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History of Earth's Climate Changes

 Dr. Abhinandan Bhardwaj PhD

History of Earth's Climate Changes

Climate Change has happened on Earth several times during its entire history. Climate change lead to extinction of many plant and animal species and also prompted the evolution of new species in both plant  and animal kingdom on Earth. Geologic data from past climates proves that Earth had experienced several periods of climate changes which resulted in several Ice ages  and warm periods. To know about various factors which caused Earth's Climate change prior to industrialization  Click here ...or Go to Causes of Climate Change Page.

Climatologists can reconstruct the Earth's past climate using  various kind of data such as:

Biological Data.  past climates and their variations can also be studied by the analysis of  fossilized pollen and other plant macrofossils, annual tree rings, the abundance and distribution of insects and other organisms in lake rives and lake sediments.Glacial

Marine Sediments (Fauna and Flora ). Climate change can also be determined  by the analysis of fossilized marine fauna and flora abundance, morpological changes in preserved organisms, coral deposits, and the oxygen isotopic concentration of marine organisms.

Ice Deposits. Climate Fluctuations can be found by the analyzing the ancient ice deposits for the gas bubbles which can shed a light on the state of the atmosphere  they were deposited.

Inorganic Marine Sediments. This type of data includes analysis of clay, aeolian terrestial dust, and ice rafted debris etc.

Geomorphology and Geological Data. Study of past glacial deposits, glacial erosional features, shoreline features, aeolian deposits, lake sediments, relict soil deposits etc can also lead to analysis of past climates.



History of Earth and  Climate Fluctuations

Pleistocene or Ice Age (2,000,000 - 14,000 ).  During Pleistocene period which is also called as Ice Age, huge glacial ice sheets covered much of the Erath including North America, Europe, and Asia. But this was not the the period when Earth had only Ice Age throughout, there were periods when there were warmer temperatures which ,made the ice sheets melt followed again by glaciations. According to historical climatic models for this periods the average Earth's temperatures was about 4 - 5 degrees Celsius colder than present day temperature.

Holocene epoc:

It is also called the most recent glaciation activity which is still going on which frequently changes into warmer and cooler climates.  The present warming trend began about 14,000 -15,000 years ago.

Younger Dryas:

 This warming was suddenly interrupted by cooling in around 10,000 - 8500 BC, this period is called Younger Dryas.  Scientists believe that this cooling happened because there was a sudden release of fresh water trapped in ice sheets of  North America which went into North Atlantic Ocean. As a result this altered the vertical currents in the ocean which exchanged  the heat energy with the atmosphere.

Climatic Optimum : 

Warming of Earth again resumed during 8000 - 8500 BC. About 5000 to 3000 BC Earth's average temperatures was about 1 to 2 degrees Celsius warmer than today. This period is called Climatic Optimum by Climatologists. But this from 3000 to 2000 BC Earth experienced cooling trend again.  Which resulted in large drop in sea level. It also resulted in emergence of many islands such as Bahamas which still are above the sea level.

A short warming trend took place from 2000 to 1500 BC, followed once again by colder conditions. Colder temperatures from 1500 - 750 BC caused renewed ice growth in continental glaciers and alpine glaciers, and a sea level drop of between 2 to 3 meters below present day levels.

Little Climatic Optimum.

Earth saw warming up during the period from 750 BC - 800 AD up to 150 BC.  Around 150 BC - 300 AD  cooling again and lasted until about 900 AD. during this time cooling caused the Nile River (829 AD) and the Black Sea (800-801 AD) to freeze.

Then came the period called Little Climatic Optimum.  It was one of the  warmest climate period. During this period, snow line of Rocky Mountains was about 370 meters higher than today.

From 1550 to 1850 AD global temperatures were at their coldest since the beginning of the Holocene. Scientists call this period the Little Ice Age. During the Little Ice Age, the average annual temperature of the Northern Hemisphere was about 1.0 degree Celsius lower than today. During the period 1580 to 1600, the western United States experienced one of its longest and most severe droughts in the last 500 years. Cold weather in Iceland from 1753 and 1759 caused 25% of the population to die from crop failure and famine. Newspapers in New England were calling 1816 the year without a summer.

Figure 1 describes the global temperature trends from 1880 to 2006.


Figure1  Near-global annual-mean temperature change for the period 1880 to 2006 (deviation from the normal period 1951-1980). (Source: NASA Goddard Institute for Space Studies)


In the 1930s and 1950s, the central United States experience two periods of extreme drought. In the seventeen year period from 1990 to 2006, ten of the warmest years in the last 100 years and possibly since the Little Climatic Optimum have occurred. Proxy and instrumental data indicate that 2005 was the warmest year globally in 1200 years of Earth history. Many scientists believe the warmer temperatures of the 20th and 21st centuries are being caused by the human enhancement of the Earth's greenhouse effect.




References: 1) Earth's Climatic History". Fundamentals of Physical Geography, 2nd Edition: 2) NASA Goddard Institute for Space Studies - Global Temperature Trends




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