标题： 年轻的弱太阳问题 显示英文标题

标题： The faint young Sun problem

摘要： 四十多年来，科学家们一直在努力解答古气候学中最基本的问题之一——“暗弱年轻太阳问题”。对于早期地球而言，恒星演化模型预测的太阳气候系统能量输入比今天低约25%。如果所有其他控制地球气候的参数都相同的话，这将导致我们星球前二十亿年的历史中出现一个完全冰冻的世界。然而，在太古代（距今38亿至25亿年）存在大量液态水甚至生命的证据，因此必须有一些效应（或多种效应）抵消了暗弱年轻太阳的影响。在过去四十年间，人们提出了许多可能的解决方案并进行了探索，其中大多数研究集中在大气温室气体浓度更高，如二氧化碳、甲烷或氨气等方面。然而，所有这些解决方案都面临相当大的困难，因此不能认为暗弱年轻太阳问题已经解决。 在此，我回顾了关于该主题的研究，包括最近提出的暗弱年轻太阳问题解决方案建议以及有关地球早期大气组成的最新地球化学限制。此外，我还将概述未来研究最有希望的方向。特别是我认为需要改进太古代气候系统的地球化学约束，并使用最先进的气候模型进行数值实验，以最终评估是什么因素阻止了太古代地球上的海洋完全冻结。 显示英文摘要

摘要： For more than four decades, scientists have been trying to find an answer to one of the most fundamental questions in paleoclimatology, the `faint young Sun problem'. For the early Earth, models of stellar evolution predict a solar energy input to the climate system which is about 25% lower than today. This would result in a completely frozen world over the first two billion years in the history of our planet, if all other parameters controlling Earth's climate had been the same. Yet there is ample evidence for the presence of liquid surface water and even life in the Archean (3.8 to 2.5 billion years before present), so some effect (or effects) must have been compensating for the faint young Sun. A wide range of possible solutions have been suggested and explored during the last four decades, with most studies focusing on higher concentrations of atmospheric greenhouse gases like carbon dioxide, methane or ammonia. All of these solutions present considerable difficulties, however, so the faint young Sun problem cannot be regarded as solved. Here I review research on the subject, including the latest suggestions for solutions of the faint young Sun problem and recent geochemical constraints on the composition of Earth's early atmosphere. Furthermore, I will outline the most promising directions for future research. In particular I would argue that both improved geochemical constraints on the state of the Archean climate system and numerical experiments with state-of-the-art climate models are required to finally assess what kept the oceans on the Archean Earth from freezing over completely.