The eruption of Tonga’s underwater volcano in 2022 may cause global temperatures to rise, raising the risk that at least one year in the next five will temporarily exceed the 1.5C warming threshold, new research finds.
On 15 January 2022, an underwater volcano in Tonga – the Hunga Tonga–Hunga Ha’apai – erupted violently, releasing billowing plumes of soot, water vapour and sulphur dioxide high into the atmosphere.
Major volcanic eruptions typically cool the planet temporarily, because, until they dissipate, sulphur dioxide particles reflect sunlight away from the planet. However, the study – published in Nature Climate Change – finds that the Tonga eruption in the south Pacific expelled an unprecedented amount of water into the atmosphere.
Water vapour is a greenhouse gas and so “it is possible that over a multiyear period Hunga Tonga–Hunga Ha’apai will cause a temporary increase in global surface temperatures”, the paper says.
The study says that, before the eruption, there was a 50-50 chance that global temperatures would exceed 1.5C above pre-industrial levels at least once by 2026. In its aftermath, the likelihood of exceeding this threshold has increased by seven percentage points – making “imminent 1.5C exceedance” more likely than not.
The authors stress that temporarily crossing the 1.5C threshold would not equate to missing the Paris Agreement target, which concerns long-term temperature trends. Nevertheless, the paper says “the first year which exceeds 1.5C will garner substantial media attention, even if a portion of this results from Hunga Tonga–Hunga Ha’apai”.