Research The Impact Of Declining Arctic Sea Ice On Climate Change In Northern Hemisphere

Satellite record shows monthly Arctic sea-ice extent has downward trend since 1979, the largest being in autumn. The Arctic sea ice minimum extent observed during September 2007 and 2012 reached its minimum in 2012 (3.41 million km2), following 2007 (4.13 million km2). While the minimum Arctic sea-ice area increases 60% in September 2013 compared with 2012. We explain the reasons of the Arctic sea-ice minimum extents have different distributions in September 2007 and 2012, and the Arctic sea-ice minimum extent increases 60% in September 2013 than 2012. Using data analysis, the results show that the different spatial distributions of sea-ice reduction are closely related with the different anomalies modes of the bottom atmospheric circulation pattern and the upper ocean state. Three positive feedback mechanism and five conditions jointly lead to the Arctic sea-ice melting.In recent years, the increased occurrence of extremely weather events over Northern-Hemisphere continent, such as freezing rain, cold winter and blizzard events and so on, which caused huge economic losses. Combining with the quickly declining of Arctic sea-ice in autumn, we used observational analyses and numerical experiments to research the impacts of declining Arctic sea-ice in autumn on changing the mid-latitudes atmospheric circulation pattern in Northern Hemisphere. The results show that the autumn Arctic sea-ice reduction causes the winter air temperature being seesaw structure in polar region and East Asia. The cold polar air easily invades into the East Asia continent in winter and results the extremely colder winter events, while the pole region appears the ’Arctic amplification’phenomenon. In addition, the autumn Arctic sea-ice reduction impacts the summer becoming hotter, the winter becoming colder in mid-latitude continent of Northern Hemisphere. So the difference of air temperature becomes larger between summer and winter. And summer easily appears scorching heat, while winter prones to cold extremely weather events. Due to the air temperature obviously increasing in spring and autumn, the summer will become longer, the spring will early entry into summer, the autumn could appear lag.The decrease speed of the autumn Arctic sea-ice is huge different from the time series of autumn Arctic sea-ice area since having the satellite record. The autumn Arctic sea-ice decreasing speed accelerates 4 times during the periods 1996-2012 than 1979-1995. This study researchs the relationship btween the atmospheric circulation trends in winter and the changes in Arctic sea-ice during the different two periods. Using observational analyses and numerical experiments, this paper shows that the corresponding atmospheric circulation modes are different when the autumn Arctic sea-ice has different declining rates. Associated with the slowly diminishing Arctic sea-ice, westerly jet stream strengthen, the warmer winter arises in mid-latitudes of the Northern-Hemisphere continent. While associated with the quickly diminishing Arctic sea-ice, the lower geopotential height, weaker westerly jet stream and poleward meridional wind in winter make the cold pole air easily invade into the Northern-Hemisphere continent, which results in colder winter in North America, Europe and East Asia. Furthermore, by numerical experiments this paper shows that the influence of decrease autumn Arctic sea-ice is greatest in polar region in autumn. The air temperature increases stronger in polar region when the autumn Arctic sea-ice melts quickly than sowly, and the higher latitudes become colder when the the autumn Arctic sea-ice melts quickly. The greatest influence in winter of decrease autumn Arctic sea-ice expands to the mid-latitudes of the Northern Hemisphere. The winter becomes warmer when the autumn Arctic sea-ice decreases slowly, while the winter becomes colder when the autumn Arctic sea-ice decrease quickly. In spring, the influence slowly becomes weaken, and it moves to the lower latitude such as the tropical regions. In summer, the atmospheric circulation in polar region change with a new round of Arctic sea-ice melting, again and again.According to the current rate of declining Arctic sea-ice in autumn, the future will soon face the risk of all Arctic sea-ice diminishing. The projection of climate model estimates a nearly Arctic sea-ice free in summer 2030. Using the numerical experiments, this study researches a possible future of Arctic sea-ice free condition in September for simulating the climate change in Northern-Hemisphere continent. The experimental results show that the Arctic sea-ice free would induce the cooler air temperature in Arctic region in autumn, and the significantly warmer winter in mid-latitude continent. The influence of Arctic sea-ice free in the atmosphere circulation transports to the Tropical areas until summer. If the Arctic sea-ice continues to melt until sea-ice free, it will make warmer in mid-latitude of Northern Hemisphere, not only appearing in the spring, summer and autumn, but also in winter. The colder extreme events in winter will disappear and turn warmer winter.The satellite data shows that the Arctic sea-ice did not continue to decline as previous years in autumn 2013. While it suddenly increases 60% compared with 2012 in the same time. However, in winter 2013, the North America has suffered extreme colder events and heavy snowfall weather. Here, using observational analyses and numerical experiments, we demonstrate that the suddenly increasing of Arctic sea-ice in autumn 2013 should be the main reason causes the extreme colder events in winter 2013 in North America at the environment of fast diminishing Arctic sea-ice in autumn. The results show that the lower geopotential height, weaker pole-ward meridional wind in winter make the cold polar air easily invade into the Northern America continent resulting in extreme colder weather. While only the declining Arctic sea-ice in autumn 2013 compared with the climatology mean may not cause the extreme colder weather in the following winter in North America.The Arctic sea-ice minimum extent is observed in September of 2007 and 2012, and its minimum is in 2012, following in 2007. However, the winter snow cover areas are being high values in the two special years in the Northern Hemisphere. Furthermore, the snow cover distribution has different pattern. It mainly increases in Middle Asia, in central and Southwestern of North America in 2007, but in 2012 it is mainly in East Asia and Northwestern Europe. Data analysis show that the different of dynamic conditions and water vapor, temperature conditions in atmospheric circulation cause the different distribution of the snow cover, the increase of snow cover region is in positive atmospheric circulation anomalies in the special two years.