Sources of the internal variability-generated uncertainties in the projection of Northeast Asian summer precipitation

Abstract

Significant uncertainties exist in climate change projections, and these mainly originate from the internal variability of the climate system. Using 40-member ensemble projections of the National Center for Atmospheric Research Community Climate System Model Version 3, we explored the uncertainties in the projected change of the Northeast Asian summer precipitation during 2006–2060 and examined the sources of the internal variability-generated uncertainties. The projected summer precipitation trends show large diversities from member to member, attributable to the superposition of the internal climate variability on the external forcing. Except for Northeast China, the signal-to-noise ratios (SNRs) are less than one, indicating the internally induced precipitation trends dominate the externally forced trends over large parts of Northeast Asia. The first mode of the internally induced precipitation trends displays widespread negative trends over Northeast Asia, and the second mode is characterized by a dipole trend pattern between Northeast China and Siberia. The atmospheric circulation trend patterns related to the first and second modes bear resemblances to those related to the Arctic Oscillation and Polar-Eurasian pattern, respectively. A dynamical adjustment was further performed on the summer precipitation trends to reduce the impact of the internal atmospheric variability. After the dynamical adjustment, the level of similarity in the residual precipitation trends across the 40 ensemble members increased significantly. In particular, the SNRs increased notably, with values larger than one over a vast area of Northeast Asia, which was in sharp contrast to values larger than one only being noticeable within Northeast China prior to the adjustment.