| The simulation results of climate change over the past 21000 years,which called TraCE-21ka(short for Transient Climate Evolution of the last 21000 years)is used to explore the temperature variation on millennial timescales during Holocene.After the validation of model performance on the temperature variation,we analyize the characteristics of temperature variation on millennial timescales and response of tempearature variation to four different forcings in different areas across the globe.Finally,we compare the linear combination of tempearature variation on millennial timescales in different single forcing runs with the variation in all forcing run.The result improves our understanding of the impact that different forcings exert on the temperature variation on millennial timescales during the Holocene.When validating the performance of the simulation result on temperature variation during Holocene,comparison between the temperature reconstruction and simulation results is conducted in three latitudinal zones,which are northern extropical area(30°N-90°N),tropical area(30°S-30°N)and southern extropical area(90°S-30°S).The result shows that temperature variation of the simulation results resides in the uncertainty boundary of reconstruction series in all three areas.We also check the performance in simulating millennial cold events which are found in the reconstruction across the entire globe.The result shows that the simulation captures five out of seven global cold events.The validation conducted above proves that TraCE-21ka simulates the temperature variation during the Holocene reasonably well and it can be used in the research on temperature variation on millennial timescales.As to the temperal characteristics of Holocene millennial variation,we extract temperature variation on millennial timescales from all forcing experiment in three latitudinal zones and global area by using Ensemble Empirical Mode Function.The result shows that the northen extropic has the greated variation amplitude among the three latitudinal zones.The tropical area has the smallest variation amplitude among the three.The millennial temperature variation range across th globe is similar to that in northern extropical area,during 12-8 ka BP and is similar to that in southern extropical area during 8-0 ka BP.A common quasi-1000-year period exists in all three latitudinal areas and the globe.We also extract temperature variation on millennial timescales from reconstruction series of the three latitudinal zones and globe.The reconstruction result shows that the millennial temperature variation range in the northern extropical area is slightly wider than the range in simulation and the range in tropical area is slightly narrower than the range in simulation.Both millennial temperature variation extracted from simulation and reconstruction series in all three latitudinal zones and globe have quasi 1000 and 1500-year period.As to the characteristics of spatial pattern of Holocene millennial variation,on global scale,the first EOF mode of millennial temperature variation shows a homogeneous pattern in the whole northern hemisphere,part of the South Pacific and the Antarctic Continent,while the North Atlantic south of Greenland shows the largest temperature variation.Over the middle and high latitude area of the northern hemisphere,the first EOF mode of millennial temperature variation shows a homogeneous pattern in the whole northern hemisphere,while the North Atlantic south of Greenland shows the largest temperature variation.Over the tropical area,the first EOF mode of temperature variation in tropical region shows a homogeneous pattern in the Caribbean Sea,central South America,Indian peninsula and southern part of Indian Ocean and Tropical Pacific Ocean,the Atlantic region to the west of Africa and the Eastern Region of South America experienced the largest millennial scale temperature variation.Over the middle and high latitude area of the southern hemisphere,the first EOF mode of millennial temperature variation shows a homogeneous pattern in most parts of the ocean from 30 to 60°S.The temperature variation becomes greater as it is closer to the interior of the Antarctica.Different single forcings have different effects on the millennial temperature change in latitudinal areas.All areas have the maximum response to meltwater forcing during 12-6 ka BP,the maximum response to orbital forcing between 6-1 ka BP and the maximum response to green house gases forcing between 1-0 ka BP.On global scale,all forcing has a common quasi-1000-year period with orbital and icesheet forcing experiment and a common quasi-1500-year period with orbital,meltwater and icesheet forcing experiment.In the middle and high latitudes of the Northern Hemisphere,all forcing has a common quasi-1000-year period with orbital and icesheet forcing experiment,a common quasi-1200-year period with meltwater forcing and a common quasi-1500-year period with orbital and icesheet forcing experiment.In the tropical area,all forcing experiment has a common quasi-1000-year period with greenhouse gas and orbital forcing experiment,all forcing experiment has a common quasi-1200-year period with all single forcing experiment and a common quasi-1500-year period with greenhouse gas,orbital and icesheet experiment.In the middle and high latitudes of the Southern Hemisphere,all forcing experiment has a common quasi-1000-year period with greenhouse gas forcing experiment and a common quasi-1000-year and quasi-1700 period with orbital,meltwater and icesheet forcing experiment.As to the relationship between the linear combination of the millennial temperature variation in the single forcing experiment and the millennial temperature variation in all forcing experiment,on global scale,the linear combination of greenhouse gases and orbital forcing has the highest correlation with the millennial variation of all forcing,so we think these two single forcings are the main driver in the millennial temperature variation.Over the mid and high latitude of the Northern Hemisphere,the linear combination of orbital forcing,meltwater forcing and greenhouse gases forcing has the highest correlation with the millennial variation of all forcing,so we think these three single forcings are the main driver in the millennial temperature variation.Over the tropical area,the linear combination of orbital forcing and meltwater forcing has the highest correlation with the millennial variation of all forcing,so we think these two single forcings are the main driver in the millennial temperature variation in the tropics.The linear combination of millennial temperature variation in different single forcings has a very week correlation with the millennial variation of all forcing.Therefore,the influence of different single forcings have on the millennial temperature change is nonlinear in the mid to high latitude of southern hemisphere.As to the relationship between millennial temperature spatial pattern in all forcing experiment with that in four different single forcings,on the global scale,the first EOF mode of millennial temperature variation in all forcing experiment has the highest correlation with that in meltwater forcing experiment,which means meltwater forcing is the main factor that influences the millennial spatial pattern on global scale;Over the mid and high latitude of the Northern Hemisphere and tropical area,the first EOF mode of millennial temperature variation in all forcing experiment has the highest correlation with that in meltwater forcing experiment,which means meltwater forcing is the main factor that influences the millennial spatial pattern on these two latitudinal zones.Over the mid and high latitude of the Southern Hemisphere,the first EOF mode of millennial temperature variation in all forcing experiment has the highest correlation with that in ice forcing experiment,which means ice forcing is the main factor that influences the millennial spatial pattern over the mid and high latitude of the Southern Hemisphere. |
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