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Reconciling Observations of Global Temperature Change (2000)

Chapter: 4 Recommendations

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Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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4—
Recommendations

In order to monitor global climate change on a decade-to-decade basis in support of national and foreign policy decisions, it will be necessary to better quantify and to substantially reduce the measurement errors inherent in estimates of global-mean temperature, as well as to develop an improved understanding of the processes that contribute to short term variability of global-mean temperature. To achieve these goals, the panel recommends the following actions:

(1) The nations of the world should implement a substantially improved temperature monitoring systems10 that ensures the continuity and quality of critically important data sets. Needed measurements include not only the conventional climatic variables (temperature and precipitation), but also the time-varying, three-dimensional spatial fields of ozone, water vapor, clouds, and aerosols, all of which have the potential to cause surface and lower to mid-tropospheric temperatures to change relative to one another. Management of climate data sets also needs additional attention and support. Raw and processed measurements and follow-on products need to be accessible in a form that enables a number of different research groups to replicate the processing of the more widely disseminated datacontinue

10 The NRC report Adequacy of Climate Observing Systems (NRC, 1999) describes characteristics that should be incorporated into the design of climate monitoring systems to facilitate the detection of climate change.

Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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sets and to develop new and improved temperature algorithms. To ensure such access, the ongoing documentation of instrumentation and observing practices, the archiving of data sets, and the provision of raw and processed data sets in electronic form to the scientific community should be regarded as integral parts of the climate monitoring effort and afforded high priority in terms of funding.

(2) The scientific community should perform a more comprehensive analysis of the uncertainties inherent in the surface, radiosonde, and satellite data sets. Such an assessment should involve a detailed analysis of the sensitivity of global-mean temperatures derived from these three different measurement systems to the various choices made in the processing of the raw data—e.g., corrections for instrument changes, adjustments for orbital decay effects in the satellite measurements, and procedures for interpolating station data onto grids. Such studies should also address the comparison of data sets with different sampling characteristics.

(3) Natural as well as human-induced changes should be taken into account in climate model simulations of atmospheric temperature variability on the decade-to-decade time scale. In particular, the studies described in Finding #4 need to be repeated with improved models and with an experimental design that reflects the uncertainties in natural and human-induced forcings.

(4) The scientific community should explore the possibility of exploiting the sophisticated protocols that are now routinely used to ensure the quality control and consistency of the data ingested into operational numerical weather prediction models, to improve the reliability of the data sets used to monitor global climate change.break

Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
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Page 24
Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
×
Page 25
Suggested Citation:"4 Recommendations." National Research Council. 2000. Reconciling Observations of Global Temperature Change. Washington, DC: The National Academies Press. doi: 10.17226/9755.
×
Page 26
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An overall increase in global-mean atmospheric temperatures is predicted to occur in response to human-induced increases in atmospheric concentrations of heat-trapping ''greenhouse gases." The most prominent of these gases, carbon dioxide, has increased in concentration by over 30% during the past 200 years, and is expected to continue to increase well into the future. Other changes in atmospheric composition complicate the picture. In particular, increases in the number of small particles (called aerosols) in the atmosphere regionally offset and mask the greenhouse effect, and stratospheric ozone depletion contributes to cooling of the upper troposphere and stratosphere.

Many in the scientific community believe that a distinctive greenhouse-warming signature is evident in surface temperature data for the past few decades. Some, however, are puzzled by the fact that satellite temperature measurements indicate little, if any, warming of the lower to mid-troposphere (the layer extending from the surface up to about 8 km) since such satellite observations first became operational in 1979. The satellite measurements appear to be substantiated by independent trend estimates for this period based on radiosonde data. Some have interpreted this apparent discrepancy between surface and upper air observations as casting doubt on the overall reliability of the surface temperature record, whereas others have concluded that the satellite data (or the algorithms that are being used to convert them into temperatures) must be erroneous. It is also conceivable that temperatures at the earth's surface and aloft have not tracked each other perfectly because they have responded differently to natural and/or human-induced climate forcing during this particular 20-year period. Whether these differing temperature trends can be reconciled has implications for assessing:

  • how much the earth has warmed during the past few decades,
  • whether observed changes are in accord with the predicted response to the buildup of greenhouse gases in the atmosphere based on model simulations, and
  • whether the existing atmospheric observing system is adequate for the purposes of monitoring global-mean temperature.

This report reassesses the apparent differences between the temperature changes recorded by satellites and the surface thermometer network on the basis of the latest available information. It also offers an informed opinion as to how the different temperature records should be interpreted, and recommends actions designed to reduce the remaining uncertainties in these measurements.

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