Showing papers on "Runaway climate change published in 1995"

Evaluation of the potential impact of methane clathrate destabilization on future global warming

Abstract: Future global warming due to anthropogenic emissions of greenhouse gases has the potential to destabilize methane clathrates, which are found in permafrost regions and in continental slope sediments worldwide, resulting in the release of methane gas. Since methane is a strong greenhouse gas, this could produce a potentially important positive feedback. Here, the coupled heat transfer and methane destabilization process in oceanic sediments is modeled in a series of one-dimensional, vertical columns on a 1°×1° global grid. Terrestrial permafrost is divided into 11 columns based on mean annual surface air temperature. Our base case clathrate distribution results in about 24,000 Gt C as methane clathrate in marine sediments and about 800 Gt C in terrestrial sediments, only a small fraction of which could be destabilized by future global warming. Scenarios of anthropogenic CO2 and CH4 emission are used to drive a simple model of the carbon cycle, yielding scenarios of CO2 and CH4 concentration increase. These increases drive a one-dimensional coupled atmosphere-ocean climate model. Globally averaged temperature changes as a function of time and ocean depth are used as upper boundary conditions to drive the heat transfer/methane clathrate release models. Three versions of the ocean model are used which result in different temperature perturbations at the sediment-water interface: a purely diffusive ocean model, an upwelling-diffusion ocean model with fixed temperature of bottom water formation, and an upwelling-diffusion ocean model with a feedback between surface temperature and the upwelling velocity. Methane release from clathrate destabilization is added to the anthropogenic CH4 emission, leading to stronger increases in both CH4 and CO2 concentration. Based on a wide variety of parameter input assumptions and anthropogenic emission scenarios, it appears that the potential impact on global warming of methane clathrate destabilization is smaller than the difference in warming between low and medium, or medium and high anthropogenic CO2 emission scenarios, or arising from a factor of two variation in climate sensitivity. Global warming increases by 10–25% compared to the case without clathrate destabilization for our scenarios using what, in many respects, are worst case assumptions.

Modeling Climate Change in the Absence of Climate Change Data. Editorial Comment

Abstract: Practitioners of climate change prediction base many of their future climate scenarios on General Circulation Models (GCM's), each model with differing assumptions and parameter requirements. For representing the atmosphere, GCM's typically contain equations for calculating motion of particles, thermodynamics and radiation, and continuity of water vapor. Hydrology and heat balance are usually included for continents, and sea ice and heat balance are included for oceans. The current issue of this journal contains a paper by Van Blarcum et al. (1995) that predicts runoff from nine high-latitude rivers under a doubled CO2 atmosphere. The paper is important since river flow is an indicator variable for climate change. The authors show that precipitation will increase under the imposed perturbations and that owing to higher temperatures earlier in the year that cause the snow pack to melt sooner, runoff will also increase. They base their simulations on output from a GCM coupled with an interesting water routing scheme they have devised. Climate change models have been linked to other models to predict deforestation.

Chapman Conference Probes Water Vapor in the Climate System

Abstract: About 125 scientists from 11 countries met in Jekyll Island, Ga., in October to discuss the unique role that water vapor plays in the climate system. Water vapor links the surface and atmospheric branches of the global hydrologic cycle. Its horizontal and vertical fluxes are key to the energy cycle, and its radiative effects are the major factor in the atmospheric greenhouse effect. Theoretical calculations indicate that global climate is highly sensitive to small changes in humidity at all levels in the atmosphere, but observations to test this hypothesis are lacking. Because few high-quality humidity observations exist, especially in the upper troposphere, researchers are uncertain of the nature and strength of climate feedback mechanisms involving water vapor and its distribution and long-term changes. Consequently, water vapor is not well treated in global climate models and requires more attention.

Chapter 15 The geophysiology of climate

Abstract: This chapter provides a geophysiological perspective on climate change, both in Earth history, and in future. Ozone in the unpolluted atmosphere is affected in the stratosphere by the biological production of chlorine and bromine-containing gases and nitrous oxide, and in the troposphere by the emission of terpenes and other hydrocarbons by vegetation. The response of the atmospheric water cycle to global warming is complex, and no credible prediction of future climate is possible without an account of the redistribution of water in the environment. Biological systems are known to affect the state and abundance of water in the atmosphere. Over land evapo-transpiration affects the water cycle on both local and regional scales. The gaseous greenhouse is a property of the geo-physiological system, not just a part of an inert environment to which organisms merely adapt. Where there is feedback from climate change on the rate of biogenic or biologically mediated removal or production of greenhouse gases, a coupled feedback system exists that inextricably links the evolution of organisms and climate.

Dusting the climate for fingerprints. Has greenhouse warming arrived? Will we ever know?

Abstract: The topic of global warming is front page news again. Although the annual average global temperature has risen by about 0.5 C since the late 19th century, investigators have had difficulty determining whether natural forces or human actions are to blame. This article summarizes the arguments pro and con and the search for a diffinative `human fingerprint` on global warming. For example, Max-Lanck researchers find it highly imporbable (1 in 20 chance) that natural forcers have caused the temperature rise. However other scientists acknowledge that uncertainties continue to plague studies aimed at detecting the human influence in climatic change. Computer climate models are the major approach, but distiguishing between recent abnormal warming due to greenhouse gases or to other causes is elusive.

Climate change: Does it matter?

Abstract: Ever since Svante Arrhenius, early in this century, calculated how much our use of fossil fuel might raise the surface temperature of the earth, there have been speculations concerning the impact of this and other human-induced climate changes on society (Arrhenius, 1908). The conversion of this speculation about impacts into well established estimates has been hampered by uncertainties concerning the rate at which the climate forcing activities are changing, uncertainties in our knowledge of the nature of the climate changes that will follow the changes in forcing, uncertainties in the reaction of important ecosystems to the changing climate, and the lack of any widely adopted and tested methodology for estimating societal impacts of a climate change. Despite these difficulties, a number of studies in the United States in the period 1991–1994 have considered the impact of a human-induced climate change, and other studies have discussed the methodological issues inherent in such work. In this review, changes in all the systems mainly involving physical processes, e.g., atmosphere, ocean, ice caps, glaciers, and the hydrological cycle, will be regarded as part of the climate and not discussed here. The effect of changes in any of these physical systems on the biosphere, including humans and human societies, will be called impacts, and studies of these impacts will be at least sampled in this review. Changes in stratospheric ozone are sometimes considered to be climate changes, but this review will be restricted to the climate changes caused by increases in the concentrations of infrared-trapping gases in the atmosphere.