Two new studies build upon the world’s understanding of the atmospheric methane cycle and changes in methane accumulation.
The first, published in the journal Earth System Science Data, outlines the global methane budget over the 13-year period from 2000 to 2012. A consortium of researchers under the Global Carbon Project have produced a biennially-updated assessment of global methane concentrations and an analysis of known sources and sinks (sinks are natural features that neutralize methane as a GHG by breaking down CH4 molecules or absorbing the gas back into the earth’s surface). This has allowed them to quantify a global atmospheric balance of methane emitted and methane destroyed or absorbed. The difference in the balance reveals the rate of accumulation (see infographic below). While providing a confident scientific estimate of total methane over the years in question, the research team expresses a high degree of uncertainty in attributing the quantities of methane emitted into and depleted from the atmosphere, stemming primarily from the geographic overlap of diffuse sources and the effects of natural phenomena on the cycle. However, more certainty exists in their understanding of human-induced sources than natural factors, which provides assurance for those who work to mitigate anthropogenic emissions. Read the study abstract and a find a link to the full article here.
A second study, from the journal Environmental Research Letters, is entitled “The growing role of methane in anthropogenic climate change.” In it, researchers show that while the growth rate of global CO2 emissions is slowing, the growth rate of CH4 emissions has been increasing over the last decade, causing rapid methane accumulation in the atmosphere. This study complements the one above by providing several more recent years of analysis. The researchers estimate that methane concentrations in 2015 reached 1,834 parts per billion (ppb), up from ~1,775 ppb in 2005 when growth rates were flat. However, as in the above study, they also indicate a significant problem in more precisely identifying prime contributors due to the acknowledged uncertainty in the global methane budget. The analysis is able to offer evidence that points to anthropogenic sources as the prime contributor – outlining increases primarily in agricultural and fossil-related emissions while showing that natural wetland emissions have remained stable – but the researchers concede that more attention needs to be paid to accurately quantifying and geographically partitioning the various factors of the budget. The study provides strategies for reducing uncertainties in the methane budget and highlights mitigation opportunities as well.
Together, these studies highlight the work that has been done to develop the methane budget as well as the work that is still needed to address the uncertainties of this important basis of knowledge in the fight against climate change. The fact that so many scientists are working together and focusing their efforts on understanding methane emissions demonstrates the growing understanding of the mounting threat that CH4 poses to climate change as the second-most abundant GHG. Their findings are critical to informing and guiding mitigation action groups, such as GMI, and we wish them continued success in bringing the global picture of atmospheric methane changes more clearly into focus.