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Some thoughts
on plantations
and global
cooling

W.J. Libby

Bill Libby is Professor Emeritus
of Forestry and Genetics at the
University of California Forest
Products Lab., Richmond, California,
United States.

Global timber shortage, or even timber famine, has been predicted on several occasions in the past. While such shortages have occurred locally, market forces and human foresight have usually worked to bring wood supply into balance with demand, and the earth's peoples have not generally suffered from severe wood shortages (Laarman and Sedjo, 1992). This history may lead current decision-makers to be complacent with respect to future demand for forests. However, there may be needs in the future for much more wood and other important forest services than existing forests can provide. Planting the forests to satisfy such requirements should be accomplished many years before they become urgent.

Predicting future needs decades or even centuries ahead is hardly an exact science. Acknowledging in advance that all such predictions are likely to be wrong, and many badly so, I will use the creative thinking of W. Sutton (Sutton 1999; 2000) to provide a framework for estimating future needs for wood. (Of course, other important forest ecosystem services will also be provided, to varying degrees, by various kinds of plantations.)

FIGURE 1
A smoothed curve of major glacial and interglacial periods during the past 1.6 million years, showing relatively short cycles until about 650 000 years ago and then longer cycles with greater differences between the warm interglacials and the coldest parts of the glacial periods

- Source: Adapted from Millar and Woolfenden, 1999, with secondary and lower-order events smoothed over.

FIGURE 2
A smoothed curve of the past 180 000 years, showing the most recent glacial period and the Eemian and Holocene interglacials, as well as secondary events such as interstadial warm events and the Younger Dryas, a tertiary cold event

- Source: Adapted from Millar and Woolfenden, 1999; and Millar, 1999, modified by more recent data, with all lower-order, most tertiary and some secondary events smoothed over.

FIGURE 3
A smoothed curve of the past 14 000 years, starting during the warming trend that began 18 000 years ago and including a few secondary and lower-order events, showing the very rapid cooling and later very rapid warming of the Younger Dryas, the fairly rapid changes associated with the Mediaeval Warm Period and Little Ice Age, and the more gradual warming to and cooling from the warmest Holocene episode, which occurred between 8 000 and 6 000 years ago

- Source: Adapted from Millar and Woolfenden, 1999, modified by more recent data.

Sutton predicted future needs for wood under two contrasting scenarios. In both, he perhaps optimistically accepted that the earth's human population would asymptote and stabilize at about 10 billion. In the first scenario, he assumed that those 10 billion people would use wood at the recent global rate of about 0.6 m3 per person per year. Annual wood harvest at recent levels would fall short of global needs by about 2.5 billion cubic metres per year, most of which Sutton estimated could be met by establishing about 100 million hectares of new forest plantations - which would almost double the current forest plantation area (about 104 million hectares in 1995 [FAO, 1999]). Sutton's second scenario anticipated that energy costs would increase relative to other costs. Wood, being much more energy-efficient than most of its substitutes, will thus increasingly substitute them. Assuming the hoped-for increase in basic standards of living, Sutton estimated that a combination of about 1 400 million hectares of plantations and 2 600 million hectares of native forests could satisfy the increased demand for wood.

Such estimates lead to the question of where additional plantations should go. An attractive answer is "near the people who will need them". Many of the largest and fastest-growing human populations are in tropical and subtropical developing countries. Should global cooling occur, it will be yet another reason to consider emphasizing plantations in subtropical and tropical locations.

Until recently, most planners and the general public assumed or accepted that the present climate was stable, and the future was planned for similar conditions. More recently, planners have begun to comprehend that increased levels of greenhouse gases will result in general warming, with uncertain but probably serious consequences for communities near sea level and for most or all ecosystems globally. However, the possibility has been raised that the world is in a general cooling phase which is being masked, or even offset, by greenhouse-gas warming.

Global warming has recently received much more attention than global cooling. However, the long-term trends shown in Figures 1 to 3 indicate repeated cycles of long glacial periods and much shorter interglacials. The seven most recent glacial periods lasted 90 000 to 125 000 years each, while their interglacial periods each lasted about 10 000 years (Figure 1). Whether some natural secondary or tertiary event has reversed the general cooling trend of the past 4 000 years and is now warming the earth is not certain. It is clear, however, that very recent anthropogenic inputs, such as greenhouse gases and vast areas paved or painted with dark materials, are warming the planet. It is not clear whether or for how long such anthropogenic inputs can forestall or even prevent the next glacial period.

Both short-term warming and longer-term cooling need to be considered. It is clear that currently extant forest tree species have survived the repeated glacial cycles of the past 2.6 million years. Boreal and temperate species have generally survived by migrating. So, there seem to be two important questions to consider:

References

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