How does ocean warming and steric sea level rise depend on carbon emissions?

人们普遍担心气候如何应对碳排放和土地利用变化导致的大气二氧化碳不断上升。在我们看来，气候响应可以分为以下几个阶段：1.过去和现在大气中二氧化碳的增加导致过去50年来全球变暖高达0.6摄氏度。然而，地区性的变化比这个全球信号要大得多。2.持续的排放正在增加大气中的二氧化碳，并推动热流进入海洋，导致海洋变暖和海平面急剧上升。气候变暖对碳排放情景以及海洋和陆地系统的碳吸收速率很敏感。3.升温和海平面上升的区域分布对海洋内部如何吸收热量很敏感，涉及到表层性质向温跃层和深海的转移。4.排放停止后，低层大气将发生热调整，进入海洋的净热通量将停止，因此海洋变暖和静止海平面最终也将停止。5.在达到热平衡的同时，大气和海洋在停止排放后也接近碳平衡，时间尺度可能是几百年到一千年。在这种平衡下，根据我们理想的理论，最终的大气二氧化碳和气候变暖的量与累积的碳排放有关。气候变暖和海平面上升的诊断将使用以下诊断方法来研究：(I)当前的温度和盐度观测，允许诊断静止的海平面；(Ii)使用一系列海洋和气候模型的思维实验，时间尺度为数百年到数千年，旨在探索海洋变暖如何从海面传播到海洋内部，这最终决定了静止的海平面上升；(Iii)与一个世纪以来集成的最先进气候模型的诊断状态进行比较；(Iv)与理想化理论的比较，这与何时停止排放有关；以及(Iv)最后是缩小尺度，以提供区域尺度上海平面变化响应的界限。这一中等复杂性的理论和地球系统模型的结合，将允许为一系列排放情景探索更广泛的参数空间，比IPCC在未来100年的评估中通常采用的参数空间要大得多。该研究有可能为海平面上升提供可触及的界限，这与对不同能源政策感兴趣的政策制定者有关，并通过与哈德利中心的合作提供了与最终用户的联系。

There is widespread concern about how climate is responding to the on going rise in atmospheric CO2 from carbon emissions and land use changes. In our view, the climate response can be divided into the following stages: 1. Past and on going increases in atmospheric CO2 are leading to a global warming of up to 0.6C over the last 50 years. The regional variability is though much larger than this global signal. 2. Continuing emissions are increasing atmospheric CO2 and driving a heat flux into the ocean, leading to ocean warming and steric sea level rise. The amount of warming is sensitive to the carbon emission scenario, as well as the rate of carbon uptake by the ocean and terrestrial system. 3. The regional distribution of warming and steric sea level rise is sensitive to how the ocean interior takes up heat, involving the transfer of surface properties into the thermocline and deep ocean. 4. After emissions cease, there will be a thermal adjustment of the lower atmosphere, and the net heat flux into the ocean will cease, and so ocean warming and steric sea level will eventually likewise cease. 5. As well as a thermal equilibrium being reached, the atmosphere and ocean approach a carbon equilibrium after emissions cease, on a timescale of perhaps several hundred years to a thousand years. At this equilibrium, the final atmospheric CO2 and the amount of climate warming is related to cumulative carbon emissions based on our idealised theory.The climate warming and steric sea level rise will be investigated using diagnostics of (i) present day temperature and salinity observations, allowing the steric sea level to be diagnosed;(ii) thought experiments with a range of ocean and climate models on timescales of centuries to several thousand years, designed to explore how the ocean warming spreads from the sea surface into the ocean interior, which ultimately determines the steric sea level rise;(iii) comparison with diagnostics of state of the art climate models, integrated for a century;(iv) comparison with idealised theory, relevant for when emissions cease;and (iv) finally a down scaling to provide bounds on the steric sea level response on a regional scale.This combination of the theory and Earth System models of intermediate complexity will allow a wide parameter space to be explored for a range of emission scenarios, much broader than that usually employed within IPCC assessments for the next 100 years. The study has the potential to provide accessible bounds for steric sea level rise, relevant for policy makers interested in different energy policies, and a link to end users is provided via the collaboration with the Hadley Centre.