Tracing the Role of Carbon Dioxide in Global Warming
|AS scientific debate continues
over the causes, mechanisms, and extent of global warming, the nations of
the world have begun acting on the plausible assumption that human
activities, particularly the release of significant amounts of greenhouse
gases into the atmosphere, are leading to global warming. While not
conclusive, evidence has been mounting that human-induced climate change is
At the Kyoto climate conference in
December 1997, policymakers, climate experts, and industrial leaders came
together to seriously consider future global climate. Their goal: to
negotiate limits on the future release into the atmosphere of carbon dioxide
(CO2), the most plentiful greenhouse gas, in order to prevent
further human-driven climate change. The conferees took to heart the latest
scientific findings on global climate processes that have resulted, in large
part, from climate models.
Climate models are a major tool that scientists use to understand the complex web of climate mechanisms. However, important uncertainties remain. Scientists at Lawrence Livermore are actively seeking answers to the questions of how much climate is changing and how much CO2 is stored naturally in the atmosphere and oceans, ultimately helping to resolve the larger uncertainty: what effect human activities have on our environment.
Determining Carbon's Fate
The Ocean Carbon Cycle
Improving Convection Models
|Then CFC uptake was
as an indirect test of the model's ability to simulate ocean uptake of anthropogenic CO2. No direct method is possible because anthropogenic CO2 cannot be reliably distinguished from natural CO2 in the ocean. By contrast, CFCs have no natural background concentration in the ocean. Moreover, CFC uptake is very closely related to the ocean's absorption of human-induced CO2, as Figure 2 shows.
Because of this close relationship, Caldeira and Duffy reasoned that the standard model treatment of ice formation, which results in excessive simulated ocean uptake of CFC, also produces excessive uptake of anthropogenic CO2. In addition, the improved treatment of ice formation, which produces greatly improved simulated uptake of CFCs, should also produce more accurate calculations of the uptake of anthropogenic CO2. Further simulations are planned to verify these results.
|Modeling Marine-Biology Effects
CO2 by Radiocarbon Proxy
|Radiocarbon by Salmon Proxy
To validate models of how the ocean absorbs nuclear-testing 14C, modelers must be able to distinguish between how much of the total 14C now in the ocean is bomb-produced and how much is natural. The modelers therefore need to know the natural 14C concentrations before the weapons tests and how quickly the 14C entered the oceans. The problem is that few open-ocean measurements of that period have been taken.
|By selecting and measuring appropriate sections of the scales, Brown obtained estimates of 14C content of North Pacific surface waters, averaged over the very large areas of the salmon's seasonal migration patterns and over the 1- to 2-year time spans represented by the sections. The 14C measurements show excellent agreement with the few direct, open-ocean measurements available of 14C content and clearly show the rise in 14C content from the atmospheric nuclear tests (Figure 5). By providing rare estimates of "prebomb" values and the initial increase of ocean 14C concentrations, Brown's measurements are a valuable help to climate scientists trying to predict future uptake of CO2 by the ocean as well as future climate.|
|Fossil Fuel Affects 14C Fluxes
Closing In on Global Climate
Key Words: carbon cycle, carbon dioxide (CO2), climate change, climate model, fossil-fuel burning, global warming, greenhouse gas, marine biology, mass spectrometry, ocean carbon cycle, ocean convection, proxy data, radiocarbon (14C).
For further information contact Philip B. Duffy (925) 422-3722 (firstname.lastname@example.org) or Ken Caldeira (925) 423-4191 (email@example.com).
PHILIP B. DUFFY is a physicist at the Laboratory, where he is group leader for the Climate System Modeling Group in the Atmospheric Science Division. Duffy worked in strategic defense systems when he joined the Laboratory in 1986. Prior to that, he received his Ph.D. and M.S. in astrophysics in 1986 and 1981 from Stanford University and an A.B. in astronomy and astrophysics in 1979 from Harvard University. Duffy has published research on astronomy, atomic physics, and numerical modeling of ocean circulation.
KENNETH G. CALDEIRA joined the Laboratory's Atmospheric Chemistry Group as a physicist in 1993 and has been an environmental scientist in the Climate System Modeling Group since 1995. He received his Ph.D. and M.S. in atmospheric science from New York University in 1991 and 1988 and his B.A. in philosophy from Rutgers University in 1978. He also served as a postdoc at Pennsylvania State University's Earth System Science Center. Caldeira has published many papers, for example, on climate stability of early Earth and the global carbon cycle as it has been affected by human activity over millions of years.