Climate change is considered one of the greatest threats to the ecosystems and also to economies and communities around the globe and, therefore, warrants mitigation actions with utmost urgency to be controlled within their possible impact. This case study will explore different techniques for mitigation towards controlling greenhouse gases while also strengthening resilience towards the climate.

It assesses technological, policy-based, and behavioural approaches at global, national, and local levels. The focus areas lie in renewable energy, energy efficiency enhancement, carbon capture and storage, and afforestation activities. The policy mechanisms that apply carbon pricing, emissions trading schemes, and international accords such as the Paris Accord are also studied.

Community initiatives, industrial initiatives at the corporate level towards sustainability, and changes in lifestyles that lessen the carbon footprint are also considered in the evaluation. The case study, in assessing the effectiveness and challenges of the approaches, highlights the necessity of having a multi-sectoral response to climate change. It concludes that technological innovation, coupled with political will and societal engagement, is critical in meaningful climate mitigation as well as a sustainable future.

Introduction
Climate change refers to long-term shifts in temperatures and weather patterns. Such changes may be caused by nature, such as a change in the sun's activity or volcanic eruption. However, since the 1800s, human activities have become the dominant cause of climate change, mostly from fossil fuel combustion, including coal, oil, and gas. Burning fossil fuels releases greenhouse gases that act as a blanket around the Earth, trapping the heat of the sun and increasing temperatures.

Carbon dioxide and methane are among the leading greenhouse gases responsible for climate change. These include the emissions resulting from gasoline when driving a car or coal when heating a building. Deforestation and the falling of trees also emit carbon dioxide. Agriculture, oil, and gas activities contribute to methane. Energy, industry, transport, buildings, agriculture, and land use are among the main sectors emitting greenhouse gases.

Climate change mitigation describes any action by governments, businesses, or people to reduce the amount of greenhouse gases, enhance carbon sinks that remove them from the atmosphere, or reduce their production. These gases trap heat from the sun in our planet's atmosphere and keep it warm.

Since the Industrial Revolution, human activities have emitted dangerous levels of greenhouse gases and triggered global warming and climatic changes. Despite the definite research regarding consequences implied by our impact on the planet's climate and increasing awareness of the grave danger climate change represents to our societies, the increase of greenhouse gas emissions continues to persist. This case study assesses these different mitigation strategies, exploring their efficacy, barriers to growth, and potential for replication. It includes examples from different sectors and regions of the real world with a view to underlining the need for addressing this challenge in a multi-faceted and coordinated way due to its complex and interlinked dimensions.

Climate Change Mitigation Strategies

There are three main climate change mitigation strategies. One is the conventional mitigation that relies on de-carbonisation technologies and techniques to reduce CO2 emissions, including renewable energy, fuel switching, efficiency gains, nuclear power, and carbon capture storage and utilisation. Most of these technologies have been proven and an acceptable degree of managed risk.

A second approach is one representing a new generation of technologies and methods that have recently been proposed. These techniques may be used in the process of capturing and sequestering carbon dioxide from the atmosphere and are known as negative emissions technologies, although they are also referred to as carbon dioxide removal methods.

The principal negative emissions techniques thoroughly explored in the literature encompass bioenergy with carbon capture and storage, biochar, enhanced weathering, direct air carbon capture and storage, ocean fertilization, ocean alkalinity enhancement, soil carbon sequestration, afforestation and reforestation, wetland construction and restoration, and alternative negative emissions utilization and storage, including mineral carbonation and use of biomass in construction.

A third approach attempts to alter the earth's radiation balance by altering solar and terrestrial radiation. These approaches are considered radiative forcing geoengineering technologies, with the primary intent being to stabilize or lower the temperature, as opposed to negative emissions technologies, because it does not alter the concentration of greenhouse gases in the atmosphere. The main geoengineering techniques discussed in the literature include stratospheric aerosol injection, marine sky brightening, cirrus cloud thinning, space-based mirrors,surface-based brightening, and various radiation management techniques.

All these techniques are still theoretical or at very early stages of trial and carry a lot of uncertainty and risk with regard to practical large-scale deployment. These geoengineering techniques, which involve radiative forcing, have not been incorporated in policy frameworks to date.

1. Conventional mitigation technologies:

   As discussed above, energy-related emissions are the primary cause of rising concentration levels of greenhouse gas in the atmosphere; therefore, available mitigation technologies and efforts should be targeted to both the supply and demand sides of energy. Most of the discussed efforts within the literature cover technologies and techniques applied in four major sectors: power on the supply side and industry, transportation and buildings on the demand side. Under de-carbonisation within the power sector, renewable energy, carbon capture and storage, nuclear power, and supply-side fuel switch to low-carbon fuels such as natural and renewable fuels. Let's get into each of these in detail:
   • Renewable Energy Renewable energy is central to climate change mitigation since it significantly reduces the emission of greenhouse gases. Other notable renewable energy sources include solar, wind, and hydropower, as these replace fossil fuel-based usage, thereby establishing lower carbon footprints and cleaner energy transitions. The most common types of renewable energy are wind, solar, hydropower, biomass, and geothermal energy. These sources of energy are renewable and generally cause relatively minimal impact on the environment, thus setting them apart from the fossil fuels that contribute significantly to emissions. Investment in renewable energy technologies generates considerable economic growth and job creation.
      
   • Nuclear Energy Nuclear energy production currently generates 10 percent of global electricity without carbon emissions. Such forms of production, therefore, remain a significant source of low-carbon electricity because they constitute about one-quarter of the world's low-carbon energy supply. By exploiting nuclear technology, countries will reduce their reliance on fossil fuels and consequently reduce their overall carbon emissions by significant quantities. Using nuclear power, one can avoid releasing about 2 billion tonnes of CO2 annually, equivalent to taking 400 million cars off the roads worldwide. Nuclear reactors have avoided the emission of more than 72 billion tonnes of CO2 compared to electricity from coal-fired generation over the last fifty years. This enormous reduction explains how nuclear power can be a force against climate change.
      
   • Carbon capture, storage and utilization Carbon capture and storage is a promising technology discussed in the literature for which decarbonization can be used for both the power and industry sectors. This technology involves separating and capturing CO2 gases from various processes that depend on fossil fuels such as coal, oil or gas. The captured CO2 is transported and stored in geological reservoirs for many years. Major scope: The scope consists of a diminution in emission levels and fossil sources' use. There exists a huge-scale deployment of carbon capture storage and utilisation technologies, yet to be proven.
     
      

2. Negative Emissions Technologies:

   The Intergovernmental Panel on Climate Change (IPCC) examined most of the climate pathways with the combinations of traditional decarbonization technologies and the negative emissions technologies, in order to assess whether and by how much the goal of the Paris agreement is feasible. To date, the IPCC assessments include only two negative emissions technologies, namely bioenergy carbon capture and storage together with afforestation and reforestation:
   • Bioenergy Carbon Capture and Storage (BECCS) BECCS or Bioenergy with Carbon Capture and Storage melds bioenergy produced from organic matter by capturing and storing carbon dioxide. Whilst plants are growing, they absorb CO₂ from the atmosphere; when such biomass is combusted as energy, the CO₂ released is captured and put below ground. The model shows that by 2050, BECCS could potentially remove between 0.5 and 5 gigatons of CO2 annually. Large-scale production of bioenergy has had a major challenge - it demands considerable land and water use, often competing with food crops.
      
   • Afforestation and Reforestation Afforestation is the practice of planting new forests on lands that in the past haven't been forested, whereas reforestation involves replanting areas where forests have been cut down. Forestation would remove 0.5 to 3.6 gigatons of CO₂ annually up to 2050. Challenges with forests are that they are susceptible to various disturbances such as fires or loggings that could, after a long time, release the trapped carbon back into the atmosphere.
      
   • Biochar Biochar is charcoal form produced from biomass applied in the soil to increase its quality and act as a carbon reservoir. The carbon in biochar is more stable and stays in the soil for hundreds and thousands of years. Biochar could sequester 0.3 to 2 gigatons of CO2 per year by 2050. The likelihood of doing so will depend on the type of biomass used and the conditions under which it is produced. Significant amounts of biomass might be required for large-scale biochar production, mainly in direct competition with food crops or other land uses.
      
   • Direct Air Carbon Capture and Storage (DACCS) The technology employs chemical processes to capture CO₂ directly from the air and store it in long-term storage options such as underground storage. A theoretical application is it may be able to remove huge amounts of CO₂, but it's very costly. One of the major hurdles for large-scale use of a process is that it has high energy demands and expense.
      
   • Enhanced weathering Enhanced weathering captures the mineral, which under natural conditions on land reacts with CO₂. The mineral will combine to covalently bond with CO₂ and the minerals will be converted into stable carbonates, locking away the carbon for millions of years. This method would sequester 2 to 4 gigatons of CO₂ per year by 2050. It would call for large-scale mining as well as mass distribution of such minerals.
      
   • Soil Carbon Sequestration Several processes by which the ocean absorbs vast amounts of atmospheric CO2 each year have already been established. These include CO2 diffusion from the atmosphere into water through partial pressure differences between the atmosphere and the ocean. Photosynthesis by phytoplankton constitutes the other route. Techniques like no-till farming, cover cropping, and other regenerative agriculture techniques increase carbon storage in the soil. This is a problem because carbon sequestered into the soil has limits, and the amounts that have been sequestered can again be released out, especially if the land management practices that led to this accumulation are not sustained.
     
      

3. Radiative forcing geoengineering technologies:

   Radiative forcing geoengineering techniques involve methods that try to change the radiative energy budget of the earth to stabilize or reduce global temperatures. These are done either by enhancing the earth's reflectivity through augmenting shortwave solar radiation reflected to space or by increasing longwave radiation emitted by surfaces of the earth to space: hence referred to as terrestrial radiation management:
   • Stratospheric Aerosol Injection Stratospheric aerosol injection injects reflective particles, such as sulfur dioxide, into the stratosphere to provide a cooling effect like an artificial volcanic eruption. It is said that the volcano at Mount Pinatubo cooled the planet by approximately 0.5°C during 1991. This technology will work to reflect some of the sun's rays back to space and cool the Earth. The potential cooling load would be 2-5 W/m² by the model's estimate; however, there are risks: hydrologic cycle disturbance and ozone layer degradation.
      
   • Marine Sky Brightening This is still at the research stage. This technique, known as marine sky brightening or cloud albedo enhancement, adds the effect of an increase in the reflectivity of clouds over the ocean. Salt crystals form by spraying seawater particles into the atmosphere, and thus enhance the reflectivity of the clouds when sunlight reflection is considered. This technique could lower global warming to the amount of 0.8 to 5.4 W/m², but so much remains to be done in the process - a big challenge posed by technology that can produce quantities of seawater particles and the full environmental impacts of this method.
      
   • Space-based Mirrors Space-based mirrors may reflect sunlight back into space to cool the Earth. The mirrors would be placed in space, perhaps at a location where Earth's gravity equals that of the Sun. Although in theory capable of being coolers by significant degrees, the technology isn't yet practical because the cost of transportation in space is now more than $10,000 per kilogram. Sustained lowering of this figure to less than $100 per kilogram and controlling risks from space debris have to come before this will be practicable.
      
   • Surface-based Brightening Brighten up the Earth by increasing its reflectivity using manipulation of surfaces, such as urban rooftops, glaciers, or deserts. The techniques include painting surface white or depositing reflective materials across deserts. Since the inherent disadvantage of these techniques is the inefficiency in radically affecting climate at a global scale, only localized cooling can be achieved at the expense of general ecosystems, such as those in deserts.
      
   • Cirrus Cloud Thinning These clouds retain heat and lead to global warming. One of the techniques to reverse this problem is through injecting aerosols into cirrus clouds so that they can be thin and life-limiting. That would cause more heat to evade from the Earth and go into outer space. Now, early models show a cooling effect of 2 to 3.5 W/m², but research is still ongoing, especially for developing a cheap delivery system, including drones or aircraft.

Conclusion
Based on the present state of the climate emergency, the urgent development of feasible mitigation and adaptation mechanisms is a matter of utmost importance. An extensive literature review focused on three main strategies for tackling climate change: conventional mitigation technologies, negative emissions technologies, and radiative forcing geoengineering technologies. It should be mentioned that for the cause, there is no ultimate solution; however, it must be noted that all technologies and techniques discussed in this review are technically and economically viable and should be deployed.

As aforementioned, decarbonisation efforts alone do not suffice to meet the stipulated targets by the Paris Agreement, hence the inevitability of utilising an alternative abatement approach. This geo-engineering of radiative forcing concept in terms of the Earth's radiation budget is intriguing. Still, since it deals only with symptoms rather than the cause of the root problem, it is not a long-term solution. It might, however, buy some time until greenhouse gas concentrations are stabilised and reduced.

However, the technologies to be deployed still have to be developed and tested and side effects adequately catered for, which may be a long process. Negative emissions technologies offer a sound solution in tandem with the efforts currently under way in decarbonization. While biogenic-based sequestration techniques have attained a relatively more mature stage and could be introduced immediately, some negative emission technologies mentioned in the literature review are still at a relatively immature stage. However, capturing CO2 through photosynthesis is very straightforward and solid; what is needed is to integrate it effectively into a technological framework, as described in the review.

The challenge at this point is that carbon pricing for negative emissions is still at a very infant stage, mainly found in voluntary markets for a very small number of carbon removal methods and technically non-existent for most of the technologies discussed. So far, carbon pricing would be insufficient for sustaining the economics of carbon removal projects in most cases, except for the existing framework for afforestation and reforestation projects.

This could evolve in the near future as carbon markets mature and provide incentives to carbon removal. Appropriate policy instruments and support frameworks devising special emphasis on carbon pricing should be developed by policymakers and governments to aggressively push negative emissions projects. In addition to this, financial industry should be able to give better access and improved financial support with introducing efficient market-based mechanisms that encourage project developers to implement carbon removal projects.

There is actually good opportunity for efficient deployment of financial resources and policy support to biogenic-based sequestration projects at the moment because most of the related technologies will be deployed immediately, although aggressive development and introduction of efficient carbon pricing mechanisms with a focus on carbon removal will be a must. Funding for technology research and development is also important in this regard moving forward.

References:

1. United Nations, What is climate change, https://www.un.org/en/climatechange/what-is-climate-change, last visited on Sep. 25, 2024.
2. Fawzy, S., Osman, A.I., Doran, J. et al. Strategies for mitigation of climate change: a review. Environ Chem Lett 18, 2069–2094 (2020)