[yvely]

It surprises me Tonga eruption rarely or ever mentioned in relation to the last years record heat. It was predicted when it happened that it might lead to some temporary years of more heat. I don't have the knowledge to say if this is the primary reason, but it seems disingenuous of experts and news media to represent this purely as a consequence of our emissions.

[southernplaces7]

The Tonga eruption should have slightly cooled the earth instead of warming it. Volcanic eruptions usually do. Their emissions of sulfur dioxide, which converts to sulfuric acid, which itself then condenses rapidly in the stratosphere to form fine sulfate aerosols are much more impactful in lowering temperatures than is their emission of carbon dioxide in increasing temperatures.

Some practical evidence in favor o this: Of the major volcanic eruptions in the last couple centuries, almost all notably cooled the Earth and none created notable warming. The, 1784 Laki fissure eruption, the 1883 Krakatoa and the 1815 Tambora eruptions being three especially obvious examples of that cooling in action.

[yvely]

Wasn't this fairly special due to the amount of vapour? I remember reading it increased atmospheric water content by like 10%. It's so unimaginable to me that it simply is not related to record years.

[jfengel]

Water vapor doesn't remain in the air for long. Unlike CO2 and sulfur dioxide, water vapor condenses to liquid water and falls out of the atmosphere.

So a volcano's water vapor effects (warming) can last days, while the sulfur dioxide effects (cooling) will last months or years.