ARM Improves Critical Climate Measurement
Office of Science’s Atmospheric Radiation Measurement (ARM) program has improved the measurement accuracy of diffuse solar radiation by a factor of three — from about +/- 6 Watts per square meter (W/m2) to about +/-2 W/m2. The accomplishment will give scientists a better chance to predict and detect climate change resulting from increases in carbon dioxide and other greenhouse gases. Considering that the increase in atmospheric heating is projected to increase by 4 W/m2 if the amount of carbon dioxide in the air doubles, this improvement in measurement accuracy is an important achievement because the measurement accuracy needs to be as small as possible to accurately predict how much atmospheric heating will occur in the future due to increasing concentrations of atmospheric CO2 and other materials in the atmosphere that scatter and/or absorb energy. In the world of climate change, scientists understand the heating and cooling of the Earth by measuring the energy from the sun in its many forms: direct, scattered, or absorbed and re-released. Their current goal is to measure all these forms to within +/- 4 W/m2. Diffuse irradiance is the scattered energy from the direct sunlight after it hits haze particles (aerosols), cloud droplets, or molecules in the atmosphere. Results of this accomplishment provides scientists with confidence in the measurements of diffuse radiation in the atmosphere, allowing them to focus their efforts and attention on improving models that predict climate change.