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Summer Soil Moisture in the Ukraine
Reference
Robock, A., Mu, M., Vinnikov, K., Trofimova, I.V. and Adamenko, T.I.  2005.  Forty-five years of observed soil moisture in the Ukraine: No summer desiccation (yet).  Geophysical Research Letters 32: 10.1029/2004GL021914.

Background
The authors note that "most global climate model simulations of the future, when forced with increasing greenhouse gases and anthropogenic aerosols, predict summer desiccation in the midlatitudes of the Northern Hemisphere (e.g., Gregory et al., 1997; Wetherald and Manabe, 1999; Cubasch et al., 2001)," and they state that "this predicted soil moisture reduction, the product of increased evaporative demand with higher temperatures overwhelming any increased precipitation, is one of the gravest threats of global warming, potentially having large impacts on our food supply."

What was done
With the explicit purpose "to evaluate these model simulations," in the words Robock et al., the three American and two Ukrainian scientists "present the longest data set of observed soil moisture available in the world, 45 years of gravimetrically-observed plant available soil moisture for the top 1 m of soil, observed every 10 days for April-October for 141 stations from fields with either winter or spring cereals from the Ukraine for 1958-2002."

What was learned
Robock et al. report that "the observations show a positive soil moisture trend for the entire period of observation, with the trend leveling off in the last two decades," noting that "even though for the entire period there is a small upward trend in temperature and a downward trend in summer precipitation, the soil moisture still has an upward trend for both winter and summer cereals."

What it means
The five researchers note that "although models of global warming predict summer desiccation in a greenhouse-warmed world, there is no evidence for this in the observations yet, even though the region has been warming for the entire period."  In attempting to explain this dichotomy, they say the real-world increase in soil moisture content possibly may have been driven by a downward trend in evaporation caused by the controversial "global dimming" hypothesis (Liepert et al., 2004).  Alternatively, it may have been driven by the well-known anti-transpirant effect of atmospheric CO2 enrichment (see Transpiration in our Subject Index), which tends to conserve water in the soils beneath crops and thereby lead to enhanced soil moisture contents, as demonstrated in a host of experiments conducted in real-world field situations (see Water Status of Soil (Field Studies) in our Subject Index).

Whatever the reason for the temporally-increasing divergence between model calculations and real-world observations of northern midlatitude soil moisture contents, it is abundantly clear that "one of the gravest threats of global warming," as it is described by Robock et al., has not only failed to materialize, it has actually become less of a threat over a period of time (1958-2002) in which the planet was host to fully 60% of the total increase in atmospheric CO2 concentration experienced since the inception of the Industrial Revolution, and when the earth experienced (or didn't!) an increase in temperature that propelled it to a level of warmth that climate alarmists claim was unprecedented over the past two millennia.

Which leads us to wonder: How much more wrong could the world's climate alarmists possibly be on this topic???

References
Cubasch, U., Meehl, G.A., Boer, G.J., Stouffer, R.J., Dix, M., Noda, A., Senior, C.A., Raper, S. and Yap, K.S.  2001.  Projections of future climate change.  In: Houghton, J.T. et al. (Eds.), Climate Change 2001: The Scientific Basis: Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, New York, USA, pp. 525-582.

Gregory, J.M., Mitchell, J.F.B. and Brady, A.J.  1997.  Summer drought in northern midlatitudes in a time-dependent CO2 climate experiment.  Journal of Climate 10: 662-686.

Liepert, B.G., Feichter, J., Lohmann, U. and Roeckner, E.  2004.  Can aerosols spin down the water cycle in a warmer and moister world?  Geophysical Research Letters 31: 10.1029/2003GL019060.

Wetherald, R.T. and Manabe, S.  1999.  Detectability of summer dryness caused by greenhouse warming.  Climatic Change 43: 495-511.

Reviewed 9 March 2005