Item

Abstract

The lower troposphere is an excellent receptacle, which integrates anthropogenic greenhouse gases emissions over large areas. Therefore, atmospheric concentration observations over populated regions would provide the ultimate proof if sustained emissions changes have occurred. The most important anthropogenic greenhouse gas, carbon dioxide (CO₂), also shows large natural concentration variations, which need to be disentangled from anthropogenic signals to assess changes in associated emissions. This is in principle possible for the fossil fuel CO₂ component (FFCO₂) by high-precision radiocarbon (C-14) analyses because FFCO₂ is free of radiocarbon. Longterm observations of (CO₂)-C-14 conducted at two sites in southwestern Germany do not yet reveal any significant trends in the regional fossil fuel CO₂ component. We rather observe strong inter-annual variations, which are largely imprinted by changes of atmospheric transport as supported by dedicated transport model simulations of fossil fuel CO₂. In this paper, we show that, depending on the remoteness of the site, changes of about 7-26% in fossil fuel emissions in respective catchment areas could be detected with confidence by high-precision atmospheric (CO₂)-C-14 measurements when comparing 5-year averages if these inter-annual variations were taken into account. This perspective constitutes the urgently needed tool for validation of fossil fuel CO₂ emissions changes in the framework of the Kyoto protocol and successive climate initiatives. [References: 23]