The main greenhouse gas is not CO2 or methane, but water vapor. The underwater volcano Tonga-Hunga, which erupted on January 15, has released over 41 billion gallons of water into the atmosphere, the equivalent of 58,000 Olympic sized swimming pools. This is the observation of the eruption, which has reached into the stratosphere, according to NASA:
According to a paper published in the journal Nature, the eruption may have become the largest explosion on Earth in modern times. A National Geographic article summarized their findings with these words:
It undoubtedly ranks among the most powerful explosions ever observed and triggered atmospheric gravity waves that reached the edge of space, reverberated around the Earth, and reached up to 100 kilometers into the ionosphere.
Gravity waves circled the globe four times as the debris spat into the atmosphere and reached a height of 50 kilometers.
According to the study The Hunga Tonga-Hunga Ha'apai Hydratation of the Stratosphere, in Geophysical Research Letters, the volume of water released into the atmosphere will warm the globe for a period that is difficult to specify but could be as long as five years.
Volcanoes, in general, contribute to the cooling of the globe. The reason is that they emit sulfur dioxide to the higher layers, which reflect the sun's rays, as explained by National Geographic. But in this case, the volume of water has been so large that the greenhouse effect has more than offset the effects of SO2 (sulfur dioxide).
NASA's Jet Propulsion Laboratory, based in California, had already published a study according to which the volcano has released a gigantic amount of water into the atmosphere. A quantity that still has to be calibrated, but whose effects on the climate were already warned by its authors: "This eruption could affect surface warming due to radiative forcing from excess stratospheric water". Radiative forcing is the term used by the IPCC to refer to the greenhouse effect.