--- In physical_sciences@yahoogroups.com, "Robert Karl Stonjek" <stonjek@...>
wrote:

Some Particles Cool Climate, Others Add To Global Warming
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Aerosols. Aerosols like sulfur, nitrate, and organic carbon are formed in the
atmosphere and cause global cooling. Thereby they contribute to mask parts of
the human induced global warming. On the other hand, black carbon absorbs
radiation and thereby has a warming effect on the earth's climate. (Credit:
iStockphoto/Daniel Stein)ScienceDaily (July 9, 2009) - There is large scientific
agreement that human made emissions of CO2 and other gasses give global warming.
But human activity doesn't just cause gas emissions. Burning of fossil fuels and
biomass also causes emissions of the particle black carbon. Other kinds of
particles are formed in the atmosphere as a cause of human made emissions.

Particles, also named aerosols, are today one of the main reasons for the
uncertainty about how humans affect the global climate. Aerosols like sulfur,
nitrate, and organic carbon are formed in the atmosphere and cause global
cooling. Thereby they contribute to mask parts of the human induced global
warming. On the other hand, black carbon absorbs radiation and thereby has a
warming effect on the earth's climate.

Models and observations

The average climate effect from particles is a cooling effect. But to which
extent particles cool down the climate, has remained an unanswered question for
scientists.

"An important reason for this uncertainty is that estimates of the climate
effect based on observations and models have not coincided", Gunnar Myhre
explained.

"For scientists, this has been frustrating. It has given us less faith in our
understanding of the models and in our understanding of the direct aerosol
effect".

Defect in the estimates

Based on satellite observations, estimates are made of the climate effect from
aerosols. If these estimates were correct, aerosols would have had a stronger
cooling effect than the models show and thereby to an even larger extent have
masked the global warming. Some estimates even show that aerosols have masked as
much as 50 percent of the warming from CO2.

But Myhre's article now points at what might have been a defect in these
estimates. By doing this, he brings scientists a big step closer to the
explanation of the discrepancy between models and estimates from observations.

"The estimates are not able to consider that the share of black carbon particles
has increased by a much faster rate than the total number of particles. This can
explain the main discrepancy we have seen between estimates from observations
and models", Myhre said.

Weaker cooling effect

According to Myhre's article, the models have until now given the best picture
of the climate effect from aerosols. The cooling effect from aerosols looks like
being a bit weaker than the estimates from observations would say.

"What I have done, is a small contribution to our understanding of the human
influence on climate change. The more we understand, the better prognoses can we
give for future temperatures", Myhre said.

Even though particles until now have masked part of the global warming, they
will not do this to the same extent in the future.

"Particles only stay in the atmosphere for a few days. If the production of
particles should remain constant in the future, the amount of particles in the
atmosphere would also be constant", Myhre said.

"CO2 is different. CO2 stays in the atmosphere for several hundred years. With
constant CO2 emissions, the concentration continues to increase and the warming
will accelerate strongly in the future. The aereosols will then be able to mask
a relatively smaller part of the global warming", Gunnar Myhre said.


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Journal reference:

1.. Myhre et al. Consistency Between Satellite-Derived and Modeled Estimates
of the Direct Aerosol Effect. Science, 2009; DOI: 10.1126/science.1174461
Adapted from materials provided by Centre for International Climate and
Environmental Research (CICERO).
Centre for International Climate and Environmental Research (CICERO) (2009, July
9). Some Particles Cool Climate, Others Add To Global Warming. ScienceDaily.
Retrieved July 9, 2009, from
http://www.sciencedaily.com/releases/2009/06/090619125905.htm

Posted by
Robert Karl Stonjek

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