The international regulations introduced by the Montreal Protocol and its amendments underline the crucial importance of continuous monitoring of the various halogen source gases. Fortunately, an extensive network of measuring stations provides high-frequency measurements of the types of sources listed in Table 1. In addition, measurement techniques for these gases trapped in fir or ice cores at high latitudes have extrapolated atmospheric concentrations of these species to the beginning of the last century (Butler et al., 1999; Reeves et al., 2005; Sturges et al., 2001; Saltzman et al., 2004). Remote sensing of all HCl and ClONO2 columns has been carried out for decades from the Jungfrauhoch, Switzerland, using a Fourier transform spectrometer (Mahieu et al., 1997, 2000). Similar measurements are also available for HF of Jungfrauhoch and Kitt Peak, Arizona (Rinsland et al., 2002). Although fluorine does not directly affect stratospheric ozone, its behavior should correlate with that of chlorine, as it is produced for the most part by the same starting gases. Finally, remote sensing of satellite instruments such as the Halogen Occultation Experiment (HALOE), the Atmospheric Chemistry Experiment (ACE) and AURA/MLS has also provided long-term measurements of HCl in the stratosphere (Anderson and Russell, 2004; Rinsland et al., 2002). The Montreal Protocol on Substances that Deplete the Ozone Layer is the historic multilateral environmental agreement that regulates the production and consumption of nearly 100 man-made chemicals called ozone-depleting substances (ODS). When released into the atmosphere, these chemicals damage the stratospheric ozone layer, the Earth`s protective shield that protects humans and the environment from the sun`s harmful ultraviolet radiation. It`s the 15th. The Protocol adopted in September 1987 is still the only UN treaty ever ratified in every country in the world – the 198 MEMBER STATES OF THE UN. AGAGE measurements show that the molar fractions (Figure 2) and latitude gradients (shown for CFC-11, CFC-12 and CFC-113 in Figure 3) of all major CFCs have decreased in the atmosphere since the mid-1990s.
While their emissions dominated by the northern hemisphere (and thus their north-south gradients) have declined sharply in response to the Montreal Protocol, their long lifespan (e.B. about 50, 90 and 100 years respectively for CFC-11, CFC-113 and CFC-12, respectively) and their emissions from „banks“ in landfills (e.B. Hodson et al., 2010) mean that their wells can only reduce their levels by about 2%. 1.1% and 1% respectively per year. The three main HCFCs (HCFC-22, HCFC-141b and H-H-142b) replace CFCs and continue to increase in recent years with significant and persistent latitude gradients (Figure 3). Growth rates declined somewhat in the late 1990s for HCFC-141b (9-year lifespan) and HCFC-142b (18-year lifespan), accompanied by a decrease in their emissions from developed countries. The rates of increase then increased again in parallel with the increase in emissions in developing countries. In contrast, the rates of increase of HCFC-22 (12-year lifespan) have remained fairly constant.
We report here on how national regulations, voluntary measures and compliance with the Montreal Protocol have protected the climate in the past and can contribute to climate protection in the future. Our comprehensive assessment of the „worlds“ avoided by ODS regulations considers three aspects: (i) time-dependent scenarios of annual ODS production, emissions, concentrations, and related RF; (ii) temporal dependence on CO2 emissions and related FH; and (iii) compensation for climate action by ODS caused by stratospheric ozone depletion and the use of ODS alternative gases. We show what the Montreal Protocol has already achieved for climate and compare it to the Kyoto Protocol target, which is likely to happen in the near future based on current ODS regulations and finally what can potentially be achieved in the future with other CLIMATE ODS regulations. The Montreal Protocol was created in 1987 to regulate ozone-depleting chemicals, primarily CFCs. Widely hailed as the world`s most successful environmental treaty, the Montreal Protocol phased out 99 per cent of all ozone-depleting substances, putting the ozone layer on the road to recovery. It was also the first UN treaty to achieve universal ratification – a true global agreement. The MR74 and NMP87 scenarios are presented as simple estimates of the worlds avoided by events and regulations to examine the fundamental consequences for climate protection. To indicate that uncertainty in these scenarios increases with the post-first year period due to unrecognizable factors, the scenario nuances in Figures 1 and 2 are modified after 2010. Using these scenarios, we recognize that others could be proposed. For example, we do not take into account the possibility that the production of ozone-depleting SUBSTANCES could have been reduced without early warning and without the Montreal Protocol due to preventive climate protection. Our scenarios show what could have happened without other national regulations, international agreements or public measures.
The Montreal Protocol was agreed in 1987 with the urgent task of regulating chemicals that directly destroy the Earth`s ozone layer and is hailed as the world`s most successful environmental treaty. We were instrumental in proposing and arguing that the protocol that so intelligently eliminated chlorofluorocarbons (CFCs) was the best mechanism to phase out harmful hydrofluorocarbons (HFCs) designed to replace CFCs. This work led to the Kigali Amendment to HFCs, which entered into force in January 2019. But the CFC industry didn`t give up so easily. As recently as 1986, the Alliance for Responsible CFC Policy (an association founded by DuPont that represents the CFC industry) argued that the science was too uncertain to warrant action. In 1987, DuPont testified before the U.S. Congress: „We believe there is no imminent crisis that requires unilateral regulation.“  And as recently as March 1988, Du Pont President Richard E. Heckert wrote in a letter to the U.S. Senate: „We will not manufacture a product unless it can be manufactured, used, handled, and disposed of safely and in accordance with appropriate safety, health, and environmental quality criteria.
At present, the scientific evidence does not indicate the need for a drastic reduction in CFC emissions. There are no available measures of the contribution of CFCs to observed changes in the ozone layer.  A well-known example is the successful global phase-out of ozone-depleting substances in the Montreal Protocol on Substances that Deplete the Ozone Layer (1987). Polychlorinated biphenyls were banned in 2001 by the Stockholm Convention on Persistent Organic Pollutants. Through REACH (EU Directive on the Registration, Evaluation and Authorisation of Chemicals, 2006), the EU has banned cadmium in certain applications. The EU Directive on the restriction of the use of certain hazardous substances (2009) restricts the use of certain substances in electronic and electronic devices. Geologically scarce mineral resources could also be banned for certain applications. Priority should be given to applications where rare raw materials can be easily replaced by less scarce materials without loss of service and with negligible (or zero) additional costs. A product ban should not focus on minor applications, but on fruits at hand, i.e. most applications of antimony.B (e.g. in flame retardants, lead-acid batteries and as a PET catalyst) and some applications of boron (e.g. B applications in glass wool and a number of detergents).
Banning applications does not offer an effective solution to reduce molybdenum, copper, silver and gold due to their relatively low substitutability. The original agreement aimed to reduce the production and consumption of various types of CFCs and halons to 80 per cent of 1986 levels by 1994 and to 50 per cent of 1986 levels by 1999. The Protocol entered into force on 1 January 1989. Since then, the agreement has been amended to further reduce and completely eliminate CFCs and halons, as well as the production and use of carbon tetrachloride, trichloroethane, hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HBFCs), methyl bromide and other OACs. Several subsequent meetings of signatory countries have been convened to monitor overall progress towards this goal and to approve further changes to the process of phasing out THE CDOs. The Montreal Protocol for the Protection of the Ozone Layer regulates many ozone-depleting fluorinated gases with the primary goal of reducing chlorine and bromine concentrations in the stratosphere. These gases include CFCs, HCFCs, chlorinated hydrocarbons, brominated hydrocarbons and halons. The observations and global cycles of these gases have recently been the subject of an in-depth review in Chapter 1 of the 2010 WMO-UNEP Ozone Assessment (Montzka et al., 2011; see also Clerbaux et al., 2007).