Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA.
Nature. 2010 Feb 25;463(7284):1066-70. doi: 10.1038/nature08831.
Tropical cyclones (also known as hurricanes and typhoons) are now believed to be an important component of the Earth's climate system. In particular, by vigorously mixing the upper ocean, they can affect the ocean's heat uptake, poleward heat transport, and hence global temperatures. Changes in the distribution and frequency of tropical cyclones could therefore become an important element of the climate response to global warming. A potential analogue to modern greenhouse conditions, the climate of the early Pliocene epoch (approximately 5 to 3 million years ago) can provide important clues to this response. Here we describe a positive feedback between hurricanes and the upper-ocean circulation in the tropical Pacific Ocean that may have been essential for maintaining warm, El Niño-like conditions during the early Pliocene. This feedback is based on the ability of hurricanes to warm water parcels that travel towards the Equator at shallow depths and then resurface in the eastern equatorial Pacific as part of the ocean's wind-driven circulation. In the present climate, very few hurricane tracks intersect the parcel trajectories; consequently, there is little heat exchange between waters at such depths and the surface. More frequent and/or stronger hurricanes in the central Pacific imply greater heating of the parcels, warmer temperatures in the eastern equatorial Pacific, warmer tropics and, in turn, even more hurricanes. Using a downscaling hurricane model, we show dramatic shifts in the tropical cyclone distribution for the early Pliocene that favour this feedback. Further calculations with a coupled climate model support our conclusions. The proposed feedback should be relevant to past equable climates and potentially to contemporary climate change.
热带气旋（也被称为飓风和台风）现在被认为是地球气候系统的一个重要组成部分。特别是，它们通过剧烈混合上层海洋，可以影响海洋的热量吸收、极向热输送，从而影响全球温度。因此，热带气旋的分布和频率变化可能成为全球变暖气候响应的一个重要因素。早中新世（约 500 万至 300 万年前）的气候是现代温室条件的潜在类似物，可以为这种响应提供重要线索。在这里，我们描述了热带太平洋地区飓风和上层海洋环流之间的正反馈，这种反馈可能对于维持早中新世温暖的厄尔尼诺型条件至关重要。这种反馈基于飓风使向赤道移动的浅层水团变暖的能力，然后这些水团在东赤道太平洋重新浮出水面，成为海洋风驱动环流的一部分。在当前气候下，很少有飓风轨迹与这些水团轨迹相交；因此，这些深层水团与表层之间的热量交换很少。中太平洋更频繁和/或更强的飓风意味着水团的加热更多，东赤道太平洋的温度更高，热带地区更温暖，进而导致更多的飓风。我们使用一个降尺度飓风模型，展示了早中新世热带气旋分布的剧烈变化，有利于这种反馈。耦合气候模型的进一步计算支持了我们的结论。所提出的反馈应该与过去的稳定气候相关，并且可能与当代气候变化相关。
