Ice Ages

CO2 is higher in interglacial times and lower in ice ages, indicating significant differences in photosynthesis between these two climatic states. 

Ice ages ended quickly. Processes that promote the increase of carbon dioxide in the atmosphere are positive feedbacks in ending an ice age. Is subglacial chemical weathering a positive or a negative feedback What circumstances would allow one to give the opposite answer (Hint ... 

Throughout this chapter many of the arguments are based on an assumption of steady state. Before the agricultural and industrial revolutions, the carbon cycle presumably was in a quasi-balanced state. Natural variations still occur in this unperturbed environment the Little Ice Age, 300-400 years ago, may have influenced the carbon cycle. The production rate of varies on time scales of decades and centuries (Stuiver and Quay, 1980,1981), implying that the pre-industrial radiocarbon distribution may not have been in steady state. 

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

It is clear from the records of ice ages (see, e.g., Fig. 1-2) that Earth can have and has had climates that are different from our current state. Other, more extreme possibilities have been suggested, each of which could be stable for considerable periods of fime. The frozen "snowball Earth" already mentioned is analogous to present-day Mars, where its CO2 green-... 

This chapter is a brief introduction to Earth s historical environmental changes, with emphasis on the recent ice-age cycles. We chose this emphasis because preservation of these environmental records is much better than for earlier times, and because the ice ages constitute drastic changes in global environment which have... 

Much of the variation in these time series for the past 700 kyr can be described by a combination of a 100 kyr cycle plus additional cycles with periods of 20 and 40 kyr. This result immediately suggests that the ice-age cycles are caused by variations in the amount and seasonality of solar radiation reaching the Earth (insolation), because the 20, 40, and 100 kyr periods of climate history match the periods of cyclic variations in Earth s orbit and axial tilt, line hypothesis that these factors control climate was proposed by Milutin Milankovitch in the early part of the 20th century and is widely known as "Milankovitch Theory." It is now generally accepted that the Milankovitch variations are the root cause of the important 20 and 40 kyr climate cycles. The 100 kyr cycle, however, proves to be a puzzle. The magnitude of the insolation variation at this periodicity is relatively trivial, but the 100 kyr cycle dominates the climate history of the last 700 kyr. Further,... 

Though an important part of the Quaternary climate puzzle, this view of the ice-age cycles is by itself quite incomplete. If Milankovitch forcings alone govern climate change then ... 

Fig. 18-19 Enhancement, relative to modem values, of marine and continental primary aerosols in Greenland through the last ice age (derived from Mayewski et al, 1997).

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