ALBERT

Description: Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable, and arguable lines of evidence, including modeling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of -1.6 to -0.6 W m−2, or -2.0 to -0.4 W m−2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted toward more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds. Key Points: - An assessment of multiple lines of evidence supported by a conceptual model provides ranges for aerosol radiative forcing of climate change - Aerosol effective radiative forcing is assessed to be between -1.6 and -0.6 W m−2 at the 16–84% confidence level - Although key uncertainties remain, new ways of using observations provide stronger constraints for models

Description: It is essential to monitor the global annual mean Earth’s Energy Imbalance (EEI) at the top of the atmosphere, as this excesss energy is accumulated in the Earth climate system, causing global warming. We propose the Earth Climate Observatory (ECO) as a new space mission concept specifically targeted to the monitoring of the global annual mean EEI. In order to reach high accuracy – with a target of 1 W/m² – and stability – with a target of 0.1 W/m²dec – we are sacrificing resolution. The core instrument is an advanced wide field of view radiometer; this instrument is capable of measuring both the incoming solar radiation, and the outgoing terrestrial radiation – both of the order of 340 W/m² - with the same instrument, and thus to make a significant measurement of the small difference – of the order of 1 W/m² (0.3%) - between these two nearly equal terms. For the sampling of the diurnal cycle of Earth’s outgoing radiation, we propose a combination of 3 orbits: 1) an orbit with precession period of 6 months, and an inclination close to 82°, providing a statistical sampling of the full diurnal cycle for midlatitude and equatorial regions every 3 months 2) an orbit with precession period of 12 months and inclination of 90°, providing a statistical sampling of the full diurnal cycle for polar regions every 6 months, 3) a noon-midnight sun synchronous orbit, providing a stable sampling of the diurnal cycle at the monthly mean level.