Since the scenarios explored here have forcings decreasing after a maximum of 25, years i. While we note the substantial uncertainties in data interpretation, climate sensitivity, base climate state, and atmospheric composition, we nevertheless conclude that a massive CH 4 release from the dissociation of gas hydrates can consistently explain the PETM climate change.
However, should future analyses lead to a substantial prolonging of the period of deep ocean warmth over that assumed above, these conclusions may have to be revisited. For instance, we have neglected temperature and humidity effects on atmospheric reaction rates, productivity changes on the uptake of carbon [ Bains et al. We also neglected the highly uncertain effects of possible increases in polar stratospheric clouds [ Sloan and Pollard , ].
Stratospheric temperature and H 2 O str changes affect ozone amounts, but thoroughly estimating those changes and subsequent radiative effects are beyond the scope of this paper.
Fire Influences on Atmospheric Composition, Air Quality and Climate
Given the size of the CH 4 source function, we anticipate that these effects may well be important especially over the longer term. Whether these feedbacks are strong enough to change the conclusions presented here, however, remains to be seen. Work also remains to be done to link the atmospheric chemistry to a more sophisticated carbon cycle model [e. Although CH 4 and H 2 O str have residence times significantly shorter than CO 2 , they will persist at high concentrations for as long as anomalous emissions last.
Predicted changes to CO 2 are small compared to the sensitivity of standard proxies, and underline the difficulty in detecting possible increases across the PETM interval. We assume that natural sources exactly balance the preindustrial ca. The variation of this chemical sink as the CH 4 concentration varies is written as S trop and is approximated from the results in Table 1.
The stratospheric sink is a photolytic reaction and is presumed proportional to the concentration, as is the biological soil sink. Their evolution can be expressed as where I is the input function of CH 4 , and M 0 , C 0 , and W 0 are the estimated preindustrial atmospheric mixing ratios 0. C M t is defined as the source of CO 2 at any point in time. Atmospheric concentrations of CO 2 are calculated following a multiple timescale decay [ Lashof and Ahuja , ] with the longest timescale set to , year to match the decay time for the PETM carbon isotope excursion [ Bains et al.
For reference, a threefold increase in surface emissions [ Sloan et al. If a Paleocene value of 6 ppmv is assumed which would require a roughly fivefold increase in emissions , the CH 4 residence time would be 15 years and the base H 2 O str level, 4. Volume 18 , Issue 1. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. If the address matches an existing account you will receive an email with instructions to retrieve your username. Open access. Paleoceanography Volume 18, Issue 1.
Free Access. Gavin A. Drew T. Tools Request permission Export citation Add to favorites Track citation. Share Give access Share full text access. Share full text access. Please review our Terms and Conditions of Use and check box below to share full-text version of article. Atmospheric Chemistry Modeling 2. Model  In order to estimate atmospheric chemistry changes over the tens of thousands of years relevant for the PETM, we require estimates of the feedback between CH 4 and OH when CH 4 concentrations are high.
Figure 1 Open in figure viewer PowerPoint. Simplified schematic of the tropospheric chemistry scheme, showing the primary pathways for OH radical generation and loss. For clarity, some intermediate reactions and the effects of CO and higher hydrocarbons are not shown. The OH radical variation is given as a percentage increase over the preindustrial climate.
The relative specific loss is the fractional change to the tropospheric sink term for CH 4 compared to the preindustrial control. The lifetime for CH 4 is defined with respect to the total source term. Figure 2 Open in figure viewer PowerPoint. Other uniform scenarios resemble the first panel. Values given correspond to the time of maximum CH 4. Maximum CO 2 levels occur a few years later but do not differ substantially.
For the B99 experiment, we highlight the equilibrium concentrations at the end of the second pulse. Radiative and Climate Forcing  Estimates of radiative forcing are a useful way to characterize the climate response to changes in GHG amounts. Figure 3 Open in figure viewer PowerPoint. Discussion  Can these simple experiments help constrain the uncertainties associated with the CH 4 release hypothesis for the PETM? Acknowledgments  We would like to thank Greg Faluvegi for running some of the radiative forcing calculations, Bernadette Walter and Francesco Tubiello for advice concerning the carbon and CH 4 cycle, Jerry Dickens and Matthew Huber for some very constructive criticism, and Doug Hammond, Lisa Sloan, and an anonymous reviewer for generously sharing their thoughts on this subject with us.
Appendix A. Their evolution can be expressed as. Bains, S. Google Scholar. Crossref Google Scholar. Citing Literature. Data Management Workshops. Data Management Assessment. The report captures new information about past, current and future climate change, and builds on the existing body of science to summarize the current state of knowledge and provide the scientific foundation for the NCA4 regional and sectoral chapters, scheduled to be released in late The report, which primarily focuses on changes in the U.
The report includes contributions from 40 American Geophysical Union members and includes more than references to scientific studies published in AGU journals. Several AGU scientists are available to comment on the report and the science behind it.
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Her research focuses on understanding what climate change means to human and natural systems at the local to regional scale. Email: ljames atmosresearch. He also leads several projects that apply climate information to impact and adaptation assessment. Email: rh columbia. His research focuses on understanding uncertainty in past and future climate change, with major emphases on sea level change and on the interactions between physical climate change and the economy. Email: robert. Bottenheim, C. Boxe, G. Carver, G. Chen, J. Crawford, F.
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