HISTORIC TEMPERATURES OF THE PAST 420,000 YEARS

During the past 420,000 years, various forces combined to cause 4 major glaciation and thawing cycles. The world temperature was about 2 - 3 C above and about 8 - 9.5 C below, the reference value of the past 10,000 years. The past four cycles indicate, the world, surrounded by outer space at near absolute zero, has a hard time warming up above reference, but a much easier time cooling down below reference, i.e., computer model global warming predictions of 4.3 C above pre-industrial likely are on the high side.

During each cycle, CO2 in the atmosphere increased from about 180 ppm during the glaciation temperatures to about 280 ppm at the peak temperatures, because of CO2 released by oceans and subsequent biomass growth.

During the most recent cycle, CO2 decreased slightly over a period of thousands of years while temperature rapidly decreased, which indicates the other forces were more influential. See URL.

http://euanmearns.com/the-vostok-ice-core-and-the-14000-year-co2-ti...

The Most Recent Cycle: The peak temperature of the most recent cycle (the fourth) was about 125,000 years BP, and its maximum glaciation was from 26,500 - 19,000 years BP. The initial temperature decrease was from a peak of +3 C above reference about 130,000 years BP to 7 C below reference about 110,000 years BP, a delta T = 10 C over a period of about 20,000 years, which is not noticeable, on a human scale. The ultimate low temperature was about 9.5 C below reference about 20,000 years BP.

NOTE: It is much harder for the earth to warm 2 - 3 C above long-term average than to cool down 9 - 10 C below long-term average, as proven by the four cycles of temperature and CO2 data obtained from 420,000 years of ice cores.

After all, the earth is surrounded by cold outer space. Cooling down is easy, whereas warming up is hard, even with a doubling of CO2.

This URL references several other URLs, which should be studied.

http://www.windtaskforce.org/profiles/blogs/historic-temperatures-o...

The high temperature of the most recent cycle was about 3.0 C above long-term average about 130,000 before present.

The temperature decreased to about 9.5 C below long-term average by about 26500 before present.

The most recent glaciation period (26500 - 19000) ended about 19000 years ago. 
A warming from about minus 9.5 C to about plus 2 C occurred over a period of about 11000 years.

The warming peaked about 8200 years ago. A cooling has been going on ever since.
The Minoan Warm Period was warmer than today.

The Roman Warm Period, warmer than today, was followed by the Dark Ages, a colder period.
The Medieval Warm Period, warmer than today, was followed by the Little Ice Age, a colder period
All that time CO2 was nearly unchanged. 
From that, any rational person would conclude, factors other than CO2 are responsible.
I am still waiting for the IPCC to explain those changes, as well as the Little Ice Age (1450 - 1850).

During the latest glaciation period (26,500 - 19,000 years before present), sea levels were about 120 meter (470 feet) below present levels. The world’s desert areas, including the Sahara, were much larger than at present. The world population (about 1 - 2 million) during that glaciation period (lasting about 7,500 years), likely had a tough time dealing with the cold. A rapid warming trend from 8 C below reference to about 2 C above reference, similar to the prior cycles, started about 18000 years BP and ended about 11,200 years BP. Unlike the prior cycles, this time the temperature did NOT rapidly decrease, but has been lingering for about 11,200 years. See upper left corner of URL.

https://wattsupwiththat.files.wordpress.com/2013/11/younger_dryas_t...

NOTE: The world surface is about 510 million km2, of which land 149, water 361. The volume of land ice that melted was approximately 361 x 10^6 x 0.120 = 43 million km3, which covered about 43 million km2, based on an average thickness of 1 km, equivalent to the area of Russia, 17.1+ Canada 10.0 + China, 9.6 + the continental United States 9.5. That would qualify as climate change.

About 15000 - 12000 years BP, most of northern Asia, northern Europe, northern America, etc., were still covered with about one MILE of ice. Almost all of the world’s population (about 1 to 3 million) lived in small groups, mostly in hunter-gathering mode, with some agriculture, in areas of southern France, Spain, Italy, Turkey, the Caucasus, the Middle East, northern Africa, Iraq, Iran, southern India and Asia. North of those areas, with few trees, much frozen tundra and ice, there lived very few people.

By about 5000 years BP, much of the ice had melted, and the world population had increased to about 10 to 15 million people. The big question remains: Why is the temperature lingering for 11,200 years, unlike the prior cycles? Why are we not yet into another ice age?

https://en.wikipedia.org/wiki/World_population_estimates

NOTE: During the past 150 years, CO2 in the atmosphere has increased from about 280 ppm to 400+ ppm, due to various factors, such as a totally unsustainable population explosion (1.0 billion in 1804, 2 billion in 1927, to 7.3 billion in 2015, heading towards 10 billion by 2050), which required deforestation, urbanization, industrial agriculture, and the worldwide production and transport of goods and services, all requiring the use and burning of huge quantities of fossil and bio fuels, which release CO2 and methane, CH4, well beyond the 280 ppm of prior cycles. The world's ecosystems and its fauna and flora are being irreparably fractured and debilitated by all those manmade activities. World-renowned biologists aver the world should have less than 1 billion people living on a minimal resources diet, and that over half of the world should be set aside/remain undeveloped to enable the other fauna and flora to survive and thrive.

NOTE: Based on a recent study, the temperature gradually increased from the glaciation low point until about 7000 years BP and then gradually decreased until about 1870, after which it increased from -0.4 C to +0.6 C, a delta T  = 1 C, concurrent with the increase in CO2 in the atmosphere. The warm part of this cycle started with a world having a lot of biomass, and CO2 in the atmosphere of about 280 ppm, but after about 1870 manmade CO2eq was added to the atmosphere. The temperature increased about 1 C, as CO2eq was added, which has been highly noticeable, on a human scale. According to the graphs in the URL, the 7000-y cooling trend is being interrupted by manmade activities of the past 150 years. See URL.

http://www.zmescience.com/research/studies/global-temperatures-reac...