Climate Change Already Reducing Crop Yields

     Climate change is already beginning to hurt maize¹ and wheat production, according to a new study.

    Higher average growing season temperatures(温度) in most major grain-producing countries are beginning to work against the progress made by improving seeds and farming practices, according to the study published in the journal Science.

    "It is better for yields if it gets warmer, but only up to a point," said economist² and study co-author Wolfram Schlenker at Columbia University.

    Once temperatures rise above a certain point, which varies for each crop, "yields fall off a cliff," he said.

    Improving technology vs. hotter climateGlobal crop yields have been increasing slowly, but steadily³, over the decades as farming technology has improved.

    Schlenker and his colleagues used mathematical models to see if rising temperatures were starting to undo⁴ some of the production gains from improving technology.

    They estimate that global maize production is as much as 3.8 percent lower than it would have been without climate change, and wheat production is 5.5 percent lower.

    That may not sound like much, but the study notes that's equal to the annual maize production of Mexico and the wheat production of France.

    Rice and soybeans have not been affected⁵ as much on a global scale because yield gains from warmer temperatures in higher latitudes⁶ offset⁷ the losses in other parts of the globe.

    Here today, more tomorrowSoil scientist Chuck Rice at Kansas State University said much of the previous research on climate change has focused on what the impacts on agriculture(农业) will be in the future. This one gives a sense of what already is happening.

    The U.N. Food and Agriculture Organization estimates that the demands on agriculture will increase by 70 percent by 2050 to feed a growing and increasingly affluent⁸ population. Rice said the new study shows the current pace of progress is not enough.

    "Even with the 1 or 1.1 percent [annual] improvement in crop yields, we won't meet those goals," he said. "So if climate change is already holding us back, that means we're going to have to almost redouble our efforts."Schlenker said his study should give policymakers some direction on how to prepare for the accelerated pace of warming that scientists expect in the coming years.

    "If you're worried about rising food prices, it might be good to funnel⁹ some research into doing breeding for heat tolerance¹⁰, and maybe even drought tolerance," he said.

    US spared, for nowWhile average growing season temperatures have been trending higher in most grain-producing nations, a notable exception is the United States, where, surprisingly, the study found those average temperatures have actually declined slightly.

    The authors say that may help explain some of the skepticism about climate change found in the U.S. farm belt.

    But they warn that the cooling trend is not expected to last.(本文由在线英语听力室整理编辑)

1 maize   

n.玉米

参考例句：

• There's a field planted with maize behind the house.房子后面有一块玉米地。
• We can grow sorghum or maize on this plot.这块地可以种高粱或玉米。

2 economist   

n.经济学家，经济专家，节俭的人

参考例句：

• He cast a professional economist's eyes on the problem.他以经济学行家的眼光审视这个问题。
• He's an economist who thinks he knows all the answers.他是个经济学家，自以为什么都懂。

3 steadily   

adv.稳定地；不变地；持续地

参考例句：

• The scope of man's use of natural resources will steadily grow.人类利用自然资源的广度将日益扩大。
• Our educational reform was steadily led onto the correct path.我们的教学改革慢慢上轨道了。

4 undo   

vt.解开，松开；取消，撤销

参考例句：

• His pride will undo him some day.他的傲慢总有一天会毁了他。
• I managed secretly to undo a corner of the parcel.我悄悄地设法解开了包裹的一角。

5 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。

6 latitudes   

纬度

参考例句：

• Latitudes are the lines that go from east to west. 纬线是从东到西的线。
• It was the brief Indian Summer of the high latitudes. 这是高纬度地方的那种短暂的晚秋。

7 offset   

n.分支，补偿；v.抵消，补偿

参考例句：

• Their wage increases would be offset by higher prices.他们增加的工资会被物价上涨所抵消。
• He put up his prices to offset the increased cost of materials.他提高了售价以补偿材料成本的增加。

8 affluent   

adj.富裕的，富有的，丰富的，富饶的

参考例句：

• He hails from an affluent background.他出身于一个富有的家庭。
• His parents were very affluent.他的父母很富裕。

9 funnel   

n.漏斗；烟囱；v.汇集

参考例句：

• He poured the petrol into the car through a funnel.他用一个漏斗把汽油灌入汽车。
• I like the ship with a yellow funnel.我喜欢那条有黄烟囱的船。

10 tolerance   

n.宽容；容忍，忍受；耐药力；公差

参考例句：

• Tolerance is one of his strengths.宽容是他的一个优点。
• Human beings have limited tolerance of noise.人类对噪音的忍耐力有限。