ABRUPT CHANGES IN THE EARTH’S CLIMATE SYSTEM
ABRUPT CHANGE IN ATMOSPHERIC
METHANE CONCENTRATION
Key Findings
- The main concerns about abrupt changes in atmospheric
methane (CH4) stem from (1) the large quantity of methane believed
to be stored as methane hydrate in the sea floor and permafrost soils and (2)
climate-driven changes in methane emissions from northern high-latitude and
tropical wetlands.
- The size of the methane hydrate reservoir is uncertain,
perhaps by up to a factor of 10. Because
the size of the reservoir is directly related to the perceived risks, it is
difficult to make certain judgement about those risks.
- There are a number of suggestions in the scientific
literature about the possibility of catastrophic release of methane to the
atmosphere based on both the size of the hydrate reservoir and indirect
evidence from paleoclimatological studies.
However, modeling and detailed studies of ice cores methane so far do
not support catastrophic methane releases to the atmosphere in the last 650,000
years or in the near future. A very
large release of methane may have occurred at the Paleocene-Eocene boundary
(about 55 million years ago), but other explanations for the evidence have been
offered.
- The current network of atmospheric methane monitoring
sites is sufficient for capturing large-scale changes in emissions, but it is
insufficient for attributing changes in emissions to one specific type of
source.
- Observations show that there have not yet been
significant increases in methane emissions from northern terrestrial
high-latitude hydrates and wetlands resulting from increasing Arctic
temperatures.
- Catastrophic release of methane to the atmosphere
appears very unlikely in the near term ( e.g., this century). However, it is very likely that climate
change will accelerate the pace of chronic emissions from both hydrate sources
and wetlands. The magnitude of these
releases is difficult to estimate with existing data. Methane release from the hydrate reservoir
will likely have a significant influence on global warming over the next 1.000
to 100,000 years.
