The Response Of Temperature And Precipitation To Global Warming In Both Observations And Models

Global near surface air temperature shows significant global warming features during the past hundred years.However,the raw temperature temporal series contain various variabilities with different time scale,such as interannual and decadal variabilities.As variabilities with varied time scale may be generated by differnet mechanisms,the studies on temperature change therefore must seperatre their variabilities based on time scales.Thus,this paper performs study about decadal variabilities of Northern Hemisphere temperature firstly.In particular,the recent global warming hiatus pheromena and its mechanisms are examined.Additionally,this paper explores the decadal variabilities of temereature in China and the corresponding mechanisms.Furthermore,temperature changes shows apparent spatial variances,such as enhanced terestrical warming and enhanced semi-arid region warming.The inhomognenous regional warming under global warming background implies that the regions with enhanced warming may be more affected.Therefore,this paper studies the spatial patterns of temperature change in Northern Hemisphere using both observations and models.In sharp contrast with global homognenous warming changes of temperature,precipitation changes shows pronounced spatial variances,say there are decreasing and increasing precipitation simultaneously.The increasing moisture with global warming leads to accelerated hydrological cycle,namely “dry get drier,wet get wetter”,when only thermodynamics is considered.However,global warming will induce changes in circulation,and circulation has important influences on precipitation changes,especially for land that relies on moistures transported from ocean via circulations.The distinct thermal conditions and circulations over veried regions make the responses of precipitation to global warming very complex.In addition,precipitation changes in China influence billions people,this paper therefore focus on precipitation changes in China in response to global warming.This paper studies the aforementioned scientific questions using both observations and models.The major conclusions are summarized as following:(1)By using mulitiple observations this study shows that temperature in Northern Hemisphere has pronounced decadal variability during the past hundred years.Comparing with Southern Hemisphere,the amplitudes of decadal variability of temperature in Northern Hemisphere are much larger.The decadal variability of temperature in Northern Hemisphere has larger amplitudes in cold season than which in warm season,and has larger amplitudes over land than which over ocean.The results by using indexes of internal climate variability modes or internal climate variability indexes from empirical orthogonal function of sea surface temperature,and using multiple methods to calculate decadal variability,suggest that decadal variability of temperature in Northern Hemisphere is mainly modulated by oceanic internal climate variabilities.(2)The results based on observations suggest that the recent warming hiatus is mainly induced by the decadal variability of temperature changes from warm phase to cold phase.Additionally,warming hiatus mainly occurs in boreal cold season,and is pretty weak in boreal warm season.The continents in Northern Hemisphere shows pronounced cooling changes during the recent warming hiatus period.Eursian and North American continents are two strongest cooling centers,and the relative contributions of them to cooling changes in Northern Hemisphere during the warming hiatus are 43% and 18%,respectively.Further studies reveal that weaker meridional thermal forcing induced by enhanced Arctic warming,and stronger zonal thermal forcing induced by oceanic internal climate variability modes stimulate both a weaker polar vortex and westerly winds,along with the amplified planetary waves,thereby facilitating southward invasion of cold Arctic air and promoting the blocking formation.As a result,the cooling over both Eurasian and North American continents,as well as warming hiatus occurred.(3)Based on the results con rmed by the multiple data and trend analysis methods,we found that the annual mean temperature in China had a cooling trend during the recent global warming hiatus period,which suggested a robust warming hiatus in China.The warming hiatus in China was dominated by the cooling trend in the cold season,which was mainly induced by the more frequent and enhanced extreme-cold events.By examining the variability of the temperature over different time scales,we found the recent warming hiatus was mainly associated with a downward change of decadal variability,which counteracted the background warming trend.Decadal variability was also much greater in the cold season than in the warm season,and also contributed the most to the previous accelerated warming.We found that the previous accelerated warming and the recent warming hiatus,and the decadal variability of temperature in China were connected to changes in atmospheric circulation.There were opposite circulation changes during these two periods.The westerly winds from the low to the high troposphere over the north of China all enhanced during the previous accelerated warming period,while it weakened during the recent hiatus.The enhanced westerly winds suppressed the invasion of cold air from the Arctic and vice versa.Less frequent atmospheric blocking during the accelerated warming period and more frequent blocking during the recent warming hiatus confirmed this hypothesis.(4)The surface air temperature trends from historical simulations of the Coupled Model Intercomparison Project Phase 5(CMIP5)were compared with observations for the period of 1955–2004.The observed spatial pattern of temperature trends was strikingly different from the CMIP5-historical simulations over mid-and high-latitude Northern Hemisphere.The strongest observed warming for the Eurasian Continent was over mid latitudes.However,the CMIP5 historical simulations indicated enhanced warming over higher latitudes,and the warming trends increased from low to higher latitudes.The zonal mean temperature trends indicated overestimated warming in high-latitude and underestimated warming in mid-latitude land over Northern Hemisphere in CMIP5 historical simulations.The overestimated Arctic and underestimated Eurasia mid-latitude warming only occurred in cold season.Further studies revealed that model bias in sea surface temperature and the exaggerated response of temperature change to Arctic sea ice decline are possible reasons for poorly simulated Arctic and Eurasia mid-latitude temperature change.(5)Based on observations and reanalysis data,the influence of autumn Arctic sea ice on the mean surface air temperature,daily mean temperature variability and frequency of extreme cold event for winter in China were examined.Correlation analysis shows that,in generally,the warmer winter in China occurs under more autumn Arctic sea ice year and colder winter with high frequency of extreme cold event occurs in the year of less autumn Arctic sea ice.Through influencing polar vortex of Northern Hemisphere and Eastern Asia winter monsoon and Siberian high,autumn Arctic sea ice plays important role for mean winter air temperature in China,in which the autumn Arctic sea ice affects the frequency of extreme cold event through its influence on the frequency of extreme high Siberia high.Further analysis shows that there is stronger North wind over the high latitude area of Eurasia and it is colder over the mid-high latitude region in China and North of China during the year of less autumn Arctic ice,which induces colder winter and extreme cold event in China with the southward breakout of cold air from Arctic and high latitude area.(6)Precipitation changes over China affect billion people,it therefore expects reliable projections.12 climate models participated the CMIP5 presented large discrepancies in precipitation changes over China in response to the 4K uniform sea surface temperature warming.The projections with simultaneous severe drying and wetting changes among CMIP5 models indicate the low credibility of the models' projections.A series of experiments using Geophysical Fluid Dynamics Laboratory(GFDL)models are preformed to explore the possible fundamental causes associated with the CMIP5 models' discrepancies.The precipitation decreases 25% in northwestern China in response to global uniform 2K sea surface temperature warming.The precipitation decrease changes to 3% increase over northwestern China by replacing the RAS convective parameterization in AM2.1 with UW.The convective parameterizations are vital to regulate both the mean water-holding and corresponding large-scale circulation changes in models.Besides the local factors,teleconnections generated by distinct subtropical precipitation changes and corresponding diabatic heating under different convective parameterizations also affects the precipitation changes over China.Convective parameterization therefore is a possible fundamental cause of CMIP5 models' large discrepancies in projections of precipitation changes over China.Despite the convective parameterizations,the results also imply that models' performances associated with their physical and dynamic frameworks seek to be evaluated by observations,before models are used to project precipitation changes based on future emission scenario.