The Problem

Ground-based measurements indicate that the amount of solar radiation reaching the surface of the Earth decreased significantly during the three decades from 1960 to 1990. The term Global Dimming was coined to describe this phenomenon. More recent surface observations as well as satellite observations suggest that this trend has reversed since 1990 (Global Brightening). The reasons for these variations are not clear, but must be linked to changes in atmospheric properties – clouds, aerosols, gases – and not the Sun, since solar irradiance variations are small compared to the observed dimming/brightening. Such trends in solar radiation could have profound effects on climate and biogeochemistry, including hydrology, agriculture and land use, on both global and regional scales. For example, dimming would reduce greenhouse warming rates, while brightening would amplify greenhouse effects. It is of critical importance to review the observational basis for these trends, the factors controlling them, and their environmental impacts.

Workshop Objectives

· Critically review the surface and satellite observational evidence for global dimming/brightening, including instrument calibration issues

· Evaluate possible causes of global dimming/brightening

· Assess the impact of global dimming/brightening on climate change and biogeochemistry, including land use, hydrology and agriculture

· Recommend research activities to advance our knowledge of all aspects of the global dimming/brightening problem

· Plan coordination mechanisms to facilitate progress on needed developments

Output

A workshop report that will summarize workshop deliberations and include a prioritized list of needed research and development plans of various research groups, and how these groups could better coordinate their activities. Workshop Summary will be submitted for publication in AMS BAMS or AGU EOS.

Participants (by invitation)

Scientists working in the following areas: surface and satellite observations of solar radiation, clouds and aerosols, aerosol physics, climate modeling, agriculture, hydrology and land use.

Papers

Papers presented at the conference may be submitted to the Journal of Geophysical Research – Atmospheres for publication in a special section devoted to the workshop. Currently we are requesting permission for this, and will inform participants later on whether it has been approved.