Volume 276 Issue 5686, 23 November 1978

Opinion

News

News in Brief

Correspondence

News & Views

Climatology Supplement

  • Climatology Supplement |

    Descriptive documentary evidence is an important source of detailed information on past climates, particularly for the period between the eleventh century and the beginning of the era of instrumental meteorology. Historical climatology is concerned with the study and climatic interpretation of this evidence. However, there are many pitfalls in using historical records, associated with the fact that such records were rarely written primarily as descriptions of climate and with the fact that many readily accessible records are of doubtful reliability. Here we take a critical look at existing work in the field, with the aim of isolating many problems which need to be recognised and overcome before historical climatology can be considered to rest on a secure methodological and factual footing.

    • M. J. Ingram
    • , D. J. Underhill
    •  & T. M. L. Wigley
  • Climatology Supplement |

    The increasingly visible impact of climatic variability on human affairs lends a sense of urgency to the task of better understanding the workings of the Earth's climatic system. Actual instrumental observations of climate are relatively short, and we must therefore turn to other sources for information about past climates to help develop and test the models that may enable us to predict climatic anomalies such as prolonged droughts or a series of severe winters. Tree -rings are one of the best sources of climatic proxy information. They can provide long, accurately dated, year-by-year records at many points around the globe, and bridge the gap between recent instrumental or historical data and the longer but more generalised geological records. Variations in the width of annual rings reflect the influence of climatic factors that limit the biological processes governing ring formation within a tree. Study of reconstructions of long records of a variety of climatic and related variables, such as temperature, precipitation, stream runoff and barometric pressure over periods of several hundred to several thousand years strongly suggests that the climate of the past century or so is not representative of the conditions that have frequently prevailed over long periods. Proxy records are thus a great help in our efforts to anticipate or predict future climate, which may be significantly different from the recent climatic past.

    • Valmore C. LaMarche Jr
  • Climatology Supplement |

    Many theories about climate change are essentially untestable, but we can still develop a consistent model based on understandable physics—in fact the data cannot be interpreted without one. Shutts and Green believe that there is some fundamental defect in all present models: it could be something physically improbable, like an unreasonable effect of tiny solar variations. More likely there is a fundamental lack in our appreciation of how very interactive systems behave.

    • G. J. Shutts
    •  & J. S. A. Green
  • Climatology Supplement |

    Detailed three-dimensional numerical models of the atmosphere, coupled as necessary to models of other parts of the climatic system, provide the most promising approach to understanding the physical basis of climate. Models of this kind can be used to investigate the impact of anthropogenic pollution on climate. At the present time, the main concern is with increasing concentrations of CO2 which might lead to overall warming of the troposphere, but chemical and thermal pollution may also pose a threat. The possible climatic changes would take place slowly and would involve the response of the slowly reacting parts of the climatic system, particularly the oceans. The problem of how to simulate such changes of climate presents many difficulties, which are currently being studied.

    • A. Gilchrist
  • Climatology Supplement |

    The chemistry of the atmosphere was a largely neglected topic until the last decade during which concern about pollution has produced a flurry of activity. The processes which may deplete the relatively small amount of ozone in the stratosphere which protects us from harmful UV light have much in common with those in the Los Angeles-type smog which generate ozone and other oxidants. Such systems involve chain reactions in which free radicals such as HO, HO2, ClO can carry out a chemical conversion process (ozone to oxygen) many times before they are destroyed. Recent research shows that nitrogen oxides from the exhausts of supersonic aircraft or derived from increased use of nitrogenous fertilisers will have little effect on stratospheric ozone but the potential effects of chlorine compounds, such as aerosol propellants, require careful examination. In contrast, the oxidation of carbon monoxide is now thought to be a major source of ozone in the lower atmosphere.

    • B. A. Thrush
  • Climatology Supplement |

    During the past century over 1,000 articles have been published claiming or refuting a correlation between some aspect of solar activity and some feature of terrestrial weather or climate. Nevertheless, the sense of progress that should attend such an outpouring of ‘results’ has been absent for most of this period. The problem all along has been to separate a suspected Sun–weather signal from the characteristically noisy background of both systems. The present decade may be witnessing the first evidence of progress in this field. Three independent investigations have revealed what seem to be well resolved Sun–weather signals, although it is still too early to have unreserved confidence in all cases. The three correlations are between terrestrial climate and Maunder Minimum-type solar activity variations, a regional drought cycle and the 22-yr solar magnetic cycle, and winter hemisphere atmospheric circulation and passages by the Earth of solar sector boundaries in the solar wind. The apparent emergence of clear Sun–weather signals stimulated numerous searches for underlying physical causal links.

    • George L. Siscoe
  • Climatology Supplement |

    A mathematical framework is presented for the study of the predictability of small changes in the climatic system. From a statistical definition of climate in terms of ensemble averages, a limit to predictability is found arising from random weather fluctuations. This limit, typically referred to as climate noise, is often able to obscure a possible climate signal produced by external forcing. A separation of timescales of climatic response is also presented as a convenient means to distinguish between the fast internal (for example, the atmosphere) and the slow external (for example, the oceans) systems. In this way, it is possible to estimate the climate signal in the internal system that arises from small changes in the slow external system. Finally, a theoretical approach is presented for the inclusion of possible feedback effects in the estimation of a climate signal. Such feedback effects could result from the external climatic system being influenced by a change in the mean properties of the fast internal climatic system.

    • C. E. Leith
  • Climatology Supplement |

    The cooling of the Northern Hemisphere since 1940 has been variously interpreted as the overture to the next Ice Age, the effect of industrial pollution in the atmosphere or of a decline in the solar output. Are we in a position to judge between these various interpretations and to make a prediction for the next few decades? The link with the next Ice Age may be dismissed as a confusion of timescales; the explanation in terms of atmospheric pollution merits careful examination but seems unlikely to be adequate on its own. Natural fluctuations must also be considered.

    • M. K. Miles

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