Moistening Atmosphere

[CC image, credit: nptel.ac.in ]

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 archive.nptel.ac.in.

The image below is from an analysis by Karina von Schuckmann et al. and shows that the Earth is heating up, as outgoing radiation is suppressed. More and more extra heat is kept captive on Earth and gets stored mainly in oceans (89%), with smaller proportions getting stored on land (6-5%), in the cryosphere (4%) and in the atmosphere (1-2%).

The above image also shows that, for the period going back to 1971, 1% more heat gets stored in the atmosphere, while 1% less gets stored on land, compared to the period going back to 2006. The image below takes a closer look at that.

Of the heat that is absorbed by continents, huge amounts of heat go into the ground (90%), with inland water bodies accounting for 0.7% and permafrost thawing accounting for 9%. At the same time, even more energy goes into evaporation from land and lakes, and into thawing permaforst. Water that previously remained present in the ground, is increasingly moving up into the atmosphere, since a warming atmosphere holds more water vapor (7% more water vapor for every 1°C warming) and thus sucks up increasingly more water. More energy gets consumed in the process of evaporation from land and from lakes, and in the process of thawing permafrost, but these are finite resources. Indeed, as land dries out, lakes dry up and permafrost shrinks, these resources dwindle. There is a point where there is no more water available in the soil, in lakes and in permafrost, and the heat previously consumed by evaporation and thawing will instead remain in the atmosphere. More water vapor in the atmosphere further amplifies the temperature rise, since water vapor is a potent greenhouse gas, and this also contributes to speeding up the temperature rise of the atmosphere.

The Land Evaporation Tipping Point can get crossed locally when water is no longer available locally for further evapotranspiration from the soil and vegetation, with the rise in land surface temperatures accelerating accordingly.

[ 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 ]

A lot of the water vapor will return to the surface in the form of more precipitation, and increasingly so, as discussed at here and here, increasing the amount of water that storms can dump and the impact of flooding, erosion and run-off of chemicals, fertilizers, pesticides, etc.

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.

Therefore, as the air increasingly sucks up moisture, many places on land will experience a net loss of moisture from the soil and from vegetation, rivers and lakes, and an increase in the impact of droughts, heatwaves and fires

[ Click on images to enlarge. Credit: UNEP Foresight Brief 025 ]

Atmospheric vapor pressure deficit

An atmosphere that sucks up more water vapor increases the atmospheric vapor pressure deficit (VPD). A 2019 study warns that increased VPD reduces global vegetation growth: "VPD greatly limits land evapotranspiration in many biomes by altering the behavior of plant stomata. Increased VPD may trigger stomatal closure to avoid excess water loss due to the high evaporative demand of the air. In addition, reduced soil water supply coupled with high evaporative demand causes xylem conduits and the rhizosphere to cavitate (become air-filled), stopping the flow of water, desiccating plant tissues, and leading to plant death. Previous studies reported that increased VPD explained 82% of the warm season drought stress in the southwestern United States, which correlated to changes of forest productivity and mortality. In addition, enhanced VPD limits tree growth even before soil moisture begins to be limiting."

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 January 2022 submarine volcano eruption near Tonga did add a huge amount of water vapor to the atmosphere, as discussed in an earlier post and also at facebook. Since water vapor is a potent greenhouse gas, this is further contributing to speeding up the temperature rise. A 2023 study calculates that the eruption will have a warming effect of 0.12 Watts/m² over the next few years.

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 rising, Earth looks set to move into a moist-greenhouse state

As temperatures keep rising, a moist greenhouse looks set to turn Earth into a lifeless planet. The danger was discussed in a 2013 post that warns that Earth is on the edge of the habitable zone and is at risk of moving into a moist-greenhouse state. As temperatures keep rising, a moist greenhouse would destroy the ozone layer, while the oceans would be evaporating into the atmosphere's upper stratosphere and eventually disappear into space, as this 2019 post also 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.