{"id":40514,"date":"2025-05-23T09:53:13","date_gmt":"2025-05-23T07:53:13","guid":{"rendered":"https:\/\/www.wearewater.org\/?post_type=waw_insight&p=40514"},"modified":"2025-05-23T14:09:41","modified_gmt":"2025-05-23T12:09:41","slug":"water-vapour-a-little-known-heater","status":"publish","type":"waw_insight","link":"https:\/\/www.wearewater.org\/en\/insights\/water-vapour-a-little-known-heater\/","title":{"rendered":"Water Vapour. A Little-Known Heater"},"content":{"rendered":"
<\/div>

Most people are unaware that water vapour is the atmosphere’s most abundant greenhouse gas (GHG). Since it is not directly linked to the burning of fuels, it is rarely associated with human activity\u2014unlike carbon dioxide (CO\u2082) and methane (CH\u2084), the better-known GHGs. The combustion of fossil fuels primarily releases CO\u2082, while methane largely comes from livestock farming, landfills, rice cultivation, and leaks during the extraction and transport of gas and oil.<\/p>\n

However, water vapour enters the atmosphere through evaporation, mainly from the oceans, due to heat. It is thus part of one of the essential phases of the planet\u2019s water cycle: evaporation, condensation, and precipitation.<\/p>\n<\/div><\/div>

\"We

Simulated ECMWF images showing how water vapour is distributed in the upper layers of the atmosphere over the African continent, as seen from a satellite. These help forecast phenomena such as storms or cyclones by identifying zones of instability and air movement up to ten days in advance. You can browse the atmospheric water vapour simulation catalogue here<\/a>. <\/em>\u00a9 <\/em>ECMWF<\/em><\/p>\n<\/div><\/div>\n\n

More Heat, More Vapour<\/h2><\/div>

In the atmosphere, water vapour acts like other greenhouse gases, such as CO\u2082 and CH\u2084, by trapping heat that would otherwise escape into space. This creates a positive feedback loop: the more heat and evaporation; the more vapour, the greater the atmosphere\u2019s capacity to retain heat. In other words, warming induces more humidity, and that humidity amplifies the warming.<\/p>\n

The ocean holds 96.5% of all water on the planet\u2014around 1,338 million km\u00b3. By contrast, the water present in the atmosphere totals just 12,900 km\u00b3, a mere 0.001% of the total. It\u2019s a tiny proportion, but one with an outsized role: beyond determining rainfall patterns, water vapour, together with air temperature, regulates the energy balance of the atmosphere.<\/p>\n

At a planetary scale, the water cycle may seem minimal. But at the scale of the biosphere\u2014the thin atmospheric layer where life thrives\u2014the axis sustains it. This is why any change in water vapour distribution can disrupt the cycle and deeply affect climate phenomena: droughts, floods, hurricanes, typhoons, or polar ice melt.<\/p>\n<\/div><\/div>\n\n

Warming Oceans Are a Key Factor in Extreme Weather<\/h2><\/div>

Warmer seas mean more water vapour, and oceans are steadily heating up<\/a>. A key effect of global warming is that most of the added energy in the climate system accumulates in the sea. It\u2019s estimated that oceans absorb around 89% of the excess heat in the atmosphere, raising water temperatures and causing thermal expansion\u2014already evident in rising sea levels<\/a>.<\/p>\n

In 2024, the average sea surface temperature reached a historic high: 20.87\u202f\u00b0C, which is 0.51\u202f\u00b0C above the 1991\u20132020 average. This warming caused a significant increase in atmospheric water vapour and an uneven redistribution of moisture on a global scale.<\/p>\n

According to the Copernicus Climate Change Service<\/a>, 2024 was the hottest year on record and was accompanied by 5% more water vapour in the atmosphere compared to the reference period. This isn\u2019t just a data point\u2014it\u2019s an accelerator of extreme events, and 2024 was devastating.<\/p>\n

Extreme rainfall intensified. A DANA storm hit Valencia,<\/a> Spain, causing 228 deaths. In Kenya\u2019s capital, Nairobi, catastrophic floods in the informal settlements of Kibera, Mathare, and Mukuru left at least 188 dead and nearly 200,000 displaced.<\/p>\n

Elsewhere, unprecedented heatwaves struck across the globe. India and Pakistan recorded 50\u202f\u00b0C in Shaheed Benazirabad, 8.5\u202f\u00b0C above average. In New Delhi, temperatures reached 49\u202f\u00b0C\u2014one of the longest heatwaves in its history. In April, Thailand, Vietnam, and the Philippines saw highs of 38.8\u202f\u00b0C. In Europe, Greece and Turkey exceeded 43\u202f\u00b0C and 44\u202f\u00b0C starting in June. During the Hajj pilgrimage, Mecca reached 49\u202f\u00b0C, contributing to the deaths of over 1,300 pilgrims. Even Antarctica, in July, experienced an unprecedented winter heatwave, with temperatures up to 28\u202f\u00b0C above seasonal norms.<\/p>\n

This warming is no fluke. In addition to ocean heating, it\u2019s linked to broader patterns such as El Ni\u00f1o <\/a>and ice loss. Scientists expected global cooling with the arrival of La Ni\u00f1a<\/a>, but it hasn\u2019t occurred.<\/p>\n<\/div><\/div>

\"We

Any change in water vapour distribution can disrupt the cycle and deeply affect climate phenomena. \u00a9 Pok Rie \/pexels<\/p>\n<\/div><\/div>\n\n

To Measure to Anticipate and Mitigate<\/h2><\/div>

More vapour in the atmosphere means more energy available to fuel intense rainfall, destructive storms, and extreme weather events. The good news is that understanding water vapour\u2019s role helps improve extreme weather prediction and design more accurate early warning systems.<\/p>\n

Organisations such as the European Centre for Medium-Range Weather Forecasts (ECMWF<\/a>), which manages the Copernicus Climate Change Service, and the US National Oceanic and Atmospheric Administration (NOAA), which runs the GFS model, lead global monitoring of key atmospheric variables like water vapour.<\/p>\n

Copernicus provides an open-access portal<\/a> where anyone, from scientists and journalists to citizens, can consult and download climate data, satellite imagery, maps, projections, and historical analysis.<\/p>\n

The atmosphere is responding to a new climatic balance, where every drop of humidity matters and every fraction of a degree transforms its behaviour. In the global climate crisis context, free and rigorous access to scientific data is more important than ever. We must understand atmospheric variables and measure them using reliable scientific tools developed by agencies with decades of experience. Climate science saves lives<\/a>, and scientists are our most reliable witnesses<\/a>. Trusting and supporting them is the responsibility of governments, the media, and each of us.<\/p>\n<\/div><\/div>

\"We

Warmer seas mean more water vapour, and oceans are steadily heating up<\/a>. A key effect of global warming is that most of the added energy in the climate system accumulates in the sea.. \u00a9 Sebastian Voortman\/pexels<\/p>\n

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