This has got them confused and I would not be optimistic about cultural sources.
A lot more CO was produced than during the past century.
For the moment, we lack an actual chart and can not look at detail. I would like to see a lot produced in pre Columbiantimes. That is because biochar makingshould have dominated
South America and I cannotimagine a better way to make CO.
For the rest of the time, the steel axe came into its own and slash andburn took over. That meant controlled forestburning to clear agricultural land every couple of years. Again a lot of CO wasproduced.
This century were better practice was possible saw the end of such methodsand depopulation of land that demanded slash and burn pretty well took place. This was likely because the expansion ofarable land farming attracted labor.
In short, better efficiency drew in the labor and lowered the land underslash and burn.
What Can Ice Reveal About Fire
General view of the drill site D47 in
Antarcticawhere the LGGE (Laboratoire du Glaciologie et Geophysique de l'Environnement)team drilled one of two cores used in the recent Southern Hemispherebiomass-burning study. The thermal drilling method the researchers used allowedthem to collect a 12-centimeter-diameter core, from which carbon monoxide andits isotopes were measured at .These analyses required close to one kilogram of ice per sample. Credit: JeromeChappellaz, CNRS/LGGE. Stony Brook University
Scientists studying a column of Antarctic ice spanning 650 years have foundevidence for fluctuations in biomass burning--the consumption of wood, peat and other materials in wildfires, cooking firesand communal fires--in the Southern Hemisphere.
The record, focusedprimarily on carbon monoxide (CO), differs substantially from the record in theNorthern Hemisphere, suggesting changes may be necessary for several leadingclimate models.
The research appearedonline in Science Express.
The scientists studiedvariations in stable (non-radioactive, non-decaying) isotopes of carbon and oxygen, the first such measurements forcarbon monoxide collected from ice-core samples.
"Combined withconcentration measurements of CO, this record allows us to constrain therelative strength of biomass burning activity over the 650-year period in theSouthern Hemisphere," said co-author and research lead John Mak, ageoscientist at SUNY Stony Brook.
"What we find isthat the amount of biomass burning has changed significantly over that timeperiod," Mak added, "and that biomass burning was in fact asignificant source of CO during pre-industrial times."
The biomass burningtrends indicated by the CO largely agree with Southern Hemisphere recordstracking charcoal particles in sediments and with measurements of methane from trapped ice.
Unexpectedly, theresearchers found that biomass burning appears to have been more prevalent 100to 150 years ago than it was during the 20th century.
"While this isconsistent with previous findings," added Mak, "there is still acommon mis-perception that biomass burning rates are much higher today than inthe past. This is significant since many researchers assume that human-inducedbiomass burning is much greater than 'naturally' occurring biomass burning.
"While this maystill be the case--there were people around in the 18th century--the fact thattoday's rates of [Southern Hemisphere] biomass burning seem to be lower thanone to two centuries ago calls for a re-evaluation of sources."
The research wassupported by NSF grant OCE-0731406. The full reference for the paper is: Z.Wang, J. Chappellaz, K. Park, J.E. Mak, "Large variations in SouthernHemisphere biomass burning during the last 650 years", Science, Dec. 2,2010