POLARPROG-Polarforskningsprogram

The main goal in GAME is to understand how emissions in different regions, atmospheric transport and chemical processes contribute to observed changes in methane distribution the last 40 years. The work is a combination of new measurements, analysis of ex isting and ongoing methane observations, and Chemical Transport Modelling (CTM). A particular focus is on the huge Arctic methane reservoirs with an aim to identify the geographical locations and seasonality of these sources. The Oslo CTM2 model has b een used to calculate distribution and changes over the last 40 years. The studies include evaluation of different methane sources and source regions, and chemical processes affecting OH distribution and changes, including changes in anthropogenic and nat ural emissions from different sources. There has been a particular focus in understanding the evolution of CH4 observed at the Zeppelin Observatory, Svalbard. This includes both the long time series as well as detailed information in the recent observatio ns supplemented with isotopic measurements within the frame of GAME. Isotopic measurements provide more information about the sources contributing to the methane levels and variations, as the various main sources have differences in their isotopic signatu re. In order to quantify the contributions to methane loss from concentration changes of individual components (e.g. CO, NOx, various aerosol types etc) varies sensitivity tests were performed. Time slice sensitivity studies were first made with the CT M2 for each decade from 1960 to 2000 and also from 1850 to 2000. Based on this we were able to identify key processes determining the changes in loss of methane from the atmosphere the last decades. The knowledge was then used to analyse the CH4 simulatio ns covering the whole period 1970-2010. In these simulations all components are varied at the same time to fully try to understand and reproduce the evolution of methane. The sensitivity study gives us an idea of the decisive factors behind the evolution and ideas for further simulations needed to verify this. Recently two full simulations for the period 1970-2010 are completed: One with changes in emission fluxes of methane and all other relevant components affecting methane, and one with fixed methane c oncentration to quantify how the other components affect the chemical loss of methane. We have compared the global average surface level from observations with the modeled results from OsloCTM3. The number of observations included in the global mean CH 4 based on observations are increasing considerable throughout the 40 year time period, still the comparison with the model is very good, generally for the full period. Also a systematic comparison over latitudinal bands from South Pole to North Pole is p erformed since 1997 until 2010 (when it starts to be reasonable number of observations available). The results are very good; Also sites shown to have very complex variations in the CH4 in the observed concentrations are now satisfactory reproduced by the model. There has been a special focus on understanding the observations at Zeppelin, Svalbard. Here also ongoing measurements if 13dCH4 is a part of GAME to provide more information about the sources. These observations have been ongoing since summer 2012, and the sampling frequency is 5 times per week. Analyzing these observations together with the model results gives strong indications about the emissions contributing to the observed changes at Zeppelin. The work is still ongoing, but preliminary r esults show that wetlands in Siberia and changes in these seem to play a crucial role. From the observations it seems that there has been a special situation in 2010-2011 with very few episodes with high CH4 at Zeppelin. This turns out also to be seen in the model results, and the reason to this is under investigation, but it seem like there is a regional source that was considerable lower in this period, and that this has increased again last year (2013). Changes in atmospheric concentrations of chemi cal species due to changes in the methane budget this century is also calculated by model simulations with Oslo CTM2 using future emission scenarios. The climate impact of these concentration changes (direct and indirect effect of methane emissions) for t he next 25-50 years in terms of radiative forcing is ongoing.

Methane is a main atmospheric compound with abundances determined by natural and man made emissions. It is the second most important anthropogenic climate gas, affecting atmospheric oxidation and air quality and a main component in the carbon cycle. Proce sses determining its distribution and changes are connected with significant uncertainties. As a result of the uncertainties related to future emissions and changes in the oxidation process methane limits the accuracy of climate change predictions. The ov erall objective of this project is to explain the recent increase in atmospheric methane and quantify the effect of realistic future development of atmospheric methane levels. The project focuses on improving the understanding of historic, current and fut ure atmospheric methane budgets. Progress in the understanding will be achieved by multi method approaches: Integration of observations, chemistry transport model (CTM) simulations and radiative forcing calculations. Long-term observations and new isotopi c measurements will be combined with isotope modelling to assess source regions for a wide range of Arctic methane sources. Oslo CTM2 will be used to simulate and assess the effects of emissions changes. Radiative forcing calculations utilising the result s from the CTM simulations and observations will be performed to predict and quantify the effects of changing methane levels on Earth's radiative balance. Also scenarios of extreme global warming and associated large emissions from Arctic reservoir source s will be investigated. As a result, the project will contribute to increased knowledge of the carbon cycle by assessing methane sources as permafrost, wetland, biomass burning, ocean and agricultural emissions. Furthermore the project is expected to prov ide new knowledge of methane as a potential strong biogeochemical climate feedback mechanism and by this reduce the uncertainty in future climate predictions.