Joint Seminar: Does greenhouse warming dry out the continents? Theory, model, observational, and paleoclimate perspectives

Global models robustly project that near-surface soil moisture and near-surface relative humidity will strongly decline in the coming century in most mid- to low-latitude land areas, even as precipitation and runoff don't change much.  These declines look very similar to declines in standard climatic wetness indices, which are driven by well-understood increases in evaporative demand with warming.  Thus the projections appear quite credible.  Yet, there are two large problems with this conclusion.  First, evaporative demand has usually been observed to decline in recent decades, likely driven by observed wind declines ("stilling") which do not appear in the models or in reanalysis.  Second, the GCMs also project widespread increases in wetness metrics at the last glacial maximum, a time when most landscapes did not look any "wetter" and if anything looked "drier" and more open, and dust deposition was higher globally.  Thus, either the GCM projections are flawed, or else metrics like topsoil moisture and Palmer index aren't relevant under global change (e.g. because they don't account for CO2 effects on vegetation.)  This talk will explore these tensions in detail.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Jack Scheff, Lamont-Doherty Earth Observatory, Columbia University


J├╝rgen Bader

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