Water vapour is a powerful greenhouse gas … and not controlled by humans (yet it is influenced by us).
What if all this extra vapour suddenly crashes back to earth? massive floods? Sea-level rise?
Surely this risk (whether it can be influenced/controlled by humans or not) underscores the importance of urgent climate action of thing we CAN control and influence — emissions cutting, urgent reform of the finance system so emerging economies can get loans more cheaply so they don’t go down the fossil-fuel route.? At the moment poor nations pay much higher interest rates than wealthy ones.
This correlation between water vapour and massive record temperatures in 2024 needs more investigation.
- The total amount of water in the atmosphere reached a record value in 2024, at 4.9% above the 1991–2020 average, markedly higher than in 2016 (3.4%) and 2023 (3.3%), the years with the second and third highest values.
Figure 11. Annual anomalies in the average amount of total column water vapour over the 60°S–60°N domain relative to the average for the 1992–2020 reference period. The anomalies are expressed as a percentage of the 1992–2020 average. Data: ERA5. Credit: C3S/ECMWF.
Figure 12. Anomalies and extremes in the amount of total column water vapour for 2024. Colour categories refer to the percentiles of the temperature distributions for the 1992–2020 reference period. The extreme (‘lowest’ and ‘highest’) categories are based on rankings for 1992–2024. Data source: ERA5. Credit: C3S/ECMWF.
Water vapour plays a crucial role in the climate system, as it significantly contributes to Earth’s natural greenhouse effect. Unlike other greenhouse gases, such as carbon dioxide and methane, the concentration of water vapour is not directly influenced by human activities. However, as the atmosphere warms, it can hold more water vapour (about 7% more for each additional degree Celsius). In turn, the greater water vapour content further amplifies warming, a process known as ‘temperature-water vapour feedback’. Increased moisture in the atmosphere also heightens the potential for extreme rainfall events and provides energy for more intense tropical storms.
‘Total column water vapour’, referred to as ‘water vapour’ here, is a measure of the amount of moisture in a vertical column of air extending from Earth’s surface to the top of the atmosphere. In 2024, the annual average water vapour over the 60°S–60°N domain reached its highest value in at least 33 years, at 4.9% above the 1991–2020 average. This is well above the second highest value (3.4%) recorded in 2016 and third highest value (3.3%) recorded in 2023. The record high water vapour value for 2024 was influenced by a combination of increased surface evaporation from the ocean due to higher sea surface temperatures and by the ability of a warmer atmosphere to hold more moisture.