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Figure 7-6 shows very wide ranges for science, policy andimpact time lags - spanning two orders of magnitude froma few years to more than a century. Many reasons havebeen suggested for these wide ranges, including factorsthat case specific and others that are more general. Theyare described in Table 7-8. Three cases – ozone layer, leadin gasoline, and climate change – are described below, inorder to illustrate the interplay between multiple factors.It is important to note that the determinations of “scientificconfidence in the causal hypothesis under scrutiny” and of“the strength of evidence deemed sufficient to justify policyaction” are based on case-specific judgments that include aconsideration of the consequences of being wrong witheither action or inaction. 738 The term is often used tojustify action based on the “precautionary principle”. Forthis report, we base our approach on that used by theIntergovernmental Panel on Climate Change (IPCC) in its“Guidance for lead authors of the IPCC 5 th assessmentreport on the consistent treatment of uncertainties”. 739 Itshould be noted also that the IPCC’s approach to assessinguncertainty has significantly evolved over the years. 740Some commonly used standards of confidence include“beyond all reasonable doubt” (as used in criminal courts)or “scientific suspicion of risk” (as in the Swedish ChemicalsLaw 1973). Often, precautionary actions are justified on thebasis of lower standards of scientific evidence than thehigher standard required for scientific ‘proof’. Examplesinclude the “reasonable grounds of concern” of theEuropean Union’s Communication on the PrecautionaryPrinciple; 741 the “balance of evidence” that humans arechanging the climate of the 1995 report of theIntergovernmental Panel on Climate Change; and “noconclusive proof …but a reasonable expectation of harmfuleffects” used by the Environmental Protection Agency ofthe USA in 1987.7.7.1. Ozone LayerIn 1974, Rowland and Molina (and independently Cicerone)suggested that long-lived organic halogen compounds, suchas CFCs, might deplete the ozone layer. 742,743 Thishypothesis was strongly disputed by representatives of theaerosol and halocarbon industries. For example, the Chairof the Board of DuPont called it "a science fiction tale ... aload of rubbish ... utter nonsense". 744 Following lab andopen air tests, in 1976 the US National Academy of Sciencesconcluded that the ozone depletion hypothesis wasstrongly supported by the scientific evidence.In response, in 1978 the United States of America, Canadaand Norway banned the use of CFCs in aerosol sprays – inthe case of the US based on “reasonable expectation” ofdamage. Similarly at the regional level, in 1980 there was aEuropean decision to restrict the use of CFCs in aerosols. In1491985, large-scale ozone depletion over Antarctica wasreported by Farman et al in Nature and confirmed byNASA. 745 At the global level, the Montreal Protocol on theprotection of the ozone layer was signed soon thereafter,in 1987.The Montreal Protocol is a showcase of a functioningscientific early warning followed by global coordinatedaction merely 13 years after the original hypothesis. Policyaction has proven effective. By 2012, combined chlorineand bromine levels had declined by 10 to 15% from theirpeak values. By 2005, the global amount of ozone in theatmosphere had stabilized. 746 Ozone concentrations in thelower stratosphere over Antarctica are expected to returnto pre-1980 levels by about 2060–2075. 7477.7.2. Leaded petrolThe toxicity of lead has been known to man for a long time.The Romans were already aware of the toxicity of lead(Pliny, ca AD 77–79). 748Leaded petrol was a global commodity between the 1930sand the 1990s. The new generation of high compressionengines that emerged in the 1920 required gasoline withfuel additives for which two additives were available at thetime – tetraethyl lead (TEL) and alcohol. 749 Although bothwere technically effective, TEL was chosen by DuPont, GM,and Standard Oil, because of its lower cost and because ofcomplications arising from alcohol prohibition in the USA atthe time. 750 The potential health dangers of TEL wereanticipated by many health professionals. In 1924, a publiccontroversy erupted over the “loony gas” which had killedits production workers in the first US TEL factories. The USPublic Health Service conducted a conference in 1925 atwhich many public health scientists warned that puttinglead into petrol would cause “insidious” health effectswhich would take many years for the public andgovernments to recognize. TEL sales were then voluntarilysuspended for one year to conduct a hazard assessment. 751The Public Health Service created an expert committee thatsuggested not to ban TEL, but to closely monitor, study, andregulate its introduction. 752 TEL was widely marketedwithout such controls until the 1980s. By 1969, the firstclinical studies were published which proved the toxicity ofTEL in humans. 753 Commercial production of the alternativefuel additive methyl tertiary-butyl ether (MTBE) to replaceTEL/lead as octane enhancer in gasoline started in Europein 1973 and in the United States in 1979. 754By 1970, the annual incidence of symptomatic andasymptomatic lead poisoning in the U.S. was as high as250,000 cases. 755 Lead poisoning in the industrializing worldcalled for preventive action, and a number of legislativeand other preventive measures were introduced in many