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Apr 21, 2009 11:30 AM | 11
In one of the oddities of parsing the regional effects of global climate change, researchers have noted that the U.S. Southeast has seen average high temperatures dip by as much as 0.38 degrees Fahrenheit (0.21 degrees Celsius) over the course of the 20th century. Curious, atmospheric scientist Robert Portmann of the National Oceanic and Atmospheric Administration (NOAA) and his colleagues decided to take a look at what might be causing it.
Their findings, published yesterday in the Proceedings of the National Academy of Sciences USA: that increasing spring rainfall during May and June each year in parts of the southeastern U.S. appeared to be keeping down average high temperatures, based on a study of thousands of readings from weather stations in the Global Historical Climatology Network Daily system.
"Wetter areas tend to have higher humidity and cloudiness and all of these could be causing reduced temperature trends in the Southeast U.S. compared with dryer areas," Portmann says. "However, one would not expect these long-term average quantities to produce negative trends in temperatures."
Instead, the researchers propose that urbanization and population growth in the area could be contributing more soot and other aerosols to the atmosphere, holding down temperatures. But similar areas in, for example, China show no such effect. So "something more uniquely tied to this region appears to be necessary," the researchers write, and offer the suggestion that the regrowth of forests in the region after clearing for agriculture in the 18th and 19th centuries is to blame.
After all, the Southeast puts into the atmosphere as much of the volatile organic compound isoprene—emitted by trees—as the Amazon, according to a 1999 study in Atmospheric Environment. That effect stops at the 100th meridian, which divides wetter eastern Texas from drier western Texas—as does the cooling effect.
"Dry places in the Southwest are experiencing hotter temperatures… maximum temperatures in the Southeast have actually decreased on average, and we show that this seems to be closely linked to the way rainfall changes moving east across the famous 'dry line' across the middle of the country," says NOAA atmospheric scientist and co-author of the report Susan Solomon. "The pattern of warming across the U.S. has a remarkable link to rainfall, especially for the maximum temperatures."
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Tags:
weather,
precipitation,
southeast,
climate change,
global warming,
rainfall
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11 Comments
Add CommentMove to Alabama. Great climate with four seasons. And yes, Birmingham is known as tree city. We hate to see them fall. And it looks like it's helping our weather pattern.
Reply | Report Abuse | Link to this"The pattern of warming across the U.S. has a remarkable link to rainfall, especially for the maximum temperatures."
Reply | Report Abuse | Link to thisDid Solomon really say THAT? Why would it be remarkable?
Soil moisture (rainfall) is directly linked to maximum temperatures. Solar heating evaporates liquid water (in soil, off foliage and open water). The energy required to evaporate the water molecules is not translated into radiative or conductive heat and so doesn't 'show up' in the air temperature. Tthe amount of energy present is the same - ie it's the humidity, dry heat, blah, blah... Furthermore, the water vapor convects strongly upward moving energy [heat] into the upper troposphere. Excess heat will turn increasingly more moisture into water vapor. I'm confused why a NOAA scientist would not know this.
This is why Phoenix has extremely high day time temps compared to Atlanta despite being at almost the exact same latitude. Atlanta's temps only rise above 100F if the soil moisture is depleted.
Make that: "Atlanta's temps rise above 100F only when the soil moisture is depleted."
Reply | Report Abuse | Link to thisTrees impact maximum and minimum temperatures and basic food supply.
Reply | Report Abuse | Link to thisDuring the day trees photosynthesis. They take up sunlight, draw water through their roots and generate the basic food of our planet. In the process they emit moisture into the surroundings. This keeps temperatures lower. In places where no trees are present sunlight would have converted to heat besides loosing the cooling effect from moisture.
If the density of trees is sufficient to prevent the moist air from blowing away, this moisture will condense during the night and return to the soil. This would keep the night temperature warmer and also conserve water.
Trees are basic generators of food and moderators of climate, you can not live without them.
Hmmmm. Planet warms. CO2, sunshine and rainwater make TREES. Trees make oxygen, temperature goes down, skies clear, sun shines, planet warms, CO2 levels increase. CO2 sunshine and rainwater make TREES. Trees make oxygen, temperature goes down, skies clear, sun shines, planet warms, CO2 levels increase.
Reply | Report Abuse | Link to thisSounds like a pretty natural cycle to me. I just wish that people would get a clue and stick with the facts before they come to some of these hair-brained human-induced global climate change theories. We're as likely to have another ice-age as we are for the average temperature to rise by 2 degrees C. Whatever's going to happen....enjoy the ride; because you can't do a thing about it.
I have a doubt with the function that moisture condensing keeps the night warm.Rain comes from the troposphere which is far from the ground and the movement of the air in there is rapid.The heat released by the moisture condensing should be sent away quickly.The long-wave radiation emited by the atmosphere keeps the night not so cold.
Reply | Report Abuse | Link to thisOf course that is my personal opinion.All critcism is welcomed.
Reply | Report Abuse | Link to thisCronus-
Reply | Report Abuse | Link to thisCondensation would serve to keep the night warmer by releasing heat over time - the released heat would be converted to mechanical or long wave radiation and then subject to the usual GHG effects (ie keep more heat near the surface longer).
PS Higher humidity increases the local temp by the usual GHG effects of water vapor.
If, as I suspect, the rain belts are shifting northward as the globe warms, the south east is not going to a favoured habitat.
Reply | Report Abuse | Link to thisCronus:
Reply | Report Abuse | Link to thisIn a forest as temperature drops, the retained moisture in the air condenses to form dew, this is what causes warming and returns the moisture to the soil to be recycled by the trees.
Forests also seem to attract rainfall, or perhaps the location of forests point to areas of rainfall.
What I just *love* about the greenies is this: No matter what happens, there's a computer simulation that proves--beyond a reasonable doubt--that it's Global Warming, and people did it.
Reply | Report Abuse | Link to thisHow long has it been Chicago sat under a mile thick sheet of ice? 100,000 years?
Yup! Damn cars.