Search Results - (Author, Cooperation:S. Rahmstorf)

2015-07-15

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-11-01

American Association for the Advancement of Science (AAAS)

2375-2548

Natural Sciences in General

1432-0894

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract  The climate at the Last Interglacial Maximum (125 000 years before present) is investigated with the atmosphere-ocean general circulation model ECHAM-1/LSG and with the climate system model of intermediate complexity CLIMBER-2. Comparison of the results of the two models reveals broad agreement in most large-scale features, but also some discrepancies. The fast turnaround time of CLIMBER-2 permits one to perform a number of sensitivity experiments to (1) investigate the possible reasons for these differences, in particular the impact of different freshwater fluxes to the ocean, (2) analyze the sensitivity of the results to changes in the definition of the modern reference run concerning CO2 levels (preindustrial versus “present”), and (3) estimate the role of vegetation in the changed climate. Interactive vegetation turns out to be capable of modifying the initial climate signals significantly, leading especially to warmer winters in large parts of the Northern Hemisphere, as indicated by various paleodata. Differences due to changes in the atmospheric CO2 content and due to interactive vegetation are shown to be at least of the same order of magnitude as differences between the two completely different models, demonstrating the importance of careful experimental design.

Electronic Resource

1432-0894

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract. The 'conveyor belt' circulation of the Atlantic Ocean transports large amounts of heat northward, acting as a heating system for the northern North Atlantic region. It is widely thought that this circulation is driven by atmospheric freshwater export from the Atlantic catchment region, and that it transports freshwater northward to balance the loss to the atmosphere. Using results from a simple conceptual model and a global circulation model, it is argued here that the freshwater loss to the atmosphere arises mainly in the subtropical South Atlantic and is balanced by northward freshwater transport in the wind-driven subtropical gyre, while the thermohaline circulation transports freshwater southward. It is further argued that the direction of freshwater transport is closely linked to the dynamical regime and stability of the 'conveyor belt': if its freshwater transport is indeed southward, then its flow is purely thermally driven and inhibited by the freshwater forcing. In this case the circulation is not far from Stommel's saddle-node bifurcation, and a circulation state without NADW formation would also be stable.

Electronic Resource

1432-0894

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract A 2.5-dimensional climate system model of intermediate complexity CLIMBER-2 and its performance for present climate conditions are presented. The model consists of modules describing atmosphere, ocean, sea ice, land surface processes, terrestrial vegetation cover, and global carbon cycle. The modules interact through the fluxes of momentum, energy, water and carbon. The model has a coarse spatial resolution, nevertheless capturing the major features of the Earth's geography. The model describes temporal variability of the system on seasonal and longer time scales. Due to the fact that the model does not employ flux adjustments and has a fast turnaround time, it can be used to study climates significantly different from the present one and to perform long-term (multimillennia) simulations. The comparison of the model results with present climate data show that the model successfully describes the seasonal variability of a large set of characteristics of the climate system, including radiative balance, temperature, precipitation, ocean circulation and cryosphere.

Electronic Resource

1572-9532

Springer Online Journal Archives 1860-2000

Physics

Abstract Arguments are given for using the deDonder instead of the synchronous gauge in describing the propagation of density perturbations in a preexisting gravitational field. Since in the deDonder gauge the corresponding reference frame is fixed on the background, the physical interpretation of results is obvious, while in the synchronous gauge it is at least very difficult to extract the physical consequences from the results. For the propagation of density perturbations, with large spatial extension, a decisive difference is found between the two gauges. While in the synchronous gauge there is a growing mode in the density contrast (at least for adiabatic perturbations on a background matter substratum withp∼ρ as equation of state), in the deDonder gauge there is not. The calculation in deDonder gauge leads to upper boundaries for the spatial extension of unstable density perturbations, and thus may give a hint for upper boundaries of galaxy masses.

Electronic Resource