Climate Change

1. Briefly describe the temporal variations in temperature and discuss possible causes of the temperature variability.

On studying the Northern Hemisphere temperature reconstruction provided it is clear that during the past millennium there have been many peaks and troughs in temperature variation. Looking at the linear trend line; temperatures on the whole decrease slightly and constantly from 1000 to 1900, however they then increase rapidly between 1900 and 2000. A few key peaks and troughs are shown through the 40 year smoothed reconstruction line, for example; the peak at 1170 coincides with the medieval warm period when volcanic activity was at a minimum, the trough at approximately 1453 coincides with two caldera volcanic eruptions in 1450 and 1452 which in turn scatter radiation which aids cloud formation and therefore leads to natural cooling, the wide trough from 1650-1710 coincides with a sunspot minima as well as the little ice age (LIA), before a peak in temperatures at 1750 which could link in with the industrial revolution and the production of greenhouse gasses, temperatures decrease between 1800 and 1900 which could be due to high amounts of volcanic activity; in particular the trough at 1816 which was known as the year without a summer after the eruption of Tambora in Indonesia in 1815, temperatures then increase rapidly due to the increase in greenhouse gases being used after the world wars.

According to the New Scientist, there were a mix of play in the factors that caused climate change and none of them can be termed to be solely responsible for the variations. Whilst some of these have been described briefly above, the key causes will be discussed further in this paragraph. Ice ages were generally , caused by an interplay of variability in solar radiation, “changes in the earth’s orbital geometry, orogenic activity and continental uplift, volcanic activity, variations in the Earth’s surface albedo, fluctuations in ocean characteristic and changes in the continental locations, arising from continental drift” (Beaty, 1978, p. 776). The cooling of the earth and eventual glaciation is caused by the albedo effect, which basically means the effectiveness of the earth to reflect the sun’s rays. Continues trend leads to the formation of the ice age. The reflective ability of the earth is itself caused by the volcanic activity. Vulcanicity has a potential of yielding huge clouds of dust that reflect the radiation from the sun for decades. If by chance this couples with the reduction in the intensity of radiation from the sun, chances are the cooling effect results. Usually, as noted above, the cooling effect that is prolonged enough to cause formation of glaciers is caused by two or more factors. There is evidence between 1645 and 1715, the so called Maunder minimum caused the Little Ice Age in the 1800s. During this period, there was a reduction in sunspot activity and also a volcanic activity that resulted in the formation of glaciers. Another evidence is the volcanic eruption of Toba that resulted in declining of temperatures of about 50C (Ahrens & Samson, 2010).

Oceanic characteristics such as circulation that occur as a result of continental drift do cause the cooling effect but not as igniters to the process. Formation of Little Ice Age needs an initiator and other factor to sustain the cooling process to formation of glaciers. Geometry of the sun’s rays whereby they the distance covered at certain times of the year and any other effect such as volcanicity can lead to formation of “Little Ice Age”. The little ice age ended in the 1700s after the Thames River was known to freeze during winter seasons. The last time was in 1804 and ever since, the temperature has been rising by 0.50C after every 100 years. The study into the past climatic variations is possible by using proxies and historical facts about events and anthropogenic activities of the then inhabitants of the northern hemisphere part of the earth. The period lasted for only about 500 years, making it not to be a “real” age and named, Little Ice Age”

Other sources suggest the Black Death that killed people eliminated human sources that result in atmospheric heating and thereby increasing vegetation that sequestrated carbon. There were no people to produce carbon dioxide and other gases to the atmosphere. This is said to have occurred in some 72000 years ago when a single volcanic eruption wiped out all people (Deppe, 2010). Heating of the atmosphere is largely due to human activities; often named anthropogenic climate change. Industrialization, deforestation and pollution from the increase in burning of fossil fuels are all contributing factors of the greenhouse effect; gasses such as, carbon dioxide, methane and sulphur dioxide are released into the atmosphere which then trap the suns energy in the ozone layer, reflecting the heat back into the atmosphere and in turn causing earth temperatures to sore.

2. Discuss possible methodological problems associated with the different approaches and techniques used to collect the data to produce the temperature reconstruction.

In investigating climatic change through time there are three main techniques analysts use to produce accurate temperature reconstructions; these consist of: instrumental, historical and proxy dating methods however all three have there own advantages and limitations.

The instrumental approach uses thermometers to take air or sea surface temperatures directly, which can then be recorded; this dating method has been used for the last 300 years in some locations, however there are still some gaps of the earth’s surface that aren’t covered by weather stations today. Possible problems associated with this method are that despite its popularity and widespread use, it is limited to 250 years back and only events in the 189th century may be available by this method (National Academy Press, 2006). Besides, the instruments tend to be give erroneous or varying data due to different calibrations and exposure to climatic conditions that compromise their accuracy. Natural occurrences or those that care created by microclimates are known to interfere with accuracy of the instruments (Linacre, 1992). The challenge is also in meeting the three conditions of homogeneity, continuity, and data quality for the method to provide reliable data.

The use of proxies and pseudo-proxies have limitation in the scale of years that they simulate and therefore are associated with greater inaccuracies. They usually lack the variability to represent long stretching periods of time. Thus, they may not fully or ably capture years in the extreme. It means even the temperature would not be accurately captured. Besides, the proxy methods such as stable isotopes do not represent any particular element of climate. They represent either temperature of rainfall but not any particular element directly. Thus, they cannot be used directly but must be adjusted empirically for them to be usable (IPCC, 2007). In the process, there may be significant compromises in what they actually represent. Other studies state the limitation of proxies in measuring temperatures in the tropics. Inaccuracies are also likely to result from the many assumptions that climate field reconstruction methods such as proxies use. They also use non-local data that make it to rely much on the assumptions to in the data collection process. A single method used as an example is the tree-ring method that has long median years of between 500 and 700 years. This long period applies well if the periods exceed 1000 years and less ineffective within a period of a millennium (Mann, Zhang, Hughes, Bradley, Miller, Rutherford &Fenbiao, 2007). The relationship between the factors and the proxies are also not linear and hence cannot be relied upon. For example, tree rings and temperature are not linear and must be manipulated to bring out a sensible relatioshipm (Climate Skeptic).

Historical data reliesn the record and the particular concern with this is inconsistencies with the facts. The method relies on logbooks, journals and court cases to trace events that occurred in the past. The ability of this approach to date back to periods such 72000 years when Black Death occurred is not possible. Then, it is limited to short periods of about a millennium or two. Even when available, the records do not have a consistent fact and these variations make it difficult to state when the actual event took place. Factors such as disease outbreaks and societal changes make it difficult for the accurate facts to be adduced.