Most of the data used for this study were derived from online data sources. Data on carbon emissions in the United States were obtained from Anderson et al. (2021) and World Bank (2017) . Tiseo (2024a) , Tiseo (2024b) , and The Climate Policy Info Hub provided data on carbon emissions in the European Union whereas the U.S. Energy Information Administration (2022, 2023) provided data on energy-related carbon emissions in the U.S. in 2000, 2010 and 2020. Data on the decarbonization strategies in the U.S. were acquired from Ristic et al. (2019) and D’Aprile et al. (2020) . Finally, Lawson (2018) and the Office of Energy Efficiency & Renewable Energy (2022, 2023) provided data on the decarbonization strategies in the European Union.

The study used a GIS-based methodology to visualise per capita energy-related carbon dioxide emissions in the United States of America and the European Union for the years 2000, 2010, and 2021. The ArcGIS software was used to combine carbon emissions data from the United States and the European Union into an attribute table, which was then linked to a shapefile. Six distinct maps were created using the symbology tool and the graduated colour option to illustrate the spatial distribution of carbon emissions. Furthermore, three bar charts were used to depict total carbon dioxide emissions and emissions by sector in the United States, as well as the percentage of total greenhouse gas abatement and the relative reduction of CO₂ in the EU compared to 1990. Furthermore, a pie chart was used to represent the RAF’s (Resource Availability Factor) sensitivity to resource availability in the EU.

The average carbon emissions per state and country for the United States and European countries data, were respectively modeled according to the following formulation.

The models for the average carbon emissions per state and country for the United States and European countries years were modeled based on the following respective formulations.

Average carbon emissions, C ∝ f(t)

Where C is the average carbon emissions per state and country for the United States and European countries.

For linear model, the expression for C can be transformed to the following equation.

C = +At + B (1)

where C is the average carbon emissions per state and country for the United States and European countries, and A is the constant of proportionality.

where A is a coefficient of proportionality and B, the vertical axis intercept, respectively.

For quadratic model,

C = At² + Bt + C (2)

where A and B are coefficients of proportionality, and C the vertical axis intercept, respectively.

Curve fitting with statistical software was next applied to data pair sets for the United States and European countries to determine the models for prediction of average carbon emission. The models are presented in section 6.3.

With reference to Figure 1 , the pattern of the data on carbon emissions in the U.S. has been undulating. Carbon emissions in the U.S. slightly decreased and increased until 2018 when the country recorded a sharp drop in emissions. There was a slight increase from 2009 to 2010 and a sharp drop from 2010 to 2012 and the carbon emission rate in the U.S. has been decreasing since then. The increase in energy-related CO₂ emissions was caused by both short-term and long-term indicators.

Increased use of petroleum products, notably in the transportation sector, contributed to more than half of the increase in CO₂ emissions in the United States. Carbon emissions from motor gasoline in the United States went up by 9%, while jet fuel rose by 27%, as tourism began to recover ( Sartor et al., 2017 ). In 2021, the United States energy consumption produced 4.9 billion metric tonnes of carbon dioxide (GtCO₂), a 7% increase over 2020 levels. Emissions fell in 2020 as a result of COVID-19, which significantly damaged polluting industries, but increased in 2021 as restrictions and lockdowns were lifted ( U.S. EIA, 2021 ). The COVID-19 pandemic had a significant impact on the US and global economies, as well as carbon dioxide emissions, by 2020. In 2021, the energy market and carbon emissions from energy began to revert to pre-pandemic levels. Overall energy-related carbon emissions in the United States rose by 7%, or 325 million metric tonnes (MMmt), in 2021, especially in contrast to 2020; nevertheless, total emissions in 2021 were still 5%, or 242 MMmt, lower than in 2019 ( Sartor et al., 2017 ).

Remarkably, certain countries have recorded lower carbon emissions in recent times which may be attributed to a decrease in their reliance on coal and other household resources for energy. For instance, an analysis of EU emissions shows that the union’s carbon emissions have decreased by 5% ( Myllyvirta, 2022 ). Data on the amount of carbon emitted by 26 countries in the EU has been represented in Table 1 .

Source: Tiseo (2024a) .

Average linear model for average carbon emission for EU countries with respect to years, based on data from Table 1 is presented in Figure 2 .

Based on 2010-2021 data, the average emissions per country in European countries has been gradually increasing, specifically from 104.5 to 134.8 metric tons per country. Figure 2 illustrates the general trend in average carbon emissions per country in Europe. However, the proportion of total global pollution attributable to Europe is reducing because of industrialization taking place in developing countries. Figure 3 , Figure 4 and Figure 5 illustrate the carbon emission rates by each country in the EU in 2000, 2010 and 2021, respectively.

In 2000, countries like Croatia, Lithuania and Denmark recorded relatively low carbon emissions ranging from 7.4 to 28 Mt, while Romania, Greece, Portugal, and Sweden had slightly higher emissions between 28 and 92.4 Mt. In contrast, France, Spain, Italy, and Poland reported significantly higher emissions exceeding 178 Mt. Germany, however, is seen to have recorded the highest emissions ranging between 311Mt to 628 Mt approximately.

In 2010, Croatia and Lithuania maintained low carbon emissions between 9.2 and 22.9 Mt, reflecting a decrease of approximately 6 Mt compared to the emissions in 2000. Romania, Greece, Portugal, Sweden, and Finland recorded slightly higher emissions between 22 and 94.6 Mt. On the other hand, France, Spain, Italy, and Poland reported emissions exceeding 226.5 Mt, with Germany recording the highest at 783 Mt, which is approximately over 100 Mt of carbon emitted since 2000.

In 2021, Croatia and Lithuania for instance continued to record low carbon emissions, ranging from 6.9 to 17.5 Mt, reflecting a further decrease of approximately 6 Mt. Meanwhile, Greece, Portugal, Sweden, and Finland saw emissions rise slightly to between 17.5 and 102.6 Mt, an increase of about 8 Mt compared to 2010. France, Spain, Italy, and Poland slightly maintained emissions exceeding 216.5 Mt, with the highest at 434 Mt, marking a notable increase. Germany recorded the highest emissions at 854 Mt, an increase from 783 Mt in 2010, continuing its upward trend over the years.

Over time, Latvia, Estonia, Lithuania, and Croatia have consistently had the lowest levels of carbon emissions among countries, while Germany has consistently been the top emitter of carbon dioxide. An increase in carbon emissions between 2000 and 2010 was observed in all the countries. However, whiles some

countries recorded a higher amount of carbon emissions between 2010 and 2020, others recorded low values. There was a drop in carbon emissions from 2010 to 2020 in countries such as Poland, Netherlands, Austria, Bulgaria, Finland, Estonia, Croatia, Lithuania, Slovenia, Luxembourg, Latvia, and Cyprus. On the other hand, countries that recorded an increase in carbon between 2010 and 2020 include Germany, Italy, France, Spain, Belgium, Czechia, Romania, Greece, Hungary, Sweden, Portugal, Ireland, Slovakia, and Denmark. The highest carbon emissions across the years were recorded by Germany and Cyprus. In 2021, the European Union generated nearly 2.73 billion metric tonnes of carbon dioxide. In comparison to 2020 levels, this represented a more than 6% increase. In 1979, the greatest amount of carbon emissions generated in the EU was 3.99 billion metric tonnes ( Tiseo, 2024c ). The significant decrease in emissions in 2020 was caused by the COVID-19 pandemic and the resultant lockdowns and restrictions. As travel was severely impacted, EU transportation emissions decreased, while emissions from industrial processes and power supply were also affected. Carbon emissions in the European Union dropped by 22% in April 2020, during lockdowns, against the same month in 2019. Germany is the EU’s largest source of CO₂ emissions. Even though there has been a nearly 24 percent decrease in emissions since 2005, Germany still discharges significantly more than other major emitters in the EU, such as France, Italy, and Poland. This is primarily due to Germany’s reliance on coal in its energy mix. Coal is the filthiest of all fossil fuels, emitting roughly half as much CO₂ as natural gas ( Tiseo, 2024c ). The Coronavirus pandemic took over the world beginning in early 2020, killing millions and halting day-to-day economic activity. These restrictions had a major and immediate impact on carbon emissions, which dropped in 2020. However, the decline was only momentary, and emissions increased as economies opened up. Following Russia’s invasion of Ukraine in March 2022 and the militarization of energy supplies to Europe, the recovery from the pandemic has been accompanied by a worldwide energy crisis ( Myllyvirta, 2022 ).

GHG emissions from the industrial sector are controlled by energy and process-related carbon dioxide, but they also encompass CH₄, N₂O, and fluorinated gases (HFC, PFC, SF6), with the fluorinated gases saturated in the chemical industry. Carbon dioxide recorded over 94% of carbon dioxide equal GHG emissions in the EU-28 manufacturing industry in 2012 ( Myllyvirta, 2022 ). According to the Karakosta (2016) , the industrial sector represents the largest share of carbon emissions in the EU, followed by the transport sector, other sectors, the agricultural sector, and the waste sector. Within the industrial sector, energy industries emitted the most carbon (31%), with manufacturing and construction following (13%), then industry processes (14%). According to new data, the European Union’s carbon dioxide (CO₂) emissions from energy use have decreased by 5% in the last three months in comparison to the same period in 2021. In the EU6, industrial emissions are responsible for more than half of total GHG emissions. Figure 6 depicts the proportion of industrial GHG emissions in the EU, along with a further dissection by the source of emissions ( Myllyvirta, 2022 ).

Data for average carbon emissions for states in the US is presented in Tables 2-6 .

An examination of the data presented in Table 2 , Table 3 , Table 4 , Table 5 and Table 6 reveals two trends that are identified as a rise (1970-2005) and a decrease (2005-2020). Hence, the models of average carbon emissions per state in the US for each trend was modeled using Microsoft Excel and presented in Figure 7 and Figure 8 respectively. In the rising trend, the emissions rose from about 80 to just below 120 Units.

According to the decreasing trend model, the average emission per state in the United States of America decreased steadily from 116 units to 100 units in 2018, according to the equation presented in Figure 8 . The drops in 2019 and 2020 resulted mainly from reduction in the emission from the transportation sector following restriction from movements following lockdowns. Also, in April 2020, the social restrictions in the United States because of COVID-19 led to a drop in electricity demand from the industrial and commercial. In 2019, truck freight slowed down because of an initial spike at the beginning of the pandemic. According to the Energy Information Administration, the emission was expected to increase in 2021 and 2022, and then stabilize in 2023 ( U.S. Energy Information Administration (EIA), 2022, 2023 ). As shown in Figure 9 , if US keeps up with its decarbonization effort, its expected average carbon emissions per state by 2030 can be estimated by linear interpolation of the decreasing model using Microsoft Excel. The expected average state emission by 2030 is approximately 83 Units.

Regression analysis using Microsoft Excel statistical tool kit was applied to the data to determine whether the decrease from 2005 to 2018 was statistically significant. The regression summary y is presented in Table 7 .

From the regression summary, the p value is less than 0.05. hence, the model is statistically significant. Hence, foe every additional year, the average carbon emission per state in US decreases by about 1.15 (in metric tons).

To make well-informed choices about how to lessen greenhouse gas emissions, it is essential to comprehend how various economic sectors play a part in greenhouse gas production and how these patterns have developed over time ( U.S. Department of Commerce, 2010 ). The transportation sector is the primary source of CO₂ emissions in the United States ( Schneer, 2019 ). Emissions of greenhouse gases have risen significantly since the pre-industrial era and are currently increasing at such a rate that their levels in the atmosphere are causing rising temperatures. For so many years, the electricity sector was the country’s largest source of carbon emissions, however, a switch away from coal-based power generation has reduced emissions from this sector. In the meantime, transportation emissions have remained on the rise, with the exception of a historic drop in 2020. By far the largest contributor to worldwide transportation emissions is the United States. Texas and California have the highest transportation-related emissions in the United States ( EIA, 2023 ).

According to Anderson et al. (2021) , the transportation sector contributes the highest emissions in the US with 29% followed by the electrical power sector with a percentage of 25 then the industry, representing 23%. The least carbon emissions were recorded by the residential and commercial sectors and the agricultural sector, representing 13% and 10%, respectively. The industrial sector in the United States makes up 30% of national greenhouse gas (GHG) output, whereas the industrial sector internationally represents 40% of total GHG emissions. Using renewable energy only outlines a small portion of industrial emissions. Nevertheless, there are technologies and methods available now to help lower industrial emissions, as well as inventions that could completely decarbonize the sector. Manufacturing industries have been one of the fastest-growing international causes of greenhouse gas emissions since 1990, massively increasing in the last 30 years. This increase was primarily driven by increasing carbon pollution, but it was also caused by increased utilization of refrigeration and air conditioning, both of which generate hydrofluorocarbons (HFCs), which are powerful greenhouse gases. Direct industrial sector emissions result from on-site fuel combustion or carbon emissions from chemical reactions ingrained in industrial production. Direct industrial emissions now represent 23% of total greenhouse gas emissions in the United States, making it the third-highest emitting sector after transportation and electricity. The US Energy Information Administration (EIA) predicts that industrial energy demand in the United States will increase by 36% by the middle of the century. The United States is one of more than sixty countries that have set a goal of becoming a net-zero economy by 2050. Lowering global carbon emissions by 45% by the year 2030 will provide the entire world with the best chance of successfully achieving those targets ( Anderson et al., 2021 ).

Source: U.S Energy Information Administration (EIA).

According to the trend in per capita energy-related carbon dioxide (CO₂) emissions in Table 8 , a significant decline is observed in the average emissions by all states from 20.79 in the year 2000 to 18.1 in 2010, and a further substantial reduction to 13.9 in 2020. Notably, these major reductions depict progress towards mitigating the environmental impact of CO₂ emissions and fostering a more sustainable environment.

For instance, in the year 2000, the highest recorded CO₂ emissions varied significantly, ranging from approximately 50 to 128 metric tons as seen in Figure 10 . By 2010, the highest emission rate narrowed to a range between 79 and 116 metric tons, and further reduced to 50 to 96 metric tons in 2020 as seen in Figure 12 and Figure 13 respectively. For the record, some of the states that recorded high CO₂ emissions in the year 2000 include Alaska, North Dakota, Wyoming and West Virginia as seen in Figure 10 . States like Texas, Montana, New Mexico, Louisiana, Alabama and Indiana however recorded the second highest CO₂ emissions ranging between 30 to 49 metric tons. On the other hand, some states like Washington, Oregon, California, New York and Florida recorded low CO₂ emissions which ranged between 8 and 15 metric tons of CO₂ as seen in Figure 10 .

With respect to the reduction in CO2 emissions recorded in the year 2010, Figure 11 shows how states such as Alaska, North Dakota and West Virginia which recorded high CO₂ emissions in year 2000, recorded lower CO₂ emission rates in year 2010 ranging between 79 and 116. Even though the highest emission rate recorded in 2010 is a reduction from year 2000, Wyoming remains the only state that still recorded high CO₂ emissions in year 2010 as seen in Figure 11 . Other significant reductions are also observed from states such as Nevada which recorded CO₂ emissions of about 23 metric tons in year 2000 but recorded lesser emissions of 15 metric tons in year 2010 and 12 metric tons by 2020 as seen in Table 8 . Similarly, a state like Texas recorded a significant CO2 emission reduction from 32 metric tons in 2000 to 24 and 21 metric tons in the years 2000 and 2010 respectively. Even though the state of Louisiana stands out as the only state where CO₂ emissions still falls within a range expanding from 30 to 49 metric tons in the year 2000 to a broader range of 36 to 78 metric tons in 2010 in Figure 11 , the state still recorded a reduction of CO2 emissions moving from 49.33 in 2000 to 44.8 and 39.4 in 2010 and 2020 respectively.

By the year 2020, as compared to 2010, a drastic reduction in CO₂ emissions was recorded from all the states by which the highest rate dropped to a range between 50 and 96 as seen in Figure 12 . While this is still a reduced emission rate as compared to year 2010, a state like Wyoming still recorded the highest emissions of CO₂ as compared to the other states. That is, Wyoming recorded CO₂ emission rates of about 128 metric tons in year 2000 with a decrease to about 116 metric tons in 2010 and about 96 metric tons in 2020, still being the highest among the other states.

However, most of the western states such as Washington, Oregon, Idaho, California and a southeastern state like Florida have consistently recorded reduced CO₂ emission rates that range from 8 to 15 in 2000, 5 to 15 in 2010 and a significant reduction range between 4 and 11 in 2020.

The declining trend of CO₂ emissions recorded in the years 2000, 2010, and 2020 by most of the USA states is therefore an indication and reflection of the states’ commitment in reducing greenhouse gas related climate change effects to create a healthy environment and a sustainable future.

Over the last decade, the United States has seen an unexpected massive increase in extreme weather events driven by climate change that has caused over $800 billion in losses and killed over 5200 people—a pattern that appears set to continue. Simultaneously, the significance of a substantial initiative to decarbonize the United States’ electricity grid has become completely obvious, as have the growing climate threats and consequences that such an initiative will encounter ( Pawar, 2021 ).

According to Lawson (2018) , the use of coal to generate electricity in the U.S. slightly increased in 2000, slightly dropped in 2015, and further dropped in 2015. The use of this energy source has been projected to be stable till 2050. Petroleum was only used to generate electricity from 1990 to 2005. There has been an increase in the use of natural gas to generate electricity from 2010 to 2050. With regards to the use of nuclear for electricity generation, the amount is stable throughout the year whereas the use of renewables is stable at the beginning but slightly increases throughout the years. Finally, there has been minimal use of other energy sources in the US for the generation of energy. On the other hand, since the country has made a conscious effort to adopt some decarbonization strategies to fight climate change, carbon emissions dropped sharply in 2015 and it is projected to further decrease in the coming years.

The Masterplan identifies four crucial technological core elements for substantially emissions reduction in the subsectors. Alternative methods have the ability to reduce 100 percent of CO₂ emissions each year. Energy efficiency; industrial electrification; low-carbon fuels, feedstocks, and energy sources (LCFFES); and carbon capture, utilization, and storage are the major decarbonization foundations (CCUS). These foundations are relevant across all industrial subsectors and have the potential to achieve current and future cuts. Entergy efficiency is a fundamental decarbonization strategy that is also the most economical alternative for reducing GHG emissions in the short term. Decarbonization efforts encompass a) tactical energy conservation strategies to optimize the system-level performance of manufacturing processes; b) systems management and enhancement of thermal heat from production process heating, boiler, and combined heat and power (CHP) sources; and c) smart factory and sophisticated data analytics to maximize energy productivity in production processes ( Office of Energy Efficiency & Renewable Energy, 2022, 2023 ).

In terms of industrial electrification, harnessing progress in low-carbon electricity from both power systems and onshore renewable power sources will be essential to decarbonization endeavors. Decarbonization initiatives include a) electrification of heat sources via induction, thermal radiation heating, or innovative heat pumps, b) electrification of high-temperature range processes such as those encountered in iron, steel, and cement manufacturing, and c) substituting high-temperature processes with electrochemical ones. Low-Carbon Fuels, Feedstocks, and Energy Sources (LCFFES) involve replacing low- and no-carbon fuels and feedstocks for manufacturing processes to reduce combustion-related emissions. Carbon Capture, Utilization, and Storage (CCUS) is a multi-component approach that entails collecting derived carbon dioxide (CO₂) from a single point and either utilizing the captured CO₂ to create value-added products or stockpiling it long-term to avoid discharge ( Office of Energy Efficiency & Renewable Energy, 2022, 2023 ).

The European Union (EU) has set a goal of achieving climate neutrality by 2050, which means that its economy will emit no net greenhouse gases. This transition to a climate-neutral society is seen as both a pressing challenge and an opportunity to create a better future for all ( European Commission, 2023 ). The European Commission proposed an ambitious plan in December 2019 to ensure that the European Union (EU) achieves climate neutrality by 2050. While this proposal outlined specific emission reduction targets for 2030 and 2050, it did not provide explicit details on the distribution of responsibilities among sectors and member states, nor did it provide estimates of the costs associated with achieving these reductions ( D’Aprile et al., 2020 ). By 2030, the European Union (EU) intends to reduce emissions significantly through two main strategies: large-scale electrification and improved energy efficiency. These strategies are expected to contribute 47 percent and 17 percent of the total reduction, respectively. Additional measures focusing on the demand side and circularity would cut emissions by 15%. The use of hydrogen as an alternative energy source is expected to contribute another 13% to the reduction of emissions. The remaining reduction is expected to come from increased biomass utilisation, changes in land use, and other innovative solutions ( D’Aprile et al., 2020 ). Member states of the EU are required to develop national long-term strategies in order to meet their obligations under the Paris Agreement and the EU’s goals. These strategies outline how they intend to reduce greenhouse gas emissions to the required levels ( European Commission, 2023 ).

Figure 14 depicts the results of the RAF analysis using all criteria (levelized cost, carbon, water, and land footprint). There were no exclusively ideal or strictly poor technologies when all preconditions were equally valued. This is due to uncertainty in performance scores as well as discrepancies in the optimality principles of various MCDM methods. A non-zero RAF value indicates that the MCDM methods disagree in assessing the complete safest alternative for the unclear performance values. Similarly, the omission of RAF = 100 indicates that the MCDM methods disagree in assessing the worst alternative. According to Figure 14 , nuclear and geothermal operate comparatively better than the other technologies. Biomass, oil, and large-scale hydropower are the poorest roughly comparable technologies. Figure 14 shows that low-carbon technologies are generally desirable to hydrocarbons. This illustrates that switching from fossil fuels to renewable sources is probable to result in co-benefits for water and land because these technologies function better throughout all these eligibility requirements. However, biomass has the prospect to provide 19.1% of the European Union’s renewable power by 2020. ( Beurskens & Hekkenberg, 2011 ). As of now, biomass accounts for 54.5% of the renewable energy goals ( Atanasiu, 2010 ). The findings show that biomass was listed as the worst energy technology by 13 of 28 MSs (RAF = 100) ( Ristic et al., 2019 ).

With reference to Figure 15 , the most used decarbonization strategy to fight climate change in the EU is electrification and carbon neutral power, followed by energy efficiency and demand side measures and circularity. On the other hand, the least used methods to reduce carbon emissions are land use or agricultural practice changes and carbon capture and storage or use. Energy efficiency and electrification could reduce emissions by approximately two-thirds by 2030. The majority of the total carbon output lowered by bioenergy carbon capture and storage is credited to biomass, with the remaining half attributed to carbon capture and storage. Massive electrification and energy efficiency improvements would represent 47 percent and 17 percent of the European Union’s decarbonization strategy by 2030, respectively ( D’Aprile et al., 2020 ). The incorporation of digitalization is regarded as a critical factor in accelerating energy decarbonization in buildings. Given that people spend roughly 80% of their lives inside buildings such as offices, schools, hospitals, and homes, the impact of digital technologies becomes significant. According to Frei (2021) , buildings are also significant capital investments for businesses ( Frei, 2021 ). The efficiency of a building’s entire lifecycle, including its design, construction, and operation, can be greatly improved by incorporating digital technologies. Greater digitalization of the building value chain is critical for increasing competitiveness and fostering innovation (ibid).