A Weblog monitoring coverage of environmental issues and science in the UK media. By Professor Emeritus Philip Stott. The aim is to assess whether a subject is being fairly covered by press, radio, and television. Above all, the Weblog will focus on science, but not just on poor science. It will also bring to public notice good science that is being ignored because it may be politically inconvenient.

Sunday, May 22, 2005

Long-term climate change.....

I have just been reading an excellent, and most timely, review paper by Stuart A. Harris of the University of Calgary: 'Thermal history of the Arctic Ocean environs adjacent to North America during the last 3.5 Ma and a possible mechanism for the cause of cold events (major glaciations and permafrost events)' [Progress in Physical Geography 29 (2), pp. 218 - 237 (June 2005)].

In this, Harris points out that long-term climate change is the product of an immensely complex interaction between many cyclical (and non-cyclical) controls with different periodicities, periodicities that may vary in time, space, wave-length, magnitude, and predictability. A significant climate change occurs when enough of these are synchronized sufficiently for air temperature to cross a critical threshold - yet, this is itself dependent on local environments and latitude.

In an earlier paper ['Global heat budget, plate tectonics and climate change', Geografiska Annaler 84A, pp. 1 - 10 (2002)], Harris helpfully provides a list of 11 major climate controls, arranged into 4 orders of temperature magnitude:

A. First Order (potential temperature change - c.30 degrees C):

1. Difference in heat absorption by sea and land as contolled by the global position of the continents and oceans;

2. Changes in the geometry of the solar system;

B. Second Order (potential temperature change - c.15 degrees C):

3. Changes in the ocean currents and thermohaline circulations;

C. Third Order (potential temperature change - <10 degrees C):

4. Milankovich cycles;

D. Fourth Order (potential temperature change - <5 degrees C):

5. Fluctuations (both natural and anthropogenic) in carbon dioxide and other 'greenhouse' gases;

6. Large-scale volcanic eruptions;

7. Elevation of large tracts of land, e.g., Tibet;

8. El Niño and La Niña events (ENSO);

9. Short-term cycles, e.g., the 2- and 7-year cycles (see below);

10. Variations in solar output;

11. Agriculture (clearing the land), deforestation, urbanization, re-afforestation, etc.

This is a valuable approach, in that it, for once, melds geological, oceanic, atmospheric, and solar cycles, and non-cycles. Its application results in some fascinating conclusions:

(a) with respect to the Arctic Ocean, a long-term cooling trend, right down to today, and evident from as far back as 3.5 Ma, which exhibits some 130 fluctuations of random spacing and magnitude, and which was primarily triggered by the drying up of the Tethys Sea;

(b) medium-scale fluctuations that are still poorly interpreted, but which appear to relate especially closely to the so-called Milankovitch cycles. For the last 15 ka, there seems to have been a strong relationship between the 23,708-year Milankovitch cycle and 8 periodicities of 1,500- to 280-years, including the Medieval Warm Period and the Little Ice Age, which are both well-defined. This relates closely to the European palaeoclimatic chronology for the last 15 ka;

(c) More strikingly, however, these periodicities would seem to predict cooling in the coming centuries (see: Figures 5 and 6, on p. 228);

(d) 150-years of climate data exhibit four short-term cycles of 2-3 years (the quasi-biennial oscillation); 5-7 years (ENSO); 20-25 years (the bidecadal oscillation); and one still only poorly defined, namely a 50-75 year cycle;

(e) Other non-cyclical climate controls, incuding changes in carbon dioxide in the air, volcanic dust, elevation of large tracts of land, variations in solar output, and landscape change, "...result in relatively minor changes in air temperature and some are quite short-lived in terms of geological time" (p.230).

Thank goodness for a study which looks at climate fully, in both geological time and geological space.

Please bear all this in mind when anyone tries to tell you that we can manage climate change entirely predictably by fiddling at the margins with one selected, non-cyclical factor.

The European 'global warming' myth is poppycock of the First Order.

By the way, this Issue [29 (2), June 2005] of Progress in Physical Geography also contains one or two other particularly interesting reviews, including Martin J. Siegert on 'Reviewing the origin of subglacial Lake Vostok and its sensitivity to ice sheet changes' (pp. 156-170), J.A. Salmond & I.G. McKendry on 'A review of turbulence in the very stable nocturnal boundary layer and its implications for air quality' (pp. 171-188), and D.M.J.S Bowman & D.C. Franklin on 'Fire ecology' (pp. 248-255).

Philip, temperature rising to boiling point. Lunch, and a cooling sauvignon blanc. Cheers. A paper well-worth the read. And don't forget to vote on that nuclear question over at the New Statesman. Thanks.

[New counter, June 19, 2006, with loss of some data]

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