Decadal changes in radiative fluxes at land and ocean surfaces and their relevance for global warming

Abstract

Anthropogenic interference with climate occurs primarily through modification of radiative fluxes in the climate system. Increasing releases of greenhouse gases into the atmosphere lead to an enhancement of thermal radiation from the atmosphere to the surface by presently about 2 W m−2 per decade, thereby causing global warming. Yet not only thermal radiation undergoes substantial decadal changes at the Earth surface, but also incident solar radiation (SSR), often in line with changes in aerosol emissions. Land‐based observations suggest widespread declines in SSR from 1950s to 1980s (‘global dimming’), a partial recovery (‘brightening’) since mid‐1980s, and indication for an ‘early’ brightening in 1930s and 1940s. No similar extended observational records are available over oceans. However, modeling studies, conceptual frameworks and available satellite‐derived records point to the existence of decadal SSR variations also over oceans. SSR changes overall match with decadal variations in observed warming rates, suggesting that SSR variations may effectively modulate greenhouse gas‐induced warming. Specifically, on the Northern Hemisphere, the lack of warming from 1950s to 1980s and its subsequent acceleration in the 1990s fits to the trend reversal from dimming to brightening and associated changes in air pollution levels. From the 1950s to 1980s no warming was also observed over Northern Hemispheric Oceans, in line with conceptual ideas that subtle aerosol changes in pristine ocean areas, effectively amplified by aerosol–cloud interactions, can substantially alter SSR, thereby modulating Sea Surface Temperatures. On the Southern Hemisphere, the absence of significant aerosol levels fits to the observed stable (greenhouse gas‐induced) warming rates since the 1950s. WIREs Clim Change 2016, 7:91–107. doi: 10.1002/wcc.372 This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change

Urbanization effect on trends in sunshine duration in China

“…Of these, 638 have sunshine duration records that cover at least 85 % of the whole measurement period since the 1950s. Moreover, it has been demonstrated that sunshine duration is able to capture variations in cloudiness and, to a lesser extent, the signal from aerosol concentrations (Sanchez-Lorenzo et al, 2009;Wang et al, 2012c;Sanchez-Romero et al, 2014Li et al, 2016;Wild, 2016). Similar to the surface solar radiation trends, a transition from decreasing to leveling off was also noted in the sunshine duration trends in China around 1990 (Wang et al, 2013.…”

“…Subsequently, a transition from a decrease to an increase in surface solar radiation occurred in many regions of the world from the mid-1980s on the order of 1 to 4 W m −2 (Wild et al, 2005;Wild, 2012Wild, , 2016. These phenomena are popularly known as "global dimming and brightening", where "global" originally referred to "global radiation" as a synonym for surface solar radiation but is often interpreted in terms of a global-scale dimension (Wild, 2009(Wild, , 2012.…”

Changes in shortwave and longwave radiative fluxes as observed at BSRN sites and simulated with CMIP5 models

“…From the longest 25 records covering 353 years, a mean increase in downward longwave radiation of +2.0 Wm -2 per decade since the early 1990s is obtained, in line with our expectations from an increasing greenhouse effect. Thereby, three quarter of the BSRN sites show positive trends (19 sites in total, 9 of them significant), while one quarter show negative trends (6 sites, 3 significant) 3 . The change in downward longwave radiation quantitatively agrees well with the respective change calculated by the latest generation of global climate models (CMIP5).…”

“…This applies not only for the longwave radiation as expected from the increasing greenhouse effect, but also for the amount of shortwave radiation that reaches the Earth surface [1][2][3] . Many of the historic records of surface shortwave radiation show substantial declines from the 1950s to the 1980s, known as "global dimming" 4 , and a partial recovery thereafter, known as "brightening" 5 .…”

Long-term series of surface solar radiation at Athens, Greece

“…Interest on the 7 solar radiation changes has also been raised after the development of solar energy applications, 8 which are continuously growing in number over the recent years. Changes in SSR have been 9 recorded over the last century and can be caused either by natural events such as volcanic eruptions 10 or human-related activities, mainly in polluted regions (Wild, 2016). At larger scales (thousands of 11 years) changes in SSR, might have been caused by changes in the Earth's orbit and Sun solar output 12 (Lean, 1997;Ohmura, 2006).…”