Are Land Volcanos affecting the climate?

The heat of the earth does not appreciably warm the climate. This flow of heat, arising from the earth’s core and from radioactivity is only 0.04 to 0.1 watts per square meter, compared to the sun’s average daily radiation of 200 watts per square meter.

Most volcanic eruptions also do not affect world climate. To do so, volcanos need to have a VEI (Volcanic Explosion Index) of 5 or more among other characteristics. (Each additional point in the VEI equals 10 times more power.) Almost all of the rare eruptions of this magnitude put up a veil of particulates and gases that blocks the sun and decreases worldwide temperatures. If the eruption is super large and long-lasting, oceans will cool, and thus a reduced worldwide temperature can persist for years. The VEI 7 eruptions, of Mount Samalas in the year 1257, of the unknown volcano of 1452, and of Mount Tambora in 1815, each have depressed worldwide temperatures for a decade¹.

A series of major eruptions during the 13th -19th century may partially explain the 0.4º temperature drop of the Little Ice Age² ³⁴in the northern hemisphere. I couldn’t discern in the temperature record any changes from the major eruptions of 1902, 1906, or 1912, but Mt. Pinatubo’s eruption in 1991 (VEI of 6 and having the largest effect in the stratosphere of the 20th century) is likely responsible for a large dip in temperature that persisted through 1993.

Volcanic eruptions can increase the earth’s temperature for a short time if they inject, immediately or through diffusion, ozone depleting compounds into the stratosphere. A warming effect sometimes follows a minor cooling one. And in 2022 the truly exceptional underwater volcano Hunga Tonga injected water into the stratosphere augmenting greenhouse warming. In general, though, extraordinary volcanic eruptions have cooled the climate, and are not responsible for climate warming.