So where in nature can we look for salvation? Until recently climate scientists hoped it would come from farther south. In temperate and tropical vegetation, they thought, a negative feedback effect called carbon fertilization might rein in the carbon dioxide rise. Plants need carbon dioxide to grow, and scientists have found that in laboratory chambers well-nourished plants bathed in high-carbon dioxide air show a surge of growth.
So out in the real world, it seemed, plants would grow faster and faster as carbon dioxide built up in the atmosphere, stashing more carbon in their stems, trunks, and roots and helping to slow the atmospheric buildup.
The outlook for an increased ocean sink is no brighter. The North Atlantic and the southern oceans have cold, nutrient-rich waters that welcome carbon dioxide. Carbon dioxide dissolves easily in cold water, and the nutrients foster marine-plant growth that quickly uses up the dissolved carbon dioxide. The traffic mostly goes the other way in warmer, less biologically rich seas.
The global balance is favorable, for now at least. More carbon dioxide dissolves in the oceans than is given off. Researchers measurements confirm that the oceans take up nearly as much carbon as the regrowing forests: an average of 2 billion tons a year. One-half of the missing carbon is ending up in the ocean. The question is whether this ratio is going to change as global warming raises the temperature of surface waters and carbon dioxide continues to build up in the atmosphere.
The future does not look particularly bright. Carbon dioxide is less soluble in warmer water. Whats more, dissolved carbon dioxide can easily slip back into the atmosphere unless it is taken up by a marine plant or combines with a buffer molecule of carbonate.
The oceans supply of carbonate is limited and is replenished only slowly as it is washed into the ocean by rivers that erode carbonate-containing rocks such as limestone. In absorbing those two billion tons of carbon from the atmosphere year after year, the ocean is gradually using up its buffer supply. It is expected that by the end of the century, its carbon appetite will have dropped by 10 percent and it may ebb much further in the long run.
If nature withdraws its helping hand if the carbon sinks stop absorbing some of our excess carbon dioxide we could be facing drastic changes even before 2050, a disaster too swift to avoid. And if the carbon sinks hold out or even grow, we might have extra decades in which to wean the global economy from carbon-emitting energy sources. Perhaps it is time for us to think about creating our own carbon sinks.
Scientists have dreamed up plenty of possibilities: planting new forests, for example. Young forests are hungry for carbon right now because they are growing vigorously. So why not try to keep a forest young indefinitely, by regular thinning? Every year or every ten years a certain amount of wood might be taken to be used in, say, paper, housing, and furniture. In this way you could make the landscape continue to take up carbon for a long time indefinitely.
The most fitting end for the carbon that human beings have tapped from the Earth, in coal, oil, and gas, might be to send it back where it came from into coal seams, old oil and gas fields, or deep, porous rock formations. That might allow humanity to keep burning fossil fuels without dire consequences for climate. Or maybe the future lies in fields of solar panels, armies of giant wind turbines, or a new generation of safe nuclear reactors. No one knows, but we dont have long to dither. The trees are doing their best, but year by year the threat of global disaster is climbing.
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16. Read the text and find the phrases in favour of alternative types of energy.
