Browsing by Author "Hyvärinen, Sara"

The mean temperature of Earth has been rising due to human-influenced climate change. Climate change has been mostly caused by the rise of greenhouse gases from anthropogenic sources. After carbon dioxide (CO2), the second most important anthropogenic greenhouse gas to climate change is methane (CH4). Approximately half of the methane emissions come from natural sources, including wetlands. The northern high latitude wetlands store large amounts of carbon in permafrost, and the thawing of permafrost could release more methane into the atmosphere. However, there is still much uncertainty related to the methane emissions from the northern high latitude wetlands. The emissions on these wetlands have an annual cycle related to the freezing and thawing of the soil with the highest emissions during summer and the lowest during winter. Climate change can affect the duration and timing of the freezing and thawing periods leaving the winter period shorter. In this thesis, the melting season for the northern high latitude wetlands was defined for four regions: non-permafrost, sporadic, discontinuous and continuous permafrost as well as two smaller regions: Hudson Bay lowlands and Western Siberian lowlands for the years 2011-2020. The melting period was defined with a new method of using the SMOS F/T soil thawing data, which has not been done before this study. The data includes daily information on the freezing state of the soil in the northern latitudes. The melting period methane emissions were defined from the inversion model Carbon Tracker Europe -CH4. The relationship between the emissions, melting period length and mean temperature was studied. Emissions during the spring melting season were detected in all the permafrost regions defined in this study. The fluxes grew stronger as spring progressed and the soil and snow melted. The melting period methane emissions were relatively small compared to the annual emissions (a few per cent of the annual budget). However, the emissions were a little larger than autumn emissions. To understand the melting season emissions better, different drivers in addition to air temperature, like the melting of the permafrost, should be studied in relation to the CH4 emissions.