Moistening Atmosphere

[CC image, credit: ]
The Atmosphere can be divided into layers. The Troposphere is the layer that is closest to the surface. When rising up in the Atmosphere, the next layer up is the Stratosphere. The next layer up is the Mesosphere and the fourth layer from the bottom is the Thermosphere.

The temperature rises or falls in a different way in each of these layers, as illustrated by the image CC from

As the temperature rises at the surface as a result of emissions by people, more water vapor enters the atmosphere. Since warmer air holds more water vapor, the amount of water vapor in the air above the surface has been increasing for some time. The atmosphere can hold 7% more water vapor for every 1°C warming. The extra water vapor is further amplifying the temperature rise, since water vapor is a potent greenhouse gas.

[ click on images to enlarge ]
The IPCC says: "Water vapour feedback acting alone approximately doubles the warming from what it would be for fixed water vapour. Furthermore, water vapour feedback acts to amplify other feedbacks in models, such as cloud feedback and ice albedo feedback. If cloud feedback is strongly positive, the water vapour feedback can lead to 3.5 times as much warming as would be the case if water vapour concentration were held fixed".

The temperature rise due to extra water vapor works immediately, i.e. it goes hand in hand with rises due to other warming elements. Research indicates that, if the temperature of Earth rises by 1°C, the associated increase in water vapor will trap an extra 2 Watts of energy per m².

Evaporation and Evapotranspiration

Most of the extra water vapor that is entering the atmosphere will come from oceans. As the sea surface heats up, more evaporation takes place.

[ image credit: NOAA ]
Some of the extra water vapor will also come from the soil and from transpiration from leaves, stems and flowers of plants. Evapotranspiration includes water evaporation into the atmosphere from the soil surface, evaporation from the capillary fringe of the groundwater table, and evaporation from water bodies on land.

A lot of the water vapor will return to the surface in the form of more precipitation, and increasingly so, as discussed at this facebook post, yet many places on land will experience a net loss of moisture from land, vegetation, rivers and lakes, and this can contribute to an increase in the severity of droughts, heatwaves and fires.

Extra water vapor in the Stratosphere

The stratosphere normally is cold and very dry. Rising temperatures can increase water vapor in the stratosphere in a number of ways. As temperatures rise, water vapor in the Troposphere increases (as described above) and the intensity of storms increases. This can result in stronger storms moving more water vapor inland over the U.S., and such storms can cause large amounts of water vapor to rise high up in the sky. As a result, water vapor can reach stratospheric altitudes causing loss of ozone, as James Anderson describes in a 2017 paper and discusses in the short 2016 video below.

Furthermore, extra water vapor in the atmosphere can result from changes taking place in the Arctic and the North Atlantic, as described at the page Cold freshwater lid on North Atlantic. As illustrated by the image below, relative humidity was as high as 35% at 10 hPa in the stratosphere over the North Atlantic on January 24, 2023 12:00 UTC (at the green circle).

Furthermore, when methane decomposes, water vapor is formed and both methane and water vapor are potent greenhouse gases. Methane already contributes strongly to the temperature rise and methane has the potential to cause even more damage on top of this, as extra water vapor can reach the stratosphere and this can damage the ozone layer.

The Importance of the Ozone Layer

Increases in stratospheric water vapor are bad news, as they speed up global warming and lead to loss of stratospheric ozone, as Drew Shindell pointed out back in 2001.

It has long been known that deterioration of the ozone shield increases ultraviolet-B irradiation, in turn causing skin cancer. Recent research suggest that, millions of years ago, it could also have led to loss of fertility and consequent extinction in plants and animals (see box right).

Sudden Stratospheric Warming

Large amounts of water vapor can enter the Stratosphere accompanying a Sudden Stratospheric Warming event. 

These phenomena occur in Winter on the Northern Hemisphere when little sunlight is reaching higher latitudes on the Northern Hemisphere and temperatures over land can get very low. Global overheating is causing deformation of the Jet Stream, at times resulting in very cold air descending from the Arctic to North America and Eurasia. At the same time, global warming has made oceans warmer and this keeps air temperatures over water relatively warm. This temperature difference strengthens the wind. Stronger wind and higher sea surface temperatures result in more evaporation, causing heat and water vapor to rise up strongly into the atmosphere, particularly from the North Atlantic Ocean and the Arctic Ocean.

[ Relative humidity at 10 hPa, Dec. 24, 2016 ]
As said, this can lead to a number of phenomena including moistening of the stratosphere and Sudden Stratospheric Warming, while a cold snap at surface level can follow the rise of heat and water vapor to higher altitudes.

Relative humidity as high as 100% is visible in the stratosphere at 10 hPa on the December 24, 2016, image on the right (green circle).

The image below shows that, on February 1, 2023 11:00 UTC, the temperature in the stratosphere at 10 hPa was as high as 14.6°C or 58.2°F (at the green circle).

As illustrated by the image below, the 1-day area weighted 2 m temperature anomaly over the Arctic was 3.46°C on February 1, 2023.

The 2023 Sudden Stratospheric Warming event was preceded by moistening of the Stratosphere over the North Atlantic and the Arctic starting in November 2022. The image below shows relative humidity as high as 34% in the Stratosphere at 10 hPa on November 29, 2022 02:00 UTC. 

Submarine volcano eruptions

Finally, extra water vapor can enter the Stratosphere as a result of submarine volcano eruptions. The Tonga eruption in January 2022 sent a huge plume up into the Stratosphere. Because it was a submarine volcano eruption, a huge amount of water vapor entered the Stratosphere, as discussed in this facebook post and the comments underneath.

As temperatures keep rise, Earth looks set to move into a moist-greenhouse state

As temperatures keep rising, runaway heating may well turn Earth into a lifeless planet. This danger was discussed in a 2013 post, warning that Earth could move into a moist-greenhouse state and without anything stopping the temperature rise, this will continue to eventually destroy the ozone layer and the ice caps, while the oceans would be evaporating into the atmosphere's upper stratosphere and eventually disappear into space, as this 2019 post warns. 

In the 2013 analysis Trajectories of the Earth System in the Anthropocene, Will Steffen et al. warn that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a “Hothouse Earth” pathway even as human emissions are reduced.