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We could infer a secular decreasing trend in the poloidal to toroidal solarmagnetic flux amplification factor ( Af) using geomagnetic observations (classic and IHV corrected aa indices) during the sunspot cycles 9-23. A similardecreasing trend is also observed for the solar equatorial rotation (W) whichimply possibly a decrease in the efficiency of the solar dynamo during theabove period. We could show correlated changes of Af and extreme space weatheractivity variations near earth since the middle of the 19th century. Indirectsolar observations ( solar proton fluence estimates) suggests that the distinctenhancements in extreme space weather activity , Af and W found during sunspotcycles 10 to 15 is probably largest of that kind during the past 400 years. Wefind that the sunspot activity can reach an upper limit (R<300) when Af becomesunity. If the current sunspot cycle 24 turns out to be weak then very severespace weather conditions is most probable to occur during this cycle.  Key words: Flux amplification,solar dynamo, space weather, predictions,cycle24

Secular Changes in Solar Magnetic Flux Amplification Factor and Prediction of Space Weather