Interesting read...
"In the 1970s a few
paleoclimatologists were concerned with the possibility of
global cooling, and suggested that the next glacial period could be rapidly approaching. The previous interglacial periods seemed to have lasted about 10,000 years each; a report in 1972 assuming that the present interglacial period would be equally long concluded, "it is likely that the present-day warm epoch will terminate relatively soon if man does not intervene".
[25] Since then, our understanding of the climate system has improved. It is known that not all interglacial periods are of the same length and that solar heating varies in a non-linear fashion forced by the
Milankovitch orbital cycles (see
Causes section above). At the same time, it is also known that
greenhouse gases are increasing in concentration with each passing year. Based on the variations in solar heating and on the amount of CO2 in the atmosphere, some calculations of future temperatures have been made. According to these estimates, the interglacial period Earth is in now may persist for another 50,000 years if CO
2 levels increase to 750 parts per million (
ppm)
[26] while the recent atmospheric concentration of CO2 is about 407 ppm by volume.
[27] If CO2 drops instead to 210 ppm, then the next glacial period may only be 15,000 years away.
[26] Moreover, studies of seafloor sediments and
ice cores from glaciers around the world, namely
Greenland, indicate that climatic change is not smooth. Studies of isotopic composition of the ice cores indicate the change from warm to frigid temperatures can occur in a decade or two.
[28] In addition, the ice cores show that an ice age is not uniformly cold, nor are interglacial periods uniformly warm (see also
stadial). Analysis of ice cores of the entire thickness of the Greenland glacier shows that climate over the last 250,000 years has changed frequently and abruptly. The present interglacial period (the last 10,000 to 15,000 years) has been fairly stable and warm, but the previous one was interrupted by numerous frigid spells lasting hundreds of years. If the previous period was more typical than the present one, the period of stable climate in which humans flourished—inventing
agriculture and thus
civilization—may have been possible only because of a highly unusual period of stable temperature.
[29]"
