Nature Climate Change

Overestimated global warming over the past 20 years

Global mean surface temperature over the past 20 years (1993–2012) rose at a rate of 0.14 ± 0.06 °C per decade. This rate of warming is significantly slower than that simulated by the climate models participating in Phase 5 of the Coupled Model Intercomparison Project (CMIP5). To illustrate this, we considered trends in global mean surface temperature computed from 117 simulations of the climate by 37 CMIP5 models. These models generally simulate natural variability — including that associated with the El Niño–Southern Oscillation and explosive volcanic eruptions — as well as estimate the combined response of climate to changes in greenhouse gas concentrations, aerosol abundance, ozone concentrations, land use and solar variability. By averaging simulated temperatures only at locations where corresponding observations exist, we find an average simulated rise in global mean surface temperature of 0.30 ± 0.02 °C per decade. The observed rate of warming given above is less than half of this simulated rate, and only a few simulations provide warming trends within the range of observational uncertainty.

The evidence, therefore, indicates that the current generation of climate models do not reproduce the observed global warming over the past 20 years, or the slowdown in global warming over the past fifteen years.

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