Trends of Studies on Controlled Halogenated Gases under International Conventions during 1999–2018 Using Bibliometric Analysis: A Global Perspective

A lot of research on international convention-controlled halogenated gases (CHGs) has been carried out. However, few bibliometric analyses and literature reviews exist in this field. Based on 734 articles extracted from the Science Citation Index (SCI) Expanded database of the Web of Science, we provided the visualisation for the performance of contributors and trends in research content by using VOSviewer and Science of Science (Sci2). The results showed that the United States was the most productive country, followed by the United Kingdom and China. The National Oceanic and Atmospheric Administration had the largest number of publications, followed by the Massachusetts Institute of Technology (MIT) and the University of Bristol. In terms of disciplines, environmental science and meteorological and atmospheric science have contributed the most. By using cluster analysis of all keywords, four key research topics of CHGs were identified and reviewed: (1) emissions calculation, (2) physicochemical analysis of halocarbons, (3) evaluation of replacements, and (4) environmental impact. The change in research substances is closely related to the phase-out schedule of the Montreal Protocol. In terms of environmental impact, global warming has always been the most important research hotspot, whereas research on ozone-depleting substances and biological toxicity shows a gradually rising trend.

Stronger Arctic amplification from ozone-depleting substances than from carbon dioxide

Arctic amplification (AA) - the greater warming of the Arctic near-surface temperature relative to its global mean value - is a prominent feature of the climate response to increasing greenhouse gases. Recent work has revealed the importance of ozone-depleting substances (ODS) in contributing to Arctic warming and sea-ice loss. Here, using ensembles of climate model integrations, we expand on that work and directly contrast Arctic warming from ODS to that from carbon dioxide (CO$_2$), over the 1955-2005 period when ODS loading peaked. We find that the Arctic warming and sea-ice loss from ODS are slightly more than half (52-59\%) those from CO$_2$. We further show that the strength of AA for ODS is 1.44 times larger than that for CO$_2$, and that this mainly stems from more positive Planck, albedo, lapse-rate, and cloud feedbacks. Our results suggest that AA would be considerably stronger than presently observed had the Montreal Protocol not been signed.

Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past two decades, primarily as a result of the phaseout of ozone depleting substances under the Montreal Protocol and the use of HFCs as their replacements. Projections from 2015 showed large increases in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 °C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2-eq inferred HFC emissions continue to increase through 2019 (to about 0.8 GtCO2-eq yr−1) but are about 20 % lower than previously projected for 2017–2019, mainly because of lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and lower reported consumption of HFC-143a in China. Because this time-period preceded the beginning of the Kigali controls, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications, in anticipation of national or global mandates. A new HFC scenario is developed based on current trends in HFC use and current policies in several countries. These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2-eq yr−1 to 1.9–3.6 GtCO2-eq yr−1. The provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2-eq yr−1 in 2050. Without current policies, HFCs would be projected to contribute 0.28–0.44 °C to the global surface warming in 2100, compared to 0.14–0.31 °C with current policies, but without the Kigali Amendment. In contrast, the Kigali Amendment controls are expected to limit surface warming from HFCs to about 0.04 °C in 2100.

Awareness and product knowledge of service stakeholders involved in the importation and distribution of HCFC-22 in Botswana

Environmental problems such as global warming, ozone depletion and climate change remain universal subjects of concern, with baneful effects on both the environment and human health. The consumption and venting of ozone depleting substances (ODS) into the atmosphere are the chief anthropogenic cause of ozone depletion. One such manmade ODS with high global warming potential Chlorodifluoromethane (HCFC-22). The MP targeted to phase-out HCFC-22 with obligatory cut-off timelines for its use by 2040 for developing nations. To comply with the HCFC-22 phase-out timelines, meant at embarking on national communications to disseminate information on HCFC-22 phase-out through key stakeholders’ involvement. The achievement of HCFC-22 phase-out strategy depends on participation of key stakeholders in the implementation process. the level of awareness and product knowledge of service stakeholders in the importation and distribution of HCFC-22 in Botswana. customs officers, officers and industrial consumers. Questionnaires and interviews were used to solicit key stakeholders’ views, opinions and perceptions on HCFC-22 phase-out awareness and product knowledge. Results revealed that 87% of the stakeholders are learned and knowledgeable in ODS related service provision. The level of HCFC-22 knowledge and awareness among stakeholders is moderate with distinguished inter-group differences. In particular, industrial consumers had the highest median level of HCFC-22 awareness than other stakeholders, indicating gaps in HCFC-22 phase-out awareness raising and training. About 67% of respondents had low levels of awareness of the HPMP and alternative technologies to HCFC-22. This proposes gaps in information dissemination to key stakeholders and this remains a crucial disparity between the country’s HPMP success lead and lag indicators. There is need to carefully select communication media used in line with the media consumption habits of target markets. Use of popular and commonly accessed social-media platforms would ensure that the HCFC-22 phase-out messages have high chance of reaching targeted stakeholders and the general population.

Global total ozone recovery trends derived from five merged ozone datasets

We report on updated trends using different merged zonal mean total ozone datasets from satellite and ground-based observations for the period from 1979 to 2020. This work is an update from the trends reported in Weber et al. (2018) using the same datasets up to 2016. Merged datasets used in this study include NASA MOD v8.7 and NOAA Cohesive Data (COH) v8.6, both based on data from the series of Solar Backscatter UltraViolet (SBUV), SBUV-2, and Ozone Mapping and Profiler Suite (OMPS) satellite instruments (1978–present) as well as the Global Ozone Monitoring Experiment (GOME)-type Total Ozone (GTO-ECV) and GOME-SCIAMACHY-GOME-2 (GSG) merged datasets (both 1995–present), mainly comprising satellite data from GOME, SCIAMACHY, OMI, GOME-2A, -2B, and TROPOMI. The fifth dataset consists of the annual mean zonal mean data from ground-based measurements collected at the World Ozone and UV Radiation Data Center (WOUDC). Trends were determined by applying a multiple linear regression (MLR) to annual mean zonal mean data. The addition of four more years consolidated the fact that total ozone is indeed on slowly recovering in both hemispheres as a result of phasing out ozone depleting substances (ODS) as mandated by the Montreal Protocol. The near global ozone trend of the median of all datasets after 1996 was 0.5 ± 0.2 (2σ) %/decade, which is in absolute numbers roughly a third of the decreasing rate of 1.4 ± 0.6 %/decade from 1978 until 1996. The ratio of decline and increase is nearly identical to that of the EESC (equivalent effective stratospheric chlorine or stratospheric halogen) change rates before and after 1996 which confirms the success of the Montreal Protocol. The observed trends are also in very good agreement with the median of 17 chemistry climate models from CCMI (Chemistry Climate Model Initiative) with current ODS and GHG (greenhouse gas) scenarios. The positive ODS related trends in the NH after 1996 are only obtained with a sufficient number of terms in the MLR accounting properly for dynamical ozone changes (Brewer-Dobson circulation, AO, AAO). A standard MLR (limited to solar, QBO, volcanic, and ENSO) leads to zero trends showing that the small positive ODS related trends have been balanced by negative trend contributions from atmospheric dynamics resulting in nearly constant total ozone levels since 2000.

Rapid increase in dichloromethane emissions from China inferred through atmospheric observations

With the successful implementation of the Montreal Protocol on Substances that Deplete the Ozone Layer, the atmospheric abundance of ozone-depleting substances continues to decrease slowly and the Antarctic ozone hole is showing signs of recovery. However, growing emissions of unregulated short-lived anthropogenic chlorocarbons are offsetting some of these gains. Here, we report an increase in emissions from China of the industrially produced chlorocarbon, dichloromethane (CH2Cl2). The emissions grew from 231 (213–245) Gg yr−1 in 2011 to 628 (599–658) Gg yr−1 in 2019, with an average annual increase of 13 (12–15) %, primarily from eastern China. The overall increase in CH2Cl2 emissions from China has the same magnitude as the global emission rise of 354 (281−427) Gg yr−1 over the same period. If global CH2Cl2 emissions remain at 2019 levels, they could lead to a delay in Antarctic ozone recovery of around 5 years compared to a scenario with no CH2Cl2 emissions.

Depletion of ozone over Antarctica during 2006

The large decrease in the ozone hole area from 2003 to 2004 and the large increase again from 2004 to 2005 and again from 2005 to 2006 cannot be explained by changes in stratospheric halogen loading but are due to interannual dynamical variability. This variability will make it difficult to detect the onset of ozone recovery in Antarctica and in particular it will be difficult to attribute any positive change in ozone to declining amounts of ozone depleting substances. In addition to analysis based on meteorological data and satellites, this paper contains results from a number of stations. Total ozone and ozonesonde data for the 2006 season have been compared to data from previous years. Several stations have observed total ozone columns that are close to the all time low for those stations. In some cases record low total ozone columns have been recorded.

Differences in Environmental Impact between Plant-Based Alternatives to Dairy and Dairy Products: A Systematic Literature Review

A large body of research suggests a more plant-based diet, including a switch to plant-based alternatives to dairy, is needed for lowering human-induced climate change as well as land and water use. With the help of a systematic literature review, we analyzed data from 21 peer-reviewed articles about the differences in emissions and resources used between various plant-based alternatives to dairy and dairy products. Emissions included were greenhouse gases, acidifying, eutrophicating, and ozone-depleting substances, and resource use included water, energy, and land. The results are presented as the quotients of the ratios of plant-based alternatives to dairy and dairy products. The comparison shows that the plant-based dairy alternatives have lower, or much lower, impacts in almost all cases, with two exceptions: water use for almond drinks (several studies) and emissions of ozone-depleting substances for margarine (one study). There is a lack of data concerning impacts other than greenhouse gas emissions for plant-based cheese alternatives; and in general, emissions of greenhouse gases are more highly covered than other impacts. In the quest for a swift transition to a low carbon economy, however, there is already enough evidence to proceed with a dietary change involving switching dairy products to plant-based alternatives.

Upper stratospheric ClO and HOCl trends (2005–2020): Aura Microwave Limb Sounder and model results

We analyze Aura Microwave Limb Sounder (MLS) monthly zonal mean time series of ClO and HOCl between 50° S and 50° N to estimate upper stratospheric trends in these chlorine species from 2005 through 2020. We compare these observations to those from the Whole Atmosphere Community Climate Model version 6 (WACCM6), run under the specified dynamics configuration. The model sampling follows the MLS coverage in space and local time. We use version 5 MLS ClO zonal mean daytime profiles and similarly binned daytime ClO model profiles from 32 to 1.5 hPa. For MLS HOCl, we use the version 5 offline product derived from daily zonal mean radiances rather than averaged Level 2 profiles; MLS HOCl is scientifically useful between 10 and 2 hPa, and the HOCl monthly zonal means are separated into day and night for comparison to WACCM6. We find good agreement (mostly within ~10 %) between the climatological MLS ClO daytime distributions and the model ClO climatology for 2005–2020. The model HOCl climatology, however, underestimates the MLS HOCl climatology by about 30 %. This could well be caused by a combination of fairly large systematic uncertainties in both the model-assumed rate constant for the formation of HOCl and the MLS HOCl retrievals themselves. The model daytime ClO trends versus latitude and pressure agree quite well with those from MLS. MLS-derived near-global upper stratospheric daytime trends between 7 and 2 hPa are −0.73 ± 0.40 % yr−1 for ClO and –0.39 ± 0.35 % yr−1 for HOCl, with 2σ uncertainty estimates used here. The corresponding model decreases are somewhat faster than observed (although the difference is not statistically significant), with trend values of –0.85 ± 0.45 % yr−1 for ClO and –0.64 ± 0.37 % yr−1 for HOCl. Both data and model results point to a faster trend in ClO than in HOCl. The MLS ClO trends are consistent with past estimates of upper stratospheric ClO trends from satellite and ground-based microwave data. As discussed in the past, trends in other species (in particular, positive trends in CH4 and H2O) can lead to a ClO decrease that is faster than the decrease in total inorganic chlorine. Regarding trends in HOCl, positive trends in HO2 can lead to a faster rate of formation for HOCl as a function of time, which partially offsets the decreasing trend in active chlorine. The decreasing trends in upper stratospheric ClO and HOCl provide additional confirmation of the effectiveness of the Montreal Protocol and its amendments, which have led to the early stages of an expected long-term ozone recovery from the effects of ozone-depleting substances.