The radiative warming effects of the atmosphere and the surface in the infrared range can be described by G a and G s 47, whose climatological means are 158 W m−2 and 345 W m−2, respectively, from 2003 to 2014. G a represents the ability of the atmosphere to trap approximately 40% of the longwave radiation emitted by the Earth’s surface (399 W m−2). G s indicates the energy sent by the atmosphere to the surface to heat the Earth. Nearly half of G s comes from G a , and the rest comprises the solar incidence, sensible and latent heat absorbed by the atmosphere49. Figure 1 represents the spatial patterns of the estimated mean G a and G s between 2003 and 2014.Although G a and G s are both spatially inhomogeneous, they share similar spatial distributions. First, on average, both G a and G s decrease with increasing latitude. The zonal means of G a (G s ) are 189 W m−2 (394 W m−2) and 90 W m−2 (231 W m−2) in the tropics (30°S–30°N) and polar zones (90°S–60°S and 60°N–90°N), respectively. The latitudinal patterns of G a and G s are mostly caused by the zonal distribution of the atmospheric water vapor content, which is the most important contributor to the greenhouse effect42. The wetter atmosphere at low latitudes thus absorbs more terrestrial radiation than the drier atmosphere at high latitudes. The surface condition is another important contributor to the G s distribution. The wetter and warmer surface in the tropics provides greater latent and sensible heat to the atmosphere, which is included in G s 47. Second, because more atmospheric and surface moisture is found at sea than on land, on average, the oceanic G a and G s (162 W m−2 and 358 W m−2) are slightly larger than the terrestrial values (148 W m−2 and 312 W m−2). When the large proportion of oceans covering the Earth’s surface is considered, the oceanic G a (G s ) contributes more than three-quarters of the global total G a (G s ). Moreover, nearly half of the global greenhouse effect is attributed to G a (G s ) over the tropical oceans. Third, either G a or G s displays a meridional heterogeneity at the tropics. On the one hand, larger G a and G s (above 220 W m−2 and 420 W m−2, respectively) are found in the Indo-West Pacific, Amazon and East Africa. This pattern coincides with the location of the tropical monsoons50 that often deliver persistent convection. In the monsoon-prone areas, a stronger greenhouse effect is induced by the wetter and cloudier atmosphere and by the moist surface. On the other hand, the G a over the East Pacific and East Atlantic is relatively low (below 180 W m−2) because these areas are generally controlled by persistent subsidence and have dry and cloudless atmospheres.

Figure 1 Spatial distributions of climatological averaged greenhouse effect parameter (G; unit: W m−2) on a 5° by 5° box between 2003 and 2014. (a,b) refer to the atmospheric and surface greenhouse effect parameters (G a and G s ), respectively. The maps were generated by the Grid Analysis and Display System (GrADS; http://www.opengrads.org/doc/wind32-v1/) version 1.90-rc1. Full size image

Based on the climatological (2003–2014) means of G a and G s , the long-term variations of their anomalies (G aa and G sa ) can be obtained (Fig. 2). Because of the shorter period of the CERES EBAF product, the areal averaged G sa is represented only between 2003 and 2014 in Fig. 2 but shows no notable trend over the globe, sea or land. Thus, the surface greenhouse effect has not been strengthened in the last decade. The temporal variations of G sa and G aa are highly correlated over the globe, sea and land in 2003–2014, with all correlation coefficients above 0.40 and significant at the 0.01 level based on Student’s t-test. By contrast, G aa can be obtained from 1979 to 2014 because of the longer instrumental observations of T s and OLR. The most obvious feature is that the decadal trends of the global averaged G aa are not uniform throughout the period (Fig. 2a). In the 1980 s, a significant increasing G aa tendency exists with a linear estimate of 0.19 W m−2 yr−1. However, this uprising trend pauses starting in circa 1992, when G aa begins to slightly decrease at a rate of −0.01 W m−2 yr−1. This statistically non-significant trend indicates that the enhancing global atmospheric greenhouse effect is slowed down. Moreover, the atmospheric greenhouse effect hiatus can be found over both sea and land (Fig. 2b–c). Because the global total atmospheric greenhouse effect is largely controlled by the atmosphere over the oceans, the temporal variation of the averaged G aa at sea is similar to the global value (Fig. 2b). The tendency of the averaged G aa over the oceans also abruptly changes circa 1992. The oceanic G aa exhibits a notable increasing trend with a rate of 0.21 W m−2 yr−1 in 1979–1991, whereas its rate of change (−0.04 W m−2 yr−1) during 1992–2014 is not statistically significant. By contrast, although a sudden change in the G aa tendency is observed overland, the breakpoint is approximately 5 years later than that of the oceanic G aa (Fig. 2c). The terrestrial G aa trends are 0.12 W m−2 yr−1 and 0.05 W m−2 yr−1 before and after 1997, respectively.

Figure 2 Monthly variations of the areal averaged atmospheric and surface greenhouse effect parameter anomalies (G aa and G sa ) from 1979 to 2014 for the (a) globe, (b) sea and (c) land. G aa and G sa are represented by blue and red lines, respectively. Thin and thick solid lines indicate the monthly and 12-month moving averaged series, respectively. Vertical, thick, gray lines represent the break points of trends using the break function regression (see Methods). Green and yellow dashed lines refer to linear trend lines before and after the break points, respectively. The figure was plotted using MATLAB software. Full size image

Because G a is jointly determined by the longwave radiation at the surface and the TOA, the T s and OLR evolutions are employed to discuss the formation of the global atmospheric greenhouse effect hiatus (Fig. S1). Here, the time period is divided into three 12-year subperiods (1979–1990, 1991–2002 and 2003–2014). The first break point is used to separate the varying long-term global G aa behavior in Fig. 2a. The second break point represents the beginning of the global warming pause because the increasing global averaged T s tendency slowed down in the early 21st century15. In the first subperiod (1979–1990), the increasing T s leads to a remarkable uprising trend in the global averaged SULR anomaly of 0.07 W m−2 yr−1, whereas the global averaged OLR anomaly exhibits a significant decreasing trend of −0.10 W m−2 yr−1. Both of these behaviors enhance the atmospheric greenhouse effect, as indicated by an increase in G aa . However, in the following subperiod, the rates of change of the SULR and OLR anomalies are both significantly positive. The former (0.15 W m−2 yr−1) is comparable to the latter (0.14 W m−2 yr−1). Therefore, their contributions to the atmospheric greenhouse effect nearly cancel each other out. As a result, an unchanged global averaged G aa is shown during 1991–2002. In the last subperiod, the global averaged SULR anomaly remains trendless (0.02 W m−2 yr−1) because T s stops rising. Meanwhile, the long-term change of the global averaged OLR anomaly (−0.01 W m−2 yr−1) is also not statistically significant. Thus, these two phenomena result in a trendless G aa .

Furthermore, the trends of G aa are spatially inhomogeneous during individual subperiods (Fig. 3). G aa increases the most over the central North Pacific with a tendency of approximately 0.12 W m−2 yr−1 in 1979–1990 (Fig. 3a). Significant upward G aa trends are also found at the tropical Atlantic and the high latitudes of Eurasia. By contrast, almost no regions exhibit a significant downward G aa trend. This finding explains why the global averaged G aa increases during this period. Similar to the previous period, an uprising G aa trend is found over the central North Pacific from 1991 to 2002 with a reduced rate (Fig. 3b). Meanwhile, G aa increases by substantially more in the western tropical Pacific, where the largest tendency (0.18 W m−2 yr−1) is found, and in the central South Pacific. However, a remarkably decreasing G aa trend (−0.27 W m−2 yr−1) exists over the central tropical Pacific, indicating a weakened atmospheric greenhouse effect in this area, which largely offsets the warming effect in the aforementioned surrounding regions. As a result, a trendless global averaged G aa is displayed between 1991 and 2002 (Fig. 2). During the latest subperiod (2003–2014), the spatial pattern of the change in G aa is quite similar to that in 1991–2002, but the proportion of regions with significant G aa tendencies is significantly reduced (Fig. 3c). Although the maximum upward and downward G aa tendencies also appear over the western tropical Pacific and the central tropical Pacific, respectively, the increasing trend is nearly absent in the extratropics. Again, no significant trend of the global averaged G aa is found from 2003 to 2014 (Fig. 2) because the enhanced warming effect over the western tropical Pacific is largely counteracted by the weakened warming influence on the central tropical Pacific.

Figure 3 Spatial structures of the atmospheric greenhouse effect parameter anomaly (G aa ) trend on a 5° by 5° box using the least-squares approach during three subperiods: (a) 1979–1990, (b) 1991–2002, and (c) 2003–2004. Regions with a significant tendency (at the 0.05 confidence level based on the F-test) are crossed. Maps were generated by GrADS (http://www.opengrads.org/doc/wind32-v1/) version 1.90-rc1. Full size image

The results above indicate that the notably downward G aa tendency over the central tropical Pacific indeed plays an important role in inducing the greenhouse effect hiatus since the 1990 s. What causes this decreasing G aa ? The variation of the greenhouse effect is substantially influenced by its contributors, including water vapor, clouds, and GHGs42. GHG concentrations have risen steadily during recent decades1. The variations of metrics related to the other two contributors are given in Fig. 4a and are based on the CERES-EBAF products between 2003 and 2014. The total column precipitable water (TCPW) anomaly significantly increases at a rate of 0.44 cm yr−1. However, the cloud area fraction (CAF) anomaly is reduced by −0.60% yr−1, which is consistent with the decreasing cloud activity described in previous publications51. Therefore, although the greenhouse effect can be enhanced by increasing GHGs and water vapor in the atmosphere, it can be weakened by decreasing clouds. If these two actions offset each other, a hiatus of the global greenhouse effect will result. To confirm this, the variations of G aa and G sa in all-sky conditions are compared with those in clear-sky conditions in Fig. 4b,c. The clear-sky atmospheric and surface greenhouse effect parameters increase significantly at rates of 0.22 W m−2 yr−1 and 0.19 W m−2 yr−1, respectively. However, the atmospheric and surface greenhouse effect parameters both become trendless when clouds are considered. Moreover, the spatial pattern of the CAF anomaly trend (Fig. S2) is very similar to that of the G aa trend (Fig. 3c) during 2003–2014. Cloud activity becomes less active over the central tropical Pacific, whereas it is enhanced over the western and eastern tropical Pacific. Overall, the downward tendency of clouds is the dominant contributor to the greenhouse effect hiatus.

Figure 4 (a) Monthly variations of the global averaged TCPW (unit: cm) and CAF (unit: %) anomalies between 2003 and 2014. Dashed lines are the linear trend lines obtained by the least squares method. (b) Monthly variations of the atmospheric greenhouse effect parameter anomaly (G aa ; unit: W m−2) from 2003 to 2014 for all-sky (red lines) and clear-sky (blue lines) conditions. Dashed lines are the linear trend lines obtained by the least squares method. (c) Same as (b) but for the surface greenhouse effect parameter anomaly (G sa ; unit: W m−2). The figure was plotted using MATLAB software. Full size image