How Long Could the Current Hiatus in Global Warming Last?

While future projections of global mean temperature show a pronounced warming over the 21st century as a whole, the rate of warming appears to have slowed during the period since about 1998—the so-called global warming ‘hiatus'. Furthermore, global mean temperature did not rise steadily since the late 1800s but rose primarily during two rapid warming periods (early 20th century and late 20th century) which were separated by a pause in warming from about 1940-1970. Could another such multidecadal pause occur at the beginning of the 21st century, and if so by what processes could this occur? While at one extreme, the global warming hiatus could end shortly (or may have already ended), at the other extreme we ask: How long could the current hiatus in global warming potentially last? To explore this issue, we analyze the internal multidecadal variability of global mean temperature in CMIP5 model control runs and test the influence of such internal variability on 21st century global mean temperature evolution, including current projections of future warming from anthropogenic forcings (e.g., CMIP5 models). We also assess the plausibility of multidecadal variability as simulated by the GFDL CM3 climate model based on comparisons with historical trends.