The following text is the submission for an article that has just been published online in the journal Science Progress:
The UN Intergovernmental Panel on Climate Change (IPCC) has recently published a report1 (abbreviated as SR15) which concludes that humankind has a mere twelve years left, during which time sufficient and dramatic carbon-emission mitigation strategies must be inaugurated to avoid the “global average temperature” from rising above the 1.5 oC limit which the 2015 Paris Climate Change Agreement2,3 aimed for, while pledging to keep it “well below 2 oC above pre-industrial levels”. The Agreement was endorsed by 195 countries2, although the United States later conspicuously withdrew from it3. Contained within the Decision of the 21st Conference of Parties, of the United Nations Framework Convention on Climate Change (UNFCCC) to adopt the Paris Agreement, was an invitation4 to the IPCC to deliver a Special Report, in 2018, which ascertained the changes that would be caused by a 1.5 oC elevation in global average temperature, and what measures might be introduced in order to hold global warming in check such that this level is not exceeded. In 2016, the IPCC Panel accepted the invitation, adding that these issues would also be considered “in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty” 4. The final report1, which was released on October 9th 2018, emphasised that reducing the degree of warming by half a degree, from 2 oC to 1.5 oC, would significantly ameliorate some of the worst effects of climate change, in particular reducing the number of people likely to be affected by water shortages by 50%, but the most significant influence would be on the Natural World: for example, it is expected that practically all (>99%) coral reefs (Fig. 1) would be lost by a 2 oC increase, whereas at 1.5 oC, this would be ameliorated to a decline of within 70–90 %.
It is known that climate change is likely to affect the ranges of pollinating insects5, and according to research by the Natural Environmental Research Council (NERC)6, which informed the IPCC report:
“Limiting global warming to 1·5°C avoids by half the risks associated with warming of 2°C for plants and animals, and two thirds of the risks to insects. Insects are particularly sensitive to climate change. At 2°C warming, 18% of insects studied are projected to lose more than half their geographical range, with the three major groups of insects responsible for pollination - vital to ensure global food security - shown to be especially sensitive to warming.
There is a significant benefit to keeping warming below 1·5°C compared to 2°C: in the former scenario, more species can keep up or even gain in range; if the latter, many species cannot keep up and far more species lose large parts of their range. Benefits occur everywhere but are greater in Southern Africa, the Amazon, Europe and Australia.”
It is thought that we may already be witnessing the consequences of the 1oC rise that has occurred since pre-industrial levels [the IPCC uses the period 1850-1900 to benchmark pre-industrial conditions, since this is the earliest period for which near-global temperature observations are available7], in terms of more extreme weather and rising sea levels, and at the current rate of warming, the 1.5 °C limit will be reached at some point between 2030 and 2052. Hence, the need for immediate, far-reaching and unprecedented actions across the entirety of global civilization. As has been pointed out by the IPCC Chair, Professor Hoesung Lee, to limit the global temperature rise by to 1.5oC” could go hand in hand with the creation of a more sustainable and equitable society” 8; thus, global sea level rise would be 10 cm lower in 2100 at a global warming of 1.5°C compared with 2°C, with clear implications for coastal regions, and low lying tropical islands1, many of which are not affluent, and some will need to consume several percent of their GDP to cope with rising sea levels, and other expected impacts of climate change9.
Moreover, at the lower temperature, food scarcity would be less severe, and the number of people at risk of climate-related poverty, mainly in poorer countries, would be substantially reduced1. It is estimated that the event of the Arctic Ocean being free of sea ice in summer would occur just once per century at a global warming level of 1.5°C, whereas at 2°C this is to be expected “at least once per decade” (Ref.1). The IPCC has identified four pathways1 to achieve the necessary “temperature control”, which involve the integration of various land use changes (planting large areas of forest is a critical factor in all of them) and technological strategies, including a greater adoption of carbon capture methods, and a widespread electrification of energy and transportation systems1.
While a 20% curbing in carbon emissions by 2030 is required1 to stay within the 2 oC limit, this must rise to nearly one half (45%) of current levels, if global warming is to be restrained at 1.5 oC, and net emissions must be brought to zero by 2050 (or 25 years earlier than is required to meet the 2 oC target)1. At the “net zero” point, any further emissions must be offset by removing CO2 from the air10. Considering that well over 80% of the energy used by humans on Earth comes from burning fossil fuels11,12, this is a truly staggering challenge, although Jim Skea, Co-Chair of IPCC Working Group III, has said10: "Limiting warming to 1.5°C is possible within the laws of chemistry and physics but doing so would require unprecedented changes.” Nonetheless, there has been acrimonious controversy over the prospects of running the world on renewable energy alone13. It has been estimated that, between 2016 and 2035, an annual average investment of 2.4 trillion USD in the energy system is needed to meet the 1.5 oC limit, which is about 2.5% of global GDP14, but in comparison with the cost of doing business as usual (i.e. changing nothing), this is still the far cheaper option, especially if a “Hothouse Earth” scenario15 were to occur, which is a runaway, and irreversible, escalation of global warming, that might finally stabilise at a temperature perhaps 4-5 oC higher than in the pre-industrial age15. The model indicates that a 2 oC rise could set a tipping point, where the earth system moves of its own volition, due to the activation of multiple feedback mechanisms. Prof Johan Rockström, from the Stockholm Resilience Centre, who is a co-author of the recent paper15, is quoted as saying16:
“What we are saying is that when we reach 2 degrees of warming, we may be at a point where we hand over the control mechanism to Planet Earth herself.
"We are the ones in control right now, but once we go past 2 degrees, we see that the Earth system tips over from being a friend to a foe. We totally hand over our fate to an Earth system that starts rolling out of equilibrium."
2. Possible mitigation measures.
There are essentially two possible means for observing the 1.5 oC target1: either a drastic curbing in carbon emissions is introduced rapidly so to prevent the temperature from rising above the limit in the first place, or it may be allowed to exceed it slightly (overshoot pathway), but remedial measures are introduced so that it is then brought back down again1. However, the latter approach carries the danger that tipping points may be traversed, meaning that certain climate responses will be triggered even if temperatures are subsequently reduced1. One example of a tipping point is the collapse of the Greenland and Antarctic ice sheets which is expected to continue over a period of centuries and probably millennia1,9.
However, all of the mitigation measures presented in the IPCC report imply massive and permanent changes for societies, especially in the industrialised nations, and involve their integration throughout global civilization, as is stated1:
“Examples of actions include shifting to low- or zero-emission power generation, such as renewables; changing food systems, such as diet changes away from land-intensive animal products; electrifying transport and developing ‘green infrastructure’, such as building green roofs, or improving energy efficiency by smart urban planning, which will change the layout of many cities. Because these different actions are connected, a ‘whole systems’ approach would be needed for the type of transformations that could limit warming to 1.5°C.
This means that all relevant companies, industries and stakeholders would need to be involved to increase the support and chance of successful implementation. As an illustration, the deployment of low-emission technology (e.g., renewable energy projects or a bio-based chemical plants) would depend upon economic conditions (e.g., employment generation or capacity to mobilize investment), but also on social/cultural conditions (e.g., awareness and acceptability) and institutional conditions (e.g., political support and understanding).”
3. Reduce CO2 emissions by almost one half.
The critical, and probably most challenging, goal is that, in order to meet the 1.5 oC target, CO2 emissions in 2030 need to be reduced by 45% from 2010 levels, and to have reached net zero by 2050 — meaning the amount of CO2 being removed from the atmosphere matches the amount being emitted into it1,17. In addition, a 35% reduction in other greenhouse gases, e.g. methane and black carbon, from 2010 levels by 2050, is required. The report concludes with “high confidence” that in order to limit global warming to 1.5°C, with no or limited overshoot, “rapid and far-reaching transitions in energy, land, urban and infrastructure (including transport and buildings), and industrial systems” are necessary. It is concluded that in terms of rapidity, such transitions may not be unprecedented, although in terms of scale they are, since they require profound reductions in CO2 emissions across all sectors of society17. Hence, a broad collection of mitigation options along with a significant enlargement of investments in them is most likely necessary. It appears certain that more rapid and pronounced changes in social systems will need to be made during the next two decades in order to meet the 1.5oC limit, in comparison with the 2oC target. Thus, it is projected that a more rapid transition to end use energy in the form of electricity will occur, and that a greater proportion of overall energy will be produced from low-carbon energy sources, particularly before 2050, by which time 70–85% is anticipated to be generated from renewable sources. The models further indicate that for the lower temperature limit, a greater proportion of nuclear power, and the use of fossil fuel fired power stations equipped with CO2 capture and storage/sequestration (CCS) (Fig. 2) will be needed: with CCS, around 8% of global electricity can be produced using natural gas in 2050, while the use of coal would be reduced virtually to zero17.
[A necessary overall massive curbing in burning coal by 2050 was concluded from a previous study18, in order to keep to the overall “carbon budget”, with clear geopolitical implications, e.g. the US and Russia would need to leave more than 90% of their vast coal reserves in the ground and unburned, while the Middle East could only exploit two thirds of its oil and gas reserves; a situation that is not changed significantly even if CCS technology is introduced during the next few decades18].
It is expected that solar energy, wind energy and electricity storage technologies are likely to result in a potential system transition in electricity generation, and that CO2 emissions from industry will need to be some 75–90% lower in 2050 than in 2010 1,17. It is anticipated that such devices as electrification, hydrogen, sustainable bio-based feedstocks, product substitution, and carbon capture, utilization and storage (CCUS) will, in combination, contribute to the required curbing in carbon emissions; nonetheless, it is noted1,17 that while such approaches are proven technically, to deploy them on the large-scale, “may be limited by economic, financial, human capacity and institutional constraints in specific contexts, and specific characteristics of large-scale industrial installations. In industry, emissions reductions by energy and process efficiency by themselves are insufficient for limiting warming to 1.5°C with no or limited overshoot.”
Energy efficiency measures1,17 are a critical feature of adapting the urban and infrastructure system, along with changes in land (use) and urban planning practices, and reductions in transport and buildings, which naturally are all more demanding if the lower temperature limit is to be attained. Land use changes are critical, and it is predicted that, by 2025, it will be necessary to reutilise up to 8 million km2 of pasture and up to 5 million km2 of non-pasture agricultural land, for growing energy crops, while a substantial increase in forest areas up to 10 million km2 is predicted. As the report notes1,17:
“Such large transitions pose profound challenges for sustainable management of the various demands on land for human settlements, food, livestock feed, fibre, bioenergy, carbon storage, biodiversity and other ecosystem services. Mitigation options limiting the demand for land include sustainable intensification of land use practices, ecosystem restoration and changes towards less resource-intensive diets. The implementation of land-based mitigation options would require overcoming socio-economic, institutional, technological, financing and environmental barriers that differ across regions.”
It is estimated that around 900 billion USD worth of investment will be needed annually during the period 2015-2050 to implement necessary means for limiting global warming to a 1.5°C rise17 (“energy-related mitigation”), which accords with total annual investments in energy supplies averaging 2700 billion USD, and total annual average energy demand investments of 850 billion USD; in terms of total energy-related investments, this represents an increase of about 12% over the requirements for meeting the 2°C target. By 2050, annual investment in technologies for providing low-carbon energy, along with energy efficiency measures, will need to be increased fivefold17 from that in 2015. A broad range of “global average discounted marginal abatement costs” (carbon prices) are predicted over the 21st century to keep to the 1.5 oC limit, which are greater by a factor of about three-to-four than those estimated for scenarios that keep global warming to below 2°C. Due to its paucity, no assessment of the literature on total mitigation costs of 1.5°C mitigation pathways was made; thus, uncertainties remain regarding the broad and integrated costs and benefits of keeping to the lower temperature target17.
5. Carbon dioxide removal (CDR).
Implicit to all modelled schemes that avoid exceeding the 1.5°C limit, is carbon dioxide removal (CDR), which over the 21st century, amounts to 100–1000 billion tonnes (gigatonnes; Gt)17. It is thought that the use of CDR can be limited to “a few hundred Gt” by means of reductions in emissions made in the near term, and attenuation of demand for energy and land, without depending on bioenergy with carbon capture and storage (BECCS)17. Among the procedures for CDR are “afforestation and reforestation, land restoration and soil carbon sequestration, BECCS, direct air carbon capture and storage (DACCS), enhanced weathering and ocean alkalinisation”, although, with the exception of afforestation and BECCS, the literature is scant regarding these methods per se, and the potential scale of their application. The report gives large ranges17 of carbon removal that might be accomplished by BECCS (0–1, 0–8, and 0–16 GtCO2 yr-1 in 2030, 2050, and 2100, respectively), while some 0–5, 1–11, and 1–5 GtCO2 yr-1 (in these same years) is predicted for agriculture, forestry and other land-use (AFOLU) strategies; however, at their upper limits, the mid-century projections are greater than those estimated from recent studies1 (up to 5 GtCO2 yr-1 by BECCS, and up to 3.6 GtCO2 yr-1 from afforestation). Some scenarios place a greater emphasis on demand-side measures and rely more on AFOLU, thus eliminating the need for BECCS entirely17.
In the case of “overshoot pathways” (where a temporarily greater than1.5°C of global warming is allowed to occur), reliance on CDR is made to remediate the emissions later in the century so that, by 2100, the global average temperature is brought back to below 1.5°C; naturally, the greater the overshoot, the more CDR is necessary17. The strategy is problematic, however, since how quickly, and on what scale, CDR methods might be adopted depends on various factors, both technical and fiscal, and also how acceptable they are to various societies; hence there is uncertainty as to how effective this approach will be in remediating an overshoot. Furthermore, present comprehension of the behaviour of the climate system/carbon cycle is insufficient to know exactly how effective the introduction of net negative emissions (by CDR) will be in bringing temperature back down after the peak17. This is a feature of the delayed response of the Earth systems, which is sometimes described as “climate inertia”.19
The large scale use of CDR is likely to affect land, soil, energy, and water, and the deployment of land to grow crops for bioenergy (biofuels and biomass) may compete with agricultural and food systems17,20; additional impacts upon biodiversity and other ecosystem functions and services are also likely. The deliberate switching of food production to regenerative agriculture20 is a strategy deliberately intended to restore and rebuild soil, capturing carbon in the process, with positive benefits on all the above mentioned factors, including protecting water supplies. It is concluded17 that good governance will be required to mitigate any trade-offs in land use, and guarantee that carbon is removed on a permanent basis, in terrestrial, geological and ocean reservoirs17. The report envisages that, rather than deploying a particular form of CDR at a very large scale, a more effective approach could be to utilise a range of such methods, on smaller scales. This would fit with the idea of localisation20-22. As noted17, those CDR strategies which implicitly restore natural ecosystems, and sequester carbon in soil, offer the combined and additional advantages of preserving and enhancing biodiversity, soil quality, and local food security20-22.
6. Adaptation measures.
Allowing that, even at 1.5 oC, the effects of climate change can at best be ameliorated, not stopped, it is necessary to ensure that the infrastructure of civilization is suitably designed to remain functional as these unfold; the most obvious example being coastal defences and flood protection measures. Various means to manage sea level rise have been proposed23, including tidal barriers, coastal armouring, elevated development, floating development, floodable development, living shorelines, and managed retreat, each of which has its particular advantages and drawbacks23. The highly ambitious strategy of geoengineering the Greenland and Antarctic glaciers directly, to hold back water, and slow sea level rise, has recently been mooted24. It has been proposed25 that “Roman concrete” might prove a robust and enduring material with which to construct sea walls for the protection of coastal cities against the effects of sea level rise, and also to fabricate tidal lagoons for electricity generation25. Since about a quarter of the Netherlands lies below sea level, and around two thirds of its land area is vulnerable to flooding (Fig. 3)11, a comprehensive water management strategy has been advanced to deal with the effects of rising sea levels, which involves accommodating some of the additional water on land, rather than simply trying to repel all of it26. However, other aspects of social infrastructure, including buildings, transportation, energy production, water supplies and Information and Communications Technology (ICT), need also to be rendered robust to the conditions anticipated to prevail as the climate changes27.
7. Comparison with other studies.
The Centre for Alternative Technology has devised an overall strategy - Zero Carbon Britain (ZCB)28 - for providing energy in the U.K. with zero carbon emissions by 2030, which involves cutting our overall use of energy from that in 2010 by 60%. ZCB can be considered as a “Green-Tech Stability” approach20. A large scale conversion of end-use energy to electricity is envisaged (eliminating oil, gas and coal) which is produced from renewable resources, particularly wind power and biomass. Energy use in buildings accounted for 45% of the U.K.’s total energy budget in 2010, and in ZCB it is assumed this can be reduced by 50%, by retrofitting existing buildings, implementing “passivhaus” standards for new build, and improving internal temperature control28. The use of computational approaches for designing buildings that are more energy efficient, along with other favourable features, has been described29,30. Similarly to the recent IPCC report1,17, ZCB also envisages substantial changes in diet (less meat) and according land use, with an appreciable expansion in the area of forest in the UK28. In a recent book31 by Dieter Helm, “Burnout”, it is proposed that natural gas can be used as a bridging fuel, en route to a future in which the primary energy source, in a largely electrified system, will be “probably solar, but not as we know it”. However, this implies a reliance on new and untried technology whose date and scale of installation is as yet unknown. Indeed, to change to a nearly “all electric” energy system would entail the installation of an entirely new distribution network, of much greater capacity than we have presently, and most likely of the smart grid kind, with the potential for energy savings, both in terms of primary (input) and end-use energy, although questions remain about how base-load power would be provided, which would require storage (battery technology) if solar is to be a key driver in the scheme31. A separate model32 suggests that we have already just passed the point at which the global average temperature can be stabilised to within the 1.5 oC rise, but we have 17 years left to restrain global warming to within the 2 oC limit32.
8. Climate restoration.
The necessity to undertake “climate restoration” 33-35 as a necessary means for ameliorating the atmospheric CO2 concentration, is being promoted, including by Professor Sir David King, a former Chief Scientific Advisor to the UK government, who has reasoned that it is necessary,“...to restore the global climate system back to the state it was in 50 years ago. This not only means de-fossilising the global economy reaching net zero emissions but also that we need to reach negative emissions. This means pulling carbon dioxide out of the atmosphere more efficiently that we are today” 36. However, there are fears that some methods of climate engineering (Fig. 4) could have unforeseen, adverse consequences37. For example, solar radiation modification/management (SRM) measures (Fig. 5) are not included in any of the available pathways assessed by the IPCC1,17, on the basis that: “although some SRM measures may be theoretically effective in reducing an overshoot, they face large uncertainties and knowledge gaps as well as substantial risks, institutional and social constraints to deployment related to governance, ethics, and impacts on sustainable development... They also do not mitigate ocean acidification.”
That the issue of global warming is inextricably connected more generally with “the world’s woes” has been emphasised38 by reference to “the changing climate” rather than the more restricted term “climate change”. Indeed, the many and various different “woe” elements, while presenting a long list, are really all symptoms of a too rapid and injudicious use of resources of all kinds, including the fossil fuels, rather than being separate problems in their own right20,38. Accordingly, when we delve into means for addressing climate change, reducing our carbon emissions, restoring and growing new forests, capturing more carbon in soils, retrofitting buildings and adapting other urban infrastructure, including transportation, to curb overall energy use, recycling phosphorus, using urban permaculture to grow more food locally, and so on, we begin to devise a plan for the inauguration of resilient and regenerative global societies, as an intrinsic and implicit part of the global climate20-22. Thus, it is a global imbalance in the human/resources system that must be redressed, in advance of systemic failure occurring. Indeed, the renowned biologist, E.O.Wilson, has proposed a “Half Earth” strategy, in which half the Earth’s land surface is kept free of humans, to allow it to recover its biodiversity, where wild plants and animals can live unimpeded by anthropogenic activities39. This begs an obvious question, of where will so many humans go, and the suggestion is “into cities”, where 54% of the human population already lives (74% in developed, and 44% in less developed countries20). Clearly, these will need to be “regenerative cities” 20, while the newly bestowed wilderness can nonetheless become home to different kinds of agriculture, which overall will need to become carbon neutral, and regenerative, and contain wildlife corridors20 and other features that do not impede the natural flow throughout such landscapes. In addition, the oceans need to be left partly unfished, and free to regenerate40.
The IPCC report1 emphasises7 the societal integration of strategies [climate resilient development pathways (CRDPs)] for limiting warming to 1.5°C, and alludes to countries which have managed to generate environmentally friendly jobs and to support social welfare programmes to reduce domestic poverty, in hand with providing sustainable transportation and green energy. Community values are also stressed7, such as Buen Vivir, which is based on how indigenous communities in Latin America live in alignment with nature, and is underpinned by “peace; diversity; solidarity; rights to education, health, and safe food, water, and energy; and well-being and justice for all.” (Ref.7). With a strong presence in Europe, the Transition Towns Movement, similarly promotes equitable and resilient communities through low-carbon lifestyles, food self-sufficiency and a focus on actions at the local level20,22. The conclusion is7 that: “such examples indicate that pathways that reduce poverty and inequalities while limiting warming to 1.5°C are possible and that they can provide guidance on pathways towards socially desirable, equitable and low-carbon futures.” The report was presented at the UN climate change COP24 conference41 in Katowice in December 2018.
The summary of the report was approved, line by line, by the governments of the world’s nations, including the US, Australia and Saudi Arabia; however, this alone does not reveal its full political dimension, and it is only on reading the document1 in depth, that its full potential ramifications emerge. Thus, while the summary emphasises that allowing a 2 oC rise will drive more extreme weather, sea level rise and ocean acidification, with detrimental effects on wildlife, crops, water availability and human health across the globe, it does not detail the further consequences of mass population displacement and migration, and possible outbreaks of war that are a likely consequence of exceeding the 1.5 oC limit. Indeed, climate change is a well acknowledged “threat multiplier” in terms of social and political instability, which enlarges the risks of conflict42. As noted in Section 4, due to a lack of published work on the subject, the total costs of 1.5 oC mitigation pathways were not assessed; however, precisely this point was addressed in another recent study, which concluded that it will cost just 50% more to keep the global average temperature from rising above1.5 oC, rather than 2 oC, by 210043.
9.1. Political considerations.
However, the politics of actually implementing the report’s conclusions are open to question, with somewhat mixed responses being received from around the world. Thus, the European Union has indicated44 that it might propose even more ambitious goals than outlined in SR15, while in India, the Centre for Science and Environment has reinforced the “catastrophic” consequences of a 2 oC temperature rise, and that even at 1.5 oC, there would be a substantial loss in crop yields and an increase in poverty45. The New Zealand minister for climate change has pointed out46 that the IPCC recommendations are “broadly in line with Government's direction on climate change and it's highly relevant to the work we are doing with the Zero Carbon Bill.” On the other hand, in Australia, the Prime Minister emphasised that the report was not specifically for Australia but for the whole world47, while its Environment Minister is quoted as saying that the report is “drawing a very long bow” to say coal should be phased out by 2050, and, "I just don't know how you could say by 2050 that you're not going to have technology that's going to enable good, clean technology when it comes to coal... That would be irresponsible of us to be able to commit to that." (Ref.47). In the US, President Trump has said that he doesn't know that human activities are responsible for climate change and "it'll change back again", adding that the scientists have "a very big political agenda" and that “we have scientists that disagree with [anthropogenic climate change].” (Ref.48).
Indeed, to meet the 1.5 oC target would require economic transformations49 at an unprecedented rapidity and scale, centred around the elimination of some 42 Gt of CO2, globally, by 20501. To achieve this, a three-fold increase in the implementation of low-carbon electricity , from the current 25% share, is necessary, along with a dramatic elimination of essentially all vehicles that use internal-combustion engines, which currently is practically all of them. Although some encouragement can be taken from the rapidly increasing number of electric cars being driven (anticipated by the International Energy Agency (IEA) to reach 125 million by 2030)50, along with the development of various zero-carbon technologies, and the increasing availability of green finance, the challenges are immense.
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Captions to figures.
Fig. 1. Bleached Acropora coral (foreground) and normal colony (background), Keppel Islands, Great Barrier Reef. https://upload.wikimedia.org/wikipedia/en/9/90/Keppelbleaching.jpg Credit: Acropora.
Fig.2. CCS. Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a fossil fuel fired power plant. https://upload.wikimedia.org/wikipedia/commons/b/b5/Carbon_sequestration-2009-10-07.svg Credit: LeJean Hardin and Jamie Payne Derivative work of: Jarl Arntzen.
Fig. 3. Extent to which the Netherlands would be flooded, without dikes. https://upload.wikimedia.org/wikipedia/commons/6/65/The_Netherlands_compared_to_sealevel.png Credit: Jan Arkesteijn.
Fig. 4. An example of climate engineering: an oceanic phytoplankton bloom in the South Atlantic Ocean, off the coast of Argentina. The aim of ocean iron fertilization, in theory, is to increase such blooms by adding some iron, which would then draw carbon from the atmosphere and fix it on the seabed. https://upload.wikimedia.org/wikipedia/commons/1/10/Phytoplankton_SoAtlantic_20060215.jpg Credit: NASA.
Fig. 5. Proposed solar radiation management (SRM) using a tethered balloon to inject sulfate aerosols into the stratosphere. https://upload.wikimedia.org/wikipedia/commons/f/f7/SPICE_SRM_overview.jpg Credit: Hughhunt