In this blog post, we’ll examine the mechanisms behind global warming, its impact on the Earth’s environment, and the international community’s efforts to mitigate and respond to it.
Even people who aren’t interested in environmental issues have likely heard the term “global warming” at least once through newspapers or the media, and they probably have a vague understanding that it is a serious environmental problem today. Literally translated, “global warming” refers to the long-term rise in the average temperature of the Earth, our home. So why has global warming become such a major issue on a global scale? First, let’s examine the principles behind global warming, its impact on the Earth’s environment, and the international efforts to address it.
To understand global warming, we must first understand the role of the atmosphere that surrounds the Earth. If we think of the Earth as the core of an apple, the atmosphere envelops the entire Earth like an apple peel; it consists of various gases—including oxygen and carbon dioxide, which are essential for life, as well as nitrogen, water vapor, argon, neon, and helium. The atmosphere plays a crucial role in making the Earth a habitable environment for life as it exchanges energy with the outside world.
The phenomenon in which the thermal energy possessed by an object is emitted in the form of electromagnetic waves is called radiation, and the Earth uses this radiation to exchange energy with the outside world. Although Earth constantly receives energy from the Sun, it emits an appropriate amount of energy into space to prevent the surface temperature from rising indefinitely. The radiation coming from the Sun is short-wave radiation, which has high energy intensity and short wavelengths. This short-wave radiation can pass through the atmosphere relatively easily, much like light passing through transparent glass. However, at the Earth’s surface—which is cooler than the Sun—long-wave radiation, which emits infrared light, is produced. Unlike short-wave radiation, long-wave radiation cannot pass freely through the atmosphere; instead, some of it is absorbed by various gases in the atmosphere, such as water vapor and carbon dioxide. Gases that act in this way are called greenhouse gases, and the phenomenon in which greenhouse gases absorb some of the energy the Earth attempts to radiate outward, thereby raising the temperatures of the Earth’s surface and atmosphere, is known as the greenhouse effect.
If the atmosphere currently enveloping the Earth did not exist, most of the Earth’s long-wave radiation would be emitted into space, and the greenhouse effect as we know it today would not occur. In that case, the Earth’s average surface temperature is estimated to have been about 33°C lower than it is today, and it would have been difficult for life forms like those we see today to survive in such an environment. The atmospheric greenhouse effect allows a wide variety of organisms to inhabit the Earth by maintaining the planet’s current temperature and moderating daily temperature fluctuations at the Earth’s surface.
As we have seen, while the greenhouse effect is an indispensable and beneficial phenomenon for the Earth, the increase in greenhouse gas concentrations due to human activities has intensified the natural greenhouse effect, giving rise to a new environmental problem known as global warming. The Earth maintains an appropriate balance between the solar radiation it absorbs and the thermal radiation it emits; however, other variables have disrupted this long-established energy balance. Global warming, caused by an excessively amplified greenhouse effect, is one such disruption. As the concentration of greenhouse gases in the atmosphere has increased, less energy is radiated into space and more energy is accumulated within the Earth’s system, causing global temperatures to rise steadily.
The Earth’s average temperature has risen rapidly since the Industrial Revolution. According to the IPCC’s Sixth Assessment Report, global surface temperatures from 2011 to 2020 were approximately 1.1°C higher than the average for 1850–1900, and this warming is assessed to have been unequivocally caused by human activities, particularly greenhouse gas emissions. In particular, the rate of increase in global surface temperature since 1970 is assessed to be faster than that of any 50-year period over at least the past 2,000 years. Human activities are known to have had a significant impact on these changes, and two main causes can be identified. First, the concentration of greenhouse gases in the atmosphere has increased significantly alongside industrialization. The combustion of fossil fuels—such as oil, coal, and natural gas—which power industry across the board, generates large amounts of carbon dioxide. The atmospheric concentrations of substances such as CFCs (used as refrigerants in appliances like refrigerators), nitrous oxide (produced by the use of nitrogen fertilizers in agriculture), and methane (released during the digestive process of livestock) have also increased significantly due to human activity compared to pre-industrial levels. Although the atmospheric concentrations of other greenhouse gases are relatively low compared to carbon dioxide, their presence cannot be ignored because some greenhouse gases have a much stronger greenhouse effect per molecule than carbon dioxide. Second, the destruction of forests has reduced their ability to absorb carbon dioxide from the atmosphere. Plants absorb carbon dioxide from the atmosphere and release oxygen through photosynthesis; however, forests have been declining due to excessive logging and land-use conversion for purposes such as regional development and securing timber resources. Consequently, the absorption of atmospheric carbon dioxide has been hindered, resulting in a greater accumulation of greenhouse gases in the atmosphere.
One might dismiss a slight rise in the Earth’s temperature as no big deal, but global warming has a massive impact on the entire planet, altering the climate and natural environment and disrupting ecosystems. If the delicate balance that the Earth has maintained over the ages is disrupted, major changes will occur in the global environment, potentially leading to situations severe enough to threaten people’s daily lives. Global warming affects the temperature and humidity of habitats, and species unable to adapt to the changed environment could, in the worst-case scenario, face extinction. While animals can migrate to new habitats in response to these changes, plants find even this difficult; consequently, their ability to adapt may not keep pace with the speed of climate change. This can lead to significant disruption across the entire interconnected ecosystem. Furthermore, as temperatures rise, the amount of water vapor the atmosphere can hold increases, affecting the patterns and intensity of precipitation. While some regions may experience an increase in average precipitation, the greater capacity of the atmosphere to hold water vapor can also heighten the risk of extreme precipitation events, such as torrential downpours, leading to associated damage. Meanwhile, global warming is causing sea temperatures to rise and the cryosphere to change, leading to rising sea levels. Thermal expansion of seawater and the loss of mass from glaciers and ice sheets are the primary causes of this rise. In particular, low-lying island nations such as Tuvalu are highly vulnerable to risks such as rising sea levels, coastal erosion, and saltwater intrusion. However, rather than simplistically explaining the situation by stating that “thousands of Tuvalu residents have already evacuated from islands submerged by the sea to Auckland,” it is more accurate to view the long-term issues of migration and adaptation resulting from climate change as critical challenges. Furthermore, a rapid rise in temperature places a strain on the human body’s ability to regulate its temperature, increasing the risk of heat-related illnesses during heat waves. Climate change can also alter the distribution and activity of disease vectors, such as mosquitoes, thereby changing the risk of infectious diseases. The problems caused by global warming are countless, as it can have a massive impact on industries directly affected by climate, such as agriculture, as well as transportation, telecommunications, and construction. The effects of climate change are already manifesting in various regions around the world through changes in extreme weather events—such as heat waves, torrential rains, and droughts—and are having widespread impacts on food and water security, human health, and the economy and society.
To prevent this global warming, we must reduce greenhouse gas emissions caused by human activities and protect forests and ecosystems that absorb carbon dioxide from the atmosphere. While it is practically impossible for humans to live without emitting any greenhouse gases at all, we can reduce emissions in areas where they are not strictly necessary. Accordingly, efforts are underway to expand the use of renewable energy sources—such as solar energy—to replace fossil fuels, which are currently the primary energy source, and to improve energy efficiency in industry and daily life through electrification and enhanced energy efficiency. Furthermore, efforts are needed to protect and restore forests and ecosystems capable of absorbing and storing carbon dioxide from the atmosphere in order to curb the rise in atmospheric greenhouse gas concentrations. Beginning with the United Nations Conference on the Human Environment held in Stockholm, Sweden, in 1972, the international community has worked together to address environmental issues and has established various international conventions and mechanisms to tackle climate change. The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) established the Intergovernmental Panel on Climate Change (IPCC) in 1988, and the IPCC has comprehensively assessed the scientific basis of climate change, its impacts, and adaptation and mitigation measures. The Sixth Assessment Cycle has now been completed, and the Synthesis Report was published in 2023. The United Nations Framework Convention on Climate Change, adopted in 1992, sets as its ultimate goal the stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous human interference with the climate system. The Kyoto Protocol, adopted in 1997, established legally binding greenhouse gas reduction targets primarily for developed countries and countries with economies in transition. Subsequently, in 2015, the international community adopted the Paris Agreement to establish a more comprehensive framework for addressing climate change. The Paris Agreement is a legally binding climate change response framework involving nearly all countries worldwide; its goal is to limit the rise in global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C. Countries are submitting their Nationally Determined Contributions (NDCs) and updating them periodically while implementing policies to reduce greenhouse gas emissions and adapt to climate change. Consequently, today’s international response to climate change is evolving beyond the Kyoto Protocol alone; centered on the Paris Agreement, it focuses on reviewing each country’s reduction targets and implementation status and promoting even stronger climate action.
