Congratulations to Sui yue Passing her Ph.D. Dissertations smoothly
Sui yue successfully passed through the doctoral dissertation defense on May8th 2015 at the 101 conference room of the IAP scientific research building. Her doctoral thesis title is the Climate change projection associated with a 2 °C global warming and simulating the impact of land use on climate.
In the past century the climate system has experienced a global change with the prominent symbol of global warming, which has and will continue to have a lot of impacts on both natural and human systems. Therefore, it is in urgent need of scientific climate change projection in order to offer the scientific basis for the sustainable development of society and economy and to provide the scientific support for the international climate change negotiations. In this dissertation, under the latest Representative Concentration Pathways (RCPs), first, from the perspective of the signal to noise ratio (the ratio of climate change signal to natural internal variability, S/N), changes in mean and extreme climate over the globe and China associated with a 2 °C global warming above pre-industrial levels are projected. Then, we examined the time of emergence (ToE) of temperature, precipitation and extreme climate over China during the 21st century and quantified the inter-model uncertainty. At last, within the framework of the Coupled Model Intercomparison Project Phase 5, three experiments are simulated from 1850 to 2100 using CESM1.0.4 to explore the different climate effects of land use change between under time-evolving external forcings and under fixed external forcings. One simulation is under full transient forcings, another is under full transient forcings without land use, and the third is under transient land use change with all other forcings remained at 1850 control experiments levels.
The primary conclusions are as follows:
(1) Relative to the natural internal variability, when the global temperature increase exceeds 2 °C above pre-industrial levels, global temperature and extreme warm (cold) temperature events significantly increase (decrease). Low latitudes show the largest signal-to-noise ratios. The globally averaged annual (seasonal) warming is five (three to four) times greater than natural internal variability, and the absolute values of signal to noise ratios in extreme temperature events are on average 1.2−7.8 over global land. Only boreal autumn and winter precipitation, very wet-day precipitation and simple daily intensity significantly increase. The percentage change in annual precipitation is averaged by 0.9% over the globe, and the associated signal-to-noise ratio is only 0.2. The signal to noise ratio of extreme precipitation events is 0.02−0.4 for global land areas.
(2) Annual (seasonal) warming over China is 0.6 °C (0.4−0.8 °C) greater than the simultaneous global warming of 2 °C. Relative to the reference period 1986−2005, temperature and extreme warm (cold) temperature events over China associated with a 2 °C global warming above pre-industrial levels significantly increase (decrease) as compared with natural internal variability. Warming gets stronger towards high latitudes and over the Tibetan Plateau compared to surrounding areas, especially in autumn and winter, while the surrounding areas of Tibetan Plateau have the largest signal to noise ratio, particularly in summer. The median and the 5% to 95% range among the models of annual warming and associated signal to noise ratio are 2.1 [1.1 to 3.2] °C and 4.0 [1.9 to 6.3] averaged in China, respectively, and the absolute value of nationally averaged signal to noise ratios in extreme temperature events are 0.9−6.2. Annual precipitation and extreme wet events over China non-significantly increase, and both extreme dry and wet events over southern China non-significantly increase. Annual precipitation and the signal to noise ratio are averaged by 7% [–9% to 29%] and 0.4 [–0.5 to 1.6] for China, respectively. The regional average of percentage change in very wet-day precipitation, max 5 day precipitation, consecutive dry days, simple daily intensity and total wet-day precipitation are 25%, 8%, –3%, 5% and 8%, respectively, with the regional averaged signal to noise ratio ranging from –0.1 to 0.5. Seasonally, precipitation non-significantly increases over most of China except in southeastern China in spring, in northeastern China in summer, in the middle and lower reaches of the Yangtze River in autumn, and in southwestern China in winter. The percentage change, signal to noise ratio, and the inter-model uncertainty for extreme precipitation events in winter are larger than that in other seasons.
(3) Relative to the reference period 1986−2005, the signal of temperature and extreme temperature events compared with natural internal variability appear during the 21st century under a median and a high representative concentration pathway. The earliest ToE of temperature occurs in the Qinghai-Tibetan Plateau between 2006 and 2009 for S/N > 1.0, then the ToE of frost days, growing season length, max daily maximum temperature and min daily minimum temperature occur sequentially before 2030, especially in summer and autumn. The inter-model uncertainty in ToE is at least 17 years, and more than 85 years in some regions. Under the RCP8.5 scenario, the ToE of precipitation and extreme precipitation events occur in western China and eastern China where is north of the Yangtze River, and the earliest ToE for S/N > 1.0 happens in the Qinghai-Tibetan Plateau around 2060, particular in winter and spring. Under the RCP4.5 scenario, only precipitation signal occurs in the northeastern Qinghai-Tibetan Plateau. The ToE of precipitation in southern China does not occur until the end of the 21st century. Generally, the earlier ToE occurs in one region (season), the smaller the inter-model uncertainty is.
(4) Under the RCP4.5 scenario, the land use change for the period 2081−2100 relative to the period of 1986−2005 is opposite to the change for 1986−2005 relative to 1850−1869. There are some differences of climate effects of land use between under time-evolving external forcings and under fixed external forcings. First, there is significant snow–surface albedo feedback in eastern North America, northern Europe and northeastern East Asia under the former external forcings, especially in boreal spring and autumn. Another is that both the increased evapotranspiration in regions where precipitation is small, e.g., West Asia, and water vapor convergence in eastern North America and southern Europe increase the precipitation in these regions. Annual temperature decreases 0.16 °C, and precipitation increases 0.01 mm d–1 for global land under time-evolving external forcings.