Dr. Andersen is among the longest-serving stratospheric ozone activist, beginning with his participation as co-author in the 1973-1974 assessment of the impact of stratospheric ozone and climate on northern latitude grain production (Schmitz et al., 1975) organized in response to the warning by Professor
Paul J. Crutzen on nitrogen oxide emissions that earned him the 1995
Nobel Prize shared by Professors
Mario J. Molina and
F. Sherwood Rowland. In 1986, Andersen joined the fledgling US
Environmental Protection Agency (EPA) team that built the scientific, technical and economic case for protecting the stratospheric ozone layer. At EPA he rose to deputy director for Stratospheric Ozone Protection and then transferred to the Climate Protection Partnerships Division, where he was Director of Strategic Climate Projects until his retirement from government in 2009. The timing of Andersen's arrival at EPA was fortuitous. 1987 proved to be a watershed moment in the effort to stop
ozone depletion, which increased risks of skin cancer and threatened to wipe out crops and ecosystems, among many adverse impacts. The
Montreal Protocol on Substances that Deplete the Ozone Layer was agreed on 16 September 1987 and created a timetable to phase out and eliminate the production of ozone depleting substances. At EPA, Andersen's responsibilities included analysis of regulatory impact, cost, and trade, technology co-operation, and sector projects in halons, foams, mobile air conditioning, and military uses. Over his tenure he pioneered EPA's voluntary approaches to ozone layer protection including the phase-out of
chlorofluorocarbon(CFC) in the manufacturing of food packaging, the recycling of CFC from vehicle air conditioning, the halt to testing and training with halon, and the accelerated CFC solvent phase-out in electronics manufacturing. Andersen also brought Soviet authorities together with NASA scientists and EPA senior officials to gain agreement for US Total Ozone Mapping Spectrometer (TOMS) be carried to space on a Soviet Meteor-3 satellite(1994) rocket in order to overcome loss of access to space (resulting from the
Space Shuttle Challenger accident); he founded and managed the first EPA international awards, the US EPA Stratospheric Protection Awards and Climate Protection Awards; and was EPA Liaison to the US
Department of Defense (DoD) on stratospheric ozone and climate, chairing several DoD committees on solvent validation, aircraft maintenance, manufacturing rockets without ozone-depleting substances, and certifying the Joint Strike Fighter for particulate emissions. Whilst at EPA Andersen co-Chaired the 1989 Economic Assessment Panel, the 1989–1997 Solvents Coatings and Adhesives Technical Options Committee, the 1992 Methyl Bromide Assessment and since 1989 co-founded and co-chaired the Technology and Economic Assessment Panel (TEAP). Andersen with
K. Madhava Sarma, the first executive director of the Ozone Secretariat and EPA colleague Kristen N. Taddonio, published a two volume history of the Montreal Protocol diplomacy, management, leadership, and
technology transfer. Over the decades, the Montreal Protocol became a victim of its own success. By 2006, some called for dismantling the treaty, claiming it had achieved its goals and outlived its usefulness. Andersen knew the Protocol needed to be not only preserved but strengthened. to research the role of the Protocol in climate protection. In 2007 Andersen and the Velders' team published "
The Importance of the Montreal Protocol in Protecting Climate." The team quantified the benefits of the Montreal Protocol, and found that it helped prevent 11 billion metric tons of CO2equivalent emissions per year from 1990 to 2010, having delayed the impacts of climate change by 7 – 12 years. The paper determined the Montreal Protocol had been the most successful climate agreement in history, it also estimated the joint ozone and climate benefits of an accelerated hydrochlorofluorocarbons (HCFC) phaseout, providing policymakers with information needed to accelerate the phaseout. In 2009, Andersen retired from the EPA and joined
Durwood Zaelke at the Institute for Governance and Sustainable Development (IGSD) as director of research, The two Velders papers helped build the foundation that inspired other scientists to calculate and communicate the interlinkages of ozone with climate and the importance of phasing out ODSs and phasing-down HFCs. Andersen's research and work at IGSD, and over his career, culminated on 15 October 2016 when the Parties to the Montreal Protocol agreed to the
Kigali Amendment, an amendment to the Protocol for the inclusion and regulation of HFCs. The Kigali Amendment will limit warming from HFCs to 0.06 °C, avoiding nearly 0.5 °C of warming by 2100 and 80 Gt CO2e by 2050. Andersen now concentrates on achieving the HFC phasedown as quickly as feasible with higher energy efficiency at affordable prices, while stopping the dumping of technically inferior appliances, and narrowing the Montreal Protocol exemption for feedstocks used to produce plastics that pollute oceans, rivers and land with hazardous and toxic waste. He is also part of the team using government procurement to purchase super-efficient room ACs at an affordable price around the world, using the
Life Cycle Climate Performance (LCCP) method to evaluate the carbon footprint and global warming impact of heating, ventilation, air conditioning (AC) and refrigeration systems, and of the team demonstrating secondary-loop motor vehicle air conditioning. Stephen is featured in the PBS Documentary "Saving the Ozone Layer: How We Saved the Planet" along with scientists
Sherwood Rowland and
Mario Molina, politicians
Ronald Reagan and
Margaret Thatcher, scientists Paul Newman and Mack McFarland and NGO Presidents David Doniger and
Durwood Zaelke, aired 10 April 2019. For his critical contribution to saving the ozone layer, Andersen was a winner of the 2021 Future of Life Award along with Joe Farman and
Susan Solomon. Professor Ted Parson from the
UCLA Emmett Institute on Climate Change and the Environment said, ''"for over a decade, Andersen brilliantly led the Montreal Protocol's Technology and Economic Assessment Panel process. Andersen made the Montreal Protocol happen."'' Dr. Jim Hansen, former Director of the NASA
Goddard Institute for Space Studies and Director of Columbia University's Program on Climate Science, Awareness and Solutions said, "in Farman, Solomon and Andersen we see the tremendous impact individuals can have not only on the course of human history, but on the course of our planet's history. My hope is that others like them will emerge in today's battle against climate change." For recovering stratospheric ozone from the planetary boundary danger zone to the path to recovery to pre-industrial health Stephen earned the Planetary Guardians Award along with D. Suely M. Carvalho, Marco Gonzalez,
Professor Mario J. Molina,
Professor. F. Sherwood Rowland, Jonathan Shanklin, and Dr. Helen Tope. Andersen was the principal investigator and lead author of the publication inventing the legal framework to stop the dumping in developing countries of inefficient cooling equipment using obsolete ozone-depleting and climate-forcing refrigerants that motivated Decisions to the Parties to the Montreal Protocol for shared responsibility in making available high efficiency cooling with climate friendly refrigerants at fair prices and profits. He also served as the lead author of the scientific and policy publication documenting that ODS and GHG feedstocks allowed under a Montreal Protocol feedstock exemption are used to produce plastics that poison workers and communities, pollute fresh water, oceans, land, and atmosphere with plastic waste and "everywhere and forever" chemicals such as trifluoroacetic acid (TFA) and per- and poly-fluoroalkyl substances (PFAS). ==Honors==