Global Climate

ENV 250.001

Isatta Musahson

October 24, 2014

 Due to the increase in the global temperature during the twentieth century, there have been many scientific research carried out to determine what was responsible for global warming. According to the Intergovernmental Panel on Climate change Fourth Assessment Report, the global mean surface temperature increased by 0.74 = 0.18 degree Celsius between the year 1906 and 2005. Based on this observation gathered many previous studies argue that global worming has been continuous. Researches believed that the increased concentration of the greenhouse gas like carbon dioxide and methane plays a key role to increase in the global mean surface temperature since the industrial period.

It is known that this abnormal warm climate occurred around AD 950-1250, which is called the medieval warm period.  The concentration of greenhouse gases during this period was relatively low and fixed during those periods in comparison with the present warm period ( Lim, Yeh, Kim, Park, Song P. 72). The medieval worm period is somehow similar to the present warm period except the concentration of greenhouse gas.

Evidence suggests that the Medieval Warm Period may have been warmer than today in many parts of the globe such as in the North Atlantic. This extreme warming cause Vikings to travel further north than had been previously possible because of reductions in sea ice and land ice in the Arctic.

The Little Ice Age was a period of cooling that occurred after the Medieval Climate Optimum.  This period has been defined as a period from the 16^th to the 19^th centuries, or from 1350 to about 1850.

However, evidence suggests that some places were very much cooler than today including the tropical pacific. The Little Ice Age can only be considered as a modest cooling of the Northern Hemisphere during this period of less than 1°C relative to late twentieth century levels. There were several cause proposed for this change in temperature: the cyclical lows in solar radiation, volcanic activity, changes in the ocean circulation, an inherent variability in global climate, or decreases in the human population.

During the period of the Little Ice Age, it brought colder winters to parts of Europe and North America. Farms and villages in the Swiss Alps were destroyed by glaciers during the mid-seventeenth century. Canals and rivers in Netherlands and Great Britain were frequently frozen.       

Sources

Hughes, Malcolm K., and Henry F. Diaz. "Was there a ‘Medieval Warm Period’, and if so, where and when?." Climatic change 26.2-3 (1994): 109-142.

Harrison, Stephan, et al. "Little Ice Age glaciers in Britain: Glacier–climate modelling in the Cairngorm mountains." The Holocene 24.2 (2014): 135-140.

Lim, Hyung-Gyu, et al. "Contributions of solar and greenhouse gases forcing during the present warm period." Meteorology and Atmospheric Physics 126.1-2 (2014): 71-79.