Many people in the climate discussion refer to volcanoes. They are used on both sides of the discussion. They are often seen as an aberration of our climate, in that they cause things to happen which would not otherwise occur, in both the short and long run. I disagree. I believe they are every bit of the natural part of our climate and that large eruptions have very little effect on our climate. More specifically our global temp anomaly. Volcanoes, in some part of this world are always erupting. I should point out there are various types and subtypes of volcanoes. For today’s purposes, I’m not making any distinction. Today I want to examine the temp responses to the large eruptions of the last century. The criteria I will use is the VEI. We will examine the volcanoes of the last century with a VEI of 5 or 6. There were no 7 or greater. The Tropospheric injection and
Stratospheric injection are described as “substantial“.
Here is the listing of 5-6 volcanic eruptions last century.
6 Santa Maria 1902 5 Ksudach 1907 6 Novarupta 1912 5 Colima 1913 5 Cerro Azul 1932 5 Kharimkotan 1933 5 Bezymianny 1956 5 Mount Agung 1963 5 Mount St. Helens 1980 5 El Chichon 1982 6 Mount Pinatubo 1991 5 Mount Hudson 1991
Starting with Santa Maria of 1902 see a slight drop of 0.2°C over a 3 year period of time. Then things continue as they were.
For Ksudach, we can’t really tell, the temps went down and then up and then down again, so we’re not certain about the effects of time but at most it can be described as causing a -0.3°C change over 4 years.
Novarupta didn’t seem to have much of any effect…. if it did the time it did was very short. and the Colima had the inverse if at all.
Again we have two volcanoes and a very negligible effect. Cerro Azul could have caused a -0.4°C decline over 2 years, but then Kharimkotan would then have had zero effect.
Here we have a WTF? moment. Bezymianny erupted over the period of time covering 55-57. And the temps responded by increasing by about 0.6°C.
Mount Agung has a near equal and opposite response!!!!
Okay, so Mt. St. Helens effect was negligible. But, the temps cooled after Chichon.
1991 marked a year in which there were two significant eruptions. Mount Pinatubo, and the less famous Mount Hudson.
One would have thought we would have seen a very strong signal with a 5 and a 6 occurring in the same year. But, temps started to climb in 1993.
Contrast these to other known climatic variations…….
The El Nino of 1998 had a temp response of a positive 0.6°C and the 2007-2008 La Nina had a temp response of -0.5°C. There is no compelling reason to believe volcanic eruptions of the 5-6 magnitude significantly alters any temp anomaly for any real duration. And they don’t seem to be outside the normal variations of just regular every year temp anomalies. We looked at 12 eruptions. Two of them the temps responded by increasing. Another’s effect seemed null. The most recent two didn’t cause anything outside normal variation in spite of occurring within the same year.