The Precarious Present - Is Global Warming Inhibiting an Incipient Ice Age?
The record of climate fluctuations that amplified over the past 5 million years indicates that the next Ice Age is imminent. However, the Antarctic ice-core record with a rapid rise in atmospheric CO2 levels over the past century suggests that global warming is underway. Warming is indeed observed. Is it inhibiting an incipient Ice Age, or is it amplifying warming that started at the Last Glacial Maximum? Geological records, and simulations with climate models of the past 10,000 years give different answers. A strategy to deal with this discrepancy between uncertain data and imperfect models, in a way that improves the models and interpretation of the records, exploits cyclic signals in the records. Thus far the focus was on glaciers but, with the data available now it is more rewarding to explore the three global, cyclic climate signals that global Milankovitch forcing (associated with orbital parameters) induces. Two of those signals, at periods of 40 and 100Kyr approximately, involve polar glaciers that wax and wane in tandem with the expansion and contraction of cloud-covered areas of cold tropical waters as the oceans and glaciers exchange vast amounts of fresh water. These fluctuations cause the third signal, the response to precession of the equinoxes, to be sporadic. That response is energetic today, an indication that the present is a precarious time with rising atmospheric CO2 levels inhibiting an incipient Ice Age, but at such a rapid rate that Earth’s inhabitants are at risk.