Understanding Earth's Deep Past Lessons for Our Climate Future (2011) / Chapter Skim
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1 Introduction
1 Introduction
Pages 16-25
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From page 16... ...
Atmospheric pCO2 could reach as high as 2000 ppmv1 if fossil fuel emissions remain unabated, all fossil fuel resources are used, and carbon sequestration efforts remain at presentday levels (Kump, 2002; Caldeira and Wicket, 2003)
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From page 17... ...
is based on modern data and paleoclimate records extending back no further than the Last Glacial Maximum of 20,000 years ago, and therefore these estimates factor in only the short-term climate feedbacks -- such as water vapor, sea ice, and aerosols -- that operate on subcentennial timescales. Climate sensitivity, however, is likely to be enhanced under higher atmospheric CO2 and significantly warmer conditions due to long-term positive feedbacks that typically are active on much longer timescales (thousands to tens of thousands of years)
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From page 18... ...
feedbacks that have operated in icehouse states of the near past, scientific understanding of the climate dynamics for past periods of global warming -- when Earth was in a "greenhouse" climate state -- is much less advanced. The paleoclimate records of deep-time worlds,2 however, are the closest analogue to Earth's anticipated future climate -- one that will be warmer and greenhouse gas forced beyond that experienced in the past 2 million years, as atmospheric CO2 contents have already surpassed by about 35 percent those that applied during the Pleistocene glacial-interglacial cycles.
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From page 19... ...
. Fluctuations in average global temperatures during the glacial-interglacial cycles of the past several hundred thousand years caused major shifts in the areal extent of continental ice sheets and greater than 100-m sea level changes, with some interglacial periods up to 2-3°C warmer than the pres ent day (Otto-Bliesner et al., 2006)
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From page 20... ...
The deep-time record thus offers the potential for a much improved understanding of the long-term equilibrium sensitivity of climate to increasing pCO2, and of the impact of major climate change on atmospheric and ocean circulation; ice sheet stability and sea level response; ocean acidifi cation and hypoxia; regional hydroclimates; and the diversity, radiation, and decline of marine and terrestrial organisms (see Box 1.2)
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From page 21... ...
have dominated most of the past ~1 billion years of Earth's history, there have been extended periods of cool "icehouse" conditions (light-blue intervals) including intervals for which there is evidence of continental ice sheets at one or both poles (shown as darker blue bars)
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From page 22... ...
Earth's deep-time history offers numerous examples of how ecosystems, geosystems, and climate systems have operated in the absence of various major groups of life and under conditions far more ex treme than those of the present day -- time intervals when oceans lacked the major elements of their current buffering capacity or were hypoxic, when the poles lacked ice sheets, and/or when atmospheric CO2 levels were higher by hundreds to thousands of parts per million of volume.
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From page 23... ...
. Periods of abundant coal and oil formation, which include the extensive coal units of the Carboniferous and Permian, Cretaceous coal, and exten sive coal deposits of the Paleogene Arctic, as well as oil deposits formed during Jurassic and Cretaceous oceanic anoxic events and Mio-Pliocene oil deposits of the Pacific Rim (Windley, 1995)
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From page 24... ...
The examination of climate states in the deep-time geological record has the potential to provide unique informa tion about how Earth's climate dynamics operate over long time frames and during changes of large magnitude. Earth's pending transition into warmer climates provides the motivation for the description of the understanding of past warm periods presented in Chapter 2, and the transitions into and out of different climate states over differing timescales is the 3 The Geosystems initiative is an interdisciplinary, community-based initiative focused on understanding the wealth of "alternative-Earth" climatic extremes archived in older parts of the geological record, as the basis for understanding Earth's climate future.
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From page 25... ...
To further our understanding of past climates, their signatures, and key envi ronmental forcing parameters and their impact on ecosystems, an NRC study will: • Assess the present state of knowledge of Earth's deep-time paleo climate record, with particular emphasis on the transition periods of major paleoclimate change. • Describe opportunities for high-priority research, with particular emphasis on collaborative multidisciplinary activities.
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