Wednesday, July 11, 2012

Missing News: Natural Variability

A few recent articles not reported on by ABC Science. For some reason covering papers that document natural variability in the climate is anathema to the ABC.

Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation
Chylek et al, 2012
GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L09705, 6 PP., 2012 doi:10.1029/2012GL051241
Key Points
The past history of the AMO is preserved in ice core data
The dominant quasi-periodicities are those of 20 years and 45-65 years
The origin of 20-year periodicity is Atlantic and of 45-65 year the Arctic

Climatic variations over the last 4000 cal yr BP in the western margin of the Tarim Basin, Xinjiang, reconstructed from pollen data
Keliang Zhao et al
Palaeogeography, Palaeoclimatology, Palaeoecology Volumes 321–322, 1 March 2012, Pages 16–23
► New pollen records for the last 4000 cal yr BP in the western Tarim Basin. ► Four humid and three dryperiods were identified in the study region. ► Increase in the strength of the westerlies resulted in the three humid periods. ► The climate was warm and dry during the early MedievalWarmPeriod (AD 690–1110).

Effects of Medieval Warm Period and Little Ice Age on the hydrology of Mediterranean region
Markonis, Y.; Kossieris, P.; Lykou, A.; Koutsoyiannis, D.
EGU General Assembly 2012, held 22-27 April, 2012 in Vienna, Austria., p.12181
Medieval Warm Period (950 - 1250) and Little Ice Age (1450 - 1850) are the most recent periods that reflect the magnitude of natural climate variability. As their names suggest, the first one was characterized by higher temperatures and a generally moister climate, while the opposite happened during the second period. Although their existence is well documented for Northern Europe and North America, recent findings suggest strong evidence in lower latitudes as well. Here we analyze qualitatively the influence of these climatic fluctuations on the hydrological cycle all over the Mediterranean basin, highlighting the spatial characteristics of precipitation and runoff. We use both qualitative estimates from literature review in the field of paleoclimatology and statistical analysis of proxy data series. We investigate possible regional patterns and possible tele-connections with large scale atmospheric circulation phenomena such as North Atlantic Oscillation, Siberian High, African Sahel Rainfall and Indian Monsoon.

A multiproxy palaeolimnological study of climate and nutrient impacts on Esthwaite Water, England over the past 1200 years
The Holocene January 2012 vol. 22no. 1 107-118
Xuhui DongHelen BennionRichard W. BattarbeeCarl D. Sayer
The response of diatom assemblages to changes in climate and nutrients over a 1200 year timescale was investigated by means of a multiproxy sediment core study involving radiometric dating, diatoms, grain size, loss on ignition and geochemical analysis. Four stages of environmental change were defined, each being consistent with changes in documented human activity and known climate patterns. From AD 750 to 880 relatively high nutrient status and a cold, unstable climate was inferred based on the high abundance of Aulacoseira subarctica and high Na/K and Na/Al values. In the following 1000 years (AD 880–1880) diatom assemblages were dominated byCyclotella comensis, Cyclotella radiosa and Achnanthidium minutissimum, suggesting a long period of relatively low productivity and, by implication, that climate was the main control on the community during this period. Two climatic phases, namely the ‘Medieval Warm Period’ (MWP) and the ‘Little Ice Age’ (LIA), were apparent. According to shifts in the diatom assemblages and other proxies, it was proposed that the MWP was initiated from ~AD 880 and was terminated by the LIA at ~AD 1350. After AD 1880 the palaeoecological data revealed a period of strong human impact in the catchment and hence higher productivity. This work illustrates the complexity of climate–nutrient interactions and the roles of the two drivers on different timescales and at various stages of the lake’s history: climate impacts were more pronounced when nutrient concentrations were relatively stable prior to ~AD 1880; while nutrients appeared to play a more important role in regulating diatom communities from the mid-eighteenth century.

No comments:

Post a Comment

Please keep to the topic. Abusive comments and bad language are simply not tolerated. Note that your comment may take a little while to appear.

Note: Only a member of this blog may post a comment.