Gene Expression

Great Dying = Great Cooling?

This is really weird, New World Post-pandemic Reforestation Helped Start Little Ice Age, Say Scientists:

Stanford University researchers have conducted a comprehensive analysis of data detailing the amount of charcoal contained in soils and lake sediments at the sites of both pre-Columbian population centers in the Americas and in sparsely populated surrounding regions. They concluded that reforestation of agricultural lands–abandoned as the population collapsed–pulled so much carbon out of the atmosphere that it helped trigger a period of global cooling, at its most intense from approximately 1500 to 1750, known as the Little Ice Age.

The same researchers published a paper on this last spring, Effects of syn-pandemic fire reduction and reforestation in the tropical Americas on atmospheric CO2 during European conquest:

A new reconstruction of Late Holocene biomass burning in the tropical Americas is consistent with the expansion of fire use by Mesoamerican and Amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years BP. The marked reduction of biomass burning after 500 years BP, a unique feature of the fire history of the tropical Americas relative to other regions of the globe, is synchronous with the collapse of the American indigenous population during pandemics accompanying European conquest. We predict that fire reduction contemporaneous with pandemics in the tropical Americas was associated with massive forest regeneration on 5 × 105 km2 of land and sequestration of 5-10 Gt C into the terrestrial biosphere, which contributed to the 2% global reduction in atmospheric CO2 levels and the 0.1‰ increase in δ13C of atmospheric CO2 from 1500 to 1750 A.D. This study 1) builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14C dates to resolve features of the Late Holocene biomass burning record in the tropical Americas; and 2) corroborates the hypothesis advanced by Ruddiman [Ruddiman, W.F., 2003. The Anthropogenic Era began thousands of years ago. Climatic Change 61, 261-293, Ruddiman, W.F., 2005. Plows, Plagues, and Petroleum. Princeton University Press, Princeton, New Jersey] that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric CO2 concentration during the past millennium.


  1. #1 bioIgnoramus
    December 19, 2008

    What about the reforestation of much of New England as agriculture moved west in the 19th century? Could it have been big enough to matter?

  2. #2 Lassi Hippeläinen
    December 19, 2008

    Was the Little Ice Age global? AFAIK it was mainly an European phenomenon.

    Besides, the Viking colonies of Greenland died out already in 14th century.

  3. #3 ziel
    December 19, 2008

    Was the Little Ice Age global? AFAIK it was mainly an European phenomenon.

    I don’t think that’s the consensus of historians (though some revisionism has cropped up recently arguing this). See for example Albion’s Seed, where David Hackett Fischer discusses how much colder New England was in the 17th century compared to today (page 52 here.)

  4. #4 hip hip array
    December 19, 2008

    Someone has floated the idea that the enormous numbers of American bison existing during white expansion arose because of native depopulation. How much would their methane release offset the carbon sequestration?

  5. #5 Enonymous
    December 19, 2008

    “What about the reforestation of much of New England as agriculture moved west in the 19th century? Could it have been big enough to matter?”

    19th century? North Americans were burning the neighborhood until the early 20th century, as an expansion of the policies which the Army willy-nilly began at Yellowstone.

  6. #6 Enonymous
    December 19, 2008

    And there’s already a proposal that we make charcoal, as the native americans did, to reduce the temperature.

  7. #7 Dave
    December 20, 2008

    The little ice age began much longer. The unequivocal and clear dating shows Atlantic ice pack growing from 1250 through the 16th century, the Greenland settlements abandoned in the late 14th Century, Greenland glaciers starting their advance int eh mid 14th century, etc. Braudel shows decreased European grain shiping beggining in the 14th century. To match this as an effect of the native American die off in the early 16th century is strange.

    @Enonymous: um, the Native Americans deforested huge areas of the NA landscape, especially by burning. They did so apparently to increase forage and they artificial created the huge and harmful massive increase in bison.

    Would the authors dare instead of blaming the Europeans, blame the native Americans themselves as we know they were peaking population and impact in the period right before the little ice age?

  8. #8 TGGP
    December 20, 2008

    I recall in Jared Diamond’s Collapse he portrays the production of charcoal as especially harmful to forests.

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