Abstract
Since the beginning of the industrial revolution, the atmospheric concentration of carbon dioxide (CO<sub>2</sub>) has increased by nearly 30%, and the Methane (CH<sub>4</sub>) concentration has more than doubled. CH<sub>4</sub> is the second most important greenhouse gas, after CO<sub>2</sub>. Emissions, extrapolated from measurements of actual gas flux from wetlands, vary from place to place, even within the same wetland. This high variability makes large-scale estimates difficult and means that average emissions levels include a large degree of estimated uncertainty. The SCIAMACHY instrument on the European Space Agency satellite ENVISAT measured greenhouse gases in the troposphere and stratosphere. In this study, the CH<sub>4</sub> source area is extracted by estimating the concentrations of methane emissions from time-series satellite data. Contamination of the data by cloud is interpolated both spatially and temporally. It is assumed that methane emission is negligible over ocean and that the concentration in the ocean area is due to advection from land. Background CH<sub>4</sub> concentration on land was defined as the ocean CH<sub>4</sub> concentration at the same latitude. Land CH<sub>4</sub> emission concentrations show that areas of concentrated high CH<sub>4</sub> emission are not in paddy fields only but also in broadleaf evergreen areas in South America and Central Africa.
Highlights
Looking at the long-term trend, the global average temperature increased by 0.74 ± 0.18 °C over the 100-year period ending in 2005 (IPCC, 2007)
The land cover layer of the Global Land Cover by National Mapping Organizations (GLCNMO) is available as a cluster dataset divided into 20 items according to the land cover classification system (LCCS) developed by the Food and Agriculture Organization of the United Nations (FAO)
We assumed that since CH4 is not emitted in ocean regions, any CH4 that does exist in the ocean regions is due to the effect of advection from continental regions
Summary
Looking at the long-term trend, the global average temperature increased by 0.74 ± 0.18 °C over the 100-year period ending in 2005 (IPCC, 2007). Much research has found that the main cause of global warming is increased greenhouse gases in the atmosphere due to the use of fossil fuels by humans and is not a natural phenomenon (IPCC, 2007; Houweling et al, 2000). The concentration of methane in the atmosphere remained virtually constant from 1999 to 2006, it began increasing again in 2007 (Rigby et al, 2008) It has been noted (WMO Greenhouse Gas Report, 2014) that no variations in the amount of emissions from the Arctic Circle have been observed, despite CH4 emissions from the tropical zones and lower latitudes in the northern hemisphere, and the exact reason for the increase is currently unknown. We compare the topographical features of CH4 sources with vegetation maps to investigate the sources of CH4 emissions
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