Changing Climate Report of the Carbon Dioxide Assessment Committee (1983) / Chapter Skim
Currently Skimming:
EFFECTS ON CLIMATE
EFFECTS ON CLIMATE
Pages 266-291
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 266... ...
This question had been addressed in l979 by a panel chaired by the late Jule Charney (Climate Research Board, l979) , and I was asked to lead a similar group to take a second look in the light of subsequent research results.
|
From page 267... ...
These impose an uncertainty beyond that arising from our necessarily imperfect knowledge of the manifold and complex climatic system of the earth. When it is assumed that the CO2 content of the atmosphere is doubled and statistical thermal equilibrium is achieved, the more realistic of the modeling efforts predict a global surface warming of between 2°C and 3.5°C, with greater increases at high latitudes.
|
From page 268... ...
The warming will be accompanied by shifts in the geographical distributions of the various climatic elements such as temperature, rainfall, evaporation, and soil moisture. The evidence is that the variations in these anomalies with latitude, longitude, and season will be at least as great as the globally averaged changes themselves, and it would be misleading to predict regional climatic changes on the basis of global or zonal averages alone.
|
From page 269... ...
However, we believe it quite possible that the capacity of the intermediate waters of the oceans to absorb heat could delay the estimated warming by several decades. It appears that the warming will eventually occur, and the associated regional climatic changes so important to the assessment of socioeconomic consequences may well be significant, but unfortunately the latter cannot yet be adequately projected.
|
From page 270... ...
Observations reveal steadily increasing concentrations of CO2, and experiments with numerical climate models indicate that continued increase would eventually produce significant climatic change. Comprehensive assessment of the issue will require projection of future CO2 emissions and study of the disposition of this excess carbon in the atmosphere, ocean, and biota; the effect on climate; and the implications for human welfare.
|
From page 271... ...
Theoretical and empirical studies of the climatic effects of increased CO2 must properly account for all significant processes involved, notably changes in the tropospheric energy budget and the effects of ocean storage and atmospheric and oceanic transport of heat. For example, studies of the isolated surface energy balance or local observational studies of the transient response to short-term radiative changes can result in misleading conclusions.
|
From page 272... ...
CLOUD EFFECTS Cloud amounts, heights, optical properties, and structure may be influenced by CO2-induced climatic changes. In view of the uncertainties in our knowledge of cloud parameters and the crudeness of cloud-prediction schemes in existing climate models, it is premature to draw conclusions regarding the influence of clouds on climate sensitivity to increased CO2.
|
From page 273... ...
The climatic effects of alterations in the concentrations of trace gases can be substantial. Since trace-gas abundances might change significantly in the future because of anthropogenic emissions or as a consequence of CO2-initiated climatic changes, // is important to monitor the most radiatively significant trace gases.
|
From page 274... ...
Because decisions of immense social and economic importance may be made on the basis of model experiments, it is important that a comprehensive climate-model validation effort be pursued, including the assembly of a wide variety of observational data specifically for model validation and the development of a validation methodology. Validation of climate models involves a hierarchy of tests, including checks on the internal behavior of subsystems of the model.
|
From page 275... ...
On the other hand, estimates with greater detail and including other important variables, e.g., windiness, soil moisture, cloudiness, solar insolation, are not yet sufficiently reliable. Nevertheless, internally consistent and detailed specifications of hypothetical climatic conditions over space and time -- "scenarios" -- may be quite useful research tools for analysis of social responses and sensitivities to climatic changes.
|
From page 276... ...
Improvement in the quality and resolution of geographical estimates of climatic change will require increased computational resolution in the mathematical models employed, improvement in the representation of the multitude of participating physical processes, better understanding of airflow over and around mountains, and extended time integration of climate models. It is clear, however, that local climate has a much larger temporal variability than climate averaged along latitude circles or over the globe.
|
From page 277... ...
However, scenarios based on contemporary data sets do not yet provide a firm basis for climatic assessment of possible CO2induced climatic changes, nor should they be considered adequate at present for validation of CO2 sensitivity studies with climate models. Studies of past climatic data are leading to important advances in climate theory.
|
From page 278... ...
As Machta describes below in Section 4.2, the growing concentrations of other radiatively active trace gases considerably complicate the problem. Tropospheric ozone, methane, nitrous oxide, and the chlorofluoromethanes also interact with thermal radiation and can produce significant additional perturbations to the Earth's heat budget.
|
From page 279... ...
have yielded results also within or very near this range. The global mean temperature index permits us to compare in general terms the potential magnitude and rate of climatic changes due to CC^ with natural changes of the past.
|
From page 280... ...
Parameters of climate other than temperature -- precipitation, storm tracks, cloud cover, for example -- and the frequencies of extreme events are at least as important in determining the real impact of climatic change. For example, tropical storm formation seems to be related to sea-surface temperature.
|
From page 281... ...
It is easy to show that small changes in cloudiness can alter the Earth's heat budget as much or more than the expected changes in CO2 concentrations. Models with different formulations for cloudiness show great differences in global and regional climate sensitivity, even if their simulations of contemporary climate and of globally averaged changes are comparable.
|
From page 282... ...
Man-made increases of CO2 and other trace gases in the atmosphere may be reasonably expected to change climate significantly within the lifetimes of a large fraction of the world's inhabitants who are alive today. (According to Ausubel and Stoto, l98l, 40% of the current population will still be alive 50 years hence.)
|
From page 283... ...
. Surface temperature sensitivity to increased atmospheric CO2.
|
From page 284... ...
. General circulation model experiments on the climatic effects due to a doubling and quadrupling of carbon dioxide concentrations.
|
From page 285... ...
Since some consideration has been given to restricting their emissions, an extrapolation of current or past growth rates to predict future atmospheric concentrations may be unwise at this time. Nitrous oxide, it is likely that most nitrous oxide in the air has come from denitrification in the natural or cultivated biosphere.
|
From page 286... ...
concentration in the atmosphere, Mauna Loa Observatory. Bottom panel: Measurements of atmospheric concentration of nitrous oxide in ground-level air at remote locations.
|
From page 287... ...
Rasmussen and Khalil suggest that the expansion in the number of farm animals and rice production might well explain, at least qualitatively, the atmospheric methane growth. Other biological activities such as termite destruction of wood (Zimmerman et al., l982)
|
From page 288... ...
The atmospheric concentrations of these trace gases are not all independent of one another. Complicated chemical reactions among these
|
From page 289... ...
Thus, unlike CO2, which generally does not undergo chemical changes in the air, these trace gases frequently do. Not only can the mean concentration be affected by other chemicals and sunlight, but distribution particularly in the vertical can be influenced (ozone is a prime example)
|
From page 290... ...
The models used to obtain these results generally gave a sensitivity to doubled CO2 between 2 and 3°C. Thus, none of the changes of individual trace gases approaches CO2 by itself, but it is clear that the summation of all of these potential changes could be of the same magnitude as CO2.
|
From page 291... ...
. Report of the Meeting of Experts on Potential Climatic Effects of Ozone and Other Minor Trace Gases.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.