"Like a musical note, a datum of information is not a pure tone. It has harmonics of purpose, inherent noise, inaccuracies of tuning, and idiosyncrasies of performance. All data . . . are collected or estimated by someone with particular skills, certain questions in mind, a notion of an acceptable level of accuracy, a limited budget, and, sometimes, social, cultural, or political constraints."

World Resources Institute, World Resources 1990-91.

"The WRI conclusions are based on patently unfair mathematical jugglery, where politics are masquerading in the name of science."

Anil Agarwal, Director of the Centre for Science and Environment, New Delhi, commenting on the data on greenhouse gas emissions in World Resources 1990-91.

The major climate conferences which have helped to place global warming on the international political agenda have been unanimous that the industrialized world bears most of the responsibility for causing the problem. The delegates at the 1988 Toronto Conference on the Changing Atmosphere, for example, concluded that: "The countries of the industrially developed world are the main source of greenhouse gases and therefore bear the main responsibility to the world community for ensuring that measures are implemented to address the issues posed by climate change." Similarly, the Ministerial Declaration of the Second World Climate Conference held in Geneva in November 1990 stressed that "developed countries must take the lead. They must all commit themselves to actions to reduce their major contribution to the global net emissions". (emphasis added).

In World Resources 1990-91, the latest annual report of the influential Washington-based research group, the World Resources Institute, 146 different countries are ranked according to the contribution they supposedly make towards global warming (see Table 1).(1) According to the director of the WRl's Program in Resource and Environmental Information, Allen L. Hammond, the figures show that "Sources of greenhouse gases are distributed widely around the world, with both developed and developing countries sharing major responsibility for emissions".(2) Hammond repeats his point several times: "Three of the six countries that are the largest contributors to the atmosphere's warming potential&emdash;the United States, the USSR, Brazil, China, India, and Japan&emdash;have heavily industrialized economies; three do not"; "Global warming is truly a global phenomenon, in both cause and effect"; and "To one degree or another, virtually all elements of human societies are involved in creating the problem. All must play a role in bringing it under control." Indeed, WRI is so eager to show "widely shared responsibility" that in the introductory chapter to their report they define the European Community as one industrialized country so they can claim that of the "ten largest emitters" in 1987, "half are industrialized and half are developing countries."(3)

To those who have generally assumed the industrialized world's culpability, WRI's figures may come as a surprise. But WRI have an impeccable reputation within official circles as publishers of environmental data and their conclusions are thus taken seriously by the "policymakers, resource managers, scholars, teachers and students" at whom WRI's reports are aimed.(4) The OECD, for example, in their latest State of the Environment report, use WRI's data and methodology to compare the contributions the organization's member states make to global warming with those of the rest of the world.(5)

However, the "greenhouse index", which according to WRI shows the equal responsibility of developed and developing countries, is far from being an accepted way of presenting data on greenhouse gas emissions. The methodology used to interpret the emissions statistics has not been endorsed by the scientific community and, indeed, has been criticized by a number of climate researchers.(6) Anil Agarwal , an ex-member of WRl's Editorial Advisory Board, has co-authored a 36-page study which accuses the WRI report of being "entirely designed to blame developing countries for sharing the responsibility for global warming."(7)

The Numbers Game

The greenhouse index, which "facilitates comparison of national contributions to the warming potential of the atmosphere", was developed by Allen L. Hammond together with a colleague at the WRI, Eric Rodenburg, and William R. Moomaw, director of the Center for Environmental Management at Tufts University, Massachusetts. It combines into a single figure&emdash;the "index score" &emdash;a country's annual emissions of carbon dioxide, methane (CH4) and the two most common CFCs, CFC-11 and 12, with each gas weighted according to its supposed contribution to global warming. These four gases probably account for some 80-90 per cent of the current global warming potential of the atmosphere. In an article in the January/ February 1991 issue of the US journal Environment, Hammond, Rodenburg and Moomaw claim that:

"The method that gives rise to the index is straight-forward and readily applied by policy-makers. Thus, the greenhouse index is ideal for diplomatic (as opposed to scientific) purposes and could serve as the basis for international agreements."(8)

WRI criticize existing methods of comparing the contributions of different gases for containing "an arbitrary element that can lead to conflicting results depending on the perspective of the analyst or country that applies them."(9) This "arbitrary element" is chiefly the choice of time-span over which the contribution of a gas to global warming is estimated. A long time horizon favours countries whose greenhouse emissions consist disproportionately of short-lived gases such as methane; a short time horizon fails to take into account the future importance of long-lived gases such as CFCs (see Table 2). This time factor, while difficult to take account of, is of crucial importance in determining responsibility. WRI claim that they have managed to avoid choosing an arbitrary time horizon by using a method which gives the equivalent of an "instantaneous" measurement of a gas's contribution to global warming.(10)

The WRI index is based on two elements: first, an estimate of the proportion of the annual release of each greenhouse gas which remains in the atmosphere at the end of a given year and, second, a factor which measures the instantaneous effect of this amount of gas on the earth's energy balance. To estimate the first element, WRI use the "airborne fraction". This is calculated by dividing the annual increase in the mass of each greenhouse gas in the atmosphere by the global emissions of that gas due to human activities. The difference between these two figures for gases such as carbon dioxide and methane is due to the large proportion of emissions which are taken up by various "sinks". The main carbon sinks are the oceans, forests and soils. Methane is broken down in the atmosphere by chemical processes, chiefly by oxidation by the hydroxyl radical molecule (OH). For CFCs, which have no natural sinks, the amount of gas released is the same as its increase in the atmosphere and therefore its airborne fraction is one.

Multiplying the airborne fraction for CO2, for instance, by a country's estimated annual release of carbon gives, in WRI's terminology, its "net emission" of carbon for that year. This is equivalent to allocating each country a share in the sinks of carbon dioxide proportionate to the size of that country's gross emissions. The "net emissions" of methane and CFCs are worked out by the same method and the results multiplied by the "radiative forcing" of the gases (their effectiveness at trapping heat in the atmosphere) compared to that of CO2. The country's "index score" is the sum of the net emissions for carbon dioxide, methane and CFCs in carbon dioxide heating equivalents. The emissions data for CO2, methane and CFCs presented in Table I are therefore not the actual amounts of greenhouse gases added to the atmosphere by each country in 1987, but rather the supposed contribution which that country has made to the observed increase in the concentration of that gas in the atmosphere.

WRI's claim to have bypassed the "arbitrary element" inherent in existing methods of assessing global warming emission potentials is highly questionable. In assessing the relative contributions of greenhouse gases, assumptions about the period over which these contributions occur cannot be avoided because of, amongst other things, their very different lifetimes. In fact, the WRI method only differs from other more sophisticated techniques in the crudeness of its timescale assumptions. The lifetime considerations explicitly used in the models of other researchers are approximated by WRI by weighting each gas with the airborne fraction. The net result is that the WRI index is not an instantaneous measure at all but rather a crude measure of the cumulative effect of each year's release over the next 100 years or more.(11) To pretend that timescale assumptions are not present suggests at the least an incomplete understanding of the problem, if not a deliberate attempt to mislead (see notes to Table 2 for some of the technical background to the problem).

A Short-Term Index for a Long-Term Problem

If the index is to be used for comparing annual differences in a country's contribution to global warming, the weighting given to the different gases it includes should not show a large variation from year to year. Unfortunately, the airborne fraction. according to WRl's calculations, does vary greatly. Between 1987 and 1988,the airborne fraction used by WRl for CO increased from 0.44 to 0.71; that for methane increased from 0.17 to 0.26. These variations make it difficult to compare "net" emission data from different years and to calculate a country's actual "gross" emissions for any year when only the "net" figure is given. The reason the variations occur is that the annual rise in concentration, on which the calculation depends, is only weakly related to emissions occurring in that particular year. By neglecting the major determining factor, which is the past history of emissions, WRI seriously oversimplify the science. The use of the airborne fraction is only appropriate in determining the relationship between concentration changes and emissions over a long period of historic time, and even that relationship may not reflect accurately the future link between emissions and atmospheric concentrations.

Perhaps the most damning indictment of the unsuitability of the greenhouse index as the basis for any climate negotiations unwittingly comes from WRI itself in its response to criticisms of the use of the airborne fraction by Kirk Smith of the Environment and Policy Institute of the East West Center in Hawaii.(12) Smith gives an example of a scenario where methane emissions increase at a steady annual rate (at present they are accelerating). Because of the lifetime of methane in the atmosphere, global concentrations would rise by a greater amount each year, but the airborne fraction would fall for about 20 years. If methane emissions were to remain constant, the fraction would fall for about 60 years, while the atmospheric burden would continue to rise. Hammond and his colleagues respond that:

"The use of airborne fractions would break down in the extreme conditions that Smith hypothesizes, but these conditions bear little resemblance to the real world of the next decade or so" (emphasis added). (13)

In other words, WRI have conceived a statistical tool for use by policy-makers which may be irrelevant in little more than 10 years, while international agreements, if they are to be effective, will have to last for many decades. A similar claim is made in a letter to Nature from I.G. Enting of the Australian research body, CSIRO, and H. Rodhe of Stockholm University.(14) Hammond et al. counter Enting and Rodhe's letter with the assertion that "there is unfortunately virtually no likelihood of stabilizing&emdash;let alone reducing atmospheric concentrations for any major greenhouse gas in the next 20 25 years. "(15) It therefore seems that WRI recognize that the validity of their index&emdash; which they hope will be used by those drawing up an international climate convention&emdash;is dependent on the convention failing to halt the build-up of greenhouse gases.

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