Multi-Source Forcing Effects Analysis Using Liang-Kleeman Information Flow Method And The Community Atmosphere Model(CAM4.0)

Climate change is closely related to the human life,and the changes in the concentration of greenhouse gases represented by carbon dioxide,sea surface temperature?SST?,sea ice coverage,and land cover types have an impact on the global climate.The observation contains the uncertain climate effects caused by all these forcings,and it is difficult to distinguish the climate effects of each forcing.In this paper,the Liang-Kleeman information flow method is used to give the causal relationship from these forcings to the temperature,proving that other forcings have the same important effect on the temperature as the carbon dioxide concentration.The results indicate that Eurasia and North America are the regions where the temperature has the most significant response to the forcings.A series of numerical experiments used the General Atmospheric Circulation Model 4.0?CAM4.0?are designed to verify the conclusion.The results of the simulation indicate that the 2-meter temperature in East Asia and North America is influenced by the net short-wave radiation and atmospheric dynamic process.The increase of₂ concentration leads to an increase in net short-wave radiation in parts of Asia in winter,and a decrease in North America.Land cover changes characterized by a decrease in forests and a large increase in farmland lead to an increase in surface albedo,which reduces radiation.Decreased sea ice coverage reduces the albedo,so net short-wave radiation increases at high latitudes.The radiation changes caused by the changes in SST are complex,in winter the net short-wave radiation increases in central North America,but decreases in central Asia and southern Asia,and decreases in Europe in both winter and summer.In addition to the direct effects of radiation changes,the role of atmospheric dynamic processes is important.More detailed,in winter,the changes of each forcing will cause the positive Pacific-North American Pattern?PNA?phase,which makes the North American colder.The negative North Atlantic Oscillation?NAO?phase caused by the changes of₂ and sea ice induces cold winter over the Europe.Whereas in summer,all forcings cause positive Arctic Oscillation?AO?phase,resulting in the most northern hemisphere warmer.Due to the existence of atmospheric dynamic process,the changes in land cover type,carbon dioxide concentration,SST and sea ice coverage enhance the wind blowing from the ocean to the East Asian.The amount of atmospheric water vapor in the East Asian increases,and the precipitable water increases,thus the precipitation overall increases.However,when₂ changes,there is a significant subsidence airflow around 30°N,so the precipitation decreases due to the lack of dynamic conditions in this region.The above research reveals the“capacitor effect”in the changes of land cover,SST and sea ice,and proves that changes in the sea ice coverage of the two poles will lead to cold winter in Europe and North America.However,the Arctic and Antarctic sea ice have different characteristics of temporal and spatial variation,but there is no clear conclusion about the comparison of climate effects caused by sea ice changes in the polar regions.Therefore,this paper further calculates the information flow from the Arctic and Antarctic sea ice to temperature respectively,and finds that the change of Antarctic sea ice coverage has an important influence on the temperature in the northern hemisphere?especially in East Asia and North America?,then the dynamic mechanism is revealed.The results show that the change of the sea ice will firstly change the temperature gradient of the lower atmosphere,bring the anomalous baroclinic pressure instability,resulting in the generation and upload of atmospheric baroclinic fluctuation anomalies.This anomalous signal of sea ice coverage is further amplified by the wave-flow interaction between baroclinic wave action flux and the high-altitude atmospheric jet.The meridional waves are transmitted,and even Rossby waves are transmitted across the equator,thus affecting the temperature changes in the other hemisphere.The CAM4.0 simulation results show that the location of the Antarctic sea ice change is located below the strong westerly jet in the southern hemisphere,which has a more significant effect on the jet stream than the Arctic sea ice.Therefore,the changes in Antarctic sea ice bring a greater response to wave flux and quickly propagates to the northern hemisphere,causing significant temperature change in East Asia and North America.