A Preliminary Study On The Climatological Problems Of Interdiurnal Temperature Variability Under Global Warming And Their Impacts On Human Health

The global climate has been changing at an unprecedented fast speed on different time scales.This change has brought many challenges,such as how this change has occurred,and what characteristics will this change have in the future,especially the sea level rise and the more frequent extreme weather and climate that define the environment for human survival.How mankind responds to such challenges is an urgent issue to be solved.This dissertation research is designed and carried out under such a demand.We seek to gain new understandings of two different but interwoven disciplines:(1)climate change itself;(2)what kind of public health challenges the ongoing climate change will bring,particularly the risks of respiratory epidemics.Because human health's perception and response to the surrounding environment are different on different time scales,we focus on the interdiurnal temperature change that plays an important role in human health but has not been well studied previously.By revealing the characteristics of spatiotemporal evolution of interdiurnal temperature as global climate changes and the relationship between interdiurnal temperature changes and respiratory diseases,we hope to estimate possible future public health risks,thereby provide new scientific basis for humans to respond to ongoing climate change.This dissertation summarizes our research progress in the following areas:(1)searching for physical quantities describing the interdiurnal temperature changes and expositing their advantages,disadvantages and applicability,(2)revealing the interannual and interdecadal dominant modes of interdiurnal temperature changes and their underlying causes,(3)extracting the main characteristics of the evolution trend of interdiurnal temperature changes as the globe continues to warm,identifying the physical reasons behind them,and projecting future scenarios of interdiurnal temperature changes,(4)establishing the relationship between interdiurnal temperature changes and seasonal influenza epidemics and projecting the future risks of influenza epidemics.The results of this dissertation are as follows:(1)Based on the analysis of the limitations of the daily temperature standard deviations that was commonly used in the past for the understanding of interdiurnal temperature changes,we designed an interdiurnal temperature change index(DTD)that captures both spatiotemporal locality of and highly sensitivity to the interdiurnal temperature difference,and verified the improved suitability and stability of this index in capturing synoptic scale signals on a global scale.(2)The climatological DTD variability in historical data contains high meridional orientation and seasonality.The value of DTD in middle and high latitudes is generally higher than that in low latitudes.It is large in winter and spring and small in summer.That characteristic reflects the seasonally changing meridional temperature gradient.In order to obtain the detailed characteristics of DTD changes,we use the empirical orthogonal function analysis method to extract the spatiotemporal modes of the interannual and the interdecadal variability of the DTD.The results show that both the primary interannual mode and the primary interdecadal mode can effectively capture the characteristics of the interdiurnal temperature change on their corresponding time scales.It is revealed that the changing interdiurnal temperature change is mainly caused by the changing heat transport(through horizontal temperature advection)to reduce the seasonally varying meridional temperature gradient.(3)The trend of DTD in historical data has a high degree of spatial locality.The weakening of the seasonally varying meridional temperature gradient associated with the ongoing spatially uneven global warming in the mid-and high-latitude has caused a large spatial scale reduction in the winter DTD in the mid-and high-latitude regions of the northern hemisphere.However,this change in not longitudinally uniform;and rather,the DTD in subtropical Asia,Europe,the Arctic Ocean coastal regions,and the southern hemisphere subtropical zone has been enhancing,with most noticeable spatial range and intensity change occurring in summer.The latter lack of zonal uniformity is attributed to the global unevenness of the land-sea distribution.By analyzing the results from the historical climate change attribution experiments using climate models,we further infer that the evolution of global-scale DTD is mainly caused by greenhouse gas emissions from human activities,rather than natural forcing.The long-term trend characteristics of DTD is likely to continue in the future;and the higher the greenhouse gas concentration,the more significant the trend.(4)The changing characteristics of this DTD will also bring about changes in the intensity of seasonal infectious diseases.Based on the relationship between the seasonality of influenza and DTD in the mid-latitudes of the northern hemisphere that we have quantified based on historical data,and the projection of future climate using climate models,we conclude that the risk of seasonal influenza in the mid-latitudes of the northern hemisphere is likely to increase by 20-50%.