A new paper is out attempting to blame the Roman Optimum warming on man. The argument is that they found a lot of methane in the ice cores. And when the C12 C13 isotope ratio was studied they found a lot of C13 which means (according to the authors) the methane came from wood burning. Keep in mind that the number one methane source today is in fact agriculture, with rice farming being #1.
“At between 50 and 100 million tonnes of methane a year, rice agriculture is a big source of atmospheric methane, possibly the biggest of man-made methane sources. The warm, waterlogged soil of rice paddies provides ideal conditions for methanogenesis, and though some of the methane produced is usually oxidized by methanotrophs in the shallow overlying water, the vast majority is released into the atmosphere.”
I know Romans burnt a lot of wood for their baths and for heating. But I also know from The Cheefio that not all plants treat C12 and C13 the same.
“C4 metabolism plants absorb more C13 than do C3 metabolism plants.”
The main C4 metabolism plants are maize, sugar cane, millet, and sorghum and about 7600 other plants.
So could Romans have been eating more C4 plants changing the C13 isotope ratio of methane?
Why yes some people in Roman times ate a lot millet and millet is a C4 metabolism plant:
“Just a few days ago, only the second isotope study of millet consumption in the Roman Empire was published, by Pollard and colleagues in the American Journal of Physical Anthropology. In a small Romano-British cemetery in Kent (late 3rd-early 4th century AD), a salvage archaeology project uncovered a dozen burials that were simple in nature: only coffin nails and hobnails from boots were found in most graves. Among these simple farmers, though, was an individual with a surprisingly high carbon isotope value, so Pollard and colleagues undertook a dietary (C/N) and migration (Sr/O) study of the individuals.
The anomalous partially complete skeleton was that of a male over the age of 45 buried wearing hobnail boots. The individual’s nitrogen isotope ratio was a bit high (11.2 permil), indicating aquatic resource consumption, but was not higher than average for Roman Britain. His carbon isotope ratio from collagen, however, came in at -15.2 permil, in stark comparison to the average of the other individuals of -19.8 permil (see below). This difference may not seem dramatic until you factor in the standard deviation – variation within the d13C ratios of the others from the site was only 0.3! This person was therefore eating a whole bunch of C4 resources – millet, sorghum, or animals foddered on those grains.”
Nothing I’ve said proves it wasn’t firewood. But people and scientists should know the C12/C13 C3/C4 ration issues and should deal with them properly.