Present and Future Conditions
As mentioned above, at present, perihelion occurs during the southern hemisphere's summer and aphelion during the southern winter. Thus the southern hemisphere seasons should tend to be somewhat more extreme than the northern hemisphere seasons. The relatively low eccentricity of the present orbit results in a 6.8% difference in the amount of solar radiation during summer in the two hemispheres.
Since orbital variations are predictable,, if one has a model that relates orbital variations to climate, it is possible to run such a model forward to "predict" future climate. Two caveats are necessary: that anthropogenic effects may modify or even overwhelm orbital effects; and that the mechanism by which orbital forcing influences climate is not well understood.
The amount of solar radiation (insolation) in the Northern Hemisphere at 65° N seems to be related to occurrence of an ice age. Astronomical calculations show that 65° N summer insolation should increase gradually over the next 25,000 years. A regime of eccentricity lower than the current value will last for about the next 100,000 years. Changes in northern hemisphere summer insolation will be dominated by changes in obliquity ε. No declines in 65° N summer insolation, sufficient to cause a glacial period, are expected in the next 50,000 years.
An often-cited 1980 study by Imbrie and Imbrie determined that, "Ignoring anthropogenic and other possible sources of variation acting at frequencies higher than one cycle per 19,000 years, this model predicts that the long-term cooling trend that began some 6,000 years ago will continue for the next 23,000 years."
More recent work by Berger and Loutre suggests that the current warm climate may last another 50,000 years.
Read more about this topic: Milankovitch Cycles
Famous quotes containing the words present and, present, future and/or conditions:
“United States! the ages plead,—
Present and Past in under-song,—
Go put your creed into your deed,—
Nor speak with double tongue.”
—Ralph Waldo Emerson (1803–1882)
“That neither present time, nor years unborn
Could to my sight that heavenly face restore.”
—William Wordsworth (1770–1850)
“One day my mother called me ... and she said, “Forty-nine million Americans saw you on television tonight. One of them is the father of my future grandchild, but he’s never going to call you because you wore your glasses.””
—Lesley Stahl (b. 1941)
“Armies, for the most part, are made up of men drawn from simple and peaceful lives. In time of war they suddenly find themselves living under conditions of violence, requiring new rules of conduct that are in direct contrast to the conditions they lived under as civilians. They learn to accept this to perform their duties as fighting men.”
—Gil Doud, U.S. screenwriter, and Jesse Hibbs. Walter Bedell Smith (Himself)