بررسی اثرات پویای مصرف سوخت‌های فسیلی روی انتشار دی‌اکسید کربن در ایران

The issue of climate change has become a significant global concern over the past few decades. Greenhouse gas emissions, specifically carbon dioxide (CO2), resulting from the combustion of fossil fuels, are a primary contributor to this phenomenon. Of the various types of fossil fuels, natural gas and petroleum products are the most widely used. Specifically, gas oil, fuel oil, and gasoline have been the most commonly utilized petroleum products in Iran over the last five decades. To examine the relationship between fossil fuel consumption and total carbon dioxide emissions in Iran from 1955 to 2018, the current study employs the autoregressive distributed lag (ARDL) model. The findings reveal that fossil fuel use has multiple impacts on carbon dioxide emissions. Specifically, a one percent increase in the consumption of gas oil, fuel oil, natural gas, and gasoline results in a corresponding increase in carbon dioxide emissions of 0.55%, 0.32%, 0.32%, and 0.18%, respectively. The analysis of long-term elasticities reveals that a one percent increase in fossil fuel consumption corresponds to a 0.83%, 0.49%, 0.09%, and 0.34% increase in carbon emissions, respectively. The study's results demonstrate that the utilization of gas oil has the greatest negative impact on the environment and carbon dioxide emissions in Iran, both in the short and long term. Fuel oil and gasoline follow closely behind. In contrast, consuming natural gas has the least negative effect on carbon dioxide emissions and the environment in the long run. However, due to supply-side constraints and increasing natural gas consumption, switching from other fossil fuels to natural gas cannot be sustained as a long-term policy to reduce carbon dioxide emissions. Therefore, it is recommended that policymakers pay attention to both price and non-price policies, such as reforming price subsidies and advancing fossil fuel-related machinery and technology.

Introduction
The International Energy Agency (IEA)(2020), reported that Iran's final energy consumption increased from 2.290 million terajoules in 1990 to more than 4.8 million terajoules in 2019, with the largest share going to electricity with 940 thousand terajoules, petroleum products with 2.9 million, and natural gas with 4.5 million. Iran consumed around 12 exajoules of energy in 2020, ranking eighth among countries according to the Statista(2020). The world's energy use per person is an intriguing comparison to Iran's. The average global energy consumption per person is 20-megawatt hours. Of the energy sources, oil ranks top with more than 6-megawatt hours, followed by coal with more than 5.6 megawatt hours, and gas with 5-megawatt hours. The third one. Additionally, the same report states that Iran has a per capita energy consumption of over 41 megawatt hours, which is higher than the world average of 26.8 and 13 (Our World in Data, 2022). A country like Iran has used a lot of energy as a result of its slow economic growth rate, particularly during the worst and most unfavorable economic conditions of the past ten years. This has resulted in an excessive amount of carbon dioxide being produced. It is important to note that there is a direct link between the use of fossil fuels and the production of carbon emissions, meaning that as fossil fuel use increases, so do carbon emissions. Different types of fossil fuel consumption result in varying amounts of carbon emissions. According to Block and Mert (2015), the consumption of coal results in greater carbon emissions than the consumption of oil or natural gas. Iran's carbon emissions rose from 171 million tonnes in 1990 to 583 million tonnes in 2019, claims research from the International Energy Agency. The biggest quantity of carbon emissions, or 390 million tonnes, are attributed to the use of natural gas, according to the statistics that have been released. Iran has the sixth highest global carbon emission rate in 2020 with 745 million tonnes of CO2, making Iran's carbon emissions more than those of a developed nation like Germany (Global Carbon Atlas, 2020). The usage of fossil fuels, it may be inferred from the aforementioned, is a significant contributor to the carbon dioxide (CO2) released into the atmosphere. Pollutant emissions, particularly those of carbon dioxide, are another major factor in climate change and global warming. Iran contributes significantly to global energy consumption and pollution emissions as a nation that uses fossil fuels. Carbon dioxide makes up more than 83% of the gases that cause the phenomenon of global warming, therefore it may be claimed that regulating this gas involves regulating the entire earth's atmosphere. The globe will experience severe climate change and other negative repercussions as a result of this consumer behavior. One of the most significant effects of climate change is the acceleration of global warming and the ensuing rise in sea levels brought on by the melting of polar glaciers. In 2020, the global temperature will have increased by 1 degree Celsius from zero degrees in 1880, according to a report on temperature change and global warming during the last 40 years. According to projections, the temperature will rise by 6 degrees by the end of the century (National Aeronautics and Space Administration (NASA), 2020). One of the main concerns and problems facing all the nations of the world in this century is how to control climate change and global warming. The health of the entire planet is seriously threatened by the process of temperature change and global warming. Adopting sensible and sensible regulations is therefore essential if we are to shift this consumption pattern and lower pollution emissions. Concern over the recent spike in greenhouse gas emissions, particularly carbon dioxide, is the driving force for this study. According to the energy balance report from 2018, carbon dioxide is responsible for 99% of the greenhouse gases brought on by the usage of fossil fuels. In the topic of examining variables influencing the amount of carbon dioxide emissions, several experimental investigations have been carried out, emphasizing the impact of fossil fuel usage, particularly petroleum products.
Methodology
This part introduces the model in this research. The review of the research background shows that several methods have been used to investigate the long-term relationship between the investigated variables over time, such as the Granger-Engle method and Autoregressive Distributed Lags (ARDL). In this study, the long-term association between variables was examined using the Autoregressive Distributed Lags (ARDL) method. The performance of the model with a small number of observations and modeling without the requirement that the degree of cointegration is the same (Stationary degree I(0) and I(1)) are two of the model's most significant benefits (Pesaran and Shin, 1999; Pesaran et al., 2001). The model also allows for the possibility of having different optimal intervals of independent and dependent variables. Another benefit is that it emphasizes the issues with autocorrelation and endogeneity in estimating the long-term association between variables (Rahman and Kashem, 2017; Barati and Fardi Tavana, 2020; Adebayo and Kalmaz, 2021). Pesran et al. were the ones who first created the ARDL model (Pesran et al., 2001). The ARDL model's consideration of both short- and long-term dynamics makes it a very valuable tool for predicting. Additionally, this model offers the researcher the chance to make predictions in addition to short-term coefficients by offering long-term estimation and demonstrating this link (Adam and Beko, 2012). Because of this, the consumption of heating oil, diesel, petrol oil, and petrol is included in Iran's carbon emission equation in addition to the consumption of natural gas (similar to the study by Martins et al., 2021). Contrary to the aforementioned article, the emphasis in this study is on the consumption of petroleum products because the relationship between carbon dioxide emissions and fossil fuel consumption is discussed and because Iran is regarded as an exporter of natural gas and oil.

Conclusion
Using the ARDL model, the current study investigated the types of relationships between the variables, their long- and short-term impacts, and both. Short-term trends show that the fuel with the greatest impact on carbon dioxide emissions is gas oil, followed by natural gas, fuel oil, and then gasoline. This suggests that there are cause-and-effect relationships between the variables, as consumption of oil products and natural gas results in the emission of carbon dioxide. Additionally, an analysis of long-term patterns reveals that the use of gas oil has the biggest impact on the nation's carbon dioxide emissions. Fuel oil, gasoline, and natural gas come in second through fourth, respectively, and have the biggest effects on carbon emissions after that. Since natural gas contributes a very small amount of carbon emissions compared to other fossil fuels, replacing it with another fuel and increasing its consumption will raise the nation's carbon emissions. However, it should be noted that due to the nation's consumption trend and the limited gas reserves, this process cannot continue, so energy policies must be reviewed and based on the advancement of renewable technologies.