Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the sun (see Milankovitch cycles). These orbital changes modify the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes (from 400 to 500 W/(m2) at latitudes of 60 degrees). In this context, the term "forcing" signifies a physical process that affects the Earth's climate. This mechanism is believed to be responsible for the timing of the ice age cycles. A strict application of the Milankovitch theory does not allow the prediction of a "sudden" ice age (sudden being anything under a century or two), since the fastest orbital period is about 20,000 years. The timing of past glacial periods coincides very well with the predictions of the Milankovitch theory, and these effects can be calculated into the future. Milankovitch cycles are also associated with environmental change during greenhouse periods of Earth's climatic history. Changes in lacustrine sediments corresponding to the timeframes of periodic orbital cycles have been interpreted as evidence of orbital forcing on climate during greenhouse periods like the Early Palaeogene. Overview It is sometimes asserted that the length of the current interglacial temperature peak will be similar to the length of the preceding interglacial peak (Sangamonian/Eem Stage). Therefore, we might be nearing the end of this warm period. However, this conclusion is probably mistaken: the lengths of previous interglacials were not particularly regular (see graphic at right). Berger and Loutre (2002) argue that “with or without human perturbations, the current warm climate may last another 50,000 years. The reason is a minimum in the eccentricity of Earth's orbit around the Sun.” Also, Archer and Ganopolski (2005) report that probable future CO2 emissions may be enough to suppress the glacial cycle for the next 500 kyr. Note in the graphic, the strong 100,000 year periodicity of the cycles, and the striking asymmetry of the curves. This asymmetry is believed to result from complex interactions of feedback mechanisms. It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in a single large step. Orbital mechanics require that the length of the seasons be proportional to the swept areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can last substantially longer. Today, when autumn