Samwik- Is most of the soot from 'natural' causes eg volcanos or bushfires, or is it from man-made sources,like industrial, or household usage, of fossil fuels? Is there any info on the Antarctic, where the ozone hole was very large again this year!! We don't need soot as well!
Ozone's impact on climate consists primarily of changes in temperature. The more ozone in a given parcel of air, the more heat it retains. Ozone generates heat in the stratosphere, both by absorbing the sun's ultraviolet radiation and by absorbing upwelling infrared radiation from the lower atmosphere (troposphere).
Consequently, decreased ozone in the stratosphere results in lower temperatures. Observations show that over recent decades, the mid to upper stratosphere (from 30 to 50 km above the Earth's surface) has cooled by 1° to 6° C (2° to 11° F). This stratospheric cooling has taken place at the same time that greenhouse gas amounts in the lower atmosphere (troposphere) have risen. The two phenomena may be linked.
This would create a possible feedback loop. The more ozone destruction in the stratosphere, the colder it would get just because there was less ozone. And the colder it would get, the more ozone depletion would occur.
Another contributing factor to the cooling may be that rising amounts of greenhouse gases in the lower atmosphere (troposphere) are retaining heat that would normally warm the stratosphere. However, scientists hold varying degrees of conviction about the nature of the link between tropospheric warming and stratospheric cooling. "The warming of the troposphere and its potential influence upon the stratospheric circulation is an important consideration," points out Ramaswamy, "though the quantitative linkages are uncertain. It is possible that they may be interdependent only in a tenuous manner."
"There is actually a very strong indication that the observed changes in radiative and chemical species are responsible for globe-wide cooling of the stratosphere."
Ozone chemistry is very sensitive to temperature changes. Since temperatures in the Arctic stratosphere often come within a few degrees of the threshold for forming polar stratospheric clouds, further cooling of the stratosphere could cause these clouds to form more frequently and increase the severity of ozone losses.
The Antarctic isn't affected by increasing greenhouse gases like the Arctic is because it's colder, and the polar wind circulation over the Antarctic is already very strong.
Shindell says that from both observations and models, he has found increasing wind speeds not only at high altitudes but also near the surface. "That's a large effect on climate," he points out. "Changes in stratospheric ozone and winds affect the flow of energy at altitudes just below, which then affect the next lower altitudes, and so on all the way to the ground. That would be the most intriguing aspect of all this, though it's still controversial."
http://www.ucar.edu/news/features/climatechange/faqs.jspAlmost a quarter of the carbon dioxide emitted by human activities is absorbed by land areas; another quarter is absorbed by the ocean. The remainder stays in the atmosphere for a century or longer. Because CO2 stays in the air so long, it becomes very well mixed throughout the global atmosphere. This makes the Mauna Loa record an excellent indication of long-term trends.
Higher up, the loss of stratospheric
ozone has led to some cooling in that layer of the atmosphere. An even larger effect comes from carbon dioxide, which acts as a cooling agent in the stratosphere even though it warms the atmosphere closer to ground level. This paradox occurs because the atmosphere thins with height, changing the way carbon dioxide molecules absorb and release heat. Together, the increase in carbon dioxide and the loss of
ozone have led to record-low temperatures recently in the stratosphere and still higher up in the thermosphere. Far from being a good thing, this cooling is another sign that increasing levels of carbon dioxide are changing our planet's climate.
*_*
...and speaking of soot!
I thought this SAG article was timely:
http://www.scienceagogo.com/news/20070506202633data_trunc_sys.shtmlI looked up the article by Zender
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D11202, doi:10.1029/2006JD008003, 2007
Present-day climate forcing and response from black carbon in snowReceived 7 September 2006; accepted 30 January 2007; published 5 June 2007.
Keywords: Black carbon; snow reflectance; snow albedo feedback.
Abstract
We apply our Snow, Ice, and Aerosol Radiative (SNICAR) model....
Building on two previous studies, we account for interannually varying biomass burning BC emissions, snow aging, and aerosol scavenging by snow meltwater.
The rate of snow aging determines snowpack effective radius (r e), which directly controls snow reflectance and the magnitude of albedo change caused by BC. For a reasonable r e range, reflectance reduction from BC varies threefold. Inefficient meltwater scavenging keeps hydrophobic impurities near the surface during melt and enhances forcing.
Applying biomass burning BC emission inventories for a strong (1998) and weak (2001) boreal fire year, we estimate global annual mean BC/snow surface radiative forcing from all sources (fossil fuel, biofuel, and biomass burning) of +0.054 (0.007-0.13) and +0.049 (0.007-0.12) W m-2, respectively. Snow forcing from only fossil fuel + biofuel sources is +0.043 W m-2 (forcing from only fossil fuels is +0.033 W m-2), suggesting that the anthropogenic contribution to total forcing is at least 80%. The 1998 global land and sea-ice snowpack absorbed 0.60 and 0.23 W m-2, respectively, because of direct BC/snow forcing.
The forcing is maximum coincidentally with snowmelt onset, triggering strong snow-albedo feedback in local springtime. Consequently, the "efficacy" of BC/snow forcing is more than three times greater than forcing by CO2.
With climate feedbacks, global annual mean 2-meter air temperature warms 0.15 and 0.10°C, when BC is included in snow, whereas annual arctic warming is 1.61 and 0.50°C.
Stronger high-latitude climate response in 1998 than 2001 is at least partially caused by boreal fires, which account for nearly all of the 35% biomass burning contribution to 1998 arctic forcing.
We predict concentrations in excess of 1000 ng g-1 for snow in northeast China, enough to lower snow albedo by more than 0.13. The greatest instantaneous forcing is over the Tibetan Plateau, exceeding 20 W m-2 in some places during spring. These results indicate that snow darkening is an important component of carbon aerosol climate forcing.
~SA
