Letters: Can Science Actually Predict Global Warming?

Those of you who still try to contend with
debunkers will have noticed that they say that
weather is hard to predict beyond the next few
days, so we sure can’t trust predictions for the
next few decades or centuries.

The two letters, below, published by Nature in
2007, will give you something to work with.
Lance

  NATURE
  Vol 448
  30 August 2007

  CORRESPONDENCE

  #1 –

  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

 
  #2 –

  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

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