A new research carried out by an independent research Ralph Ellis from France suggests that albedo (the reflectivity of the Earth) – and not CO2 – is the primary temperature feedback controlling ice ages. The new research further proposes that albedo is also most likely the major feedback agent controlling the modern climate.
Ice-age cycles were discovered about two centuries ago, and since then scientists have gathered a large amount of geological evidence regarding these cycles. Several hypotheses have been proposed to explain the approximate 100 kyr periodicity and asymmetric, saw-tooth temperature response of these cycles. Some studies – involving improved calculations of Milankovitch isolation cycles – have demonstrated that each major deglaciation happens along with maximum summer sunlight (insolation) in the northern hemisphere. However, these studies also suggest that many insolation maxima only trigger minor warming events, and as a result, interglacials occur only after four or five insolation cycles. Scientists have so far failed to propose any generally accepted explanation for this weird intermittent climate response.
The new peer-reviewed paper – “Modulation of Ice Ages via Precession and Dust-Albedo Feedbacks” – proposes a novel explanation for the modulation and rhythm of ice-ages and interglacials during the late Pleistocene. The paper states that the long gaps between interglacials can be accounted for by a novel forcing and feedback system which involves albedo, CO2, and dust. The paper suggests that “during the glacial period, the high albedo of the northern ice sheets drives down global temperatures and CO2 concentrations, despite subsequent precessional forcing maxima.”
Polar ice sheets are highly reflective and therefore have a high albedo. They have been found to reflect up to 90% of the incident sunlight during the all-important northern summer. This high albedo causes a cooling effect which eventually results in growing of polar ice sheets, year after year, and therefore reflecting more and more incident sunlight in the process. This ice-albedo reflection mechanism is so strong that it can even resist the next Great Summer when northern insolation is once again at a maximum.
With passage of time, more CO2 is sequestered in the oceans and ultimately, atmospheric concentrations reach critical minima of 190 ppm. This effect, in combination with arid conditions, results in a “die-back of temperate and boreal forests and grasslands, especially at high altitude.” The resulting soil erosion generates dust storms, causing increased dust deposition on northern ice sheets. This dust deposition considerably reduces the albedo of ice sheets. The paper claims that a period of about 10,000 years of intense dust storms precedes every interglacial warming period. In Greenland, most of this dust most likely originates from the Gobi Desert.
During the next Milankovitch cycle, as the northern hemisphere insolation increases, the dust-laden ice-sheets start absorbing significantly more insolation and therefore undergo rapid melting, forcing the climate into an interglacial period.
The researcher claims that the key elements of the proposed mechanism are well supported by empirical evidence.
This paper – written by Ralph Ellis and mentored by Prof Michael Palmer – has passed peer-review. It is scheduled to be published in Geoscience Frontiers in July this year.