RIV-ESCAPE · RIVEr emissions of greenhouse gases from warming landSCAPEs

Rivers around the world release large quantities of greenhouse gas, with an estimated 1.8 ± 0.3 PgC yr-1 released as carbon dioxide (CO2), and ~20-25 TgC yr-1 as methane (CH4). These fluxes are equivalent to half of the annual increase in CO2 and CH4 concentrations in the atmosphere due to human activities. However, we cannot yet quantify how river CO2 and CH4 emissions will change, nor assess their potential to amplify future climate warming. There are two main challenges: i) the main drivers of CO2 and CH4 release from rivers (supply of carbon and the dynamics of river flow) change simultaneously, and their relative importance is obscured in existing data, limiting our ability to build and test predictive models; ii) the age of river CO2 and CH4 is poorly constrained, meaning that we cannot determine whether this is anthropogenic carbon that is leaking out from prior storage on land, or whether it derives from ancient carbon stores in the landscape. RIV-ESCAPE will transform our understanding by recognising the need for direct measurements that combine river CO2 and CH4 flux, river flow dynamics and C supply at high temporal resolution (minutes to hours) over seasonal timescales, across nested scales in river catchments. Such novel field installations could be used anywhere to improve our understanding: we will focus on Arctic rivers that are experiencing pronounced warming and hold large stores of ancient carbon in soils. In parallel, we will use cutting-edge isotope geochemistry methods for river gases, waters and sediments to quantify the controls on the age and source of CO2 and CH4 in rivers around the world. The new empirical data will combine with physical and numerical experiments to provide a step-change in our knowledge of how changes in temperature and precipitation set river greenhouse gas source and the rate of release, allowing us to assess for the first time the sensitivity of river CO2 and CH4 emissions to future warming.