Past 2,000 Years

The main methods found to be the most useful to find climate change evidence of the past 2000 years:

Drilling cylinders of ice out of glaciers and polar ice sheets does this method. Paleoclimatologists study the sediments encapsulated in the Antarctic ice to compare the glaciers in the Holocene period as compared to earlier glacial periods. It also supports evidence from studies that use deep-sea sediment to reconstruct changes in past sea level and oceanic temperatures. The Vostok research station has been drilling out ice cores for more than 37 years. It started in the 1970s in the Soviet Union when researchers drilled a set of holes 500-952 meters deep in ice that have been used to study the amount of oxygen isotope. Through isotope study, we can determine the temperature at which an oxygen-bearing geologic material formed. Ice cores also help to determine local temperature and precipitation rate, humidity, and wind speed. They record changes in atmospheric composition, trace gas concentrations, chemical impurities of the land or ocean, extraterrestrial material and aerosols of volcanic and anthropogenic origin. They can determine the earlier eruptions from acidic material being ejected into the atmosphere deposited on the glaciers surface during snowfall. Then, when the snow turns to ice, it has high acidity so we can count the ice layers and measure acidity, coming up with time periods of volcanic eruption.

Pollen data helped to determine the Holocene climatic optimum. It shows information to reconstruct past vegetation of a certain area. The pollen used is usually obtained from lake and bog sediments. Quaternary terrestrial palaeoecology has pollen analysis as its main source of historic data. It helps in the study of selected species and their distribution and performance in relation to two to three ecologically important climatic variables. There is the vegetational approach, which uses mathematical transfer functions to regulate modern pollen groupings in terms of modern climate. These methods are used to transform pollen data into quantitative estimates of past climate.

This is done by counting the annual tree rings and recording growth characteristics through the width of rings, which relates to temperature and moisture. Reflects the climatic conditions in which the tree grew, then compared and matched with the trees growing in the same area.

Scientists started using this technique in the early 20^th century. A.E. Douglas first discovered it finding that wide rings show wet years and narrow rings show the more dry years. The process of these forming tree layers is new wood growing from the cambium layer between the old wood and the bark. During springtime, the tree gets enough moisture to devote its energy to produce new growth cells. As summer comes, these new, large cells shrink until in the fall growth stops and cells die and then the process starts all over again in the spring.

This shows the volcanic impact on climate and environment and the chronology. Chronology forms dating framework to compare to other dating techniques to be checked and validated. Measuring the tephra layers distributed down wind from explosive volcanic eruptions does it. Tephra is all the solid material produced from a volcanic eruption. The tephra layers are mapped across intercontinental scale distances. After finding the age of the layer we can compare it to the documented information, tree ring counts, and bracketing radiocarbon dates. It is used to assess the age of landforms and sediments. This also helps to determine patterns of climate change during volcanic eruptions.

From documentary accounts we have paintings, sketches and lithographs used to document and estimate the sizes of glaciers in those periods. This only dates back to the seventeenth century, though. In the last century we have had the advances of aerial photography and satellite imagery, as well as on site documentation.

From a period of 1100 to beginnings of the instrumental meteorological era we can rely on documented, detailed information on past climates. Rainfall and wind direction records have survived from the first century A.D. A man named Brooks started the trend and influence of documenting climate with a book called Climate through the ages. This led the scientific community to urge the value of documenting climatology.

The mid seventeenth century is when the era of instrumental meteorology began with the development of the barometer by Torricelli and the thermometer more than a century earlier by Galileo. There is instrumental data documented back to that period. Johnson and Lamb produced pressure maps in 1966 dating back to 1750. There is also documented evidence of glaciers in the Swiss Alps covering villages, as well as population decline found from abandoned houses and farms contributing to the findings of ìThe Little Ice Age.í

Through this we have found vague chronological sequences of culture history but we wonder why certain events happened in the past and it is most commonly thought that environmental change and climatic conditions were a factor in these archaeological events. From this data we find things such as finding the High Arctic was once again occupied by Palaeoeskimos about 500-600 and determining that the summers were becoming warmer. Or such as finding the new world dry lands around 1500 which could conclude that continued drying is a result of a decrease in winter precipitation.