Global Warming 全球性暖化 - 10
Global warming is the increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation. The term "global warming" is a specific example of the broader term climate change, which can also refer to global cooling. In common usage the term refers to recent warming and implies a human influence.
So we're talking about two and a half to three billion more mouth to feed on a world with limited amounts of good arable land and water. And so to, to achieve food security forty to fifty years out, the amount of food we're going to have to produce, it's going to be at least sixty percent greater than the amount of food we're producing today. M39中国英语学习网
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So we're dealing with serious questions, the world's foremost food crop is at risk. Coastlines are eroding. Our western heartland is drying up, and human health is under threat. The more science we do, the more we understand how future climates might work. But some of those findings may bring unpleasant surprises. Could we be nearing some invisible tipping point? Will sudden changes in the climate stop civilization in its tracks? Or could Mother Nature turn on us? A case in point: it's widely assumed that forests store away much of our excess CO2 emissions which help us breathe better. But investigators in the Rocky Mountains have unsettling evidence that an excess of fixed nitrogen coming in from the atmosphere may be upsetting all that. M39中国英语学习网
M39中国英语学习网
We're studying nitrogen because it is part of carbon dioxide story. You, me, plants, every other living thing on Earth is made up of carbon plus other elements, other nutrients. And nitrogen is one of those and in fact it's an essential nutrient. Now it's interesting...M39中国英语学习网
M39中国英语学习网
Basically like you or I, anybody else, the soil and all that everything that lives underneath, there are plants and microbes, breathes. So, as they breathe, just like us again, they're releasing carbon dioxide.M39中国英语学习网
M39中国英语学习网
What the team is investigating is whether elevated levels of nitrogen in this soil are stimulating microbes into a feeding frenzy down in the old stored carbon.M39中国英语学习网
M39中国英语学习网
So by adding nitrogen, the hypothesis is that we've given them more excess to that food. More food, more respiration, more carbon dioxide coming out the soils. M39中国英语学习网
M39中国英语学习网
If nitrogen is triggering the release of more stored carbon, where is that nitrogen coming from? Well, apparently it's coming from us. Every time we burn fossil fuels, we produce nitrogen. Every time we fertilize fields, or manure piles up, we are spreading nitrogen around. M39中国英语学习网
M39中国英语学习网
In Colorado, we have this very nice situation where we can actually pinpoint where our pollutants come from, because there isn't very much out of here. Every night when cold air drains down from the bottom of the mountains, because you know, cold air sinks, it sinks down to an area in the middle of the South Platte River Basin about the town of Greeley. And it pours there. So all the air pollution that comes with it from Denver, from the agricultural fields, pour down there. In every morning when the air rises as it warms up, it comes back up the mountains. So it's coming from Greeley, from the lower part of the mountains, against the prevailing winds, because it's moving with hot air rising, moves up here to the tops of the mountains where you get summertime clouds. These summertime clouds condense, take all those pollutants, dump them down on the ground. And that's where we're getting the nitrogen. M39中国英语学习网
M39中国英语学习网
If this nitrogen cycle is repeated elsewhere, many of the world's forests won't be absorbing much CO2. They may even start releasing it. Out of the far end of the climate spectrum is a worst case scenario, in which increasingly warm atmosphere we trigger abrupt climate changes. Unpredictable and stunning shifts in both temperature and precipitation that can bring on almost instant drought or deep freeze, devastating perhaps just one region or the entire planet, and lasting for decades, even centuries. It has happened before.M39中国英语学习网
M39中国英语学习网
M39中国英语学习网
tipping point: In sociology, a tipping point or angle of repose is the event of a previously rare phenomenon becoming rapidly and dramatically more common. The phrase was coined in its sociological use by Morton Grodzins, by analogy with the fact in physics that when a small amount of weight is added to a balanced object, it can cause it to suddenly and completely topple.M39中国英语学习网
M39中国英语学习网
a case in point: an instance or example that illustrates what is being discussedM39中国英语学习网
M39中国英语学习网
prevailing wind: a wind from the predominant or most usual directionM39中国英语学习网
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