Global warming won't mean more stormy weather

January 29, 2015, University of Toronto
A storm developing over the Bali Sea. Credit: Frédéric Laliberté

A study led by atmospheric physicists at the University of Toronto finds that global warming will not lead to an overall increasingly stormy atmosphere, a topic debated by scientists for decades. Instead, strong storms will become stronger while weak storms become weaker, and the cumulative result of the number of storms will remain unchanged.

"We know that with we'll get more evaporation of the oceans," said Frederic Laliberte, a research associate at U of T's physics department and lead author of a study published this week in Science. "But circulation in the atmosphere is like a heat engine that requires fuel to do work, just like any combustion engine or a convection engine."

The atmosphere's work as a heat engine occurs when an air mass near the surface takes up water through evaporation as it is warmed by the Sun and moves closer to the Equator. The warmer the is, the more water it takes up. As it reaches the Equator, it begins to ascend through the atmosphere, eventually cooling as it radiates heat out into space. Cool air can hold less moisture than warm air, so as the air cools, condensation occurs, which releases heat. When enough heat is released, air begins to rise even further, pulling more air behind it producing a thunderstorm. The ultimate "output" of this atmospheric engine is the amount of heat and moisture that is redistributed between the Equator and the North and South Poles.

"By viewing the atmospheric circulation as a heat engine, we were able to rely on the laws of thermodynamics to analyze how the circulation would change in a simulation of global warming," said Laliberte. "We used these laws to quantify how the increase in that would result from global warming would influence the strength of the atmospheric circulation."

The researchers borrowed techniques from oceanography and looked at observations and climate simulations. Their approach allowed them to test global warming scenarios and measure the output of atmospheric circulation under warming conditions.

"We came up with an improved technique to comprehensively describe how air masses change as they move from the Equator to the poles and back, which let us put a number on the energy efficiency of the atmospheric and measure its output," said Laliberte.

The scientists concluded that the increase in water vapour was making the process less efficient by evaporating water into that is not already saturated with water vapour. They showed that this inefficiency limited the strengthening of atmospheric circulation, though not in a uniform manner. Air masses that are able to reach the top of the atmosphere are strengthened, while those that can not are weakened.

"Put more simply, powerful storms are strengthened at the expense of weaker storms," said Laliberte. "We believe will adapt to this less efficient form of heat transfer and we will see either fewer storms overall or at least a weakening of the most common, weaker storms."

Explore further: Ocean warming could drive heavy rain bands toward the poles

More information: Constrained work output of the moist atmospheric heat engine in a warming climate, Science, www.sciencemag.org/lookup/doi/ … 1126/science.1257103

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9 comments

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HeloMenelo
4.2 / 5 (5) Jan 29, 2015
In Africa last night we had the worst thunderstorm i've ever seen during my entire life, the storms are indeed more intense and where we used to have stable seasons, sunny for 2 weeks then overcast for a day or two, we now have all seasons in one day. If this is not related to climate change, then i must be seeing the spaghetti monster doing it right...
Water_Prophet
1 / 5 (4) Jan 29, 2015
@runrig,
I need a dummy check on this one.
plaasjaapie
2.3 / 5 (3) Jan 30, 2015
One thing I am totally certain of, if the frequency of storms picks up there will immediately be a new study that attributes it to global warming. :-D
Eddy Courant
1 / 5 (2) Jan 30, 2015
"The atmosphere's work as a heat engine occurs when an air mass near the surface takes up water through evaporation as it is warmed by the Sun and moves closer to the Equator. The warmer the air mass is, the more water it takes up. As it reaches the Equator, it begins to ascend through the atmosphere, eventually cooling as it radiates heat out into space."
---------------------
Cool.

outersphere
3.7 / 5 (3) Jan 30, 2015
Logic would tend to indicate that as heat/energy builds up in a System that both frequency and intensity would be affected.
Water_Prophet
1 / 5 (2) Jan 30, 2015
@outersphere, that's the question I see.
Though with a diminishing difference between equator and pole, there should be those effects.
adam_russell_9615
3.3 / 5 (4) Feb 02, 2015
Just as it takes a huge amount of heat energy to evaporate enough water to make a cloud, the reverse is equally true. When that water distills back into rain water, every bit of the energy that went into evaporation HAS to be released. If we could find a way to capture that released energy it would go a long way toward solving the renewable energy problem. Clouds are potentially a huge energy resource.
Water_Prophet
1 / 5 (3) Feb 07, 2015
runrig said
Water:

"Air masses that are able to reach the top of the atmosphere are strengthened, while those that can not are weakened."
This happens in supercell storms.
If there is a "lid" on convection say at 800mb in a hot airmass, under the right upper air conditions, when that lid "pops" the up-rush can be immense, the cloud top breaking through the Tropopause into the Strat.
Look at a logskewT (Tephigram for Brits) and you will see how the LH component really adds in energy at those extreme temps.
The "damping" of convection is more troublesome but one possibility is that supercells, because of their massive outflow aloft (anvil Ci) suppress convection around, due shading of solar input and there is of course convergence aloft that produces subsiding air around the storm.
Water_Prophet
1 / 5 (2) Feb 07, 2015
I greatly appreciate the consult rr.

So basically, the article says not very much at all, since the effects are going to be proportional to effects in volume increase and it's ability to fight gravity.

So the article is true, but the relevance and impact would be difficult if not impossible to measure, and you still have the basal impacts of the storms that would be there.

Thanks runrig.

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