Quantifying the Sources and Sinks of Greenhouse Gases: What Does It Take to Satisfy Scientific and Decision-Making Needs?
Abstract:Changes in the sources and sinks of greenhouse gases (GHGs) are key drivers of anthropogenic climate change. It is hence not surprising that current and emerging U.S. governmental science priorities and programs focused on climate change (e.g. a U.S. Carbon Cycle Science Plan; the U.S. Carbon Cycle Science Program, the U.S. Global Change Research Program, Executive Order 13653 'Preparing the U.S. for the Impacts of Climate Change') all call for an improved understanding of these sources and sinks.. Measurements of the total atmospheric burden of these gases are well established, but measurements of their sources and sinks are difficult to make over spatial and temporal scales that are relevant for scientific and decisionmaking needs. Quantifying the uncertainty in these measurements is particularly challenging.
This talk reviews the intersection of the state of knowledge of GHG sources and sinks, focusing in particular on CO2 and CH4, and science and decision-making needs for this information. Different science and decision-making needs require differing levels of uncertainty. A number of high-priority needs (early detection of changes in the Earth system, projections of future climate, support of markets or regulations) often require a high degree of accuracy and/or precision. We will critically evaluate current U.S. planning to documents to infer current perceived needs for GHG source/sink quantification, attempting to translate these needs into quantitative uncertainty metrics. We will compare these perceived needs with the current state of the art of GHG source/sink quantification, including the apparent pattern of systematic differences between so-called “top down” and “bottom-up” flux estimates. This comparison will enable us to identify where needs can be readily satisfied, and where gaps in technology exist. Finally, we will examine what steps could be taken to close existing gaps.