New paper rules out volcanoes as the cause of the 'pause'

A paper published today in Atmospheric Science Letters effectively rules out volcanoes as the main cause of the 'pause' in global warming over the past 17 years. According to the authors, "We deduce a global mean cooling of around −0.02 to −0.03 K over the period 2008–2012. Thus while these eruptions do cause a cooling of the Earth and may therefore contribute to the slow-down in global warming, they do not appear to be the sole or primary cause."

The authors find volcanic eruptions were only responsible for ~0.025C cooling over the 5 year period from 2008-2012, a rate of 0.005C cooling per year. By contrast, the globe was warming at a rate of 0.017C/year from 1979-2000 before the 'pause' in global warming, a rate that was 3.4 times higher than the cooling effect of volcanic eruptions calculated in this new paper. In addition, volcanic activity was much greater before the 'pause' than after.

Thus, volcanic activity can effectively be ruled out as an IPCC excuse for no global warming over the past 17 years.

IPCC AR5: ‘There is medium confidence that this difference between models and observations is to a substantial degree caused by unpredictable climate variability, with possible contributions from inadequacies in the solar, volcanic, and aerosol forcings used by the models and, in some models, from too strong a response to increasing greenhouse-gas forcing.’

What this means: The IPCC knows the pause is real, but has no idea what is causing it. It could be natural climate variability, the sun, volcanoes – and crucially, that the computers have been allowed to give too much weight to the effect carbon dioxide emissions (greenhouse gases) have on temperature change.

The impact of volcanic eruptions in the period 2000–2013 on global mean temperature trends evaluated in the HadGEM2-ES climate model

Jim M. Haywood, Andy Jones, Gareth S. Jones


The slow-down in global warming over the last decade has lead to significant debate about whether the causes are of natural or anthropogenic origin. Using an ensemble of HadGEM2-ES coupled climate model simulations we investigate the impact of overlooked modest volcanic eruptions. We deduce a global mean cooling of around −0.02 to −0.03 K over the period 2008–2012. Thus while these eruptions do cause a cooling of the Earth and may therefore contribute to the slow-down in global warming, they do not appear to be the sole or primary cause.

Related:
New paper finds effect of volcanoes on climate has been overestimated by factor of 2, & finds lower climate sensitivity to CO2

The '95% certainty' is that the IPCC can't be trusted