1 、Are we overlooking potential abrupt climate shifts? （我们是否忽略了潜在的气候剧变的可能性？）

 Most of the studies and debates on potential climate change, along with its ecological and   economic impacts, have focused on the ongoing buildup of industrial greenhouse gases in the atmosphere and a gradual increase in global temperatures. This line of thinking, however, fails to consider another potentially disruptive climate scenario. It ignores recent and rapidly advancing evidence that Earth's climate repeatedly has shifted abruptly and dramatically in the past, and is capable of doing so in the future.
气候变化的主流学界的争论和研究所以工业化发展投入到大气中的温室气体和日渐转暖的全球气候为焦点，然而这样的思考方式却没能把其他潜在的破坏性气候变化。它忽略了最近大量显现的，关于历史上地球上的曾有过的多次突如其戏剧性的气候转变的证据。这样的转变在过去发生了，在将来依然可能发生。

Fossil evidence clearly demonstrates that Earth's climate can shift gears within a decade, establishing new and different patterns that can persist for decades to centuries. In addition, these climate shifts do not necessarily have universal, global effects. They can generate a counterintuitive scenario: Even as the earth as a whole continues to warm gradually, large regions may experience a precipitous and disruptive shift into colder climates.

化石遗迹清楚的表明地球的气候曾在一个时段内发生急剧的转变，由此形成的新的气候模式有可能在几十年甚至数百年内保持稳定。此外，此类气候转变不一定是全球性的。他们能导致一些反常规的情形：即使全球气候依旧日渐暖化，一些大的区域的气候却有可能急剧变冷。

This new paradigm of abrupt climate change has been well established over the last decade by research of ocean, earth and atmosphere scientists at many institutions worldwide. But the concept remains little known and scarcely appreciated in the wider community of scientists, economists, policy makers, and world political and business leaders. Thus, world leaders may be planning for climate scenarios of global warming that are opposite to what might actually occur.1
早在20世纪末全球范围内多个机构的海洋，地球和气象学家们就已经在研究过程中建立起了这种气候突变的新型范式在。然而这个概念却一直未能被人们所熟知，在更广大的群体中的，科学家，经济学家，政策制定者以及世界政坛和商业领袖们对这个概念极少持认可的态度。
It is important to clarify that we are not contemplating a situation of either abrupt cooling or global warming. Rather, abrupt regional cooling and gradual global warming can unfold simultaneously. Indeed, greenhouse warming is a destabilizing factor that makes abrupt climate change more probable. A 2002 report by the US National Academy of Sciences (NAS) said, "available evidence suggests that abrupt climate changes are not only possible but likely in the future, potentially with large impacts on ecosystems and societies."2
在这里有必要澄清的是，我们正在讨论的不是单纯的气候突然变冷或者全球暖化，而是与全球暖化大趋势下的地区性的突然降温。的确，温室效应的存在作为一个不稳定因素，是的区域性的气候突变可能性增大。2002年的一份美国国家科学院的研究报告指出：“现有证据显示，气候的突变在未来不仅仅是可能的而且有很大发生几率，并对生态系统和社会系统造成巨大冲击。”
The timing of any abrupt regional cooling in the future also has critical policy implications. An abrupt cooling that happens within the next two decades would produce different climate effects than one that occurs after another century of continuing greenhouse warming.

2 、Are we ignoring the oceans' role in climate change? （我么是否忽略了海洋在气候变化中的作用？）
Fossil evidence and computer models demonstrate that Earth's complex and dynamic climate system has more than one mode of operation. Each mode produces different climate patterns.

The evidence also shows that Earth's climate system has sensitive thresholds. Pushed past a threshold, the system can jump quickly from one stable operating mode to a completely different one - "just as the slowly increasing pressure of a finger eventually flips a switch and turns on a light," the NAS report said.

Scientists have so far identified only one viable mechanism to induce large, global, abrupt climate changes: a swift reorganization of the ocean currents circulating around the earth. These currents, collectively known as the Ocean Conveyor, distribute vast quantities of heat around our planet, and thus play a fundamental role in governing Earth's climate.

The oceans also play a pivotal role in the distribution and availability of life-sustaining water throughout our planet. The oceans are, by far, the planet's largest reservoir of water. Evaporation from the ocean transfers huge amounts of water vapor to the atmosphere, where it travels aloft until it cools, condenses, and eventually precipitates in the form of rain or snow. Changes in ocean circulation or water properties can disrupt this hydrological cycle on a global scale, causing flooding and long-term droughts in various regions. The El Niño phenomenon is but a hint of how oceanic changes can dramatically affect where and how much precipitation falls throughout the planet.

Thus, the oceans and the atmosphere constitute intertwined components of Earth's climate system. But our present knowledge of ocean dynamics does not match our knowledge of atmospheric processes. The oceans' essential role is too often neglected in our calculations.

3 、Does Earth's climate system have an 'Achilles' heel'? （地球的气候系统也有软肋吗？）

Here is a simplified description of some basic ocean-atmosphere dynamics that regulate Earth's climate:

The equatorial sun warms the ocean surface and enhances evaporation in the tropics. This leaves the tropical ocean saltier. The Gulf Stream, a limb of the Ocean Conveyor, carries an enormous volume of heat-laden, salty water up the East Coast of the United States, and then northeast toward Europe.

This oceanic heat pump is an important mechanism for reducing equator-to-pole temperature differences. It moderates Earth's climate, particularly in the North Atlantic region. Conveyor circulation increases the northward transport of warmer waters in the Gulf Stream by about 50 percent. At colder northern latitudes, the ocean releases this heat to the atmosphere - especially in winter when the atmosphere is colder than the ocean and ocean-atmosphere temperature gradients increase. The Conveyor warms North Atlantic regions by as much as 5° Celsius and significantly tempers average winter temperatures.

But records of past climates - from a variety of sources such as deep-sea sediments and ice-sheet cores - show that the Conveyor has slowed and shut down several times in the past. This shutdown curtailed heat delivery to the North Atlantic and caused substantial cooling throughout the region. One earth scientist has called the Conveyor "the Achilles' heel of our climate system."3

4、What can disrupt the Ocean Conveyor? （什么能阻碍“传达者——海洋？）

Solving this puzzle requires an understanding of what launches and drives the Conveyor in the first place. The answer, to a large degree, is salt.

For a variety of reasons, North Atlantic waters are relatively salty compared with other parts of the world ocean. Salty water is denser than fresh water. Cold water is denser than warm water. When the warm, salty waters of the North Atlantic release heat to the atmosphere, they become colder and begin to sink.

In the seas that ring the northern fringe of the Atlantic - the Labrador, Irminger, and Greenland Seas - the ocean releases large amounts of heat to the atmosphere and then a great volume of cold, salty water sinks to the abyss. This water flows slowly at great depths into the South Atlantic and eventually throughout the world's oceans.

Thus, the North Atlantic is the source of the deep limb of the Ocean Conveyor. The plunge of this great mass of cold, salty water propels the global ocean's conveyor-like circulation system. It also helps draw warm, salty tropical surface waters northward to replace the sinking waters. This process is called "thermohaline circulation," from the Greek words "thermos" (heat) and "halos" (salt).

If cold, salty North Atlantic waters did not sink, a primary force driving global ocean circulation could slacken and cease. Existing currents could weaken or be redirected. The resulting reorganization of the ocean's circulation would reconfigure Earth's climate patterns.

Computer models simulating ocean-atmosphere climate dynamics indicate that the North Atlantic region would cool 3° to 5° Celsius if Conveyor circulation were totally disrupted. It would produce winters twice as cold as the worst winters on record in the eastern United States in the past century. In addition, previous Conveyor shutdowns have been linked with widespread droughts throughout the globe.

It is crucial to remember two points: 1) If thermohaline circulation shuts down and induces a climate transition, severe winters in the North Atlantic region would likely persist for decades to centuries - until conditions reached another threshold at which thermohaline circulation might resume. 2) Abrupt regional cooling may occur even as the earth, on average, continues to warm.