BBC reports:
It appears that much of the gas came from the burning of biomass - the likes of wood and grass - rather than other known sources of methane, such as the burning of fossil fuels, or natural emissions of methane from swamps and wetlands.
"Fire has been known to mankind for hundreds of thousands of years - even though the human population was very small, they set off large fires on a regular basis," lead researcher Dominic Ferretti, of the National Institute of Water and Atmospheric Research Limited in Wellington, New Zealand, told the BBC News website.
"It shows that in pre-industrial times there were much higher levels of methane from wood and grassland fires than we ever thought before.
Then there's this interesting tidbit:
In the Americas, large swathes of grassland appear to have been burnt every year, for farming or to drive animals into the path of hunters.
Large-scale fires were also lit in the Amazon jungle, to produce charcoal for improving the fertility of the soil.
The data suggests that methane emissions from burning tailed off by about 1700.
The researchers say this may have been due to a natural trend toward cooler and wetter conditions, as well as the decline in the indigenous population in the Americas because of the introduction of diseases by European explorers. [emphasis mine]
In recent years historians have focused a lot of energy on studying the ecological and environmental consequences of European settlement of the Americas. This is one that had not been anticipated. It has long been known that American indigenous populations practiced slash and burn agriculture, but the global effect of that practice had not been appreciated until now.
Read the article here.
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