Showing papers on "Runaway climate change published in 1996"

Climate change scenarios for Great Lakes Basin ecosystem studies

Abstract: Significant change in global climate could occur due to human-induced changes in the chemistry of the atmosphere. We provide a basis for the continuing assessment of potential impacts of climate change on aquatic ecosystems. A series of climate change scenarios have been developed for the Great Lakes Basin using general circulation models (GCMs), climate spatial transpositions, and historical climate analogs. The direct impacts of climate change on the Great Lakes ecosystem would occur through higher air and water temperatures. Indirect climate change impacts include both positive and negative changes in precipitation, decreases riverine runoff, less snowfall and snowpack accumulation, higher evapotranspiration, and a reduction in lake levels and connecting channel flows. These climate and hydrologic changes affect the quantity and quality of wetland and aquatic habitats, alter the frequency and timing of lake turnover, and change dissolved oxygen, and alter fish community composition and dynamics. We provide an integration of Great Lakes climate scenarios. We also illustrate, for the first time, the spatial variability of the climate change ’ scenarios on a tributary river-basin scale. There is growing concern that human activities such as burning of fossil fuel and various land-use practices are altering the composition of the atmosphere. Concentrations of radiatively active gases such as carbon dioxide, methane, ozone, nitrous oxide, and chlorofluorocarbons are increasing in the atmosphere. Enhancing the “greenhouse effect” could lead to significant warming with global mean temperatures attaining levels higher than experienced in recorded history. The warming as well as indirect effects on precipitation, soil moisture and runoff, for example, would have important implications for human and ecological systems. Generally, past climate has been considered a reliable guide for planning in the future through the use of 30-yr climate normals; however, this perspective needs to be reassessed in relation to climate change. Climate change scenarios are a technique that may be used to simulate plausable climate “futures” for assessing potential impacts on the Great Lakes and other aquatic ecosystems within the basin. Climate scenarios, defined as descriptions of possible climate conditions at some unspecified future time that are physically consistent (Lamb 1987), are used to develop an understanding of the sensitivity of a region, activity, or ecosystem to climate variability and change. These scenarios are not single predictions or forecasts. They represent a range of possible futures-“what if’ situations for exploring the implications of a changed climate system or future climate variability not represented in the instrumental record. The scenarios represent climatic conditions that could occur. At present, there is no way ‘of determining which scenario is best nor can probabilities of occurrence be assigned due to the many uncertainties that remain. However, a range of climate scenarios can provide an indication of the nature and extent of sensitivities to climate variability and change.

Changing probabilities of daily temperature extremes in the UK related to future global warming and changes in climate variability

Abstract: The impacts of 2 greenhouse gas emissions scenarios (one from the IPCC and one from Greenpeace International) on the occurrence of extreme daily temperature events are considered at several sites in the UK. For each site, a number of probability distributions were tested for goodness-offit to 1961-87 observed daily maximum and minimum temperature data using the KolmogorovSmirnov test. The parameters of the best-fitting distributions were then perturbed to take into account clunate change, both mean and variability. Probabilities of the occurrence of particular temperature threshold events were calculated for both present and future climates. Changes in climate variability were considered in 3 ways: (1) by assuming the present variance stays the same in the future; (2) by imposing standardised percent changes in variance; and (3) by imposing variance changes derived from the UK Meteorological Office high resolution GCM equilibrium climate change experiment. Results presented for 2 contrasting sites illustrate the importance of including changes in variability in climate change studies. Specific results depend on the site and threshold temperature chosen and on the distribution characteristics. However, for example, at Fortrose the 1961-87 mean maximum temperature in July is below 20°C. With increases in global-mean temperature, the probability of this threshold being exceeded increases, although the rate of increase depends on the variance change being considered. The largest rate of increase in probability occurs with a 20% per "C increase in variance. The approach described here has been used in one component of a climate change scenario generator for the UK developed for the UK Ministry of Agriculture. Fisheries and Food.

Greenhouse gas induced climate change

Abstract: Simulations using global coupled climate models predict a climate change due to the increasing concentration of greenhouse gases and aerosols in the atmosphere. Both are associated with the burning of fossil fuels. There has been considerable debate if this postulated human influence is already evident. This paper gives an overview on some recent material on this question. One particular study using optimal fingerprints (Hegerl et al., 1996) is explained in more detail. In this study, an optimal fingerprint analysis is applied to temperature trend patterns over several decades. The results show the probability being less than 5% that the most recently observed 30 year trend is due to naturally occurring climate fluctuations. This result suggests that the present warming is caused by some external influence on climate, e.g. by the increasing concentrations of greenhouse gases and aerosols. More work is needed to address the uncertainties in the magnitude of naturally occurring climate fluctuations. Also, other external influences on climate need to be investigated to uniquely attribute the present climate change to the human influence.

The earth’s changing climate

Abstract: Various human activities have contributed to an increase in the levels of greenhouse gases. The contribution that these make to global warming requires further investigation, because there are several negative feedback mechanisms which inhibit the warming process.

The influence of greenhouse warming on the atmospheric component of the hydrological cycle

Abstract: An atmosphere-ocean climate box model is used to examine the influence of cloud feedback on the equilibria of the climate system. The model consists of three non-linear ordinary differential equations, which are simplified forms of the first law of thermodynamics for the atmosphere and ocean and the continuity equation for the atmospheric component of the hydrological cycle. The mass continuity equation expresses the cloud liquid water content as a function of the evaporation rate from the ocean surface and the precipitation rate. Cloud formation releases latent heat. The model clouds also absorb solar energy at a rate consistent with recent findings. The model simulates snow-ice albedo feedback, water vapour feedback and cloud feedback. The global mean precipitation and surface temperature are analysed as they respond to enhanced greenhouse warming. Model results show that cloud feedback can lead to the occurrence of multiple climate equilibria. Some of these are warmer than the present equilibrium, with increased precipitation, while others are colder, with reduced precipitation. If the cloud feedback is weak, enhanced greenhouse forcing leads to a small alteration of the present equilibrium. If the cloud feedback is strong enough, the climate system can be forced into a warmer and wetter equilibrium.

The role of clouds and oceans in global greenhouse warming. Final report

Abstract: This research focuses on assessing connections between anthropogenic greenhouse gas emissions and global climatic change. it has been supported since the early 1990s in part by the DOE ``Quantitative Links`` Program (QLP). A three-year effort was originally proposed to the QLP to investigate effects f global cloudiness on global climate and its implications for cloud feedback; and to continue the development and application of climate/ocean models, with emphasis on coupled effects of greenhouse warming and feedbacks by clouds and oceans. It is well-known that cloud and ocean processes are major sources of uncertainty in the ability to predict climatic change from humankind`s greenhouse gas and aerosol emissions. And it has always been the objective to develop timely and useful analytical tools for addressing real world policy issues stemming from anthropogenic climate change.

Climate Stability in a Simple Climate Model with a Hydrological Cycle

Abstract: An atmosphere-ocean climate box model is used to examine the influence of the atmospheric component of the hydrological cycle on the steady-state and time-dependent behaviour of the climate system. The model consists of three nonlinear ordinary differential equations that are simplified forms of the first law of thermodynamics for the atmosphere and ocean and the continuity equation for the atmospheric component of the hydrological cycle. In this model, energy is exchanged between the ocean, atmosphere and space by short and long-wave radiation and by sensible and latent heat. The mass continuity equation expresses the cloud liquid water content as a function of the evaporation rate from the ocean surface and the precipitation rate. The model also simulates snow-ice albedo feedback and water vapor feedback. Cloud feedback can lead to the occurrence of multiple climate equilibria. Some are warmer with increased precipitation and others colder with reduced precipitation. The present equilibrium may be accompanied by other equilibria that are either stable or unstable. Oscillations of the climate can occur around the present equilibrium as a result of cloud feedback.