Earth's outgoing longwave radiation linear due to H2O greenhouse effect
Earth's outgoing longwave radiation linear due to H2O greenhouse effect
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DOI：
10.1073/pnas.1809868115
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发表时间：
2018-10-09
影响因子：
11.1
通讯作者：
Cronin, Timothy W.
中科院分区：
文献类型：
--
作者：
Koll, Daniel D. B.;Cronin, Timothy W.
卫星测量和辐射计算表明，地球的出射长波辐射 (OLR) 在很宽的温度范围（大于或接近 60 K）内基本上是表面温度的线性函数。线性意味着辐射强迫在温暖气候和寒冷气候中具有相同的影响，因此对于理解过去和未来的气候变化至关重要。尽管近线性关系的证据在 50 多年前就首次被指出，但目前还不清楚为什么这种关系有效以及何时失效。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 解释为温室效应主要由可凝结气体主导的大气的新兴特性。线性度是由于表面不断增加的热发射与随着变暖而缩小的光谱窗口区域之间的竞争而产生的，一旦连续吸收切断光谱窗口，线性度就会在高温下崩溃。我们的模型提供了一种理解长波对地球气候敏感性的贡献的方法，并表明含有其他可凝结温室气体的太阳系外行星可能具有与地球相似的气候动态。
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 (greater than or similar to 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.