On this auspicious occasion, celebrating the 50th anniversary of the World Meteorological Organization (WMO), I am pleased to address you on the important subject of climate change, which concerns every one of us. Concern about climate change and climate variability has created new demands for scientific, economic and social information. It is a question that I believe is of considerable interest to the future of humankind. In this regard, the media has a crucial role to play in informing and raising awareness among the public and decision makers. I would therefore like to share with you today some of the latest scientific insights on the subject by addressing the following questions:

• What do we mean by climate change?

• How has climate been changing?

• Will the climate change in the future?

• Should we be concerned about possible future climate change and, if so, what can we do about it?

• How have WMO and the national Meteorological and Hydrological Services (NMHSs) been addressing the climate change issue?

2. WHAT DO WE MEAN BY CLIMATE CHANGE?

To start with, we need to understand what climate is and what controls it. If you were planning a trip weeks or months in advance to some part of the world that you are not familiar with, you would probably want to know what type of weather to expect. Alternatively, it would be helpful to know about the climate of the place for the time of year. In a very simplistic way, climate can be considered average weather conditions, including seasonal to interannual extremes and variations, locally, regionally or across the globe. At any one location, weather can change very rapidly from day to day while climate is more stable. In other words: "climate is what you expect, weather is what you get".

The climate of any particular place is determined by the global climate system that includes the atmosphere, the hydrosphere (liquid water), the cryosphere (ice and snow), the lithosphere (rock and soil) and the biosphere (plant and animals, including humans), as shown in Figure 1. The complex interactions among these components of the climate system under the effects of solar radiation, the rotation and the orbital motion of the Earth around the Sun determine its climate. The axis of rotation of the Earth is inclined at an angle of about 66.5 degrees to its orbital plane, and the angles of inclination of the parallel rays from the Sun falling on Earth are highest in the equatorial region and decrease polewards (Figure 2). The Earth itself radiates energy back to space. The energy so radiated is approximately the same in all latitudes. As such, the equatorial region has net supplies of radiational surplus while the polar cap has a net radiational deficit (Figure 3). This makes the equatorial region to be on average warmer than the polar region. As the surplus energy cannot continue to accumulate, this necessitates air and ocean water to move. In view of the rotation of the Earth, synoptic systems are developed to play the important role of maintaining the balance requirements of the general circulation of the atmosphere. The presence of some greenhouse gases (GHGs) in the atmosphere, such as carbon dioxide and water vapour, ensures that the mean global temperature of the Earth is about 15°C. If there were no GHGs, the temperature would have been 30°C cooler.

The movement of the Earth around the Sun once every year results in having the seasons (Figure 4). Fundamentally, the long-term energy balance between the Earth’s surface and its atmosphere controls climate. Any process that can alter the balance can affect the climate of the place. From a climatological point of view, the term climate change refers to a change in the long-term meteorological statistics, that is, a change from one climate mode to another climate mode, which is outside the normal range of natural climate variability, whatever the cause may be.

3. HOW HAS THE CLIMATE BEEN CHANGING?

Evidence from paleo-climatological records (Figure 5) have shown that:

(a) Glacial-interglacial cycles of periods such as those of about 21000, 40000 and 100000 years recurred, associated with alterations of the Earth’s orbital parameters (Milankovitch hypothesis), when climate was mostly cooler than at present, with global mean surface temperature variations of 4 to 5°C through these ice age cycles;

(b) The period since the end of the last glaciation (about 10500 years ago) has been characterized by smaller changes in global average temperature with a range of probably about 2°C;

(c) Large regional changes in hydrological conditions had occurred, particularly in the tropics, e.g. wetter conditions occurred in the Sahara from 12000 to 4000 years before present; north-west India was particularly humid by today’s standards with frequent floods in the period 8000 to 2500 before present;

(d) The late tenth to early thirteenth centuries (950–1250 AD) had been exceptionally warm in western Europe, Iceland and Greenland — a period that is known in Europe as the "Medieval Climatic Optimum"; and

(e) During the last 1000 years there has been occurrences of periods which were cooler and warmer than the normal periods. The most recent cooler period, the "Little Ice Age" from the sixteenth to nineteenth centuries, has witnessed marked advances of glaciers in almost all alpine regions. They were much more extensive 100–200 years ago than now. Since around 1850, most glaciers have been retreating rapidly (Obasi, 1996, 1998 and 1999a). Furthermore, there has been an unprecedented increase in the mean global temperature during the 20th century.

Since the beginning of the industrial era, significant increase has been observed in the atmospheric concentration of greenhouse gases (GHGs), especially due to enhanced pollution through increased use of fossil fuel such as coal, oil, and gas (Figure 6). Today, carbon dioxide (CO2) has increased by 31 per cent and is at present 367 parts per million by volume since pre-industrial times. Similarly, the others such as methane (CH4) and nitrous oxide (NO2) have increased by about 145 and 15 per cent, respectively. Atmospheric pollution has also led to serious depletion of the ozone layer. Greenhouse gases, such as carbon dioxide and water vapour, trap some heat in the lower part of the atmosphere. This is called natural greenhouse effect, which has operated in the Earth’s atmosphere for millions of years. The emerging threat of climate change is based on a human-induced enhanced greenhouse effect caused by increases in the atmospheric concentrations of the GHGs. Coincidentally, pronounced global warming has occurred during a period (Figure 7) when carbon dioxide emissions from the burning of fossil fuels have injected into the atmosphere a total of about 180 billion tonnes since 1860s (Obasi, 1991). The 1995 scientific assessment by WMO/UNEP IPCC (IPCC, 1995a) based on the available instrumental observational records spanning through the period since the industrial era has shown that:

(a) The global mean temperature has increased by between 0.3–0.6°C since the 19th century, with a corresponding global mean sea-level rise of between 10 and 25 cm;

(b) Night-time minimum temperatures over land have generally increased more than daytime temperatures;

(c) Recent years have been among the warmest since 1860, despite the cooling effect of the 1991 Mt Pinatubo volcanic eruption; and

(d) Some regional changes are also evident, for example in precipitation distribution over land in high latitudes of the northern hemisphere especially during the cold season.

The IPCC observed that the global mean warming trend is unlikely to be entirely natural and concluded that "the balance of evidence suggests a discernible human influence on global climate" (IPCC, 1995a). Recent data show that record warming has been broken many times since the early 1990s, with 1998 currently standing as the warmest year since the 1860s, the oldest period with credible instrumental records (Obasi 1999b). Even with the cold La Niña condition that dominated the year 1999, it was still the fifth warmest year in the 20th century. Recent records show that a number of unprecedented extremes have also occurred over the recent past. For instance, the El Niño phenomenon (warm El Niño/Southern Oscillation (ENSO) phase) has been more frequent than La Niña (cold ENSO phase) since the early 1970s. This may have resulted in changes in the frequency and intensity of floods, droughts, cyclone activities, and other extreme climate events in some regions where El Niño signals are strong (Obasi, 1999a). The extreme weather- and climate-related events have resulted in extensive economic damages and human suffering that have led to growing concern in recent years as to whether the frequency and distribution of extreme weather events around the world are changing (Figure 8). Other most recent examples include the 1997 tsunami that swept over coastal regions of Papua New Guinea; the 1998 Hurricane Mitch that affected Central America; and the recent floods in Mozambique and Southern Africa.

4. WILL THE CLIMATE CHANGE IN THE FUTURE?

A straightforward answer to this question is given in the IPCC 1995 assessment that stated explicitly that: "Climate is expected to continue to change in the future". IPCC projections of future climate changes are based on the output of general circulation model (GCM) simulations driven by future projections of socio-economic trends including population and economic growth, technological changes, energy demand, fuel mix, etc. The ability of the GCMs to simulate anthropogenic influence must therefore be assessed first. Figure 9 further shows that the observed global surface temperature anomaly over the recent past is well above the natural variability derived from models where anthropogenic climate forcing is not included (Obasi, 1991). Figure 10 gives the simulated and observed temperature and precipitation patterns, while Figure 11 shows successful prediction of the effect of the Mt Pinatubo volcanic eruption by the GCMs. The figures show that apart from local and regional details, the large-scale patterns are well represented by the GCMs. IPCC projections (Figure 12) based on six alternative socio-economic assumptions (IPCC, 1995a) have shown that:

(a) The mean global temperatures would rise by between 1 to 3.5°C, although the most likely value is about 2°C by the end of this century (Figure 13);

(b) The corresponding rise in sea-level will be within the range of 15 to 95 cm, with the "best estimate" of about 50 cm (Figures 14);

(c) Energy generation and uses and volcanic eruptions are also releasing aerosols such as sulphate aerosols that have a cooling effect on radiative balance; and

(d) Regional temperature changes could differ substantially from the global mean value.

5. SHOULD WE BE CONCERNED ABOUT POSSIBLE FUTURE CLIMATE CHANGE?

If climate should change as predicted by the general circulation models, the average rate of warming would probably be
greater than any observed in the last 10000 years. This will have far-reaching physical, environmental, biological and socio-economic implications, including the potential threat of serious socio-economic disruption (Obasi, 1992, 1996, 1999b). The IPCC (1995b) noted that the potential impacts include:

(a) The natural ecosystems such as forests, pastures, deserts, mountain regions, lakes, streams and wetlands, coastal systems and oceans may have difficulties in adapting, where it is possible to lose some of the flora and fauna. This accounts for the current United Nations Convention on Biodiversity;

(b) Sea-level rise: Global warming will cause mass expansion of sea water, melting of glaciers and rise in sea level with possible impacts on the populations living in the low lying coastal areas and small islands; on agriculture; on wetlands; on freshwater resources and other life supporting systems, infrastructure including harbours; and on economic activities. About half of the global population lives in coastal zones and it is estimated that, every year, about 46 million people are at risk of flooding from storm surges. Sea-level rise and any increase in storm-surge will exacerbate these problems (Figure 15);

(c) Regional crop distribution: This could vary quite considerably although the overall global crop production is unlikely to be affected. Some countries are likely to experience a decrease in crop yields, while others could expect an increase;

(d) Human health: The impact on human health can be both direct and/or indirect including an increase in the transmission of diseases, such as malaria, dengue and yellow fever (see table);

(e) Natural disasters: Small changes in the mean climate can produce relatively large changes in the frequency and/or intensity of extreme weather events and therefore in the number of some natural disasters;

(f) The global hydrological cycle: Warmer temperatures would make the hydrological cycle more vigorous, with the likely result that there could be more severe droughts in some places and floods in other places. This would also most likely have major impacts on regional freshwater resources. At the same time, the risk of desertification will increase as the environment becomes drier and the soil becomes further degraded through erosion, compaction and human activities.

For these reasons, accurate local and regional climate change scenarios are required by policy and decision makers. Strategies for continuous assessment and realistic projections of future socio-economic trends, as well as the associated GHG emissions require joint multidisciplinary research that addresses all climate change processes, including improvement of climate change models and availability of realistic local- and regional-scale climate change scenarios. This is one of the major research priority areas of WMO and other cosponsors of the World Climate Research Programme (WCRP) and the Global Climate Observing System (GCOS).

6. WHAT CAN WE DO ABOUT CLIMATE CHANGE?

As highlighted by the United Nations Conference on Environment and Development (UNCED) that was held in Rio de Janeiro (Brazil) in 1992, protection of the atmosphere is a broad and multi-dimensional endeavour involving various sectors of economic activity. Humankind must meet its future energy, food and water needs without seriously affecting climate. Thus, humankind must develop strategies that can satisfy current and future energy and food demands without continuously increasing the accumulation of GHGs in the atmosphere. Such strategies could include, among others:

(a) The promotion of social and economic practices that would not harm the environment further. The implementation of the international agreements designed to minimize or reverse the trends in climate, such as the United Nations Framework Convention on Climate Change (UN/FCCC) and its Kyoto Protocol, the United Nations Convention on Biodiversity (UNCB), the United Nations Convention to Combat Desertification (UNCCD), and the Convention for the Protection of the Ozone Layer. In particular, the Kyoto Protocol requires the developed countries (Annex I countries) to reduce their overall emissions of six major GHGs by at least 5 per cent below the 1990 level between the years 2008 and 2012;

(b) Strategies for the development, applications and transfer of efficient and environment-friendly (clean) technologies, including enhanced use of clean renewable energy resources such as wind, solar and hydropower that would minimize GHG emissions;

(c) Strategies for addressing sustainable food production and minimization of pollution of freshwater resources by agricultural activities and for the preservation of forests that are vital sinks for CO2. As the world population is projected to increase from its present 6 billion to 8 billion by 2025 and 10 billion by 2050, arable land available for agriculture and food production will be under enormous pressure;

(d) The need for improvement in the collection, distribution and application of information related to energy resources, and greater awareness and understanding by the general public and the policy makers regarding the potential hazards of climate change and the need for remedial actions. In this regard, the media has a crucial role to play; and

(e) The need to monitor, understand, detect, predict and attribute better the complex and closely related climate change processes.

7. How are WMO and the associated NMHSs addressing the climate change issue?

The history of internationally-coordinated efforts on climate issues including climate change dates back to the latter part of the last century and involved the predecessor of WMO, the International Meteorological Organization (IMO) which was created in 1873. As a specialized agency of the United Nations, WMO coordinates worldwide cooperation in meteorology, hydrology and the related sciences that has provided credible scientific information on climate, its variability and change. In fact, WMO issued the first major international statement on climate change in 1976 and further convened the first and second World Climate Conferences in 1979 and 1990, respectively. WMO also established a World Climate Programme (WCP) in 1979. Together with the United Nations Environment Programme (UNEP), WMO established the IPCC in 1988 for regular assessment of the science; impacts, adaptation, and mitigation; and economic and social dimensions of climate change.

A major endeavour of WMO is devoted to enhanced monitoring and research for improved understanding of all components of the global climate system in order to narrow down the uncertainties in climate prediction. Other efforts include applications of climate information and services in support of sustainable development as well as WMO’s Global Atmosphere Watch (GAW), which monitors the accumulation of the GHGs in the atmosphere. Currently GAW has about 350 stations worldwide and regularly provides information on greenhouse gases, ozone and the pollutants. In addition, WMO, in collaboration with other partners, has established the Global Climate Observing System (GCOS) and supports the Global Ocean Observing System (GOOS), the World Hydrological Cycle Observing System (WHYCOS) and the Global Terrestrial Observing System (GTOS) (Figures 16–19). WMO has continued to provide standards and practices that are vital for meteorological and hydrological measurements and climate change studies and impact assessments. Scientific and technical support are being provided to the IPCC and the Subsidiary Body for Scientific and Technological Advice (SBSTA) of the UN/FCCC. Projects are also under way on climate change detection and attribution.

WMO will further continue to promote international co-operation on research on climate system within the World Climate Research Programme (WCRP). WMO has programmes in capacity building and transfer of appropriate technology to support the efforts of developing countries in acquiring modern and environment-friendly technology, and to address relevant national climate challenges, including monitoring and prediction of extreme meteorological and hydrological events such as tropical cyclones, tornadoes, floods, and droughts (Figure 20). WMO has established a Climate Information and Prediction Services (CLIPS) for enhanced application of climate information and prediction services.

8. Conclusion

What has been presented clearly shows that climate change is a science, not a fiction. Concern about climate change has created new demands for scientific information that would help reduce the remaining uncertainties and provide accurate information on many critical scientific and technical questions that may help assist policy makers in formulating realistic sustainable development plans and take appropriate policy decisions. WMO maintains its strong support to the IPCC and the implementation of the UN/FCCC. We would have to continue to support and enhance international activities in climate variability and change including monitoring, application, research and prediction and provide credible and scientific information that are vital for the protection of the Earth’s climate, and support sustainable development aspirations of humankind. The media has a vital role to play in creating awareness and understanding by the general public and policy makers regarding the negative consequences of climate change and the needed remedial actions.

9. REFERENCES

Haltiner,G. J. and Martin G. L. 1957: Dynamic and Physical Meteorology. McGraw-Hill Book Company.

IPCC, 1995a: Climate Change 1995 — The Science of Climate Change. Second Assessment Report. J. T. Houghton, L. G. Meira Filho, B. A. Callander, N. Harris, A. Kattenberg and K. Maskell (eds.), Cambridge University Press, Cambridge, United Kingdom, 572 pp.

IPCC 1995b: Climate Change 1995 — Impacts, Adaptation and Mitigation of Climate Change: Scientific–Technical Analyses. Second Assessment Report. R. T. Watson, M. C. Zinyowera, R. H. Moss, D. J. Dokken (eds.), Cambridge University Press, Cambridge, United Kingdom.

Obasi, G. O. P., 1991: Global climate change: African perspectives. A Change in Weather. Acts Press, pp. 13–19.

Obasi, G. O. P., 1992: Rising challenge of the sea. Statement at the International Workshop on the Rising Challenge of the Sea, 9–13 March 1992, Margarita Island, Venezuela.

Obasi, G. O. P., 1996: Climate change focus on policy decisions in the next several decades. Lecture Presented at the Forty-first IMO Prize-giving Ceremony, Florida States University, Tallahassee, 4 March 1996, WMO SG/7.

Obasi, G. O. P., 1998: Climate variability and change: consequences for human activities. Lecture Presented at the Tenth Annual Bahrain Science Day, University of Bahrain, 21 May 1999, WMO SG/57.

Obasi, G. O. P., 1999a: Protecting the atmosphere: achievements and challenges. Environment 2000 and Beyond, Ahmad K. Hegazy (ed.), pp. 137–162.

Obasi, G. O. P., 1999b: Climate change: a challenge to humanity. Lecture Presented at the Seminar on Climate Change in the Arab Region. Thirteenth Session of the League of Arab States, 13 March 1999, Damascus, Syria, WMO SG/92.