Narrowing the uncertainty

A key question constantly asked by policymakers is: 'How long will it be before scientists are more certain about the projections of likely climate change, in particular concerning the regional and local detail?' They were asking that question 20 years ago and then I generally replied that in 10 to 15 years we would know a lot more. As we have already seen, there is now more confidence that anthropogenic climate change has been detected and more confidence too in climate change projections than was the case a decade ago. However, some of the key uncertainties remain and their reduction is urgently needed. Not surprisingly, policymakers are still asking for more certainty. What can be done to provide it?

For the basic science of change, the main tools of progress are observations and models. Both need further development and expansion. Observations are required to detect climate change in all its aspects as it occurs and also to validate models. That means that regular, accurate and consistent monitoring of the most important climate parameters is required with good coverage in both space and time. Monitoring may not sound very exciting work, often even less exciting is the rigorous quality control that goes with it, but it is absolutely essential if climate changes are to be observed and understood. Because of this, a major international programme, the Global Climate Observing System (GCOS) has been set up to orchestrate and oversee the provision of observations on a global basis. Models are needed to integrate all the scientific processes that are involved in climate change (most of which are non-linear, which means they cannot be added together in any simple manner) so that they can assist in the

Space observations of the climate system

For forecasting the weather round the world - for airlines, for shipping, for many other applications and for the public - meteorologists rely extensively on observations from satellites. Under international agreements, five geostationary satellites are spaced around the equator for weather observation; moving pictures from them have become familiar to us on our television screens. Information from polar orbiting satellites is also available to the weather services of the world to provide input into computer models of the weather and to assist in forecasting (see for instance Figure 5.4).

Figure 9.2 The ENVISAT Earth Observation Satellite of the European Space Agency launched in 2002. Instruments included in its payload are: the Advanced Along-Track Scanning Radiometer (AATSR), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the MEdium Resolution Imaging Spectrometer (MERIS), the SCanning Image Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY), the MicroWave Radiometer (MWR), the Global Ozone Monitoring by Observation of Stars (GOMOS), the Radar Altimeter - second generation (RA-2), the Advanced Synthetic Aperture Radar (ASAR), and other instruments for communication and exact tracking. DORIS stands for Doppler Orbitography and Radiopositioning Integrated by Satellite. In its 800-km Sun-synchronous orbit with the solar array deployed, it measures 26 m x 10 m x 5 m and weighs 8.1 tonnes.

Figure 9.2 The ENVISAT Earth Observation Satellite of the European Space Agency launched in 2002. Instruments included in its payload are: the Advanced Along-Track Scanning Radiometer (AATSR), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the MEdium Resolution Imaging Spectrometer (MERIS), the SCanning Image Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY), the MicroWave Radiometer (MWR), the Global Ozone Monitoring by Observation of Stars (GOMOS), the Radar Altimeter - second generation (RA-2), the Advanced Synthetic Aperture Radar (ASAR), and other instruments for communication and exact tracking. DORIS stands for Doppler Orbitography and Radiopositioning Integrated by Satellite. In its 800-km Sun-synchronous orbit with the solar array deployed, it measures 26 m x 10 m x 5 m and weighs 8.1 tonnes.

These weather observations provide a basic input to climate models. But for climate prediction and research, comprehensive observations from other components of the climate system, the oceans, ice and land surface are required. ENVISAT, a satellite launched by the European Space Agency in 2002, is one example of the most recent generation of large satellites in which the latest techniques are directed to observing the Earth (Figure 9.2). The instruments are directed at the measurement of atmospheric temperature and composition including aerosols (MIPAS, SCIAMACHY and GOMOS), sea surface temperature and topography, the latter for ocean current information (AATSR and RA-2), information about ocean biology and land surface vegetation (MERIS) and sea-ice coverage and ice-sheet topography (ASAR and RA-2).

analysis of observations and provide a method of projecting climate change into the future.

Take, for instance, the example of cloud-radiation feedback that remains the source of greatest single uncertainty associated with climate sensitivity.9 It was mentioned in Chapter 5 that progress with understanding this feedback will be made by formulating better descriptions of cloud processes for incorporation into models and also by comparing model output, especially of radiation quantities, with observations especially those made by satellites. To be really useful such measurements need to be made with extremely high accuracy - to within the order of 0.1% in the average radiation quantities - that is proving highly demanding. Associated with the better measurements of clouds is the need for all aspects of the hydrological (water) cycle to be better observed.

There is also inadequate monitoring at present of the major oceans of the world, which cover a large fraction of the Earth's surface. However, this is beginning to be remedied with the introduction of new methods of observing the ocean surface from space vehicles (see box) and new means of observing the interior of the ocean. But not only are better physical measurements required: to be able to predict the detailed increases of greenhouse gases in the atmosphere, the problems of the carbon cycle must be unravelled; for this, much more comprehensive measurements of the biosphere in the ocean as well as that on land are needed.

Stimulated by internationally organised observing programmes such as the GCOS, space agencies around the world have been very active in the development of new instruments and the deployment of advanced space platforms that are beginning to provide many new observations relevant to the problems of climate change (see box).

Alongside the increased understanding and more accurate predictions of climate change coming from the community of natural scientists, much more effort is now going into studies of human behaviour and activities, how they will influence climate through changes in emissions of greenhouse gases and how they in turn might be affected by different degrees of climate change. Much better quantification of the impacts of climate change will result from these studies. Economists and other social scientists are pursuing detailed work on possible response strategies and the economic and political measures that will be necessary to achieve them. It is also becoming increasingly realised that there is an urgent need to interconnect more strongly research in the natural sciences with that in the social sciences. The integrated framework presented in Chapter 1 (Figure 1.5) illustrates the scope of interactions and of required integration between all the intellectual disciplines involved.

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