Tungurahua volcano spewing gas and ash near Banos, about 178 km south of Quito, Ecuador. The volcano has been in an active state since October 1999. Photo: Carlos Campana/Reuters

Volcanoes have cancelled out some of the effects of global warming over the past decade and given a false impression of the rate of climate change, research has shown.

The atmospheric impact of volcanic eruptions was not included in climate forecasts, leading them to overestimate the speed at which temperatures were rising, say scientists.

Critics have questioned the predictions of climate experts after surface temperature measurements indicated a slowdown in warming since 1998.

The new research suggests volcanic activity played a major role in bringing about the climate change “pause”.

Other explanations have included natural climate variability and observational errors.

Incorporating volcanic influences into the climate models reduced the difference between observed and simulated trends by up to 15 per cent.

The US scientists, led by Benjamin Santer, from the Lawrence Livermore National Laboratory in California, wrote in the journal Nature Geoscience: “We show that climate model simulations without the effects of early 21st century volcanic eruptions overestimate the tropospheric warming observed since 1998.

“To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.”

Powerful volcanic eruptions send small sulphur droplets, or aerosols, high into the atmosphere where they act as a mirror to reflect the sun’s rays and prevent them from warming the ground.

In 1991, the second largest volcanic eruption of the 20th century occurred when Mount Pinatubo in the Philippines exploded with enormous force, killing almost 1,000 people and causing widespread damage.

Millions of tons of ash and gas were blasted into the atmosphere from the mountain, reaching an altitude of 33.7 kilometres. Over the next two years, average temperatures across the whole of the earth fell by up to 0.5˚C.

The research showed that Mount Pinatubo and the earlier major eruption of El Chichon in Mexico in 1982 “had important impacts on decadal changes in warming rates”.

In addition, 17 “small” eruptions occurred after 1999 which had a cumulative effect increasing the reflective effect of aerosols in the upper atmosphere by up to seven per cent per year from 2000 to 2009.

British climate expert Piers Forster, from the University of Leeds, said: “Volcanoes give us only a temporary respite from the relentless warming pressure of continued increases in CO2 (carbon dioxide).”