From the University of Maryland Center for Environmental Science, somebody finally gets it. We’ve changed our local climates significantly, and the plants have figured this out long ago.
Mid-Atlantic suburbs can expect an early spring thanks to the heat of the big city
If you’ve been thinking our world is more green than frozen these days, you’re right. A recent study has found that spring is indeed arriving earlier – and autumn later – in the suburbs of Baltimore and Washington, D.C. The reason? The urban landscape traps heat in the summer and holds it throughout the winter, triggering leaves to turn green earlier in the spring and to stay green later into autumn. The result is a new, extended growing season.
Scientists used high-resolution satellite data collected over the past 25 years to look at the number days that trees have green leaves in the forests of the Mid-Atlantic. The study found that urban heat islands affected the growing season in areas within 20 miles of the city. As a result, gardeners may have more time to grow their vegetables and plant new varieties.
The longer growing season also has a profound impact on forests. Forests are, in effect, the world’s air filters. Green leaves on trees turn carbon dioxide – a greenhouse gas that traps heat in our atmosphere – into oxygen. Carbon dioxide also helps trees grow since they use energy from the sun to convert the gas into plant matter. A longer growing season could change how quickly forests grow and increase the amount of carbon dioxide taken out of the atmosphere.
“Everything changes when the leaves turn green,” said the study’s lead author Dr. Andrew Elmore of the University of Maryland Center for Environmental Science. “Trees start pumping water into the atmosphere. They take carbon dioxide out of the atmosphere. They make sugars and build plant tissue. It’s as if the entire landscape goes from exhaling to inhaling.”
The study also pinpointed other factors that influence the timing of spring and autumn in areas outside the influence of urban heat islands, including the elevation of the landscape, proximity to tidal water, and cold air drainage in small valleys.
Not all forests are the same, however, and predicting which forests will grow faster during a longer growing season requires detailed satellite measurements. This study is the first to apply high-resolution satellite data to the problem. “We are trying to understand how forests function so we can understand how they might respond to global warming,” said Dr. Elmore. “With more detailed data, we can do better job of predicting what might happen to a forest impacted by urbanization, for instance.”
The study, “Landscape controls on the timing of spring, autumn, and growing season length in mid-Atlantic forests,” was published in the February issue of Global Change Biology by Andrew Elmore and Steven Guinn of the University of Maryland Center for Environmental Science, Burke Minsley of the U.S. Geological Survey, and Andrew Richardson of Harvard University.
UNIVERSITY OF MARYLAND CENTER FOR ENVIRONMENTAL SCIENCE
The University of Maryland Center for Environmental Science unleashes the power of science to transform the way society understands and manages the environment. By conducting cutting-edge research into today’s most pressing environmental problems, we are developing new ideas to help guide our state, nation, and world toward a more environmentally sustainable future through five research centers—the Appalachian Laboratory in Frostburg, the Chesapeake Biological Laboratory in Solomons, the Horn Point Laboratory in Cambridge, the Institute of Marine and Environmental Technology in Baltimore, and the Maryland Sea Grant College in College Park. www.umces.edu
UPDATE: kadaka writes in comments-
Paper found, can be freely downloaded, 3.25MB pdf.
This is an Accepted Article that has been peer-reviewed and approved for publication in the Global Change Biology, but has yet to undergo copy-editing and proof correction. Please cite this article as an “Accepted Article”; doi: 10.1111/j.1365-2486.2011.02521.x
http://andrew.elmore.cc/pubs/Elmore_gcb2521.pdf
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We are missing out on a prime opportunity to point out a major blunder when statements like “a greenhouse gas that traps heat” are used, when referring to CO2. We need an absolute minimum of at least 110 to 120 ppm or so of the gas just so we don’t run out of oxygen and food, for at that low level plant life stops growing and starts to die off, and at that minimum level, essential just to barely sustain life on this planet, most of the heat trapping has taken place when compared to the current level of CO2. So when one says we are adding heat trapping gas, this is not true when the effect is the additional gas is considered instead. We have got to shout this out, make it clear that most of the heat trapping is with the minimum levels that we absolutely must have for sustained life on this planet, whenever some one uses the words “heat trapping” to try to win their alarmist arguments.
This is actually a very lovely experimental technique. It is unfortunate that the usable data is rather sparse (all the gray areas) but that simply means more sites need to be examined.
Repeating this in as many urban areas as possible may make it possible to produce a rather nice “averaged” effect of various size cities. Possibly, some distortions will need to be corrected for each city. I suspect that Baltimore and DC are unusually “circularly symmetric”, and other cities will be much less so, and some diddling will be needed to gain as much information as possible. What I would hope to be able to generate from such a major study would be “contour lines” of growing season changes varying with population size. Hmm… it is also likely that some adjustment function will be needed for different base temperature as well as size. I wonder what other adjustments will be required.
Anyway, after generating such a “contour line” of growing season difference versus size, it ought to be simple to translate that to the effective average temperature difference based on distance from that size city using standard and well known gardener’s growing season vs. temperature charts.
Voila – a way to systematically correct historical temperatures near growing cities based on experimental method and data instead of mere hand-waving and “homogenization” … well, at least it would have some real science arguments instead of mere statistical processing to back it up.
Shame on you skeptics! Correlation is not Causation.
Perhaps there are Natural Heat Islands that attract people to build Urban Areas.
What’s so hard to believe? Harbors attract people so that cities get built around them. 😉
I’ll suggest 3 possible causes other than increasing temperatures.
Increased precipitation. Its well known that precipitation increases in and around cities. One study in China found that after they had built a city from scratch, precipitation rose 300% in a nearby forest.
Increased CO2 availability. There is more CO2 available in cities. There have been several recent studies that CO2 is the limiting factor in plant growth.
Increased solar insolation. There have been large reductions in urban aerosols in the developed world. These aerosols both scatter sunlight and seed clouds. Reduce them and you get more solar insolation.
I think the third is probably the main cause of the increased growing season.
Jay Davis says:
March 9, 2012 at 2:31 pm
“Where was Baltimore’s UHI in 2011?”
You have a point and JDN above offers his explanation that the UHI is dependent on prevailing conditions. However. over a year the average temp will be higher in urbanised and agricultural land. On hot days the heat coming off buildings, roads and cultivated land can be spectacular. This is not heat that is trapped or going round a second time by some feedback, it’s simply exposed surfaces that are good at absorbing sun heat then warming up the air above it by contact (/lecture).
It doesn’t even take a mile. I live in an apartment complex, with tomato and flower gardens between two of the buildings, and a garden in the large back yard behind the parking lot, about 100 feet away from the buildings. Winter comes much later to the between-buildings garden, and Spring comes weeks sooner.
Following is a peer-reviewed article on how the urban heat island effect impacts opossums–extending their range northwards:
Kanda, L. Leann, Todd K. Fuller and Paul R. Sievert, 2006. Landscape Associations of Road-killed Virginia Opossums (Didelphis virginiana) in Central Massachusetts, Am. Midl. Nat 156:128-134.
Humans have a beneficial effect on some wild creatures, but tend to reduce biodiversity quite sharply. We are learning now how to improve this. A nice example is the river that flows through downtown Denver–the Platte. Ten or twelve years ago, it was filled with old bedsprings and other trash.It was cleaned up and native plants were planted. Now it is home to several species of wild ducks, red-winged blackbirds, bluejays, and other birds, foxes and other creatures.
The coming greenie shift from cAGW hysteria to a focus on biodiversity could be a very good thing. We can indeed increase biodiversity and at a reasonable cost. But unless the greenies learn to reason better than they have about the climate, they cannot do anything right.
Lady Life Grows says:
March 10, 2012 at 7:16 pm
It doesn’t even take a mile. I live in an apartment complex, with tomato and flower gardens between two of the buildings, and a garden in the large back yard behind the parking lot, about 100 feet away from the buildings. Winter comes much later to the between-buildings garden, and Spring comes weeks sooner.
Many apologies for repeating this but I mentioned the walled kitchen gardens earlier, which have been around for centuries and provide shelter for whatever is cultivated there:
http://en.wikipedia.org/wiki/Walled_garden
“The shelter of walling can raise the ambient temperature within the garden by several degrees, creating a microclimate that permits plants to be grown that would not survive in the unmodified local climate. Most walls were constructed from stone, but lining walls with brick, which absorbs and retains solar heat, raised the temperature against that wall, allowing peaches, nectarines and grapes to be grown as espaliers against south-facing walls as far north as southeast Great Britain and southern Ireland.”