Uncertainty In Climate Predictions Research Articles

Multi-century simulations with the coupled GISS–HYCOM climate model: control experiments

Multi-century climate simulations obtained with the GISS atmospheric general circulation model coupled to the hybrid-isopycnic ocean model HYCOM are described. Greenhouse gas concentrations are held fixed in these experiments to investigate the coupled model’s ability to reproduce the major features of today’s climate with minimal drift. Emphasis is placed on the realism of the oceanic general circulation and its effect on air–sea exchange processes. Several model runs using different closures for turbulent vertical exchange as well as improvements to reduce vertical numerical diffusion are compared with climate observations. As in previous studies, the Southern Ocean emerges as the Achilles Heel of the ocean model; deficiencies in its physical representation had far-reaching consequences in early experiments with the coupled model and have provided the strongest impetus for model improvement. The overarching goal of this work is to add diversity to the pool of ocean models available for climate prediction and thereby reduce biases that may stand in the way of assessing climate prediction uncertainty.

Source and evolution of the marine aerosol—A new perspective

The “indirect effect of aerosols” refers to their ability to influence cloud radiative properties, and is considered to be one of the larger uncertainties in climate prediction. Oceans cover about 70% of the world's surface and the aerosols that they produce are therefore likely to represent an important part of the indirect effect. A description of the ultimate sources of all aerosol constituents and their susceptibility to climate change is then required in order to assess the potential of an aerosol‐cloud‐climate feedback. Here we argue that in the high Arctic in summer, cloud condensation nuclei (CCN) concentration is not determined by the oxidation products of dimethyl‐sulfide as has usually been assumed but by the concentration in the air of small insoluble organic particles derived from the surface microlayer of the ocean by bubble bursting, on which the acid gases condense. Examination of the aerosol over lower latitude oceans suggests that similar processes occur over all oceans.

Lindenberg Aerosol Characterization Experiment 1998 (LACE 98): Overview

Backscattering and absorption of solar radiation by aerosol particles are an important source of uncertainty in climate predictions. Integrated research on the radiative properties of aerosol may reduce this uncertainty. The Lindenberg Aerosol Characterization Experiment 1998 (LACE 98) contributes to this aim. LACE 98 took place between 13 July and 12 August 1998, near Berlin, Germany. The Lindenberg Meteorological Observatory (52.2°N, 14.1°E) was chosen as the central field site because of its long record with aerosol optical‐depth data. Measurements were performed from three aircraft, with one airborne and four ground‐based lidars, and at a ground station. The meteorological situations in which intensive observations were carried out included clean and polluted air masses as characterized by low and high aerosol optical depths. This introductory paper gives an overview of the LACE 98 goals, instrumentation, meteorological and aerosol properties, and reports on the key findings as a guide to the results presented in the more detailed papers that follow. A very remarkable finding should be mentioned beforehand because of its unique character: on 9–10 August 1998, a free‐tropospheric aerosol layer was observed that originated from forest fires in western Canada.

The Two‐Mile Time Machine: Ice Cores, Abrupt Climate Change and Our Future

Enhanced greenhouse warming attributable to our profligate consumption of fossil fuels has established itself as perhaps the most contentious environmental issue currently being debated in the international political arena. To a large extent, the debate over whether societies should undertake actions to mitigate potentially adverse effects of climate change focuses on uncertainties in climate predictions and societal impacts. In an effort to reduce some of the uncertainty the climate community has expended considerable efforts to obtain detailed records of past climates, recognizing that the past may hold the key to our future.The Two‐Mile Time Machine by Richard Alley tells the captivating story of how one such record reconstructed from the GISP2 core, drilled through the more than 3‐km thick Greenland Ice Sheet, has revealed startling clues about past climates and shattering many of our ideas on how climate operates.

Large differences in tropical aerosol forcing at the top of the atmosphere and Earth's surface

The effect of radiative forcing by anthropogenic aerosols is one of the largest sources of uncertainty in climate predictions. Direct observations of the forcing are therefore needed, particularly for the poorly understood tropical aerosols. Here we present an observational method for quantifying aerosol forcing to within +/-5 per cent. We use calibrated satellite radiation measurements and five independent surface radiometers to quantify the aerosol forcing simultaneously at the Earth's surface and the top of the atmosphere over the tropical northern Indian Ocean. In winter, this region is covered by anthropogenic aerosols of sulphate, nitrate, organics, soot and fly ash from the south Asian continent. Accordingly, mean clear-sky solar radiative heating for the winters of 1998 and 1999 decreased at the ocean surface by 12 to 30 Wm(-2), but only by 4 to 10 Wm(-2) at the top of the atmosphere. This threefold difference (due largely to solar absorption by soot) and the large magnitude of the observed surface forcing both imply that tropical aerosols might slow down the hydrological cycle.

System of information in NOPEX — retrieval, use, and query of climate data

The uncertainty in climate predictions caused by improper understanding of the role of the land-surface is underestimated and easy access to data from a series of landscape types around the globe would improve this. Such data exist from a series of large-scale land-surface experiments but access to them has been difficult. It is the objective of this paper to demonstrate how the System for Information in NOPEX (SINOP) could be set up to provide a combination of data archive and tool for executing various time-limited and long-term field activities. Setting up and running SINOP involved both technical and psychological issues. The major technical problems were associated with (i) the uninterrupted flow of large data volumes, (ii) data homogeneity, and (iii) the exploding technology development. The psychological and organisational problems were more difficult to tackle than the technical problems. Funding agencies assumed somebody else would take care of data archiving and documentation, academic organisations have difficulties to compete with the private market for database managers, many individual scientists were unwilling to deliver their datasets and, especially, unwilling to document them. It is suggested that changes in attitudes from scientists, academic organisations, and publishers are needed to give credit for the publication of good datasets and for the production of good documentation about them. CDs incorporating a subset of SINOP with well-documented datasets from NOPEX operations in 1994 and 1995 are published together with this NOPEX Special Issue. The CDs include climate variables, such as radiation, fluxes of heat, momentum, and water vapour, and various energy storage terms as well as hydrological variables from 13 sites within the central-Swedish NOPEX region, at the southern boundary of the boreal zone. The publication of these data is seen as a step towards giving data-set owners proper and citeable credit for their work.

Greenhouse effect and climate change: scientific basis and overview

Climate change due to ‘enhanced greenhouse effect’, arising as a result of human activities is considered a major global environmental threat to mankind. A review of the topic including the physics of the greenhouse effect is given. The Earth provides a unique life-supporting environment. Solar radiation has been responsible for maintaining the Earth's climatic system, the biosphere and fuelling the present technological age. Earth's temperature is a result of the equilibrium between the solar energy absorbed by the Earth and the long wave (infra-red) radiation from the Earth escaping into space. The natural greenhouse effect arises due to some of the trace gases, called the greenhouse gases, which are nearly transparent to solar radiation but strongly absorb the infra-red radiation emitted by the Earth. This results in a warming of the Earth by about 30°C and makes it habitable. Since industrialization, human activities have resulted in steadily increasing concentrations of the greenhouse gases—carbon dioxide, methane, nitrous oxide and chlorofluorocarbons—in the atmosphere, leading to fears of the ‘enhanced greenhouse effect’. Carbon dixoide alone contributes roughly two-thirds to the ‘enhanced greenhouse effect’. Past records suggest that the Earth has warmed by 0.5°C and the global sea level has increased by 15 cm since the beginning of this century. Climate models predict a further warming of 0.3°C per decade if no efforts are made to decrease emissions of greenhouse gases. This warming rate is higher than that at any time during the past 10 000 years and is likely to cause global changes in agricultural patterns, precipitation, water resources, rise in sea levels and inundation of coastal areas, occurrence of more frequent and intense extreme events such as droughts and hurricanes. African nations will be particularly vulnerable to some of these changes. Uncertainties do remain in the predictions of climate change at regional level and the scale and timing of such changes. Limitation and adaptation strategies need to be developed and implemented. Decreasing use of fossil fuels and increasing use of alternative sources of energy—solar, wind, hydro, biomass—coupled with energy conservation strategies are needed to reduce emissions of greenhouse gases. Reducing deforestation and embarking on reforestation programs is needed to increase the sinks of carbon dioxide. More research is needed to enable better understanding of climate processes and decrease uncertainties in climate predictions. Climate data, analyses and information need to be utilised in planning processes.

Energy and the new politics of the environment

The public, policymakers, and industry have failed in general to fully understand the ramifications of the UN's unprecedented scientific advisory process on global warming, culminating in the 1990 report of the Intergovernmental Panel on Climate Change. For their part, the world's climate scientists have failed — amid the many uncertainties in climate prediction — adequately to impress on policymakers' the worst-case analyses of global warming. In consequence, as a result of the perceived costs of emission-limitation policies, collective risk-analysis is erring on the side of potential adaptation rather than emission limitation. This paper argues that the current predictions of the IPCC — much less the worst-case analyses — brook no other course of action than a radical shift to a new global energy infrastructure; that societal feedbacks may yet come to impose the management of such a paradigm shift on industry and policymakers in the 1990s; and that the long-term winners in the energy industry will be those with the prescience today to see the writing on the greenhouse wall.