From Microclimates To Macroclimates

The same factors which affect microclimates, including the plants themselves, translate into larger effects on the heat balance and moisture balance of the earth's surface. In many respects, the macroclimate (over hundreds of kilometers) is the sum total of all the microclimates across broad areas. For example, the local effect of a boreal forest canopy heating up in the sun because it has shed the snow from its branches can make a great difference to regional climate if it occurs on a broad enough scale. When an individual leaf in a rainforest canopy evaporates water and cools itself, this makes a contribution to the heat balance of the whole tree, the whole forest and the whole region. In its own tiny way it also ultimately helps to affect the distribution of heat and water vapor all around the world. So. if anything changes about the average shape of leaves, or size of trees, or the amount of bare ground around the world, this could all add up to a global change in climate.

The sort of way that changes in plant microclimates might scale up to alter global climates was neatly expressed by the "daisyworld" model of James Lovelock (see Box 4.1 and Figure 4.7).

Models Microclimates

Figure 4.7. Thedaisyworld model of Lovelock illustrates how the microclimate effects of plants could scale up to global climates. There are black and white daisies which do better under hot and cool conditions, respectively. If the sun gets weaker or stronger, the abundance of the two types shifts according to which does better in their local microclimates (top graph). In the bottom graph, the line "C" shows how temperature would change without the daisies changing their abundance. Line "G" shows how in fact things might change if the white and dark daisies adjust their abundance to exploit the microclimatic conditions: the temperature of the whole planet is regulated by a process that is essentially controlled at the level of microclimates. After Schwartzman, from Lovelock.

Figure 4.7. Thedaisyworld model of Lovelock illustrates how the microclimate effects of plants could scale up to global climates. There are black and white daisies which do better under hot and cool conditions, respectively. If the sun gets weaker or stronger, the abundance of the two types shifts according to which does better in their local microclimates (top graph). In the bottom graph, the line "C" shows how temperature would change without the daisies changing their abundance. Line "G" shows how in fact things might change if the white and dark daisies adjust their abundance to exploit the microclimatic conditions: the temperature of the whole planet is regulated by a process that is essentially controlled at the level of microclimates. After Schwartzman, from Lovelock.

In this simple thought experiment, there is a planet inhabited by only two types of plants (daisies, in Lovelock's model): dark-colored plants and light-colored ones. If a plant is dark in color it can absorb more sunlight, which makes its leaves warmer. By making its own tissues warmer it also makes a contribution to the local climate, and ultimately the temperature of the whole planet. Imagine that the planet starts to cool, because the "sun" gets weaker lor some reason. Plants will be starved of warmth, and the darker ones that can gather more heat and keep themselves warm will be favored. They will grow more vigorously and push out the cooler, lighter-colored ones. As the darker plants spread across the planet they not only warm up their own leaves, they also warm the air around them. If the dark-colored plants blanket the whole surface they will tend to make the global climate warmer, counteracting the cooling. So, the planet's temperature will adjust back up towards the point that it was at before.

Now imagine that instead the "sun" gets stronger, delivering too much solar energy and tending to overheat the planet. The dark plants will suffer by being overloaded with heat; they not only have to cope with the warm air temperatures but they are also absorbing a lot of sunlight which tends to heat them up even more. In this situation, the dark plants do not grow well and they get pushed out by the white plants that can keep themselves cool by reflecting back most of the sun's energy. As the white plants spread across the overheated planet, more and more of the solar radiation gets reflected back into space, and this cools the climate. Temperature is again brought down towards a more moderate level. It is as if the planet has a thermostat, regulating its temperature to prevent its climate from becoming too extreme.

Box 4.1 James Lovelock and Gaia

James Lovelock is an independent scientist whose work has inspired a whole new way of thinking about the world. Of his many important contributions to science, probably the greatest has been the message that earth's environment is to a large extent controlled by life itself. Much of this book is about the ways that living organisms have seized control of climate and atmosphere. Although there have always been scientists who worked on the effects of life at the broad scale, in the last 35 years there has been an enormous expansion in this way of looking at the world. Many of the scientists who nowadays work on the effects of plants on climate or the carbon cycle attribute much of their inspiration to Lovelock's view that life has an integral role in controlling the global environment.

Lovelock honored the global system with life at its center with the name "Gaia" after the ancient Greek earth goddess. This choice of a label has proven controversial, and some scientists have even accused Lovelock of venturing into religious mysticism. Lovelock himself has said that the name Gaia was merely intended as an inspiring metaphor, but there is no doubt that his view of the earth system has gained a lot more attention because of his choice of this name.

Daisyworld is a hypothetical example that demonstrates a general principle: that living organisms acting in their own short-term interest on a local microclimatic scale (both responding to and changing their microclimate) might add up to very big global changes. The overall result can be a control mechanism that regulates the earth's climate. Although daisies have never changed the world, it is possible that things rather like this have actually happened in the past. More than a billion years ago in the Precambrian, the first life on land was probably dark-colored algae and perhaps lichens. By altering the amount of sunlight absorbed at the earth's surface (the albedo), these plants may have brought about rather similar changes in heat balance of the world. It is thought that at that time the sun would have been fainter, and the earth in continual danger of freezing up. Indeed, there arc some signs of very severe and long-lasting ice ages before about 800 million years ago. In some of these cold phases ice sheets may have spread down closc to the equator, suggesting that almost the whole planet was iced up. Once the first simple land-living plants appeared, they may have helped to moderate the climate, keeping the earth within the band of temperatures suitable for maintaining life.

In the more recent geological past, since large plants with leaves and roots evolved, it is likely that the influence of plant microclimates in regulating broad-scale climates has become even more important. In the next couple of chapters (Chapters 5 and 6) we will explore some of these possible effects of plants on both regional and global climate.

Was this article helpful?

0 0
Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

Get My Free Ebook


Responses

  • Veikko Luostarinen
    Why are microclimates important?
    6 months ago

Post a comment