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The International Astronomical Union passed a resolution on August 24, 2006 that redefined planets, essentially relegating Pluto to the status of a dwarf planet. For humans, the contraction of the solar system means that the list of planets suitable for terraforming has been whittled down by one. The loss is not so great;

Pluto was never a likely candidate for terraforming as a result of its distance from the sun.

Terraforming, literally earth-forming, is a process of planetary engineering by which we may some day be able to render the planets closest to us, such as Mars and Venus, suitable habitats for humans. Terraforming is still thought to be largely a denizen of the realm of science fiction because of the huge energy expenditures and currency injections that it would demand. With our current scientific capabilities, it would take several millennia to shape the atmosphere and climate of a planet so that they closely resemble those of Earth. New technologies could shift the timeframe to several centuries rather than millennia, but some experts deny the possibility of terraforming a planet even on the longer timescale because of the economic and political difficulties it would inspire.

These skeptics should be reminded that Earth is itself a terraformed planet. Every species that has lived on this planet has altered its chemical and biological makeup in some way. Blue-green algae are responsible for the existence of oxygen on Earth, for example. Subsequent plant and animal species are responsible for the constant cycling of organic and biological matter. The changes that species impose on the earth are an integral part of the ecological processes of Earth, but the speed and force with which these changes occur can at times be a cause for concern. Now is one of those times.

At the dawn of the Neolithic Revolution approximately ten thousand years ago, the current wave of terraformation began. With the advent of agricultural systems, humans domesticated plants and animals, unconsciously acting as agents of natural selection along the way, as other species have done for other types of evolution. Among our contributions to Earths ecosystems were the enlarged and elongated corn with which we are familiar, the horse, and long stalks of wheat. By cultivating plant and animal species, humans produced food surpluses, leading to the first social hierarchies, settled or semi-settled societies, and increasing human populations. This last variable quickly eclipsed the others as the most notable contribution of the Neolithic Revolution.

Enlarged social groups demanded more territory and more farmland. Parts of the Earth not naturally suitable for growing crops were made suitable by the dedicated and sometimes inspired efforts of humans. Techniques such as deforestation, irrigation, and terracing converted wooded areas, deserts, and mountains into fertile farmland. Europe, which used to be covered in forestland, has only a few forests remaining. The rainforest of Brazil is gone, as are the grasslands of Argentina and the forests of China. They have all been replaced by farmland.

The expansion of agriculture has altered the chemical makeup of soils, some of which must lie fallow as compensation for the depletion of nitrogen that occurs when crops such as wheat are grown year after year. Irrigation has left salt and mineral residue in previously fertile soils.
Without the challenge of food production as a bulwark against settlement, humans became even more adventurous with their environments, adapting places that could not even grow food to human habitation by building dams or exurban communities in the middle of deserts.

Essentially, humans have terraformed the world around them so that it is a relatively perfect place for their own species. I say relatively because humans are in fact threatened by their own alterations to the environment. We now face the ramifications of terraformation on a nearly daily basis. The current strain of E. coli in spinach has been traced back to farms in California, where overflow water from the rivers used to irrigate cropland used to grow spinach and lettuce has been known to contain E. coli. The Mississippi River may be redirected in the near future because its current artificial path is threatening areas of human habitation. Crises such as global warming, acid rain, desertification, and species loss have been exposed too many times to count.

When humans began to experiment with terraformation ten thousand years ago, they were unaware of its potentially negative consequences. Current scientific data allows us to be far more prescient in future endeavors. We should focus on the implications of terraformation for our own planet before we even turn our attention to others.