Tree-ring stable carbon isotope-based June–September maximum temperature reconstruction since AD 1788, north-west Thailand

The first study of tree-ring stable carbon isotopes in Thailand has demonstrated that stable carbon isotope in northwestern Thailand represents a promising proxy for the temperature reconstruction of core-monsoon periods. A tree-ring δ¹³C chronology was constructed based on four cores covering the period of 1788–2013. After removing the long-term decreasing trend reflecting atmospheric CO₂ concentrations, the ∆¹³C chronology was able to capture both temperature and hydro-climate signals. ∆¹³C chronology showed particularly strong and significant negative correlation (r = –0.62, p < 0.0001) with June–September maximum temperature (CRU TS 3.24). The maximum temperature was reconstructed, which explained 37.8% of the variance in the instrumental maximum temperatures over the period of 1901–2013. The maximum temperature reconstruction revealed that four cooler and three warmer periods, as well as a slightly increasing temperature trend, occurred during the late seventeenth to mid-eighteenth centuries, which were followed by severe temperature fluctuations during the twentieth century century. While the sea surface temperature anomaly in the Indian Ocean might not affect the maximum temperature, its unstable relationship with the El Niño-Southern Oscillation (ENSO) was detected. In addition, a close relationship was observed between the maximum temperature and ENSO during the negative phase of the Pacific Decadal Oscillation (PDO), but this relationship was lost during the positive phase of the PDO.