Terrestrial Palaeoecology and Global Change

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Chapter 7. Climate change 263 Table 5. Four-phase climate cycles of different scales. Climate stages as in Table 3. Phase Ma Neogene Ka Holocene Century Historic CH 1.8 Piacenzian/ Calabrian WH 4.3 Zanclean WD 6 Messinian XXI-XXII Near future CD 9.5 Tortonian 0.7 Sub-Atlantic XIX-XXI Modern CH 13 Serravallian 3.5 Sub-Boreal XIII-XIX II Little Ice Age WH 16 Llangian 4.5 Atlantic IX-XII Viking Warming WD 19.5 Burdigalian 6.8 Boreal IV-VIII Great Migrations CD 21 Aquitanian 11 Younger Dryas I-III I Little Ice Age The present-day warming repeats that of the 1940’s with a brief cooling event in between – the minor fluctuations over the CD/WD transitional interval. The millennial dynamics suggests that we have at least about two centuries of mid-latitude WD before us. The following interpretation of a lower-rank four-stage climatic cyclicity (Fig. 106) for a glacial climate (as argued in VII.3, the climate was mildly glacial over most of the Phanerozoic history) is derived from the theory of atmospheric disturbance as a leading factor of climate change (Lorenz, 1967; Palmen & Newton, 1969; Wallace & Blackmon, 1983). WH: Glacioeustatic sea-level rise and melting of sea-borne ice enhance the maritime polar front surges, resulting in an intense mid-latitude cyclogenesis. The meridional heat transfer is intensified decreasing the temperature gradient. The atmospheric pCO 2 level rises with SST and the expanding thermocline. CH: Polar ice caps expand owing to snowfalls brought by cyclonic air masses to Arctic lands. The polar atmospheric fronts advance with the snow cover. The Arctic air surges push cyclonic vortices to the lower mid-latitudes entailing an increase in precipitation and expansion of forests. The atmospheric pCO 2 level drops with SST and afforestation. CD: Meridional heat transfer is restricted by the advancing polar fronts. The tropical/ temperate temperatures diverge: an overheating of the tropical zone is accompanied by a cooling of the temperate zones. Later in the phase, the ice caps shrink in consequence of a reduced snowfall. WD: Outbreaks of overheated tropical air shift the subtropical highs to the mid-latitudes where the persistent meridional anticyclone/cyclone couples are formed (Wallace & Blackmon, 1983). Their blocking of the westerlies (as observed in the northern midlatitudes during El-Nño: Davidson et al., 1990) results in deforestation of continental interiors and a build-up of atmospheric CO 2 (also recorded during the El-Niño). The four-phase model implies an autocyclic restriction of meridional heat transfer resulting in overheating of the tropical zone – cooling over the mid-latitudes, with consequences for land biota and the carbon cycle. A restricted heat exchange generates zonal temperature anomalies that are resolved by atmospheric disturbances stirring an interzonal heat transfer. This mechanism explains the abruptness of climate changes, a phe-
264 Valentin A. Krassilov. Terrestrial Palaeoecology Fig. 106. A schematic interpretation of four-phase climate cycle over tne northern mid-latitudes related to the shifting positions of polar front (PF), southern front (SF), cyclonic/anticyclonic air masses, and the alternative roles of the ocean as sink or source of atmospheric CO 2 .
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Terrestrial Palaeoecology and Global Change

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