The sensitivity of a thermodynamic sea ice model to changes in surface energy fluxes in the Arctic is investigated. The main emphasis of the paper is on the testing of the model sensitivity to changes in surface albedo parameterization. Climatologies of turbulent and long-wave fluxes in the Arctic are scarce, and those that exist are shown to generate significant differences in the predicted ice thickness. There is considerable disagreement in the literature on albedo values, and in particular, proposed albedos of bare, puddled ice range from 0.4 to 0.66. The differences among published model simulations are shown to be potentially explicable in terms of this range in bare ice albedo. A new ice albedo parameterization is proposed, and its sensitivity is tested. It is shown that the increase in surface albedo with cloud cover can cause a doubling of the ice thickness, and the need to include melting snow as an albedo class distinct from dry snow is demonstrated. The value of bare-ice albedo is shown to be important in determining whether the ice is in a multiyear or a seasonal ice zone, and the need for more observational data on the extent and role of melt puddles is emphasized.A.

Climate modelling is now a mature discipline approaching its fortieth birthday. The need for valid climate forecasts has been underlined by the recognition that human activities are now modifying the climate. The complex nature of the climate system has resulted in the development of a surprisingly large array of modelling tools. Some are relatively simple, such as the earth systems and energy balance models (EBMs), while others are highly sophisticated models which challenge the fastest speeds of the most powerful supercomputers. Indeed, this discipline of the latter half of the twentieth century is so critically dependent on the availability of a means of undertaking powerful calculations that its evolution has matched that of the digital computer. The multi-faceted nature of the climate system demands high quality, and global observations and innovative parameterizations through which processes which cannot be described or calculated explicitly are captured to the extent deemed necessary. Interestingly, results from extremely simple, as well as highly complex and many intermediate model types are drawn upon today for effective formulation and evaluation of climate policies. This paper discusses some of the important developments during the first 40 years of climate modelling from the first models of the global atmosphere to today's models, which typically consist of integrated multi-component representations of the full climate system. The pressures of policy-relevant questions more clearly underline the tension between the need for evaluation against quality data and the unending pressure to improve spatial and temporal resolutions of climate models than at any time since the inception of climate modelling.

The greenhouse effect is now commonly accepted by the scientific community, politicians and the general public. However, the misnomer 'greenhouse effect' has perpetuated, and there are a number of aspects of the effect which are poorly understood outside the atmospheric sciences. On such misconception is that greenhouse research is a recent phenomenon; another is that glasshouses are warmed by the same mechanism as lies at the heart of the greenhouse effect. This review traces the theory as far back as 1827, highlighting new directions and significant advances over that time. Four main themes can be discerned: 1) certain radiatively active gases are responsible for warming the planet ; 2) that humans can inadvertently influence this warming; 3) climate models are designed to permit prediction of the climatic changes in the atmospheric loadings of these gases but that they have not yet achieved this goal of prediction; and 4) many scenarios of changes, and especially of impact, are premised on relatively weak analysis. This latter point is illustrated by an examination of the relationship between increasing temperature and sea level change (the oceanic response to atmospheric warming). Current research suggests that sea-level rise is not likely to be as high as had previously been anticipated.

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Natural changes in surface (and particularly land surface) albedo are described in terms of their impact upon climate. Emphasis is placed upon the importance of the regional or 'synoptic' scale view of albedo change and upon a methodology of monitoring such variations using current satellite surveillance. A case study of the United Kingdom during the 1976 drought reveals the large scale changes in reflectivity that can occur during extreme events. It is possible that such surface changes could have caused positive feedback in the atmospheric circulation thus prolonging the drought conditions.The understanding of natural climatic variability has taken on new urgency in our times (Schneider and Dickinson, 1974)