Rapid Caspian Sea Level Change, and How to Prepare for Natures Trend Breaks
by
Salomon B. Kroonenberg
Delft University of Technology

Three times in the last century Caspian shore dwellers were caught by surprise. In 1929 Caspian Sea level, until then rather stable at -26 m below oceanic level, unexpectedly started to drop strongly, over two metres in less than fifteen years. Harbours silted up, rivers extended their courses downstream, wetlands desiccated, and sturgeons hardly could reach their spawning grounds anymore, recalling disasters like that of the Aral Sea in the more recent past. Plans were made to divert northwards flowing rivers in northern Russia and Siberia towards the Caspian, and a dam was built to isolate Kara Bogaz Bay from the Caspian. Scientists predicted sea level fall would continue. But in 1977, when sea-level had dropped already three metres, the Caspian suddenly started to rise, at a rate of 13 cm per year, a hundred times the present eustatic sea-level rise in the oceans. Relief soon turned into concern. Villages were inundated, people had to evacuate, infrastructure built on recently emerged terrain was destroyed, soils suffered salinization, wildlife habitats drowned, and Kara Bogaz Bay was hastily reopened. Plans were made to divert sea water to the drying Aral lake. Scientists predicted that sea level would continue to rise. But in 1995 sea level, now back at -26 m as in the twenties, suddenly started to drop again, stabilizing around -27 m in the last ten years.

The causes of Caspian Sea level change are as yet ill understood. Influx from the Volga river, accounting for 80% of the input side of the water balance, and evaporation at sea level on the output side, are controlled by different climatic zones. Short-term cycles such as the 1929-1995 cycle may be forced by internal atmospheric processes such as the North Atlantic Oscillation. But in historic times oscillations of much higher amplitudes have occurred, from -22 m during the Little Ice Age to -34 m, or possibly even -48 m in the Warm Mediaeval Period, an amplitude of 12-26 metres in less than millennium, possibly synchronous to cycles in solar activity. There was an Early Holocene lowstand at -80 m, and a Last Glacial highstand at +50 m, an amplitude of 130 metres in probably not more than 20, 000 years. Unlike elsewhere in the world, present Caspian shores are somewhere halfway the most recent highstand and lowstand. In spite of the great advances in understanding of our climate system, in spite of the predictive power of our Global Ciculation Models, in spite of the accurate monitoring by detailed monitoring by satellite systems such as Topex-Poseidon/Jason, opinions about future Caspian sea-level trends diverge.

Nature has three ways of time keeping: time's arrow, time's cycle and time's spike. Time's arrow refers to one-directional processes such as radioactive decay and the deceleration of earth rotation by tidal friction through geological time. Time's cycle refers to often astronomically forced cycles such as tide, day and night, the seasons, and the climatic cycles of different amplitudes and duration; time's spikes are the unexpected catastrophes such as earthquakes, volcanic eruptions, sudden floods, often derived by non-linear processes from cyclic ones such as plate tectonics and astronomically regulated changes in energy input at different latitudes at the earth's surface.

Caspian shore dwellers have experienced what we tend to forget: that climate and sea-level changes are cyclic processes, some of them at human time scales like the Caspian, but often at greater-than-human scales: on Nature's time scales. If we are prepared to see the present period of global warming as part of time's cycle, or even as a short spike in Nature's time, if we try to look beyond the future global sea-level highstand, Nature might look less dark to us.

Date received: July 13, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-29.