A new study has found that greenhouse gases are accelerating the rise of sea levels, but the impact has been masked by a volcanic eruption that occurred more than 25 years ago.
Recorded as the second largest of the 20th century, the June 15th 1991 eruption of Mount Pinatubo in the Philippines has been distorting calculations of sea level rise acceleration for the last couple of decades.
Satellite observations of sea level began in 1993 and show that the rate of sea level rise has been quite steady at about three millimetres per year. Yet the study, led by the National Centre for Atmospheric Research (NCAR), discovered that the predicted acceleration – due to climate change – is probably hidden in satellite records because of coincidental timing.
The observations began soon after the Pinatubo eruption, which briefly cooled the planet, causing sea levels to drop.
The study, which was funded by NASA, the US Department of Energy and the National Science Foundation, supports climate model projections which show the rate of sea level rise escalating over time as the climate warms. The findings were published today in Nature journal Scientific Reports.
NCAR scientist John Fasullo, who led the study, said: “When we used climate model runs designed to remove the effect of the Pinatubo eruption, we saw the rate of sea level rise accelerating in our simulations.
“Now that the impacts of Pinatubo have faded, this acceleration should become evident in the satellite measurements in the coming decade, barring another major volcanic eruption.”
Study co-author Steve Nerem, from the University of Colorado Boulder, added: “This study shows that large volcanic eruptions can significantly impact the satellite record of global average sea-level change.
“We must be careful to consider these effects when we look for the effects of climate change in the satellite-based sea level record.”
The findings may be useful to coastal communities, as it has implications for the extent of sea level – it has been debated whether they should plan around the rate of sea level rise measured in recent decades, or on the future accelerated rate expected by climate scientists.