Wednesday, June 8, 2011

New paper shows Western N. America drought was far more extreme and variable PRIOR to 500 years ago

A peer-reviewed paper published online today in the journal Geophysical Research Letters shows that drought of Western North America was considerably worse during the Medieval Warming Period than at the end of the 20th century. The paper also shows much more variation and extremes in the drought record over the past 5200 years than since the advent of industrialization and rising CO2 levels in the latter 20th century. The proxy records clearly show no correlation of drought with the claimed steady CO2 levels until ~ 1950 and subsequent steady rise.
Western North American drought in bottom graph is on an inverse scale, showing significantly more drought during the Medieval Warming Period ~ 900 - 1250 AD than the year 2000. Year 2000 drought index is at the approximate mean level seen throughout the Little Ice Age (LIA) ~ 1550- 1850 AD.
Going back 5200 years, Lake Athabasca, a major lake in Western Canada, had water levels  considerably lower than the present during the Medieval Warming Period, and even lower levels for at least a 3000 year period covering the 1st half of the record.


A 5200-year record of freshwater availability for regions in western North America fed by high-elevation runoff

Brent B. Wolfe, et al

Shrinking glaciers and snowpacks are reducing discharge in rivers that drain the central Rocky Mountain region – water that supports downstream societies and ecosystems of western North America. However, a new 5200-year record of Lake Athabasca water-level variations, which serves as a sensitive gauge of past changes in alpine-sourced river discharge, reveals that western Canadian society has developed during a rare period of unusually abundant water ‘subsidized’ by prior glacier expansion. As the ‘alpine water tap’ closes, much drier times are ahead. Future water availability is likely to become similar to the mid-Holocene when Lake Athabasca dropped 2–4 m below the twentieth-century mean. Regions dependent on high-elevation runoff (i.e., western North America) must prepare to cope with impending water scarcity of magnitude not yet experienced since European settlement.

note: this conclusion may be somewhat premature given the record North American snowpacks of the past couple years, decline in solar activity, and negative PDO phase.

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