Word: earths
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Dates: during 1990-1999
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This means that in an economic--if not a political--sense, we have become a single, enormous population. The system in which we are living, extracting our energy and other supplies, is global: the totality of Earth's atmosphere, its waters, its soils and crust, and all its living things. This is the sum total of all the world's local ecosystems--ecosystems we have allowed to decay as we have chosen (quite successfully!) to live outside them...
...tide is running back toward Malthus. We are emerging from a 10,000-year vacation from nature still not fully realizing that our own survival hinges on reducing the damage we do to Earth's natural systems. We may not drive ourselves to the complete oblivion of biological extinction, but I fear that the Malthusian specters of famine, warfare and disease will rise in the comparatively short run (the next few centuries), coupled with an accelerating loss of human cultural diversity and, ultimately, quality of life...
Here's what we know. Since sunlight is always falling on the earth, the laws of physics decree that the planet has to radiate the same amount of energy back into space to keep the books balanced. The earth does this by sending infrared radiation out through the atmosphere, where an array of molecules (the best known is carbon dioxide) form a kind of blanket, holding outgoing radiation for a while and warming the surface. The molecules are similar to the glass in a greenhouse, which is why the warming process is called the greenhouse effect...
...greenhouse effect is nothing new; it has been operating ever since the earth formed. Without it, the surface of the globe would be a frigid -20[degrees]C (-4[degrees]F), the oceans would have frozen, and no life would have developed. So the issue we face in the next millennium is not whether there will be a greenhouse effect, but whether humans, by burning fossil fuels, are adding enough carbon dioxide to the atmosphere to change it (and our climate) in significant ways...
...accept that there has been moderate warming, we turn to computer models to see if humans are to blame and what will happen to the earth's climate in the future. These models are complex because climate depends on thousands of things, from Antarctic sea ice to sub-Saharan soil conditions. While the electronic simulations are monuments to the ingenuity and perseverance of their creators, they provide us with, at best, a fuzzy view of the future. They have difficulty handling factors like clouds and ocean currents (two major influences on climate), and if you fed the climate...