Study Warns of Rapid Rise In Earth's Temperature
A study warns that the Earth's temperature is approaching a level not seen in a million years, implying that we are getting close to "dangerous" levels of human pollution.
The study finds that, while the world warmed slowly during the century to 1975, it has warmed at a more rapid rate of about 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade thereafter. The researchers say the global mean temperature is now within one degree Celsius (1.8 degrees Fahrenheit) of the maximum mean temperature of the past million years. Based on a 0.2-degree-Celsius increase per decade, that high point could be reached within 50 years.
The authors' conclusion: Further warming of one degree Celsius could suggest a critical level after which potential consequences -- such as higher sea levels and species extinction -- might be especially hard to manage.
"If further global warming reaches two or three degrees Celsius, we will likely see changes that make Earth a very different planet from the one we know," said James Hansen, lead author and head of the National Aeronautics and Space Administration's Goddard Institute for Space Studies in New York, in a prepared statement. "The last time it was that warm was in the middle Pliocene, about three million years ago, when sea levels were estimated to have been 25 meters (80 feet) higher than today."
The researchers also suggest that an increased temperature difference between the Western and Eastern Pacific could increase the likelihood of strong El Ni?os, such as occurred in 1983 and 1998. An El Ni?o is a large climactic disturbance rooted in the tropical Pacific Ocean that recurs every few years and is linked to extreme weather patterns of rainfall and drought.
Dr. Hansen has taken an active and high-profile role in debating critics of global warming, including the Bush administration. In 1988, he set off alarms by testifying in Congress that a global-warming trend had likely begun. He became a cause célèbre when the White House Office of Management and Budget tried to censor his testimony. Many of his critics concede the planet has warmed but remain skeptical that it is triggered by human activity.
The latest research was published in the Proceedings of the National Academy of Sciences and was led by Dr. Hansen and colleagues from the Columbia University Earth Institute, New York, and the University of California, Santa Barbara.
Many scientists believe that the Earth has warmed partly because greenhouse gases released by humans -- mainly carbon dioxide -- trap energy from the sun. The Proceedings paper notes that the United Nations Framework Convention on Climate Change has the goal of stabilizing greenhouse-gas emissions at a level preventing "dangerous" interference caused by human activity. Although the treaty doesn't specifically define such interference, the authors propose that it be defined in terms of the potentially harmful and irreversible effects caused by sea-level changes and species extinction.
地表温度可能已接近危险水平
一项研究报告警告称，地球表面温度即将升至100万年从未有过的水平，人类污染已经接近“危险”的程度。
研究发现，1975年之前的一百年间地球表面只是缓慢变暖，但此后平均气温的升幅明显加快，每十年上升0.2摄氏度（0.36华氏度）。该报告的研究人士称，全球平均气温较过去100万年的最高平均值仅差不到1摄氏度（1.8华氏度）。按照目前每年上升0.2摄氏度的速度来看，50年内就将达到这一高点。
报告作者总结道：地表气温再上升1摄氏度就将进入临界水平，超过这一水平就很可能造成包括还平面升高和物种灭绝等一系列难以控制的后果。
“如果全球温度进一步上升2-3摄氏度，则地球可能会变成我们从未想像的另外一个星球，”该报告第一作者、美国国家航空航天局(National Aeronautics and Space Administration) Goddard空间研究院负责人詹姆士?汉森(James Hansen)说。“地球上次达到这一温度是在上新世中期，即大约300万年前，当时的海平面比今天高25米（80英尺）。”
撰写该报告的研究人士还指出，东、西太平洋温差的扩大有可能引发更多类似1983年和1998年的强烈的厄尔尼诺现象。厄尔尼诺现象是赤道附近太平洋海水流动引发的一种气候异常现象，每隔几年发生一次，通常会出现大量降雨和严重干旱等极端天气现象。
关于地球变暖的问题，汉森与包括布什(Bush)政府在内的对立派展开了激烈争论，也受到了业内的广泛关注。1988年，他在国会作证时警告称，全球变暖的趋势可能已经开始。随后白宫预算管理办公室(White House Office of Management and Budget)试图审查他的证词，一时间引发了不小的轰动。他的很多对立派承认地球的确在变暖，但他们对所谓是人类活动导致地球变暖的说法表示怀疑。
上述报告在Proceedings of the National Academy of Sciences发表，汉森与他在哥伦比亚大学(Columbia University)地球研究所和加州大学(University of California)的同事们牵头撰写了这份报告。
很多科学家相信地球变暖在一定程度上是因为人类排放的温室气体－－主要是二氧化碳－－能增加地球大气层对太阳能的吸收。Proceedings的报告指出，联合国气候变化纲要公约(United Nations Framework Convention on Climate Change)已制定目标，希望将温室气体排放量稳定在能防止人类活动引发“危险”的干扰的水平。尽管该公约并未对此类干扰作出明确定义，但该报告作者建议以潜在的危害和因海平面变化和物种灭绝而引发的不可逆的影响来定义这种干扰。
Gautam Naik
