"Methane makes up just 0.00018 percent of the atmosphere, compared to 0.039 percent for carbon dioxide. (CO2 is roughly 200 times more abundant.) Yet scientists attribute about one-sixth of recent global warming to methane emissions; what methane lacks in volume it makes up for in potency. Over a 20-year period, one ton of methane has a global warming potential that is 84 to 87 times greater than carbon dioxide. Over a century, that warming potential is 28 to 36 times greater. The difference occurs because methane is mostly scrubbed out of the air by chemical reactions within about ten years, while carbon dioxide persists in the atmosphere for much longer than a century."
PEAT
BOGS AS SOURCE OF METHANE
The
UCLA-Russian Academy of Sciences team found no peatland dates earlier than
about 16,500 years ago, suggesting that no large northern peatland complex
existed before that time. At that time, methane levels hovered around 360 parts
per billion by volume and the Earth was still in a deep freeze. But as surface
temperatures and atmospheric methane levels rose, northern bogs appeared in
lockstep, the team found.
Over the course of the next 2,500 years, atmospheric
methane levels doubled and temperatures in central Greenland — where the ice
core is located — jumped 18 degrees Fahrenheit.
Between 8,000 to 12,000 years ago, the area covered
by peatlands increased dramatically and methane levels rose to 750 parts per
billion by volume — a level they would not reach again until the Industrial
Revolution. Temperatures over Greenland likewise jumped an additional 7 degrees
Fahrenheit, reflecting a period of warming which in turn thawed more ice,
particularly in North America, and freed up more land for bog formation,
MacDonald said.
In the
past, scientists have attributed the 8,000-to-12,000-year-old methane release
to wetlands in the tropics or liquefied deposits of very cold methane buried
deep in the ocean. What — if any — part was played by tropical wetlands is still
unclear, but the role of ocean deposits has been disputed by two recent
studies.
“It is now clear that the northern peatlands have to
be considered a major part of this prolonged early rise in methane,” said
MacDonald, who is chair of the UCLA Geography Department and a professor in the
UCLA Department of Ecology and Evolutionary Biology.
In addition to pinpointing a new source of methane
that helped end the ice age, the team’s work has established a much earlier
date for the formation of these bogs. Until a related discovery announced two
years ago by the same researchers, scientists had thought that the northern
peatlands did not start forming until 8,000 years ago. But the new research
suggests that by that time, 50 percent of today’s northern peatlands were
already formed.
Over the
past 8,000 years, the rate of bog formation has steadily declined, the new
research shows. Meanwhile, starting 6,000 years ago methane levels began to
steadily increase before jumping dramatically by between 2.5 and 3.0 times
following the start of the Industrial Revolution about 200 years ago. Some
researchers have attributed the latter increase to human activities, including
early rice cultivation, cattle domestication and biomass burning. Other
researchers have suggested the increased growth of northern peatlands is
responsible.
The human role in the increase 6,000 years ago
remains controversial, but major increased expansion of northern peatlands is
probably not the culprit, MacDonald said.
“The rate of development of these peatlands has been
slowing down and they have been maturing into low-methane producing moss bogs,
so they don’t seem to be responsible for the steady growth of atmospheric
methane that began 6,000 years ago,” MacDonald said. “The source of that
methane — human or otherwise — remains an important question.”
