By Daniel Brouse
October 28, 2023
What causes sea level rise? If the melting ice and snow isn’t going into the sea, where is it going?
NOAA says:
The volume of the ocean is expanding as the water warms. Thermal expansion happens when water gets warmer, which causes the volume of the water to increase. About half of the measured global sea level rise on Earth is from warming waters and thermal expansion.
There is a shift of liquid water from land to ocean due largely to humans depleting ground water.
United Nations DRR says:
For every degree Celsius in warming, the water-holding capacity of the atmosphere increases by about 7%. Record-high sea temperatures ensure there is more moisture (in the form of water vapour) in the atmosphere, by an estimated 5-15% compared to before the 1970s, when global temperature rise began in earnest.
Water vapour is a powerful greenhouse gas. Since the 1970s, its rise likely increased global heating by an amount comparable to that from rising carbon dioxide. We are now seeing the consequences. In the current climate, for average all-sky conditions, water vapour is estimated to account for 50% of the total greenhouse effect, carbon dioxide 19%, ozone 4% and other gases 3%. Clouds make up about a quarter of the greenhouse effect.
The main greenhouse gases – carbon dioxide, methane, nitrous oxide and ozone – don’t condense and precipitate. Water vapour does, which means its lifetime in the atmosphere is much shorter, by orders of magnitude, compared to other greenhouse gases. On average, water vapour only lasts nine days,
The most common measure of water vapour in the atmosphere is relative humidity. Deadly humid heat affects billions including the US Midwest this century. “It’s very disturbing,” study co-author Matthew Huber of Purdue University. “It’s going to send a lot of people to emergency medical care.”
The study Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance was conducted by Purdue and George Mason University and published August 15, 2023.
These results indicate that a significant portion of the world’s population will experience — for the first time in human history — prolonged exposures to uncompensable extreme moist heat. Humans will struggle to adapt to these conditions in a warmer world as they will present widespread challenges across many aspects of food-energy-water security, human health, and economic development including in the world’s most populous and most vulnerable regions.
At 3C (5.4F) of yearly average warming, more than 1.5 billion people will suffer. In the summer of 2023,
the Earth experienced about a month of warming at 3C above pre-industrial levels. Both 2022 and 2023 saw a record number of heat related deaths. More than 61,000 Europeans died from extreme heat in the summer of 2022.
Sea Level Rise in the Sky
So how much of the melting ice is going into the sky instead of just dripping into the sea?
NASA says:
Hot air expands, and rises; cooled air contracts – gets denser – and sinks; and the ability of the air to hold water depends on its temperature. A given volume of air at 20°C (68°F) can hold twice the amount of water vapor than at 10°C (50°F). The relationship of how much water a given mass of air actually holds compared to the amount it can hold is its relative humidity.
When air holds as much water vapor as it can for a given temperature (100% relative humidity), it is said to be saturated. If saturated air is warmed, it can hold more water (relative humidity drops), which is why warm air is used to dry objects–it absorbs moisture. On the other hand, cooling saturated air (said to be at its dew point) forces water out (condensation). This is why a container of a cold beverage sweats: it cools the air next to it and moisture from the air condenses on the outside of the can.
Air warmed by ocean currents picks up a lot of moisture. As the heated air rises, it expands, which is measured at the surface as low air pressure. Expanding air cools, which forces it to lose its moisture as rain or snow. The opposite is true for sinking air. Such air compresses and warms. In a zone of high pressure like this, moisture is absorbed by the air from its surroundings.
According to the USGS, the volume of all water on Earth is estimated to be 332.5 million cubic miles. As a result of the hydrologic cycle, Earth’s water is never in one place for too long. It evaporates, turns to vapor, condenses to create clouds and falls back to the surface as precipitation. The cycle then begins again.
“On average, there is about the equivalent of 30 mm [1.2 inches] of rain in the form of vapor available to fall over any point of Earth’s surface,” Frédéric Fabry, the director of the J. Stewart Marshall Radar Observatory and an associate professor of the environment and the Department of Atmospheric and Oceanic Sciences at McGill University in Canada said. “That’s around 55 pounds [25 kilograms] of water over every square yard, most of which is in the form of vapor,” he said. Given that the surface area of Earth is about 197 million square miles (510 million square kilometers), there’s around 37.5 million-billion gallons of water in the atmosphere, Fabry said. If all of this mass were to fall at once, it would raise the global ocean level by about 1.5 inches (3.8 centimeters), he added.
Climate Change Post reports, “Just a few cm of sea-level rise may double the frequency of coastal flooding.”
A study published in the journal Scientific Reports, if sea levels rise between 2 and 4 inches (5 and 10 cm), it will double the flooding frequency in a host of regions, “particularly in the tropics.”
It looks like the atmosphere currently holds about 1.5 inches of sea level rise…
as the temperature rises will it be able to hold 3 inches?
What happens when the atmosphere can’t hold any more?
