Investigating the trend of night temperature changes in Iran and the effect of carbon dioxide

According to scientific evidence, the concentration of large amounts of greenhouse gases in the atmosphere leads to an increase in temperature not only at the Earth's surface but also in the troposphere. Despite short-term fluctuations, evidence indicates ongoing global heat accumulation. At night, after sunset, the short rays are no longer present and the outgoing long rays determine the air temperature. Therefore, the nighttime temperature is particularly influenced by variations in greenhouse gases, including CO2. A portion of the Earth's long-wave radiation passes through the atmospheric windows, while the rest is sent back to the Earth's surface as long-wave radiation by greenhouse gases. This process is crucial for maintaining the Earth's temperature balance, particularly during nights and the winter season. In this study, the AIRS sensor images were utilized for the first time to analyze nighttime temperature and carbon dioxide levels in Iran. Research and studies in this regard help managers and planners to raise awareness and promote climate policies to reduce and prevent possible risks caused by changes in the amount of carbon dioxide emissions and, as a result, climate change.

To investigate the changes in CO2 and night temperature and to assess the effect of carbon dioxide on the night temperature variable from 2003 to 2016 (January, May, July and November), monthly and seasonal time series graphs were examined. The Mann-Kendall test was used to assess the significance or non-significance of the trends and the type of trend. Pearson's correlation test and inverse non-linear regression were used for statistical analysis of night temperature and CO2 data. Night temperature maps were produced and classified using the IDW interpolation method.

Statistical analysis of the average night temperature distribution in Iran showed that the average temperature at the end of the study period (2016) was 0.42 o K higher than the average for the entire study period. The highest fluctuations in night temperature were associated with the winter season and the months of November and January, and the lowest fluctuations were associated with the summer season and July. The seasonal average trend of CO2 was completely increasing in all seasons and showed little fluctuation. Based on the distribution of the seasonal mean night temperature, the minimum night temperature was observed in the Northwest, Alborz, Zagros, and North Khorasan regions in all seasons. The southern coasts and southern coastal cities from Khuzestan province to Sistan and Baluchistan province, as well as the Kavir and Lut deserts, have the maximum night temperature in all seasons. Based on the average night temperature maps from 2003, 2006, 2009, 2012, 2015, and 2016, the spatial distribution of night temperatures in Iran shows an increase in January in certain central areas. These areas include parts of Semnan, Yazd, Isfahan, South Khorasan, and southeastern Iran. According to the results of the Mann-Kendall test, the trend of night temperature in July was upward and significant, and the trend of CO2 was upward and significant in all months. According to the results of Pearson's test, the night temperature in July has a high correlation (0.66) with CO2. The results of the non-linear regression model between the two variables showed that, with a coefficient of determination of 0.44, the maximum CO2 had the greatest influence on the maximum July night temperature during the study period.

According to the results of this research, the relationship between the rising trend of night temperature and carbon dioxide in July has been confirmed. Thus, the possibility of increasing night temperatures due to increasing carbon dioxide emissions in different regions of the world can be the subject of research by scientists. It should also be noted that in long-term trends there are sometimes periodic changes that last more than a year. If another study and research related to the subject of the present research is conducted and a longer time series (several decades) is studied, perhaps the dominant trend in Iran will show different conditions.