Earth’s energy balance since 1950

Combining the powerful notion that energy is conserved with observational data on surface temperature, ocean heat content, and radiative fluxes, researchers have determined our planet’s energy budget for the past half century—without recourse to any climate models. Energy in the form of heat is added to Earth by the Sun’s direct radiation and by the well-characterized radiative contributions from greenhouse gases. Those positive contributions (so-called forcings) are balanced, as shown in the figure, by stratospheric aerosols of volcanic origins that reflect incoming sunlight, increased outgoing IR radiation from a warming Earth, long-term heating of Earth—almost entirely of its oceans, which have far higher heat capacities than the atmosphere, land, or ice—and a residual term that mainly represents direct and indirect cooling effects of anthropogenic aerosols throughout the atmosphere. The analysis shows that the anthropogenic aerosols contribute a net cooling of 1.1 Wm², in agreement with the 2007 assessment by the Intergovernmental Panel on Climate Change but with tighter error bars. The researchers, led by Daniel Murphy of the National Oceanic and Atmospheric Administration in Boulder, Colorado, say that the agreement gives confidence both in their technique and in the global circulation models used by the IPCC. They also found that the aerosols’ effects over time reflected the stabilized amount of atmospheric sulfates that resulted from the adoption of emission controls in North America in the 1970s. (D. M. Murphy et al., J. Geophys. Res. 114 , D17107, 2009. http://dx.doi.org/10.1029/2009JD012105 )