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Despite having little impact on global mean temperatures, waste heat may alter weather significantly

A diverse team of researchers from Scripps Institution of OceanographyUniversity of California, San Diego (UCSD); Florida State University (FSU); and the National Center for Atmospheric Research (NCAR) have teamed up to examine the long term effects of waste heat on local surroundings.

I. Waste Heat Shifts Temperature Balance

Urban heat originates from a variety of sources -- buildings with central heating, power plants, cars, and more.  Human machines dump waste heat into the environment on a large scale locally.  But globally waste heat is only estimated to account for around 0.3 percent of the total heat transported across higher latitudes by atmospheric or oceanic circulation, bumping temperatures by a mere 0.01 degrees C (about 0.02 degrees F).

The "urban heat island" effect -- local warming from waste heat -- is well known.  But the research team suspected that waste heat might have longer-range effects too, effects that might be masked by the global trend.  They dug into the issue and developed models that suggest that waste may indeed have longer-range impact, in addition to the urban heat island effect.

The new, more detailed smaller-scale models show that waste heat from cities may heat up northern regions of North America and Asia by as much as 1 degree Celsius (1.8 degrees Fahrenheit) in the winter.  The heating effects can be felt up to 1,000 miles away from their source, the simulations showed.  At the same time, the North American/Asian heating is coupled with a 1 degree Celsius (1.8 degrees Fahrenheit) cooling effect in Europe, which is forcing cooler winters.

Waste Heat
Waste heat is warming North America and Asia's north, while cooling the European north.
[Image Source: Ecofriend]

NCAR researcher Aixie Hu comments, "The burning of fossil fuel not only emits greenhouse gases but also directly affects temperatures because of heat that escapes from sources like buildings and cars.  Although much of this waste heat is concentrated in large cities, it can change atmospheric patterns in a way that raises or lowers temperatures across considerable distances."

II. What Can be Done?

Humans by and large produce much less waste heat than nature (respiration itself, the process by which living organisms harvest energetic chemicals to drive the processes of life, puts off a fair deal of waste heat).  But many human cities happen to be located directly under jet stream troughs, which causes the localized impact to be amplified.

Globally in 2006 energy consumption globally was estimated to have occurred at an average of 16 terawatts (TW).  The 86 largest metropolitan areas in the Northern Hemisphere are estimated to have consumed 6.7 TW of that total.

Urban heat map
U.S. urban centers often sit under jet stream troughs. [Image Source: Blue Moon/Panoramio]

The study is arguably less about prevention, and more about understanding and coping with mankind's localized impact on weather/climate.  After all, you can't reasonably ask people to turn off the heat in the winter or stop driving (even EVs put off waste heat).

But perhaps future urban expansion can be guided by models that place new construction in areas that suck less of the waste heat into the jet stream or alternatively suck up more in regions that are currently being cooled.

Additionally materials may be able to recapture some waste heat, decreasing the global output, while at the same time lowering costs. (But such materials are still in their very nascent stages.)

The study was published in the peer-reviewed journal Nature Climate Change.

Sources: UCAR [press release], Nature Climate Change [abstract]



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The real point
By geddarkstorm on 1/28/2013 6:03:15 PM , Rating: 3
The real point about UHI isn't in regards to the absolute values (recent empirical, experimental tests by NOAA have also found UHI is far more substantial than previously believed, affected night temperatures the most); the real point about the UHI affect and how it impacts our perception of climate change is that all those long temperature records we have were mostly rural locations that have -become urban- or become -more urban- over time.

That change to increasing urbanicity over the temperature record, as well as loss of the majority of temperature stations from the good quality citing to poor or worst quality citing, has a material impact in our measurements over time. It's the over time component that is most important. The growing affect of UHI would appear as an upward trend in the temperature record.

Consequently, the satellite measurements show less of a trend, though more variability, over their albeit short runs compared to most land stations.

Thankfully, we do still have good land stations to compare with, and people have done that analysis, showing far less warming than we've been told (in line with the satellites); while NOAA's brand spanking new USCRN temperature station network, which was set up to avoid the UHI problem, shows indeed reduced absolute temperatures (consequently, many "records" were not actually broken on the USCRN network).

The last bit of interesting research I've seen on this lately, was using satellites and other measurements to clock when trees gain green leaves. They found that trees kept their leaves longer and got them earlier in the spring when within 20 miles of a city or so. That seems to be the stretch by which the UHI can reach. Thus, some "rural" stations aren't actually free of increasing UHI contamination. It's a complicated issue!

http://www.sciencedaily.com/releases/2012/03/12030...




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