Plants are flowering faster than scientists predicted（预测）in reaction to climate change, which could have long damaging effects on food chains and ecosystems.

    Global warming is having a great effect on hundreds of plant and animal species around the world, changing some living patterns, scientists say.

    Increased carbon dioxide（CO2）in the air from burning coal and oil can have an effect on how plants produce oxygen, while higher temperatures and changeable rainfall patterns can change their patterns of growth.

    “Predicting species' reaction to climate change is a major challenge in ecology,” said the researches of several U.S. universities. They said plants had been the key object of study because their reaction to climate change could have an effect on food chains and ecosystem services.

    The study, published on the Nature website, uses the findings from plant life cycle studies and experiments across four continents and 1,634 species. It found that some experiments had underestimated（低估）the speed of flowering by 8.5 times and leafing by 4 times.

    “Across all species, the experiments under-predicted the speed of the advance — for both leafing and flowering — that results from temperature increases,” the study said.

    The design of future experiments may need to be improved to better predict how plants will react to climate change, it said.

    Plants are necessary for life on the Earth. They are the base of the food chain, using photosynthesis（光合作用）to produce sugar from carbon dioxide and water. They let out oxygen which is needed by nearly every organism on the planet.

    Scientists believe the world's average temperature has risen by about 0.8℃ since 1900, and nearly 0.2℃ every ten years since 1979.

    So far, efforts to cut emissions（排放）of planet-warming greenhouse gases are not seen as enough to prevent the Earth heating up beyond 2℃ this century — a point scientists say will bring the danger of a changeable climate in which weather extremes are common, leading to drought, floods, crop failures and rising sea levels.

已知等比数列{a_n}的前n项和S_n＝t·5^n－2－ ，则实数t的值为(  )．

阅读下文，回答相关问题。
        ①小时候猜一道智力题，问：从地球上的什么地方出发，无论往哪里走，都是朝向南? 答案是：北极。现在无论同谁聊天，无论从哪说起，都会很快谈到钱。钱成了当今社会的极点。
        ②我当过许多年的医生，虽是无钱之人，却凭医疗常识，想像钱的功能是有限的，理由从人的生理结构而来。钱能买来山珍海味，可再大的富豪也只有一个胃，一个胃的容积就那么大，至多装上两三斤的食物，外加一罐扎啤，也就物满为患了。你要是愣往里揣，轻则是慢性胃炎，重了就是急性胃扩张，后者有生命危险呢。更不用说，长期的膏粱厚味，引起高胆固醇糖尿病等等。钱能买来绫罗绸缎，可再娇美的妇人也只有一副身段，一次只能向世人展现套在身体最外层的那套衣服。
        ③人和动物在结构上实在是大同小异，从翩飞的蝴蝶到一只最小的蚂蚁，都有腹腔和眼睛。人和动物最大的区别就在于思想，而恰恰在这一面钢铁盾牌面前，金钱折断了蜡做的枪头。比如理想，比如亲情，比如自由……都是金钱的盲点。它们可以因了金钱而卖出，却不会因了金钱而被买进。金钱只是单向的低矮的闸门，永远无法积聚起情感的洪峰。
        ④造物给予人的躯体是有限的，作为补偿，造物给人以无限的精神。人的躯体的每一个细微之处，都是很容易满足的。造物以此来制约人对物质的欲望，鼓励思想的飞翔。于是人类在有了果腹的兽肉和蔽体的树叶之后，就开始创造语言、绘画和音乐……积蓄了一代又一代的精华，于是我们有了文学，有了艺术，有了哲学的探讨和对宇宙的访问……那都是永无穷尽的奥妙啊，只要人类存在一天，就会上天入地呕心沥血地寻找与提炼。
        ⑤我们现在是站在钱的极点上，但人们在新的一轮物质需要满足之后，回过头来仍然要皈依精神。精神才是人类最大的财富。