Big
storms to get bigger, small storms to shrink, experts predict
University of Toronto, Science
Daily
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.
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 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 water
vapour 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
heat engine 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 air 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 atmospheric
circulation 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."
Story
Source:
The above story is based on materials provided by University of Toronto. Note: Materials may be edited for
content and length.
Journal
Reference:
F. Laliberte, J. Zika, L. Mudryk, P. J. Kushner, J. Kjellsson,
K. Doos. Constrained work
output of the moist atmospheric heat engine in a warming climate.Science,
2015; 347 (6221): 540 DOI: 10.1126/science.1257103
Cite
This Page:
University of Toronto. "Global warming won't mean more
storms: Big storms to get bigger, small storms to shrink, experts
predict." Science Daily,
29 January 2015.
<www.sciencedaily.com/releases/2015/01/150129143040.htm>.