark terms at 1& +- 7 W yr m-2 K-1, equal to about 100 m of water.
He estimated response time using autocorrelation functions, citing “Einstein’s fluctuation theorem”. This gave a response time of about 5 years, which combined with the ocean heat capacity estimate, gave a much lower sensitivity than conventionally thought. He said that the response time estimate was the most sensitive and that a response time of 15 years or so yielded 1.5 deg K. He acknowledged that his calculations had been criticized. IT’s not clear/unlikely that the data set meets the stationarity assumptions necessary for his methodology.
He noted that the aerosol forcing from his method worked out to about – 0.3 wm-2 in the 20th C.
Ramanathan spoke on atmospheric brown clouds. Ramanathan is not as famous as Hansen, but, as far as I can tell, he is the originator of the 4 wm-2 forcing for doubled CO2. I always ask critics to provide an exposition of how doubled CO2 leads to 2.5 deg K; nobody seems to be able to answer: Ramanathan’s papers from the 1970s are where I’d start and I’ve been unable to locate any better expositions.
More recently Ramanathan raised the issue of “anomalous atmospheric absorption”, something that he believes to be resolved by aerosols and soot, which have been his recent interest. He’s been involve in some major and sophisticated measurement programs.
Determining the impact of aerosols is complicated by the fact that there are several types of aerosols with different properties. Some absorb in the atmosphere, some scatter, some reflect. HE stated categorically that aerosols had redistributed energy from the surface to the atmosphere and that:
1) they accounted for dimming of 5-10% in Asia
2) masked about 50% of surface warming in S Asia;
3) forcing was asymmetric;
4) brown cloud and soot forcing may have as large a role as GHGs in warming in Himalayas
5) brown clouds were also an (lesser) effect in the US
plus other points.
While critics have observed that aerosols seem to have been a deus ex machina solution for the failure of the climate to warm as much as the models predict and while the handling of aerosols in the GCMs seems opportinistic according to Kiehl’s results, the opportunism doesn’t mean that the effect doesn’t issue. Although it seems a formidable problem at present to develop an objective 20th century aerosol forcing history.
A discussion of aerosol optical depth in the US over the past 10 years, observing that the highest aerosol depth was in the SE; that aerosol decreased in the East, increased in the west; however he observed that the western increase was related to upward spikes in some years, which was associated with wildfires.
Presented an interesting and original theory of why N and S hemispheres moved in parallel in Milankowitch scale. He pointed out (and I’d not seen this before) that NH summer intensity follows exactly the same pattern as SH summer duration and thus attribution to one rather than the other cannot be done on statistical grounds. He suggested that SH Milankowitch warming could be accounted for by SH summer duration better than NH export.
He made an interesting distinction between NH and SH glaciers: that Antarctica was so cold that glaciers ablated in the sea by calving and the response was arguably to summer duration; while NH glaciers ablated on land (Greenland) and thus more sensitive to summer intensity. So a symmetric response could be achieved by an asymmetric response.
A discussion of methane time series. Methane sources are from wetlands, predominantly in the NH but also S America. GISP2 dO18 levels are very level through the Holocene, while methane levels decline in the early Holocene and have increased in the late Holocene ( the latter increase attributed by Ruddiman famously to early anthropogenic effects.) GISP2 and Siple Dome series were compared.
A discussion of loess records. Showed a high-resolution record from Nussloch, Germany with grain size index. Argued that this series was characteristic to less deposits. Showed a section from a quarry with nicely distinctive sediments in Holocene and Eemian.
Discussed some high-res records: Lake Huguang Maar, China; Cariaco, Meerfeld Maar, Germany, observing similarities.
Argued that central American rainfall was linked to Greenland moisture source. PRoxies discussed: Hulu Cave, Mora Cave MI-2 Burns 2003, GRIP 2001, Cariaco Ti, Costa Rica stalgmite CT-6, ocean MD95-2042, MD95-2040, GeoB 3910-2, LEa et al Gapapagos, Leduc et al, Hodell Peen Itza, SChmidt et al CAribbean.
Argued tha GRIP dD excess and Costa Rica rainfall linked. Also that SST differences between Atlantic and Pacific proxies (SChmidt minus Lea) was important to rainfall in Costa Rica.
discussed the role of tropical SST to medieval drought in the US. Suggested that droughts in 1130-70, 1240-65, 1856-65 and 1932-5 had common cause. Model-based results.
discussed Chinese speleothems: Shanbao, Hulu Dongge. Compared Hulu cave to Vostok methane; that 65N insolatin had beautiful match to speleothem series.
presentation of Peten Itza sediments, a new sediment series, especially PI-6, 71 m. Mag susceptibility is key series. LGM pollen (in thick clay units) showed cool and moist, oak and pine forest. Discussed proxies OCE 326, SU8118, CAriaco, PI-6.
Discussed African proxies: Lake Malawi drilling, a hole at 592 m. A 383 m hole covered 150 kyr. The last 70000 years were a deep lake and anoxic; the previous 70000 years were quite different, had a shallow lake. The sequence was different than at NH latitudes.
Observed the very srong coherence between Makassar Mg-Ca series and Antarctic dO18 – r2 of 0.84 without fiddling. Indeed this relationship between unrelated proxies is something that is very impressive. He observed that his indicated a coherence between Antarctic and tropical proxies, arguing against primacy of NH high latitude forcing at Milankowitch scake. He argued that forcing originated in the Southern Ocean and was transmitted globally through CO2.
These notes are spotty, enough for now.