Pointing the finger at the US

The recordings by the Jungfraujoch instruments were therefore a first step. “The second was to contact some of our colleagues in the NDACC (Network for the Detection of Atmospheric Composition Change), who work on the American continent. We informed them about the detection of this trend reversal and asked them to analyse their data to see what the result would be. In the end, the stations at Toronto in Canada, the Great North, Greenland, Colorado and Hawaii sent us their series”. The stations in the North and in Hawaii, which were further away from the gas wells, should provide a background level, an indication of the average state of the atmosphere over the Northern Hemisphere. On the other hand, those of Colorado and Toronto are closer to many drilling zones and here we were able to observe a higher concentration of ethane. 

Emissions seen to be increasing

All over the world, studies aim to estimate and create inventories of the emissions of harmful constituents into the atmosphere and to make them freely available. One of the most recognised inventories is the HTAP2, which combines the results from all the regions of the globe. This is as much information as it is possible to integrate into and use in atmospheric models. “In the context of our research, Louisa Emmons, of NCAR in Colorado, integrated this data into a model to compare them with our measurements. She noticed that the estimates for ethane emissions in these inventories were too low and this also applied to the decade before 2009. This signifies that these inventories under-estimate gas emissions and therefore the degradation of the air. In order to obtain a result that is a reliable indication of the average emission from the 2000s, these needed to be multiplied by two”.

But that wasn’t all, the researcher then suggested as a supplementary theory, that the responsibility for the recent increase in ethane production was attributable only to the US. “Beyond the initial multiplication, it was still necessary to increase annual emissions by 75% in order to model the growth observed between 2009 and 2014”. In more concrete terms, in the inventory, the emission of ethane in North America was estimated at 0.8 million tonnes per year before 2009 while, in reality, it had risen to 1.6 million tonnes. But in 2014, the emissions reached the startling figure of 2.8 million tonnes. “The result was quite unequivocal”, says Emmanuel Mahieu. “The researcher fully succeeded in reproducing the trends we had observed. This meant that it was even more possible to identify the exploitation of shale gas as a real cause of the problem”.