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 incurrent studies.