12 research outputs found
Carbon and climate system coupling on timescales from the Precambrian to the Anthropocene
Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 32 (2007): 31-66, doi:10.1146/annurev.energy.32.041706.124700.The global carbon and climate systems are closely intertwined, with
biogeochemical processes responding to and driving climate variations. Over a range of
geological and historical time-scales, warmer climate conditions are associated with
higher atmospheric levels of CO2, an important climate-modulating greenhouse gas. The
atmospheric CO2-temperature relationship reflects two dynamics, the planet’s climate
sensitivity to a perturbation in atmospheric CO2 and the stability of non-atmospheric
carbon reservoirs to evolving climate. Both exhibit non-linear behavior, and coupled
carbon-climate interactions have the potential to introduce both stabilizing and
destabilizing feedback loops into the Earth System. Here we bring together evidence
from a wide range of geological, observational, experimental and modeling studies on the
dominant interactions between the carbon cycle and climate. The review is organized by
time-scale, spanning interannual to centennial climate variability, Holocene millennial
variations and Pleistocene glacial-interglacial cycles, and million year and longer
variations over the Precambrian and Phanerozoic. Our focus is on characterizing and,
where possible quantifying, the emergent behavior internal to the coupled carbon-climate
system as well as the responses of the system to external forcing from tectonics, orbital
dynamics, catastrophic events, and anthropogenic fossil fuel emissions. While there are
many unresolved uncertainties and complexity in the carbon cycle, one emergent
property is clear across time scales: while CO2 can increase in the atmosphere quickly,
returning to lower levels through natural processes is much slower, so the consequences
of the human perturbation will far outlive the emissions that caused them.S. Doney acknowledges support from the NSF Geosciences Carbon and Water program
(NSF ATM-0628582) and the WHOI W. Van Alan Clark Sr. Chair. D. Schimel
acknowledges support from the NSF Biocomplexity in the Environment program (NSF
EAR-0321918)
Testing the climate intervention potential of ocean afforestation using the Great Atlantic Sargassum Belt
Ensuring that global warming remains 2 emissions reduction. Additionally, 100–900 gigatons CO2 must be removed from the atmosphere by 2100 using a portfolio of CO2 removal (CDR) methods. Ocean afforestation, CDR through basin-scale seaweed farming in the open ocean, is seen as a key component of the marine portfolio. Here, we analyse the CDR potential of recent re-occurring trans-basin belts of the floating seaweed Sargassum in the (sub)tropical North Atlantic as a natural analogue for ocean afforestation. We show that two biogeochemical feedbacks, nutrient reallocation and calcification by encrusting marine life, reduce the CDR efficacy of Sargassum by 20–100%. Atmospheric CO2 influx into the surface seawater, after CO2-fixation by Sargassum, takes 2.5–18 times longer than the CO2-deficient seawater remains in contact with the atmosphere, potentially hindering CDR verification. Furthermore, we estimate that increased ocean albedo, due to floating Sargassum, could influence climate radiative forcing more than Sargassum-CDR. Our analysis shows that multifaceted Earth-system feedbacks determine the efficacy of ocean afforestation