The global status of the atmosphere, apart from being variable has been found to be maintaining a dangerous trend of warming due to the accumulation, at the top of the atmosphere, of Green House Gases (GHGs). Also is known that some of these gases are reacting with the umbrella-like protective ozone layer and destroying it. The end result is an increased exposure and vulnerability to the dangerous UV-B radiation from the sun through this thinner -than-before layer and an increasing temperature at ground level. Some countries near the ozone hole are experiencing a higher incidence of catarac and skin cancer. With WMO in the lead, several other UN Organisations, such as UNEP, WHO, FAO, UNESCO are conducting sector-wise monitoring of the different elements of the atmosphere, of the human, animal and plant habitat and of ecological factors falling under their respective jurisdiction.

While some have had a tendency to believe that global warming would benefit certain areas of the globe, especially of the cold regions, by the release of more land for crop cultivation and for longer portion of the year than actually is the case, the present assumption is more pessimistic. At least the situation in the advent of warming would become worse before becoming better, if ever. This is reflected by the fact that several buildings put up decades ago in the "permafrost" with then available climate data collapsed when the annual temperatures stayed above normal for several consecutive years in the nineties. Health and crop yields are other valid concerns.

In the tropics, although the magnitude of warming is estimated to be of a much lesser magnitude, it is believed that living conditions will be greatly affected. The adaptation period throughout the globe may not be long enough to permit the present lifestyle. The foundation of society itself would be disturbed by the need for devoting resources to mitigate the effects and cater for adaptation. Most countries would fail in this as even at the present they are still struggling to afford the essentials amenities.

But in all assumptions and predictions, there is always the element of uncertainty. Those who cannot afford to devise and implement adaptation and mitigation policies and measures prefer to waive off the theory of global warming and therefore carry on a business-as-usual life. This is by far the easier option in the short term. To disapprove such a belief, and even more, to prove that global warming is in fact taking place the need for systematic observation of climatic parameters become the essential tool.

The rationale behind all systems be they economic, social or physical is that they be practical and rewarding. In as far as climate data is concerned the rationality of the observing system should and is driven by the following:

1 Goals (utilisation) to be clearly defined,
2 Most efficient ways of observation,
3 Best means of storage,
4 Minimum duration of observation period for different usages,
5 Category of users, and
6 Products to be derived.

The answer to the above may seem obvious but they are certainly not, in all the cases, the same as they were 50 years or so ago when the primary aim was to produce weather forecasts for the day. At present more stress is laid on monitoring through systematic observation. The discovery and threat of global warming imposed on scientist the search for exact and reliable data besides the usual need for deriving correct mathematical conclusions, and therefore of long series of data from which reliable conclusions could be drawn.

The means of observation have seen tremendous changes in the past few decades. As we all know the traditional land-based observation is greatly supplemented by spaced-based observations. Manual observation on land are gradually yielding to automatic ones. Whereas in the old days manufacturers were only a handful, therefore allowing for better standardisation, at present electronic revolution has enabled the mass production of certain equipment. Despite all mechanisms in place (Regional Calibration Centers, Roving Training seminars etc.) not all thermometers, for example function in identical ways. This inaccuracy is even more blatant in upper air equipments. Automatic sensors show the same disparity and deficiency in accuracy.

The WMO Commission for Climatology at almost all of its session been pondering on the issue of station siting, accuracy of equipments, consistency in data collection, quality control and homogeneity both in space and time. Thus, in order that observations are conducted in a standardised manner, it recommended at its 9th Session in 1985 the setting up of Climate Reference Stations. These should have been kept in top conditions with standard sensors. The idea was to collect from these stations comparable data for the purpose of monitoring of the climate.

The present state of the observation network does not look equally bright among all WMO Members. In some places, due to financial constraints and other more pressing priorities, climate matters are tagged low priority. This problem is being addressed in several forums.

The siting of observation plots is very important. The WMO Guide to Climatological Practices (WMO No. 100) provide extensive guidelines for siting observation plots for best results. But not all circumstances can be predicted. For example, with present rate of urbanisation and change in land-use and planning, numerous observation plots are no longer conveying the same message. One concrete example cited is the case of data collection in a highly urbanised area. Several questions need to be asked when installing sensors in such areas:

a) What is the most representative site of the area?
b) What is the optimum and practical interval between sensors?
c) What type of sensors are most suitable for these particular areas?

In fact, due to microclimates created by humans, vehicular traffic, mechanical activities, exhaust from air conditioners and possibly industries in the vicinity, the exteremely rough surface (due to buildings of varying shapes and heights, towers) and materials of different reflectivity, no one can with certainty determine the exact number of sensors necessary to represent an urban area.

One of the objectives of WMO is to "provide an international mechanism and framework for cooperative efforts to obtain data and provide services".
This is achieved by the:

- Establishment of networks of observing stations for the making of meteorological, hydrological and other geophysical observations,
- Development and maintenance of systems for processing and rapid exchange of data,
- Stadardisation of observation and processed products etc.

WMO has several programmes where the need for accurate and homogeneous data are essential. Some of these are:

1 The World Climate Application and Services Programme. Projects related to human comfort and health, to the establishment of climate change indices, seasonal forecasting and most important of all probably making annual assessment of the global climate are dealt with.

2 The World Weather Watch

3 The Hydrology and Water Resources Programme

4 The Agricultural Meteorology Programme

5 The Atmospheric Research and Environment Programme (AREP).

Other programmes with WMO commitment are GCOS, The World Climate Imapacts and Resources Programme (WCIRP), the IPCC and the ICSU-led Iternational Biosphere Geospheres Programme(IGBP).

Those data utilised in numerical models can be qualified as conventional data. These have defined ranges, understood since frequently utilised and relatively easily obtained. But there exists other types of data, the use of which have not been clearly defined in the different WMO and other Programmes. Some of them are:

1 Data related to the EL NINO La NINA phenomena

2 Coastal Zone parameters

3 Phenological Data

Although phenology may characterise climate, this vital information is observed in only some countries. There does not exist any system allowing for global exchange or sytematic storage.

As science progresses new possibilities in data collection unfold themselves. Thus a host of space-based data are obtained and others by remote sensing. They are:

1 Cloud amounts and water vapour.
2 Upper wind
3 Radiation Data
4 Enviromental Data etc.

Forums of this kind need to scrutinize these and other similar data and decide on ways and means of making them optimally usable. Another question, although seemingly negligible, that needs to be addressed is the quality control and homogenisation of data disseminated through the GTS. These data are only quality-controlled by those Members conducting research but it should be well understood that the data actually disseminated is not quality controlled.

The Second Seminar on the Homogenisation of Surface Climatological Data held in this very place made the following pertinent recommendations:

1) Homogenisation is important for building of reliable database but the development is slow.
2) Homegeneous series of data are essential for research, especially for investigation in climate change and variability.
3) For producing high quality time series efficient measures for testing the homogeneity should be applied.
4) However most homeogenisation methods have been developed for the analysis of temperature and precipitation. It is necessary to adopt the same principle for other elements as well.

The other serious problems encountered for conducting homogenisation of data are due to : inadequate training, lack of manpower, standard methods and means and the necessary hardware. Somehow this Seminar should recommend ways and means of tackling these problems too.

The paper intended to compare the results of different methods of precipitation measurements. Advantages as well as disadvantages of the various instruments were pointed out. For precipitation information with a high resolution in time the weighing gauge gives the most reliable information. The ombrometer on the south side of the Sonnblick Observatory provides good correlation results to the independent winter mass-balance measurements but the total amount of precipitation is underestimated. Totalisers give best results of monthly amounts, but the time resolution is insufficient.

Collection and quality control of data is not an end in itself. It needs to be followed by archiving that allows easy access for later use. For example the CLICOM Data Base Management System(DBMS) allowed the storage, quality control and manipulation of a large number of different elements. With time it has been found that better performing DBMSs are required and currently some WMO Members are working in the formulation of such DBMSs.

Some of the requirements of CDBMS as recommended by CCl Task Group on a Future WMO CDBMS are:

1) The aims of the proposed CDBMS should be clearly defined. These could be to:
- Put climate data into a usable form.
- Reduce storage space and convert data into more readily available format.
2) Be user friendly,
3) Have an efficient data entry process with standardised quality control procedures,
4) Cater for the processing of different types of climatic and related environmental data,
5) Allow for linkage with other systems such as the Internet or the GTS,
6) Make data and metadata easily accessible for national and international data exchange,
7) Be flexible and adaptable to national particularities,
8) Be designed to run on different hardware platforms,
9) Allow for evolutionary development and be easily upgradable,
10) Comply with WMO Guide to Climatological Practices.

For the above to be feasible, it is evident that users should be involved and consulted at all the stages of development fo such a CDBMS.

More and more the need for reliable data both in space and time becomes apparent for too much is at stake to rely on innacurate data. The very existence of our society is threatened. Therefore, it is important for all WMO Members to produce and make available homogeneous series of data and metadata.

Basher, R.E, 1999. Data Requirements for Developing adaptations to Climate Variability and Change.
Mitigation and Adaptation Strategies for Global Change 4: 227-237, 1999.
Koch, E. Phenology in Austria. Central Institute for Meteorology and Geodynamics, Austria.
WMO 1983: Guide to Climatological Practices. WMO-No.100
WMO 1986: Abridged Final Report of the Ninth Session of the Commission for Climatology. WMO- No.
WMO 1999: Proceedings of the Second Seminar for Homogenisation of Surface Climatological Data. WMO/TD-No.962
WMO 1999:Report of the meeting of the WMO Commission for Climatology Task Group on a Future WMO CDMS. WMO/TD-No.932