They used solar and volcanic variations much larger than those that actually occurred since 1979.
They ran the different models under various physical scenarios, including changes in solar irradiance, volcanic eruptions, and increased sulfate aerosols and greenhouse gas emissions.
Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions, and persistent anthropogenic changes in the composition of the atmosphere or in land use".
As an example, we focus on the response to solar and volcanic forcing in the context of the Maunder Minimum, a cool period of the late 17th century and demonstrate that although (northern) hemispheric mean temperature changes can be reasonably simulated in most models, the details of regional patterns depend more heavily on the included physics.
There are greenhouse gases, yes, but there are also solar variations, volcanic eruptions and the El Niño-La Niña oscillation.
Examples of external forcings include changes in atmospheric composition (e.g., increased concentrations of greenhouse gases), solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun.
But Jones was very clear that neither scenario, nor any other prior periods of solar and/or volcanic forcing, would be relevant to the rise in global temperatures during the past 60 years.
We also attempted to relate the spatial distribution of European temperature anomalies to known solar and volcanic forcings.
However, further work is needed to understand the role of external forcing, perhaps through indirect aerosol effects [ Booth et al., 2012; Dunstone et al., 2013], which are not included in these models or natural forcing (such as solar and volcanic: [ Menary and Scaife, 2014]).
