(1) Scientific studies have shown:
"The Holocene Climate Optimum (HCO) was a warm period during roughly the interval 9,000 to 5,000 years B.P. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.
This warm period was followed by a gradual decline until about two millennia ago.
West African sediments additionally record the "African Humid Period", an interval between 16,000 and 6,000 years ago when Africa was much wetter due to a strengthening of the African monsoon by changes in summer radiation resulting from long-term variations in the Earth's orbit around the sun. During this period, the "Green Sahara" was dotted with numerous lakes containing typical African lake crocodile and hippopotamus fauna. A curious discovery from the marine sediments is that the transitions into and out of this wet period occurred within decades, not millennia as previously thought.
In the far southern hemisphere (e.g. New Zealand and Antarctica), the warmest period during the Holocene appears to have been roughly 8,000 to 10,500 years ago, immediately following the end of the last ice age.
By 6,000 years ago, the time normally associated with the Holocene Climatic Optimum in the Northern Hemisphere, these regions had reached temperatures similar to those existing in the modern era, and did not participate in the temperature changes of the North. However, some authors have used the term "Holocene Climatic Optimum" to describe this earlier southern warm period as well.
This climatic event was probably a result of predictable changes in the Earth's orbit (Milankovitch cycles) and a continuation of changes that caused the end of the last glacial period.
The effect would have had maximum Northern Hemisphere heating 9,000 years ago when axial tilt was 24° and nearest approach to the Sun (perihelion) was during boreal summer. The calculated Milankovitch Forcing would have provided 8% more solar radiation (+40 W/m2) to the Northern Hemisphere in summer, tending to cause greater heating at that time. There does seem to have been the predicted southward shift in the global band of thunderstorms called the Intertropical convergence zone.
However, orbital forcing would predict maximum climate response several thousand years earlier than those observed in the Northern Hemisphere. This delay may be a result of the continuing changes in climate as the Earth emerged from the last glacial period and related to ice-albedo feedback. It should also be noted that different sites often show climate changes at somewhat different times and lasting for different durations.
At some locations, climate changes associated with this event may have begun as early as 11,000 years ago, or persisted until 4,000 years before present. As noted above, the warmest interval in the far south significantly preceded warming in the North.
While there do not appear to have been significant temperature changes at most low latitude sites, other climate changes have been reported. These include significantly wetter conditions in Africa, Australia, and Japan and desert-like conditions in the Midwestern United States. Areas around the Amazon in South America also show temperature increases and drier conditions."
(2) Just as scientific studies have shown mankind is currently on the pathway to destroying the environment on Earth needed to foster and support life. If we do not believe current scientific studies, why should we believe previous ones? Who knows, thousands of years from now someone may be sending a "Rover" to Earth to see if it can be determined what destroyed life on Earth as we are today doing by sending probes to the Moon and Mars.
So why don't we discard all scientific studies, historical data and other information and proceed on a daily basic and when the environment is destroyed complain because no one said or did anything about it.