China Cooled Nearly 0.2°C During Global Warming Hiatus

During the global warming hiatus between 1998 and 2014 temperatures in the whole of China declined sharply, dropping by nearly 0.2°C by the end of the hiatus period. The delayed cooling observed in the Tibetan Plateau was even steeper.

Abstract

A reduction in the warming rate for the global surface temperature since the late 1990s has attracted much attention and caused a great deal of controversy. During the same time period, however, most previous studies have reported enhanced warming over the Tibetan Plateau (TP). In this study we further examined the temperature trend of the TP and surrounding areas based on the homogenized temperature records for the period 1980–2014, we found that for the TP regions lower than 4000 m the warming rate has started to slow down since the late 1990s, a similar pattern consistent with the whole China and the global temperature trend. However, for the TP regions higher than 4000 m, this reduction in warming rate did not occur until the mid-2000s. This delayed warming hiatus could be related to changes in regional radiative, energy, and land surface processes in recent years. […]

3 Results

3.1 Annual Mean Temperature Variations

For the global, whole China, the TP regions lower and higher than 4000 m, the annual mean temperature showed evident rapid warming since 1980 (Figures 1 and S2). Trend analysis showed relatively little temperature change for the TP regions lower than 4000 m since 1998 (Figures 1b and S2b), and similar pattern existed for the whole China and the global temperature at the same time (Figures 1c and 1d, and S2c andS2d). The temperature for the TP regions lower than 4000 m showed almost flat trend with a rate of 0.07°C/decade during period 1998–2014 (Table 1). However, for the TP regions higher than 4000 m, the annual mean temperature kept increasing until the mid-2000s, followed by a significant decreasing trend in recent years (Figures 1a and S2a).

Figure 1. Observed annual mean temperature anomalies for the TP regions (a1) higher than 4000 m, (b1) lower than 4000 m, (c1) whole China, and (d1) global mean temperature during 1980–2014. Trend lines were estimated using the nonparametric LOESS regression technique with a span of 0.5; the shading area represents the 95% confidence intervals of the estimated trends. The (a2, b2, c2, and d2) insets in each figure show the decadal change rate of temperature variations (°C/decade) and corresponding error bars during the period of 1980–1997 and 1998–2014.

3.2 Warming Rates of Annual Mean Temperature

To examine changes in the warming rates over time, we first smoothed the temperature time series using the LOESS regression with the span of 0.5. Based on the smoothed trend lines, we calculated the annual change rate for the mean temperature of the global, the whole China, and the TP regions lower and higher than 4000 m. Consistent with the reported global warming hiatus period [Fyfe et al., 2013], the increase rate of global mean temperature peaked around 1997 and started to decline. However, since about 2010, the annual change rate of global mean temperature started to increase again, indicating the general warming trend in global temperature. By contrast, the results showed that for the TP regions lower than 4000 m and the whole China, the warming rates started to decline sharply and persistently since about 1998, indicating a significant warming slowdown (Figure 2). It seems that the TP regions lower than 4000 m responded fairly quickly to the global warming hiatus, and this temperature slowdown was intensified in recent years with negative annual change rates (Figure 2).

Figure 2. Comparisons of annual change rates for the TP regions higher than 4000 m, the TP regions lower than 4000 m, and global and whole China mean temperature from 1981 to 2014. The annual change rates were estimated based on the nonparametric LOESS regression technique with a span of 0.5.

However, the temperature trajectory for the TP regions higher than 4000 m was different. For this region, the rapid warming continued until about 2005, when the warming rate peaked and started to decline (Figure 2).