So it appears that past climate
models had such low resolution in the data that variability in the data was not
measurable. That is usually a great
reason to produce large plus and minus signs and little reason to believe the
results.
I grew up in country in which
much of the summer moisture was provided by random thunderclouds passing over
that often watered a two mile swath intensely for about thirty minutes. This meant that a point based data collection
system was likely to be unreliable as hell.
The only answer to that would be belts of detectors and careful
adjustment against measured soil content.
Better still, check the river flows.
Right now I am not sure that it
is possible to determine if they were measuring the same thing in 1980 as
today. There is certainly agreement that
the climate is generally warmer than the decades of the fifties and sixties. I certainly think it is true
subjectively. It certainly appears easier
to grow grapes but that could be simply better culture.
We had a foul November in Vancouver last year with
the ice freezing here and there yet the recently planted palm trees did
fine. Of course we know how to protect
them.
There is more heat and an
increase in variability as the air mass works harder to shake off the
surplus. Something worth mentioning is
that as heat increases over land, the humidity increases and the temperature
increases until you reach saturation point and a thunderstorm dumps the
excess. Ergo greater heat implies
greater variability.
Erratic, extreme day-to-day weather puts climate change in new light
by Staff Writers
The first climate study to
focus on variations in daily weather conditions has found that day-to-day
weather has grown increasingly erratic and extreme, with significant
fluctuations in sunshine and rainfall affecting more than a third of the
planet.
Princeton University researchers recently reported in the Journal of
Climate that extremely sunny or cloudy days are more common than in the early
1980s, and that swings from thunderstorms to dry days rose considerably since
the late 1990s.
These swings could have consequences for ecosystem stability and the
control of pests and diseases, as well as for industries such as agriculture
and solar-energy production, all of which are vulnerable to inconsistent and
extreme weather, the researchers noted.
The day-to-day variations also could affect what scientists could
expect to see as the Earth's climate changes, according to the researchers and
other scientists familiar with the work.
Constant fluctuations in severe conditions could alter how the
atmosphere distributes heat and rainfall, as well as inhibit the ability of
plants to remove carbon dioxide from the atmosphere, possibly leading to higher
levels of the greenhouse gas than currently accounted for.
Existing climate-change models have historically been evaluated against
the average weather per month, an approach that hides variability, explained
lead author David Medvigy, an assistant professor in the Department of Geosciences
at Princeton .
To conduct their analysis, he and co-author Claudie Beaulieu, a
postdoctoral research fellow
in Princeton's Program in Atmospheric and Oceanic Sciences, used a recently
developed computer program that has allowed climatologists to examine weather
data on a daily level for the first time, Medvigy said.
"Monthly averages reflect a misty world that is a little rainy and
cloudy every day. That is very different from the weather of our actual world,
where some days are very sunny and dry," Medvigy said.
"Our work adds to what we know about climate change in the real
world and places the whole problem of climate change in a new light," he
said.
"Nobody has looked for these daily changes on a global scale. We
usually think of climate change as an increase in mean global temperature and
potentially more extreme conditions - there's practically no discussion of
day-to-day variability."
The Princeton findings stress that analysis of erratic daily conditions
such as frequent thunderstorms may in fact be crucial to truly understanding
the factors shaping the climate and affecting the atmosphere, said William
Rossow, a professor of earth system science and environmentalengineering at
the City College of New York.
"It's important to know what the daily extremes might do because
we might care about that sooner," said Rossow, who also has studied
weather variability. He had no role in the Princeton
research but is familiar with it.
Rossow said existing climate-change models show light rain more
frequently than they should and don't show extreme precipitation. "If it
rains a little bit every day, the atmosphere may respond differently than if
there's a really big rainstorm once every week. One of the things you find
about rainstorms is that the really extreme ones are at a scale the atmosphere
responds to," he said.
Although climate-change models predict future changes in weather as the
planet warms, those calculations are hindered by a lack of representation of
day-to-day patterns, Rossow said.
"If you don't know what role variability is playing now, you're
not in a very strong position for making remarks about how it might change in
the future," he said. "We're at a stage where we had better take a
look at what this research is pointing out."
Medvigy and Beaulieu determined sunshine variation by analyzing
fluctuations in solar radiation captured by the International Satellite Cloud
Climatology Project from
1984 to 2007. To gauge precipitation, the researchers used daily rainfall data
from the Global Precipitation Climatology Project spanning 1997 to 2007.
Medvigy and Beaulieu found that during those respective periods,
extremes in sunshine and rainfall became more common on a day-to-day basis. In
hypothetical terms, Medvigy said, these findings would mean that a region that
experienced the greatest increase in sunshine variability might have had partly
cloudy conditions every day in 1984, but by 2007 the days would have been
either sunny or heavily cloudy with no in-between.
For rainfall, the uptick in variation he and Beaulieu observed could be
thought of as an area experiencing a light mist every day in 1997, but within
ten years the days came to increasingly fluctuate between dryness and downpour.
The researchers observed at least some increase in variability for 35
percent of the world during the time periods analyzed. Regions such as
equatorial Africa and Asia experienced the
greatest increase in the frequency of extreme conditions, with erratic shifts
in weather occurring throughout the year.
In more temperate regions such as the United States , day-to-day
variability increased to a lesser degree and typically only seasonally. In the
northeastern United States ,
for instance, sudden jumps from sunny to bleak days became more common during
the winter from 1984 to 2007.
In the 23 years that sunshine variability rose for tropical Africa and Asia , those areas also showed a greater occurrence of
towering thunderstorm clouds known as convective clouds, Medvigy said. Tropical
areas that experienced more and more unbalanced levels of sunshine and rainfall
witnessed an in-kind jump in convective cloud cover.
Although the relationship between these clouds and weather variations
needs more study, Medvigy said, the findings could indicate that the sunnier
days accelerate the rate at which water evaporates then condenses in the
atmosphere to form rain, thus producing heavy rain more often.
Storms have lasting effect on daily weather patterns
Although the most extreme weather variations in the study were observed
in the tropics, spurts of extreme weather are global in reach, Rossow said. The
atmosphere, he said, is a fluid, and when severe weather such as a
convective-cloud thunderstorm "punches" it, the disturbance spreads
around the world. Weather that increasingly leaps from one extreme condition to
another in short periods of time, as the Princeton
research suggests, affects the equilibrium of heat and rain worldwide, he said.
"Storms are violent and significant events - while they are
individually localized, their disturbance radiates," Rossow said.
"Wherever it's raining heavily, especially, or variably is where
the atmosphere is being punched. As soon as it is punched somewhere in the
tropics it starts waves that go all the way around the planet," he said.
"So we can see waves coming off the west Pacific convection
activity and going all the way around the planet in the tropical band. The
atmosphere also has the job of
moving heat from the equator to the poles, and storms are the source of heat to
the atmosphere, so if a storm's location or its timing or its seasonality is
altered, that's going to change how the circulation responds."
These sweeping atmospheric changes can interact with local conditions
such as temperature and topography to skew regular weather patterns, Rossow said.
"Signals end up going over the whole globe, and whether they're
important in a particular place or not depends on what else is happening,"
he said. "But you can think of storms as being the disturbances in an
otherwise smooth flow. That's why this is a climate issue even though we're
talking about daily variability in specific locations."
The impact of these fluctuations on natural and manmade systems could
be as substantial as the fallout predicted from rises in the Earth's average
temperature, Medvigy said.
Inconsistent sunshine could impair the effectiveness of solar-energy
production and - with fluctuating rainfall also included - harm agriculture, he
said. Wetter, hotter conditions also breed disease and parasites such as
mosquitoes, particularly in tropical areas, he said.
On a larger scale, wild shifts in day-to-day conditions would diminish
the ability of trees and plants to remove carbon from the atmosphere, Medvigy
said. In 2010, he and Harvard University researchers reported in the journal the
Proceedings of the National
Academy of Sciences that
erratic rain and sunlight impair photosynthesis.
That study concluded that this effect upsets the structure of
ecosystems, as certain plants and trees - particularly broad-leafed trees more
than conifers - adapt better than others.
In the context of the current study, Medvigy said, the impact of
variability on photosynthesis could mean that more carbon will remain in the
atmosphere than climate models currently anticipate, considering that the
models factor in normal plant-based carbon absorption.
Moreover, if the meteorological tumult he and Beaulieu observed is
caused by greenhouse gases, these fluctuations could become self-perpetuating
by increasingly trapping the gases that agitated weather patterns in the first
place.
"We have not yet looked for direct ties between weather
variability and increased carbon dioxide concentration in the atmosphere, but I
would not be surprised if they are connected in some way," Medvigy said.
"Increases in variability diminish the efficiency with which
plants and trees remove carbon dioxide from the air," he said.
"All of a sudden, the land and the atmosphere are no longer in
balance, and plants cannot absorb levels of carbon dioxide proportional to the
concentrations in the environment. That will affect everybody."
The study was published online Oct. 14 by the Journal of Climate, and
was funded by grants from the Princeton Carbon Mitigation Initiative and the
Fonds Quebecois de la Recherche sur la Nature et les Technologies.
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