[MCN] 2-What did climate science know, and when did it know it?

[Lance Olsen]

1st of 2: NATURE Vol 448  August 30, 2007
CORRESPONDENCE
Fires and climate linked in nineteenth century
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).

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; 1884).

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.

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.
Stefan Brönnimann
Institute for Atmospheric and Climate Science,
ETH Zurich, Universitätsstraße 16,
CH-8092 Zürich, Switzerland
*********************************************
2nd of 2: NATURE Vol 448 August 30, 2007
CORRESPONDENCE
Climate: Sawyer predicted rate of warming in 1972
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; 1972). 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.

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.

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; 1861) and 
Guy Callender's in the mid-twentieth (for 
example, G. S. Callendar, Weather 4, 310-314; 
1949). 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.

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.

Neville Nicholls
School of Geography and Environmental Science,
Monash University, Victoria 3800, Australia
===================================================
"As an endangered species and an endangering one, we need, collectively,
all the self-understanding and self-direction that we can muster."

M. Brewster Smith. "Perspectives on Selfhood."
American Psychologist, December 1978
==================================================================
"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."

Barnovsky et al. "Approaching a state shift in Earth's biosphere."
Nature.  07 June 2012,Volume 486, Pages:52-58
doi:10.1038/nature11018




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