Correction of Inhomogeneities in Observed Land Surface Temperatures over China

Land surface temperature T-s and near-surface air temperature T-a are two main metrics that reflect climate change. Recently, based on in situ observations, several studies found that T-s warmed much faster than T-a in China, especially after 2000. However, we found abnormal jumps in the T-s time series during 2003-05, mainly caused by the transformation from manual to automatic measurements due to snow cover. We explore the physical mechanism of the differences between automatic and manual observations and develop a model to correct the automatic observations on snowy days in the observed records of T-s. Furthermore, the nonclimatic shifts in the observed T-s were detected and corrected using the RHtest method. After corrections, the warming rates for Ts-max, Ts-min, and Ts-mean were 0.21 degrees, 0.34 degrees, and 0.25 degrees C decade(-1), respectively, during the 1960-2014 period. The abnormal jump in the difference between T-s and T-a over China after 2003, which was mentioned in existing studies, was mainly caused by inhomogeneities rather than climate change. Through a combined analysis using reanalyses and CMIP5 models, we found that T-s was consistent with T-a both in terms of interannual variability and long-term trends over China during 1960-2014. The T-s minus T-a (T-s - T-a) trend is from -0.004 degrees to 0.009 degrees C decade(-1), accounting for from -3.19% to 5.93% (from -3.09% to 6.39%) of the absolute warming trend of T-s (T-a).