Changes And Attribution Of Temperature Extremes Over China Under 1.5? And 2? Global Warming

mThe long-term goal of the 2015 Paris Agreement is to limit global warming to well below 2°C above pre-industrial levels and to pursue efforts to limit it to 1.5 °C.However,for climate mitigation and adaption efforts,further studies are still needed to understand the regional consequences between the two global warming limits.This research provides an assessment of changes in temperature extremes over China(relative to 1986-2005)at 1.5 °C and2 °C warming levels(relative to 1861-1900)by using the 5th phase of the Coupled Model Intercomparison Project(CMIP5)models under three RCP scenarios(RCP2.6,RCP4.5,RCP8.5).On this basis,the tie when the significant climate change emerges from natural variability is investigated from the perspective of signal-to-noise ratio.The anthropogenic influence on the risk of temperature extremes is examined based on the Probability Ratio.The major findings are as follows:(1)With respect to 1986-2005,the temperature of hottest day and coldest night are projected to increase about 1°C/1.6°C and 1.1°C/1.8°C,whereas warm days and warm spell duration index will increase about 7.5%/13.8%and 15d/30d at the 1.5°C/2°C global warming levels,respectively.Under an additional 0.5°C global warming,the projected increases of temperature in warmest day/night and coldest day/night are both more than 0.5? across almost the whole China.In Northwest China,Northeast China and the Tibetan Plateau,the multi-model mean increase in coldest day and coldest night will be about 2 times higher than a change of 0.5? global warming.Although the area-averaged changes in temperature extremes are very similar for different scenarios,spatial hotspot still exists,such as in Northwest China and North China,the increases in temnpratures are apparently larger in RCP8.5 than that in RCP4.5.(2)Relative to natural variability,in the 21st century,there are significant changes in the temperature extremes over China under the RCP8.5 scenario.When the climate change signals emerge from natural internal variability,the ToE(Time of Emergence)is generally earlier for warm nights,warm days,warm spell duration index and frost days,which is earlier than 2020s.ToE of the warmest day and night is generally earlier for lower latitudes(<2030s),whereas later for higher latitudes(2040-2050).The earlier ToE of a indice,the smaller inter-model uncertainty is and vice versa.Cold days are vey likely to have changed significantly over the middle part of Northwest China,northeast of the Tibetan Plateau,North China and Northeast Chinaof before 1.5°C global warming.When the climate change exceeds 2 standard deviation of natural internal variability,warm days and warm spell duration index are likely to have significant changes in most areas.(3)Results show that occurrence probability of daily extremes differ substantially between the two global warming levels over China,for instance,the probability of hot extremes(expected every 1,000 days)has increased by 15 and 23 times relative to the natural conditions at 1.5°C and 2°C warming over China.The north area of the Tibetan Plateau and Southeast China are in greater risks suffering such a hot event due to anthropogenic influence.Human influence have increased the risk of warmest day(night)while have reduced the risk of coldest day(night).There are greater risks and larger uncertainties in warm events for a higher percentile,whereas it is less evident for cold events owing to its small variability.An additional 0.5°C global warming will make the occurrence probability of a natural 10-year warmest night and warmest day event increase about 22%and 30%,respectively,whereas further decrease the likelihood of coldest night and coldest day about 10%.