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know it?</title></head><body>
<div><font face="Geneva" size="-1" color="#000000"><b>1st of 2:</b><i>
NATURE</i> Vol 448 August 30,<b> 2007</b></font></div>
<div><font face="Geneva" size="-1"
color="#000000">CORRESPONDENCE</font></div>
<div><font face="Geneva" size="-1" color="#000000"><b>Fires and
climate linked in nineteenth century<br>
</b>SIR - 'Atmospheric brown clouds', resulting from the burning of
fossil fuels and biomass, have recently been reported to have a large
effect on climate by altering the atmosphere's absorption of solar
radiation (V. Ramanathan et al. Nature 448, 575-578; 2007).</font><br>
<font face="Geneva" size="-1" color="#000000"></font></div>
<div><font face="Geneva" size="-1" color="#000000">Interestingly, even
in the nineteenth century, some scientists held the view that tiny
particles, or aerosols, produced from burning affect solar radiation,
clouds and precipitation on a large scale - all factors that play into
climate. One of them, German geographer Alexander Freiherr von
Danckelman, wrote an insightful but little-noticed paper on the topic
(A. von Danckelman Z. österr. Ges. Met. (Meteorol. Z.) 19,
301-311;<b> 1884</b>).<br>
<br>
After observing huge savannah fires in Africa during the 1880s, von
Danckelman reported that fires were accompanied by cumulus clouds,
which subsequently spread and thinned, forming a brownish or blueish
haze that persisted for days to weeks. He argued against the view that
fires were an immediate cause of rain showers, and proposed instead
that they affected cloudiness and precipitation in an "indirect
way". He realized that by providing cloud condensation nuclei,
fires might contribute to the fog and drizzle typical of the dry
season. Estimating the amount of biomass burned in Africa each year,
he concluded that savannah fires must have a major influence on
large-scale climate.</font><br>
<font face="Geneva" size="-1" color="#000000"></font></div>
<div><font face="Geneva" size="-1" color="#000000">Von Danckelman's
descriptions of haze produced from burning biomass and its effects on
climate are surprisingly accurate. Although not every detail is
correct, his theories anticipated many aspects of the current
discussion on biomass burning and the effects of aerosols. Sadly his
work, published in French and German, is almost forgotten today and
references to his papers are absent in current studies.</font></div>
<div><font face="Geneva" size="-1" color="#000000">Stefan
Brönnimann<br>
Institute for Atmospheric and Climate Science,<br>
ETH Zurich, Universitätsstraße 16,</font></div>
<div><font face="Geneva" size="-1" color="#000000">CH-8092 Zürich,
Switzerland</font></div>
<div><font face="Geneva" size="-1"
color="#000000">*********************************************</font></div
>
<div><font face="Geneva" size="-1" color="#000000"><b>2nd of 2:</b><i>
NATURE</i> Vol 448 August 30,<b> 2007</b></font></div>
<div><font face="Geneva" size="-1"
color="#000000">CORRESPONDENCE</font></div>
<div><font face="Geneva" size="-1" color="#000000"><b>Climate: Sawyer
predicted rate of warming in 1972</b></font></div>
<div><font face="Geneva" size="-1" color="#000000">SIR - Thirty-five
years ago this week, Nature published a paper titled 'Man-made carbon
dioxide and the "greenhouse" effect' by the eminent
atmospheric scientist J. S. Sawyer (Nature 239, 23-26;<b> 1972</b>).
In four pages Sawyer summarized what was known about the role of
carbon dioxide in enhancing the natural greenhouse effect, and made a
remarkable prediction of the warming expected at the end of the
twentieth century. He concluded that the 25% increase in atmospheric
carbon dioxide predicted to occur by 2000 corresponded to an increase
of 0.6 °C in world temperature.<br>
<br>
In fact the global surface temperature rose about 0.5 °C between the
early 1970s and 2000. Considering that global temperatures had, if
anything, been falling in the decades leading up to the early 1970s,
Sawyer's prediction of a reversal of this trend, and of the correct
magnitude of the warming, is perhaps the most remarkable long-range
forecast ever made.</font><br>
<font face="Geneva" size="-1" color="#000000"></font></div>
<div><font face="Geneva" size="-1" color="#000000">Sawyer's review
built on the work of many other scientists, including John Tyndall's
in the nineteenth century (see, for example, J. Tyndall Philos. Mag.
22, 169-194 and 273-285;<b> 1861</b>) and Guy Callender's in the
mid-twentieth (for example, G. S. Callendar, Weather 4, 310-314;<b>
1949</b>). But the anniversary of his paper is a reminder that, far
from being a modern preoccupation, the effects of carbon dioxide on
the global climate have been recognized for many decades.<br>
<br>
Today, improved data, models and analyses allow discussion of possible
changes in numerous meteorological variables aside from those Sawyer
described. Hosting such discussions, the four volumes of the
Intergovernmental Panel on Climate Change 2007 assessment run to
several thousand pages, with more than 400 authors and about 2,500
reviewers. Despite huge efforts, and advances in the science, the
scientific consensus on the amount of global warming expected from
increasing atmospheric carbon dioxide concentrations has changed
little from that in Sawyer's time.</font></div>
<div><font face="Geneva" size="-1" color="#000000"><br>
Neville Nicholls<br>
School of Geography and Environmental Science,<br>
Monash University, Victoria 3800, Australia<br>
</font><font face="Times New Roman"
color="#000000">===================================================<br
>
"As an endangered species and an endangering one, we need,
collectively,</font></div>
<div><font face="Times New Roman" color="#000000">all the
self-understanding and self-direction that we can muster."<br>
<br>
M. Brewster Smith. "Perspectives on Selfhood."<br>
<i>American Psychologist</i>, December 1978</font></div>
<div><font face="Bookman Old Style"
color="#000000"
>==================================================================</font
></div>
<div><font face="Bookman Old Style" color="#000000">"Localized
ecological systems are known to shift abruptly and irreversibly from
one state to another when they are forced across critical thresholds.
Here we review evidence that the global ecosystem as a whole can react
in the same way and is approaching a planetary-scale critical
transition as a result of human influence."<br>
<br>
Barnovsky et al. "Approaching a state shift in Earth's
biosphere."</font></div>
<div><font face="Bookman Old Style"
color="#000000"><i>Nature.<b> </b></i> 07 June 2012,Volume 486,
Pages:52-58<br>
doi:10.1038/nature11018</font><br>
<font face="Bookman Old Style" color="#000000"></font></div>
<div><font face="Bookman Old Style" color="#000000"><br></font></div>
<div><font face="Geneva" size="-1" color="#000000"><br>
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