Is there a nexus with global climate change? - Extreme Weather

UN Chronicle,  Dec, 2002  by Rajendra K. Pachauri

• E-mail
• Print
• Link

Several extreme weather events have taken place recently in different parts of the world which have sparked interest in the subject of climate change in general. Questions have been asked in the media and by policy makers in several countries on the extent to which these events are related to the problem of global climate change. Clearly, a categorical statement cannot be made on the linkage between the two, but even by association it appears that the extent of increase in these extreme events has something to do with the process of global climate change, which has also been highlighted in the work of the Intergovernmental Panel on Climate Change (IPCC).

The changes that have taken place in global temperatures and precipitation levels in recent years appear to indicate trends that generate some degree of concern, and have even led to alarm in many parts of the world. The World Meteorological Organization has assessed that in the last ten years the number of extreme events has actually doubled. It is also significant that the 1990s have been the hottest decade worldwide since temperature data have been recorded. The year 1998, in fact, is known to have been the hottest during this entire period of formally recorded temperatures.

The Third Assessment Report explores the influence of increasing atmospheric concentration of greenhouse gases and aerosols on climate, and arrives at projections of human-induced change in climate regionally, as well as globally. It covers issues related to the frequency and magnitude of climate fluctuations, including daily, seasonal, inter-annual and decadal variability. It also explores the duration, location, frequency and intensity of extreme events. The Assessment highlights higher maximum temperatures, more hot days and heat waves over nearly all land areas as very likely outcomes. Similarly, higher minimum temperatures, fewer cold days, frost days and cold waves are very likely over nearly all land areas.

It was also concluded in the Assessment Report that there would be more intense precipitation events over many areas, which would lead to increased floods, landslides, avalanches and mud-slide damage, as well as increased soil erosion. This problem would be particularly serious in those areas that have mountain slopes characterized by prolonged deforestation, such as parts of the Himalayan range. Economically, these would have important implications for the cost of insurance if provided by the private sector, and much higher government expenditure if covered by the public exchequer.

For Asia, the Assessment indicates increased summer monsoon precipitation variability, increasing the magnitude of floods and droughts, some of which we are perhaps already witnessing today. It is also projected that precipitation in areas that get significant quantities of snow may actually undergo a change in mix, with a larger share of rainfall and smaller quantities of snow. The result would be substantially higher flows during winter, but much lower levels in post-winter when the snow melts and flows into river streams and other water bodies.

An important observation in the IPCC Report is that the climate system involves many processes that interact in complex non-linear ways, which can give rise to potentially abrupt changes if the system were perturbed sufficiently. There is no doubt that a large degree of uncertainty exists about the mechanisms involved in phenomena, like a collapse of the thermohaline circulation and disintegration of the Antarctic and Greenland icesheets. ["Thermohaline circulation", or global ocean circulation, is driven by differences in the density of the sea water, which is controlled by temperature (thermal) and salinity (haline).]

An equally serious problem relates to the rapid melting of non-polar ice stocks. Glaciers around the world have been observed to be receding at a rapid rate, which would have serious implications for the local ecology, as well as on the flow of water that has been fed by these glaciers at a reasonably steady level over hundreds of years. Climate change would exaggerate other existing environmental circumstances, which could lead to a rapid breakdown of the ecosystems, including the drying of the Tundra, boreal and tropical forests, and susceptibility to a higher incidence of fires. It is pertinent to note that in the past few years, there were some very serious forest fires in different parts of the world, ranging from Australia and Indonesia to the western region of North America.

On all these subjects, there is no doubt a need for much greater research, not only on the nature of changes that are currently under way but also on the underlying factors which bring them about and the interrelationships between different sets of variables that affect the climate system in different parts of the world and create the likelihood of the occurrence of extreme events. It is expected that the research being undertaken on various aspects of climate change will advance adequately to make it possible for the fourth Assessment Report of the IPCC and its subsequent outputs to come up with more precise estimation of these phenomena and the likelihood of their occurrence.