A Weblog monitoring coverage of environmental issues and science in the UK media. By Professor Emeritus Philip Stott. The aim is to assess whether a subject is being fairly covered by press, radio, and television. Above all, the Weblog will focus on science, but not just on poor science. It will also bring to public notice good science that is being ignored because it may be politically inconvenient.

Wednesday, May 26, 2004

Humans, fire and climate change.....

One of the many areas in which ecologists and climate scientists tend to make totally unsupported assumptions is in their assessment of the potential contribution of biomass fires to modern climate change. They have no sense of the ecological history of the last 18,000 years to 1 million years. I therefore welcome this excellent (and how often can we say that!) report in today's The Independent (May 26): 'The burning issue': "Israeli researchers have pushed back the date at which humans harnessed fire by half a million years."

Although there have been various earlier claims for the controlled use of fire by hominids as far back as 1.4 million years (in Africa), "Richard Klein, an expert on early humans, from Stanford University in California, says the Israeli scientists have made an important discovery. 'I think they have made by far the best case yet for humanly controlled fire before 250,000 years ago.'"

What we can certainly assert is that humans/hominids have been managing fire as a tool for a very long time, and may be for some hundreds of thousands of years.

Yet, in many climate and palaeoecological studies, it is just assumed that we have witnessed a significant modern increase in gas and particulate emissions from biomass burning. This is likely to be completely wrong on two basic accounts:

(a) First, we know that around 12,000 years ago, and earlier, there were far more savannas and grasslands in the world than there are today. Indeed, fire-prone savannas 'ruled' the tropics and the sub-tropics, there being hardly any true forests at all (so much for the myth of the ancient rain forest, by the way). Most of South East Asia, Africa, and even large portions of Amazonia were covered by savannas. Moreover, quite independent of the human use of fire, these savannas burnt annually through natural fires resulting from lightning strikes and other causes, thus contributing historic major (non-anthropogenic) emissions into the atmosphere;

(b) Secondly, and as now supported by the latest Israeli study, we must accept that humans have themselves been employing fire, both directly and indirectly, in ecosystems for hundreds of thousands of years.

The real position is thus probably entirely the opposite of that so often assumed. Today, gas and particulate emissions from biomass fires are probably at one of their lowest levels ever in the last 1 million years because of the long-term retreat of the grasslands and savannas and because of the many curbs in place on the human use of fire.

Although world historic fire ecology is only one small example, it illustrates just too clearly the inadequacy of so many of the 'assumptions' built into current, short-term ideas about modern climate change. In certain parts of the world, grasslands have dominated for millions of years (e.g. southern Africa), while, in others, savannas were far more widespread at the end of the last Ice Age, to be replaced by forests as the Earth warmed.

In summary: our current knowledge of world landscape change over the last 18,000 years to 1 million years shows how dangerous it is to make untested assumptions about current 'greenhouse gas' emissions and particulates and to employ these in models. As a long-time savanna specialist, you can see precisely why I think many climate scientists are suffering from a severe bout of 'presentism'.

Philip, off to graze.

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