Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 20139
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 20139.
Proc Natl Acad Sci U S A. 2018 Oct 9;115(41):10293-10298. doi: 10.1073/pnas.1809868115. Epub 2018 Sep 25.
Satellite measurements and radiative calculations show that Earth's outgoing longwave radiation (OLR) is an essentially linear function of surface temperature over a wide range of temperatures (≳60 K). Linearity implies that radiative forcing has the same impact in warmer as in colder climates and is thus of fundamental importance for understanding past and future climate change. Although the evidence for a nearly linear relation was first pointed out more than 50 y ago, it is still unclear why this relation is valid and when it breaks down. Here we present a simple semianalytical model that explains Earth's linear OLR as an emergent property of an atmosphere whose greenhouse effect is dominated by a condensable gas. Linearity arises from a competition between the surface's increasing thermal emission and the narrowing of spectral window regions with warming and breaks down at high temperatures once continuum absorption cuts off spectral windows. Our model provides a way of understanding the longwave contribution to Earth's climate sensitivity and suggests that extrasolar planets with other condensable greenhouse gases could have climate dynamics similar to Earth's.
卫星测量和辐射计算表明，在很宽的温度范围内（≳60 K），地球的长波辐射（OLR）与地表温度呈基本线性关系。线性关系意味着辐射强迫在较暖气候和较冷气候中的影响相同，因此对于理解过去和未来的气候变化具有根本重要性。尽管早在 50 多年前就首次指出了这种近乎线性关系的证据，但仍不清楚为什么这种关系是有效的，以及何时会失效。在这里，我们提出了一个简单的半解析模型，该模型将地球的线性 OLR 解释为一种大气的突现特性，其温室效应主要由可凝结气体主导。线性关系源于随着变暖，表面热辐射的增加与光谱窗口区域变窄之间的竞争，一旦连续吸收切断光谱窗口，线性关系就在高温下失效。我们的模型提供了一种理解地球气候敏感性中长波贡献的方法，并表明具有其他可凝结温室气体的系外行星可能具有与地球相似的气候动力学。
