(1) St.Petersburg Branch (Filial) of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowaves Propagation of RAS, St.-Petersburg, Russia, (2) Ioffe Physico-Technical Institute of RAS, St.Petersburg, Russia. O.M. Raspopov (1), V.A. Dergachev (2), LONG-TERM SOLAR ACTIVITY VARIATIONS AS A STIMULATOR OF SHARP CLIMATE CHANGES International Conference “50 years of International Geophysical Year and Electronic Geophysical Year”, September, 2007, Suzdal, Russia

It is known that deep solar activity minima are accompanied by sharp climate changes. For example, the Maunder minimum of solar activity ( ) stimulated the beginning of the Little Ice Age. Goal of the presentation: to give experimental evidence that not only deep solar activity minima, but also a high solar activity level can lead to sharp global climate changes through stimulation of dynamic processes at the Earth’s surface.

Long-term cyclicity of solar activity ● 11-year cycle of sunspot numbers (Schwabe) ● year cycle of solar magnetic polarity changes (Hale) ● year cycle of amplitude modulation of 11-year cycles (Gleissberg) ● year cycle (~210-year - deVries) ● year cycle (Hallstattzeit)

Record of variations of sunspot numbers W. Evidence of 11-, , and year solar activity variations year cycle year cycle 11-year cycle

Relation between variations of sunspot numbers W and variations of galactic cosmic ray fluxes

10 Be Recording of cosmic rays and Recording of cosmic rays and cosmogenic isotopes generation cosmogenic isotopes generation Atmosphere 10 Be Galactic cosmic rays  14 C Earth surface 14 СО 2 Neutron monitor

Variations of 14 C concentration in tree-rings and the Earth’s magnetic dipole moment during the Holocene Geomagnetic dipole Maunder minimum Homeric minimum ~ years minimum ~7200 years minimum The Holocene

Maunder minimum Homeric minimum ~ years minimum ~7200 years minimum Low solar activity High solar activity Δ 14 C Variations of 14 C concentration in tree-rings and the Earth’s magnetic dipole moment during the Holocene Variations of 14 C concentration relating to solar activity year variations of 14 C concentration

High solar activity The Holocene Low solar activity Variations of aerosols in Greenland ice year cyclicity in atmospheric circulation Global glaciers extension Swiss alpine glaciers retreat year solar cyclicity ( Δ 14 C variations filtered in year period range) Long-term solar activity variations and climate change during the Holocene

Changes in high-latitude timber line location in Scandinavia and Canada Changes in high-latitude timber line location in Finnish Lapland Reconstructed summer temperature changes in Finnish Lapland Changes in high-latitude timber line location in northern Sweden Number of dated subfossil trees collected in northern Finnish Lapland Changes in high-latitude timber line location in northern Canada Reconstructed summer temperature changes in northern Canada Timber line change in Scandinavia and Canada shows cold time intervals similar to glacier expansion time intervals

What could be reason for sharp cooling events during the high solar activity time intervals? Possible reason: ice-rafting events in the North Atlantic during Ice Age and the Holocene developed during warm climate condition (high solar activity) Ice-rafting event abruptly change the North Atlantic overturning circulation and displace the position of northern edge of the Gulfstream to the South and develop of sharp climatic cooling.

Ice-rafting events during the Holocene [Bond et al. 2002]

Changes of solar activity and ice-rafting events during the Holocene High solar activity Solar activity (Δ 14 C) Low solar activity Ice-rafting events (IRE) Grand solar activity minima Beginning of IRE correlate well with time intervals of high solar activity and sharp climate changes

Sharp climate changes during the Pleistocene: Dangard-Oeschger and Henrich events

Solar activity ( 10 Be), temperature changes, and ice-rafting events development over the past 40 ky in the North Atlantic region Solar activity Temperature changes Ice-rafting events Sharp climate changes correlate well with solar activity variations and development of ice-rafting events

Conclusion The influence of long-term solar activity variations on climatic parameters at time scales from 40,000 to 10,000 years ago (the Pleistocene) and from modern period to 10,000 years ago (the Holocene) has been analyzed. Comparative analysis of temperature oscillations and solar activity variations (variations in the concentration of cosmogenic 10 Be isotopes in Greenland ice and 14 C isotopes in tree rings) has revealed the solar influences on climate of two kinds. On the one hand, deep solar activity minima create conditions for sharp climate changes with the 2,400-2,300-year periodicity that manifest themselves in the most pronounced way during the Holocene. On the other hand, a high solar activity level and, hence, a high level of solar irradiance gives rise to dynamic processes at the Earth’s surface, such as ice-rafting events in the North Atlantic. Computer simulation has shown that these ice-rafting events can be caused by an increase in the surface ocean temperature, i.e., the condition created by high solar activity and solar irradiance levels. Ice-rafting events sharply change the character of the North Atlantic overturning circulation (NAOC), thus displacing the Northern edge of the Gulf Stream southwards, which leads to sharp climate changes of the global nature. Analysis of the experimental data has shown that a high solar activity level was responsible for development of ice-rafting events during both the Pleistocene and Holocene. Therefore, it can be concluded that both deep solar activity minima and a high solar activity level can create conditions for sharp climate changes.

Conclusion Проведен анализ воздействия долговременных вариаций солнечной активности на климатические параметры на временных шкалах от до лет назад (плейстоцен) и от современной эпохи до лет назад (голоцен). Сравнительный анализ температурных изменений и вариаций солнечной активности (вариации содержания космогенных изотопов 10 Be в гренландском льду и 14 C в кольцах деревьев) выявил двоякого рода солнечное воздействие на климатические изменения. С одной стороны, глубокие минимумы солнечной активности создают условия для резких климатических изменений, проявлявшихся особенно четко в голоцене с летней периодичностью. С другой стороны, высокий уровень солнечной активности и, следовательно, солнечной иррадиации создают условия для развития процессов на земной поверхности, а именно, массового сброса ледниковых масс в Северную Атлантику (ice-rafting events). Результаты моделирования свидетельствуют, что подобные сбросы ледяных масс могут быть стимулированы повышением поверхностной океанической температуры, т.е. условиями, создаваемыми высокой солнечной активностью и высоким уровнем солнечной иррадиации. Ice-rafting events резко изменяют характер North Atlantic overturning circulation (NAOC), отодвигая северную оконечность Гольфстрима к югу, что приводит к резким климатическим изменениям глобального характера. Проанализированные экспериментальные данные свидетельствуют, что высокий уровень солнечной активности стимулировал развитие ice-rafting events как в плейстоцене, так и в голоцене. Таким образом, как глубокие минимумы солнечной активности, так и высокий уровень солнечной активности могут создавать условия для развития резких климатических изменений.