F (W/m2) F(W/m2) Sensitivity 3/4°C per W/m3 1.2°C warming at equilibrium Today: 3/4° C warming + 0.6 W/m2 remaining imbalance Figure 2. Estimated change of climate forcings between 1850 and 2000, based on (1) with five principal aerosols delineated. stratospheric H2O tropospheric aerosols Figure 3. Climate forcings in the past 50 years, relative to 1950, due to six mechanisms (6). The first five forcings are based mainly on observations, with stratospheric H2O including only the source due to CH, oxidation. GHGs include the wellmixed greenhouse gases, but not O, and H2O. The tropospheric aerosol forcing is uncertain in both its Figure 4. Simulated and observed climate change for 1950-2000 (6). These simulations with GISS climate model (3) employ empirical mixing rates and fixed horizontal heat transports in the ocean (5). Climate forcings are those of Figure 3. 1.5 1.0 (a) Stratospheric Temperature (°C) [MSU Channel 4] (c) Planetary Energy Imbalance (Heat Storage in Ocean, W/m2) Figure 5. Simulated temperatures and planetary energy imbalance for the forcings in Figure 3 (6). The business-asusual (1% CO/year) adds 2.9 W/m2 forcing in 2001-2050. The alternative scenario adds a greenhouse gas forcing of Figure 6. Cartoon depicting approximate added climate forcings between in an extreme "business-as-usual" scenario and the "alternative" scenario. Figure 7. Measured greenhouse gas amounts and "alternative scenario" extensions to 2050. IS92a scenarios of IPCC (2) for CO2, CH, and N2O are illustrated for comparison. The sum of CFC and “other trace gas" forcings is constant after 2000 in the alternative scenario. |