THE world will warm by 3·C，even under the most optimistic emissions projections for 2050, according to the UN group that studies global warming.

联合国全球变暖研究小组表示，即使是对废气排放量最乐观的预测，世界的温度仍会在2050年上升3摄氏度。

projections = estimate

The increase, which would cause drought and famine for 400 million people and devastate wildlife, is predicted by the Intergovernmental Panel on Climate Change in its most confident assessment yet of how greeenhouse gases are affecting global temperatures.

研究气候变化的政府间工作组对温室气体如何对全球温度产生影响做出了迄今为止最有把握的评估，从而做出了上述的升温预测，这一预测将导致四亿人口将面临着饥餓和干旱的威胁，动物也面临着灭绝的危险。

A draft of part of the panel's fourth report, which the US Government has released on the Internet, shows that it has, for the first time, placed a likely figure on the progress of global warming, indicating a degree of scientific certainly that it has avoided in the past.

该工作组的第四次报告的部分草案，由美国政府发表在互联网上，显示出这份报告首次在全球变暖的过程中，给出了估计的数值，体现了某种程度上科学的精确性，而这是该工作组过去所回避的。

a degree of scientific certainly  某种程度上科学的精确性

It says that temperatures could increase by between 2·C and 4.5·C when atmospheric carbon dioxide reaches double the pre-industrial level, but it declares 3·C to be the "most likely value" for such change.

该报告称，在大气层中二氧化碳的浓度达到前工业化级别的两倍时，温度可上升2到4.5摄氏度，但其指出，就这样的变化而言，上升3摄氏度是“最有可能的数值”。

A 3·C rise is the leval at which a British Meteorological Office conference last year judged that "dangerous" climate change would occur.

去年，在英国气象局会议(British Meteorological Office)上，人们做出这一判断，在温度上升3摄氏度这一水平上，“危险”的气候变化就将发生。

Previous reports from the IPCC, a tranditionally cautious body, have given only wider ranges of possibilities, which it acknowledged to be highly uncertain.
气候变化政府间工作组(IPCC)是具有谨慎传统的组织，其以往的报告仅仅给出较为广泛的可能性，该工作组也承认这是很不精确的。

While the panel does not indicate when this rise will occur, experts think it probable that pre-industrial carbon dioxide levels will double by 2050, even given successful efforts to contain greenhouse gas emissions.
尽管该工作组并没表明温度会于何时上升，但专家认为即使温室气体排放得到有效控制，但二氧化碳前工业时期的含量仍有可能到2050年前翻一番。
successful 翻成 “有效”

David King, Britain's chief scientific adviser, has argued that stabilisation of carbon dioxide at this level -550 parts per million - is the best target that the world can hope for, and his view is endorsed by many leading climatologists.
英国首席科学顾问大卫·金(David King)认为，二氧化碳浓度稳定在百万分之五百五十是人类期望的最好结果，他的观点也得到了许多气候权威学家的认可。
world 可意译为 “人类”