Subscribe
Wildfires and volcanic eruptions have long been known to affect the Earth’s climate by releasing smoke, greenhouse gases and aerosols into the atmosphere. A new study has found that both events can also have significant indirect impacts on the planet by increasing the amount of water vapour entering the stratosphere.
The July 1 study, published in the journal Nature by researchers from China and the US, explored how moderate volcanic eruptions and extreme wildfires contribute to atmospheric water vapour, a greenhouse gas (GHG). The scientists found that between 2005 and 2021, these sources increased stratospheric water vapour by 76-203 million tonnes at 83 hectopascals (hPa, a unit used to measure atmospheric pressure that corresponds to more than 17,000 metres above mean sea level). This volume accounts for 36 per cent of the observed rise in stratospheric water vapour during the period under study.
This finding is significant because changes in the stratosphere, the second layer of the Earth’s atmosphere some 10-50 km above the surface, has major impacts on the planet’s climate. Water vapour decreases the temperature in the stratosphere by reflecting back radiation coming from space. It also interacts with the radiation coming from the Earth’s surface and reflects it back towards the planet. This increases the temperatures towards the Earth’s surface.
These changes, in turn, modify weather patterns in the troposphere, the atmospheric layer closest to the Earth, causing extreme events such as heatwaves, cold waves and storms.
Previous research has shown that water vapour enters the stratosphere through different sources; for instance, it can travel up through the tropopause, or the boundary between the troposphere and stratosphere. This movement is strongest in the tropics, Martin Jucker, climate scientist with University of New South Wales, Australia, tells Down To Earth (DTE). “The tropics are the one place on Earth where air generally moves upward in both the troposphere and the stratosphere. Due to this upward motion, which cools the air, the tropical tropopause is also where the troposphere is coldest,” he says.
Jucker adds that cold temperatures regulate how much water vapour enters the stratosphere. As air passes through the coldest part of the atmosphere, most water vapour is removed—a process known as “freeze drying”. Due to this, only trace amounts of water vapour remain as gas and enter the stratosphere. This is also the reason that stratospheric water vapour is at its minimum rate during…
This article was originally published in the September 1-15, 2026 print edition of Down To Earth