No. 84 Climate Change 95: An Appraisal (summary)

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Last year, the Intergovernmental Panel on Climate Change (IPCC) released Climate Change 1995: The Science of Climate Change, a 572-page report presenting the current state of scientific knowledge on global warming. The report is widely cited as proof of a "scientific consensus" on the need for immediate action to prevent global warming. Dr. Vincent Gray, who serves on the IPCC's peer review panel, contends that Climate Change 95 provides no evidence to support drastic measures to control greenhouse gas emissions.

1. Climate Change 95 is imprecise in its measurements and unscientific in its terminology.

Those accustomed to seeing scientific data presented using measures of precision--such as mean and standard deviation--will be disappointed with Climate Change 95, which is laden with such imprecise and unscientific terms as estimate (including best estimate), guess (including best guess), tend towards, could be largely due to, and essentially the same as. This lack of precision makes it easier to exaggerate the extent of climate change, and to claim unjustified agreement of climate data with computer models.

Climate Change 95 does, however, show evidence of a retreat from consensus: a term that belongs in the realm of politics, not science. Climate Change 90 stated that some scientists "formed a minority opinion which could not be reconciled with the larger consensus." That "minority opinion" was not permitted to be expressed in the 1990 report. In Climate Change 95, by contrast, there is no mention of "consensus," and some critics are given a fair hearing.

2. Climate Change 95 distorts carbon dioxide emission and atmospheric concentration data.

The concentration of carbon dioxide in the atmosphere, its variability, and its rate of increase are fundamental to the greenhouse effect. Yet there is no paragraph, let alone a chapter, in Climate Change 95 addressing the emission of carbon dioxide by the combustion of fossil fuels.

In its 1993 report, the IPCC listed 69 sets of figures for monthly mean concentrations of atmospheric carbon dioxide from measurement stations around the world. Yet for Climate Change 95 it insists on selecting only two of these, at Mauna Loa (Hawaii) and the South Pole. No explanation is offered for the IPCC's failure to use global mean figures supplied by the U.S. National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory. The current measurements are pictured below.

The global average CO2 concentration increased from about 340ppm in 1981 to 358ppm in 1994, an increase of about 5.3 percent in 14 years. During the 1980s, the average annual change in global average CO2 concentration was about 0.4 percent. The average annual change from 1990 to 1994 was about 0.3 percent. Yet nearly all of the computer climate models relied on by the IPCC assume that, starting in the year 1990, carbon dioxide in the atmosphere will increase by 1 percent per year. This is 2½ times the measured rate of carbon dioxide increases in the 1980s and 1990s (0.4 percent).

The exaggerated rates of change in carbon dioxide assumed by the models have important consequences. It seems to be universally believed by the media that carbon dioxide in the atmosphere will double "by the middle of the next century" (1 percent a year compounded gives 70 years). But the 1980s' rate of 0.4 percent would double in 174 years, if compounded, or 250 years if linear. If the average for the past decade persists, it will take 226 years for the concentration to double, if compounded, and 325 years if linear.

There has been a downward trend in the growth rate of atmospheric methane from 1983 to 1994, with an average growth rate for 1995 of about 5ppbv/yr. Yet the IPCC states in Climate Change 95 that "in 1994 global methane growth rates recovered to about 8ppbv/yr . . ." This statement is clearly refuted by the graph on this page and ignores the obviously falling growth rate.

The IPCC authors show the 1994 growth rate as 10ppbv/yr, as averaged over the decade beginning 1984, again ignoring the decline. The graph shows that the "upturn" is turning down again, and that the decline in global growth rate of methane in the atmosphere continues, such that it may become zero by the year 2000.

Similarly inaccurate interpretations of nitrous oxide growth rates are used by the IPCC in its various scenarios. The rate of growth of nitrous oxide in 1993 was 0.5ppbv/yr, yet the figure assumed for 1990-1995 is 0.8ppbv/yr. The IPCC acknowledges that for both methane and nitrous oxide, its estimates of 1990 emissions "do not accord with emission estimates based on observed concentration data and current lifetime estimates." In other words, they admit to using inaccurate data.

Climate Change 95 reports that "recent years have been among the warmest since 1860," thus isolating the only features of the global temperature record that suggest a possible agreement with greenhouse theory. The IPCC ignores those features that cast doubt on the theory, such as:

• the fact that the greatest temperature rise of this century (about 0.65°C) took place between 1910 and 1945. Atmospheric carbon dioxide rose only 3 percent over this period. Climate Change 90 said, "The rather rapid changes in global temperature seen around 1920-1940 are very likely to have had a mainly natural origin";

• the fact that the period from 1945 to 1978, 33 years, saw a fall in temperature of 0.2°C, at a time when atmospheric carbon dioxide rose by 9 percent;

• the fact that the rise "over the last forty years" of 0.3°C took place (as a rise of about 0.4°C) over the short period of 1978-1996, only 18 years. The temperature since 1990 has shown signs of leveling off.

According to the IPCC, any climate change, however short, that agrees with greenhouse theory is a long-term trend. Any climate change, however extensive, that does not agree with greenhouse theory is either ignored (like the global drop in temperature between 1945 and 1978); too short to be representative; or an anomaly that has to be explained.

Climate Change 95 admits that the surface temperature record is subject to error: from poor sampling (particularly over the oceans), from instrumental and operational differences, and from urban development around land measurement stations. Yet its authors ignore radiosonde (weather balloon) measurements, which have been made since 1958, and the NASA satellite measurements, which have been operating since 1978. There is no evidence of a global warming trend over the past 37 years if the radiosonde measurements are considered, or over 18 years if the satellite measurements only are considered. Once again, inaccurate data are preferred to accurate data, because the former better "fits" a flawed theory.

The IPCC emissions scenarios--IS92a, b, c, d, e, and f--comprise a range of assumptions regarding greenhouse gas emissions, energy usage, and economic and population growth, between 1990 and 2100. Though a plausible set of scenarios should encompass all possibilities, including reality, the IS92 scenarios all exaggerate current climate and economic trends.

The previously discussed upwards bias in the projected future emissions and atmospheric concentrations of carbon dioxide, methane, and nitrous oxide is built into all scenarios. In order to justify the assumed increases in carbon dioxide, IPCC postulates large increases in world coal production. IS92a, the "central" scenario, assumes a sevenfold increase in world coal production between 1990 and 2100, and IS92e assumes an elevenfold increase over the same period. Yet between 1990 and 1995 world coal production fell by 4½ percent. World population and economic growth trends are similarly exaggerated and should be cause for rejecting most IPCC emission scenarios.

When it first presented its trend predictions, the IPCC warned that "Scenarios deal with the future, so they cannot be compared with observations." The scenarios all begin in 1990, so we have six-and-a-half years of observations to check their plausibility. When this is done (see table below), it is evident that all of the IS92 scenarios exaggerate what has happened over the past five years, whichever set of assumptions is chosen.

IPCC future projections for the year 2000 compared with likely range from current trends IPCC Emission Scenarios Trend Prediction Parameter IS92a IS92b IS92c IS92d IS92e IS92f CO2 emissions 7.0GtC/yr 6.8GtC/yr 6.0GtC/yr 6.4GtC/yr 7.6GtC/yr 7.3GtC/yr 6.0-6.4 GtC/yr Temp increase over 1990 0.1-0.25°C 0.1-0.25°C 0.05-0.15°C 0.05-0.15°C 0.15-0.3°C 0.15-0.3°C 0.0- 0.1°C CO2 concentration 373ppmv 373ppmv 373ppmv 373ppmv 373ppmv 373ppmv 362-365ppmv CH4 concentration 1810ppbv 1810ppbv 1787ppbv 1787ppbv 1824ppbv 1817ppbv 1750ppbv Coal production 3.9Gt 3.8Gt 3.6Gt 3.9Gt 4.2Gt 4.0Gt 3.0-3.3Gt World population 6.2b 6.2b 6.1b 6.1b 6.2b 6.4b 6.1b

The only scenarios with any plausibility are IS92c and IS92d, and even those exaggerate likely trends in greenhouse gases, temperature, and coal production. IPCC projections to the year 2100 can therefore be taken seriously only for scenarios IS92c and IS92d, with a probability that the true figure will be below both of these. After adjusting for the exaggerated rates of increase in CO2 and methane, we can expect the maximum temperature rise between 1990 and 2100 to be 1°C.

Few professional economists would be prepared to make forecasts beyond fifty years, and most would be reluctant to go beyond twenty years. The main reason is the difficulty in predicting future changes in technology. Nevertheless, the IPCC makes no apology for projecting one hundred years into the future. In its Stabilization Calculations, the IPCC goes one better, presenting graphs showing the emission controls required to achieve different levels of atmospheric stabilization of carbon dioxide concentrations to the year 2400. Those projections have been widely reported as reliable, although they must surely be categorized as science fiction, not science.

IPCC scientists are under substantial pressure from those who believe that human activity is having a harmful effect on the global climate. It is to the credit of the IPCC that it has largely resisted this pressure.

Much has been made by the media of the one advance of Climate Change 95 over its predecessors: the pronouncement that "the balance of the evidence suggests a discernible human influence on the climate." Note that this is only a suggestion, and that the nature and extent of the influence are not specified.

Humans are undoubtedly influencing the climate. The important point, though, is whether the influence is significant, and whether it matters. The IPCC provides no answers to those two important questions. As of yet, we have no firm evidence that human influence on the climate can be disentangled from other climate influences; no evidence of a significant human influence; and certainly no evidence that changes due to human activity could be harmful.

Based on Heartland Policy Study #84, “Climate Change 95: An Appraisal,” by Vincent Gray M.A. Ph.D. Printed copies are available from The Heartland Institute for $10 each. You can also download the full text, free of charge, in Adobe's PDF format; click here.

Copyright 1997 The Heartland Institute. Nothing in this Executive Summary should be construed as reflecting the views of The Heartland Institute, nor as an attempt to aid or hinder the passage of any legislation. Permission is hereby given to reprint or quote from this Executive Summary; please send tearsheets to The Heartland Institute, 19 South LaSalle Street #903, Chicago, Illinois 60603.

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6. Climate Change 95 provides no useful guidance on the question of how to respond to human influence on the global climate.

5. The emissions scenarios presented in Climate Change 95 are unrealistically exaggerated and do not comport with reality.

4. Climate Change 95 relies on computer models that have not been validated against actual current and past temperature records.

3. Climate Change 95 also distorts the data on atmospheric methane and nitrous oxide concentrations.