Global Warming Is Driven by Anthropogenic Emissions: A Time Series Analysis Approach

The solar influence on global climate is nonstationary. Processes such as the Schwabe and Gleissberg cycles of the Sun, or the many intrinsic atmospheric oscillation modes, yield a complex pattern of interaction with multiple time scales. In addition, emissions of greenhouse gases, aerosols, or volcanic dust perturb the dynamics of this coupled system to different and still uncertain extents. Here we show, using two independent driving force reconstruction techniques, that the combined effect of greenhouse gases and aerosol emissions has been the main external driver of global climate during the past decades.

Figure 1

Time-series data employed in this study. Yearly averages of (a) temperature anomalies ($°\mathrm{C}$), (b) solar total irradiance ($\mathrm{W}/{\mathrm{m}}^2$), (c) equivalent radiative forcing for ice core volcanism ($\mathrm{W}/{\mathrm{m}}^2$), and (d) anthropogenic components ($\mathrm{W}/{\mathrm{m}}^2$). Solid line: Equivalent radiative forcing for ${\mathrm{CO}}_2$ and other well-mixed trace gases (methane, nitrous oxides, and chlorofluorocarbons). Dashed line: Direct radiative forcing effect of tropospheric aerosols (no cloud feedback).

Figure 2

Reconstruction of external forcing (thin line) using the first estimation methodology. Dashed lines embrace 1 standard deviation. For comparison, the evolution of combined GHG and aerosol radiative forcing levels is indicated with a thick line.

Figure 3

Estimated external driving force (thin line) acting on global climate using the second reconstruction methodology. The profile of combined GHG and aerosol radiative forcing effects is again represented with a thick line.

Figure 4

Point-by-point prediction errors of a $3:10:1$ ANN model of temperature anomalies as a function of time.