Monitoring global warming with radiative forcing measurements

Climate scientists often testify before congress and other bodies on the state of the global warming problem by using temperature records; it is the wrong variable to demonstrate the state of global warming. Temperature and other changes are delayed by 25 years after changes in radiative forcing. Hence radiative forcing is the fundamental variable which should be monitored. Radiative forcing is the currency of global warming used to compare greenhouse gases and other climate forcing factors.

A new network has been proposed to monitor the radiative forcing of global warming by greenhouse gases. The calibrated spectrum of greenhouse radiation at the surface was measured for 12 years at 44N. From these measurements the radiative flux from each greenhouse gas was extracted. A 12-year record exists of the radiative fluxes from carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons. The increase of these fluxes represents the forcing function of global warming.

A world monitoring network should be set up similar to the world total ozone monitoring network consisting of ground and satellite measurements. For the ground network, the AERI instrument already exists; 22 AERIs, manufactured by ABB BOMEM, are deployed around the world. Well calibrated infrared spectral measurements of the downward infrared long-wave radiation have been made routinely with the AERI at three ARM sites for more than 7 years with a 14-year record at the SGP site. These measurements will be processed into long wave radiation fluxes from each of the major greenhouse gases using a methodology already developed for the measurements at 44° N. The satellites, IASI, GOSAT and TES are already collecting spectral data and CLARREO will fly in the future. A comparison of radiative forcing from the 44 N site with radiative forcing extracted from overpass IASI spectral measurements showed excellent agreement. A similar comparison of an ARM AERI flux measurement against an IASI overpass will be shown.

A comparison of ground fluxes with surface fluxes calculated from GCMs will be conducted. The network data could be used to investigate the seasonal and climate regime variations of the surface greenhouse radiation flux, compare the measurements with climate model simulations of the surface forcing radiation fluxes for each greenhouse gas, evaluate the reduction of the surface forcing radiation by various types of clouds by measuring the reduction in surface radiation forcing under cloudy conditions, and conduct complementary measurements of surface radiation forcing with radiative trapping measured from space with overpasses of satellites. This network will provide a new experimental dataset to complement the calculated radiative forcings from climate models currently used for policy determination of safe levels of greenhouse gases in the atmosphere. It will provide the experimental capability to conduct long-term monitoring of increases in radiative forcing from individual greenhouse gases without using an intervening climate model.

An outstanding research need is to determine the effect of clouds on radiative forcing, particularly on a regional basis. Preliminary analyses of radiative fluxes will be shown that indicate that the global warming problem is more severe than indicated by temperature records. Progress is slow due to a lack of funding. The analysis of the full dataset from ARM AERI sites, combined with the existing AERI instruments deployed around the globe, would be a significant step towards advancing the world network to monitor radiative forcing. New AERIs were setup in 2008 at Zugsptize and Eureka; these and other newer orders indicate that the potential network for radiative forcing is expanding.