On the Time Evolution of Climate Sensitivity and Future Warming
On the Time Evolution of Climate Sensitivity and Future Warming
复制标题
DOI：
10.1029/2018ef000889
复制
发表时间：
2018-09-01
期刊：
影响因子：
8.2
通讯作者：
Goodwin, Philip
中科院分区：
文献类型：
--
作者：
Goodwin, Philip
简而言之，地球气候对辐射强迫的敏感性仍然是未来气候变暖预测中不确定性的一个关键来源。最近的文献越来越多地认识到，研究必须超越平衡和仅考虑二氧化碳的观点，转向考虑气候敏感性将如何随着时间的推移而演变，以响应来自多个来源的人为和自然辐射强迫。本文使用改进的能量平衡模式探索气候敏感性的瞬时行为，在该模式中，多个气候反馈随着时间的推移独立地演变为多个辐射强迫源，结合来自观测和气候模式比较项目第五阶段(CMIP5)的约束。首先，产生了一个由10(7)个模拟组成的大型初始集合，其气候反馈强度的分布从次年到10(2)年的时间尺度受CMIP5集合的约束，包括普朗克反馈、组合水汽流失率反馈、雪和海冰反照率反馈、快速云反馈以及云对海表面温度调整反馈的响应。然后，将这些10(7)个模拟与代表变暖、热量和碳吸收的十年趋势的观测指标进行测试，只留下与CMIP5总体和历史观测相一致的4.6x10(3)个历史匹配模拟。结果显示，年时间尺度的气候敏感性为2.1摄氏度(在95%的不确定性下从1.6摄氏度到2.8摄氏度)，在世纪时间尺度上上升到2.9摄氏度(从1.9摄氏度到4.6摄氏度)。这些发现提供了根据气候系统当前的瞬变状态对气候敏感度的较低估计与基于复杂模型的长期行为和古气候证据的较高估计之间的联系。地球的气候敏感度是衡量大气二氧化碳水平翻一番时地表平均温度将增加多少的衡量标准。目前对地球在平衡状态下的气候敏感度的估计有很大的差异，从1.5摄氏度左右的低估计到4.5摄氏度左右的高估计。许多不同的气候过程影响气候敏感度的值，例如对云层表面变暖的反应，大气水蒸气，以及随着冰雪融化地球表面反射率的变化。这些过程在不同的时间尺度上发生，例如，大气中的水蒸气需要几天的时间才能改变，但融化大冰盖的时间要长得多。这项研究将一系列观测约束应用于气候模型模拟，以限制地球的气候敏感性，考虑到气候敏感性如何在不同的时间尺度上变化。气候敏感性的最佳估计是每年2.1摄氏度(不确定性从1.6摄氏度到2.8摄氏度)。然而，在世纪时间尺度上，气候敏感性增加到2.9摄氏度(从1.9摄氏度到4.6摄氏度)，影响未来的人为变暖。
Plain Language Summary The Earth's climate sensitivity to radiative forcing remains a key source of uncertainty in future warming projections. There is a growing realization in recent literature that research must go beyond an equilibrium and CO2-only viewpoint, toward considering how climate sensitivity will evolve over time in response to anthropogenic and natural radiative forcing from multiple sources. Here the transient behavior of climate sensitivity is explored using a modified energy balance model, in which multiple climate feedbacks evolve independently over time to multiple sources of radiative forcing, combined with constraints from observations and from the Climate Model Intercomparison Project phase 5 (CMIP5). First, a large initial ensemble of 10(7) simulations is generated, with a distribution of climate feedback strengths from subannual to 10(2)-year timescales constrained by the CMIP5 ensemble, including the Planck feedback, the combined water vapor lapse rate feedback, snow and sea ice albedo feedback, fast cloud feedbacks, and the cloud response to sea surface temperature adjustment feedback. These 10(7) simulations are then tested against observational metrics representing decadal trends in warming, heat and carbon uptake, leaving only 4.6x10(3) history-matched simulations consistent with both the CMIP5 ensemble and historical observations. The results reveal an annual timescale climate sensitivity of 2.1 degrees C (ranging from 1.6 to 2.8 degrees C at 95% uncertainty), rising to 2.9 degrees C (from 1.9 to 4.6 degrees C) on century timescales. These findings provide a link between lower estimates of climate sensitivity, based on the current transient state of the climate system, and higher estimates based on long-term behavior of complex models and palaeoclimate evidence.The Earth's climate sensitivity is a measure of how much the average surface temperature will increase if atmospheric carbon dioxide levels are doubled. There is currently a wide variation in estimates of the Earth's climate sensitivity at equilibrium, from low estimates around 1.5 degrees C to high estimates around 4.5 degrees C. Many different climate processes affect the value of the climate sensitivity, for example the responses to surface warming of clouds, atmospheric water vapor, and changes in the reflectivity of Earth's surface as snow and ice melt. These processes occur on different timescales, for example it takes days for water vapor to change in the atmosphere, but much longer to melt a large ice sheet. This study applies a range of observational constraints to climate model simulations in order to constrain the Earth's climate sensitivity, considering how the climate sensitivity varies on different timescales. A best estimate for climate sensitivity is found to be 2.1 degrees C (with uncertainty ranging from 1.6 to 2.8 degrees C) over yearly timescales. However, climate sensitivity increases to 2.9 degrees C (ranging from 1.9 to 4.6 degrees C) on century timescales, affecting future anthropogenic warming.