The Telegraph, January 9, 2012
Researchers from Cambridge University who examined variations in the Earth's orbit and global climate patterns calculated that the next ice age should begin within the next 1,500 years.
But the impact of carbon dioxide emissions on the environment means that the global freeze which should be on its way will not be able to take hold, they said.
The period between the end of an ice age and the beginning of the next is typically about 11,000 years due to a natural cycle related to the Earth's orbit.
The temperate stretch in between global freezes can be longer or shorter depending on a number of factors, but with the last ice age having ended 11,600 years ago the arrival of another already appears overdue.
The onset of an ice age is triggered by small changes in the Earth’s orbit including the rotation of its axis and the extent to which it is inclined, which change gradually according to a cycle lasting tens of thousands of years.
It is unclear exactly how these factors influence the climate but the early seeds of change are followed by rising levels of carbon dioxide in the atmosphere as the planet warms up, and by the absorption of the gas by the sea as the Earth cools and ice sheets form.
By comparing current conditions with a similar period between ice ages 780,000 years ago, the researchers estimated that glacial inception – an early sign of an imminent ice age - should start in the near future.
Extreme swings in temperature between Greenland and Antarctica suggest that this process is beginning, they said.
But despite the impact of the Earth’s natural cycle, an ice age would only be able to begin if the concentration of carbon dioxide in the atmosphere were to fall from 390 parts per million (ppm) to 240ppm or lower, according to the study published in the Nature Geoscience journal.
Separate research has shown that even if we cut our carbon emissions instantly, concentrations in our atmosphere would remain artificially high for the next 1,000 years.
Dr Luke Skinner, who led the new study with colleagues from University College London, the University of Florida and Bergen University in Norway, said: “From 8,000 years ago, as human civilisation flourished, CO2 reversed its initial downward trend and drifted upwards, accelerating sharply with the industrial revolution.
“Although the contribution of human activities to the pre-industrial drift in CO2 remains debated, our work suggests that natural insolation (solar radiation) will not be cancelling the impacts of man-made global warming.”
The Global Warming Policy Foundation said the study demonstrated that man-made carbon dioxide emissions were preventing a "global disaster".
The think tank, set up by Lord Lawson, cited a controversial theory proposed by Sir Fred Hoyle and Professor Chandra Wickramasinghe in 1999 which said we "must look to a sustained greenhouse effect to maintain the present advantageous world climate."
Dr Skinner told the BBC such an argument would be "missing the point" that man-made climate change will heat the planet much more than current temperatures, and that failing to slow the rate of carbon emissions could have "huge consequences."