In this blog post, we will examine the principles and causes of global warming, the problems it causes—such as extreme weather and rising sea levels—and the measures that the international community and individuals can take to address it.
Global warming is one of the major environmental issues facing humanity today and has become a very familiar concept to us. As the term suggests, it refers to the long-term rise in the Earth’s average temperature. In the past, global warming was often explained based on temperature changes over specific periods, but current scientific observations show that the Earth’s temperature is rising distinctly over the long term. According to the IPCC, the average global surface temperature from 2011 to 2020 was approximately 1.09 degrees higher than that of 1850–1900, and it has been clearly confirmed that this warming was caused by human activities, particularly greenhouse gas emissions. Furthermore, recent observations indicate that high temperatures continue to persist. The World Meteorological Organization (WMO) reported that 2015–2025 was the hottest 11-year period on record, and that the global average temperature in 2025 was approximately 1.43 degrees higher than pre-industrial levels. Therefore, global warming should be understood not merely as a temporary rise in temperature in a specific region, but as a phenomenon involving long-term changes in the Earth’s entire climate system.
To understand the principles of global warming, one must be familiar with three concepts: solar radiation, Earth’s radiation, and the greenhouse effect. First, to examine the effects caused solely by radiation—excluding the greenhouse effect—let’s assume that the Earth’s atmosphere consists only of nitrogen and oxygen. Since nitrogen and oxygen do not efficiently absorb or emit the infrared radiation emitted from the Earth’s surface, this assumption allows us to rule out the greenhouse effect. In this scenario, the average surface temperature—at which the energy the Earth receives from the Sun balances the Earth’s radiant energy emitted into space—would be much lower than the Earth’s actual average temperature. In the past, this value was sometimes estimated to be approximately minus 6 degrees Celsius, but today, the natural greenhouse effect is cited as the reason why the Earth’s average surface temperature reaches about 15 degrees Celsius. In other words, while nitrogen and oxygen make up the majority of the atmosphere, greenhouse gases such as water vapor and carbon dioxide—present in relatively small quantities—play a significant role in raising the Earth’s surface temperature. The greenhouse effect refers to the phenomenon in which some of the radiant energy emitted from the surface of a planet with an atmosphere is absorbed by greenhouse gases before it escapes into space, and as that energy is re-emitted in various directions, both the Earth’s surface and the atmosphere are warmed. This principle is similar to that of a greenhouse, where visible light passes through the glass almost unimpeded to be absorbed by the plants and soil inside, while thermal radiation emitted by the plants and soil is partially absorbed by the glass. Of course, the greenhouse effect in the actual atmosphere is not exactly the same as the operating principle of a glass greenhouse; it involves a complex interplay of radiation, convection, water vapor, and clouds. When the air near the Earth’s surface warms up, its density decreases, causing it to rise; as the air rises and expands, it cools. Meanwhile, greenhouse gases absorb and re-emit a portion of the infrared radiation emitted from the Earth’s surface. A key point here is that the amount of thermal radiation emitted by an object is related to its temperature. Therefore, as the Earth emits energy into space, changes in the amount of greenhouse gases and the structure of the atmosphere alter the energy balance. Greenhouse gases can be thought of as acting like a blanket covering the Earth’s surface. Just as the outside of a blanket is cold and the inside is warm, greenhouse gases in the Earth’s atmosphere regulate the escape of thermal energy into space, thereby warming the Earth’s surface and the lower atmosphere. This natural greenhouse effect is essential for life on Earth. The problem is that human activities are increasing the concentrations of greenhouse gases such as carbon dioxide, methane, and nitrous oxide, thereby amplifying the natural greenhouse effect. Although water vapor is also an important greenhouse gas, its role differs from that of carbon dioxide directly emitted by humans, as the amount of water vapor in the atmosphere varies significantly with temperature. As greenhouse gas concentrations rise, thermal radiation escaping from the atmosphere into space is emitted at higher altitudes than before; since temperatures at those altitudes are relatively lower, the amount of energy radiated into space temporarily decreases. Consequently, the Earth warms up to restore the balance between the energy received from the Sun and the energy radiated into space. During this process, various feedback mechanisms—such as increased water vapor and reduced ice and snow—can further amplify global warming. The IPCC is analyzing the relationship between rising carbon dioxide concentrations and increases in global average temperatures using various climate models and observational data, and there is a very high level of scientific consensus that as carbon dioxide concentrations rise, the Earth will become warmer in the long term.
So, what are the problems caused by global warming? First and foremost, there is an increase in abnormal and extreme weather events. As global warming progresses, the likelihood and intensity of various extreme weather events—such as heat waves, torrential rains, and droughts—are changing. In the past, it was easy to think of global warming primarily as a problem of rising average temperatures, but in reality, it affects the entire climate system and can cause different types of weather-related disasters in various regions. Natural climate variations, such as El Niño, also have a significant impact on global temperatures and precipitation. When an El Niño event occurs, changes in sea surface temperatures and energy distribution in the tropical Pacific, along with shifts in atmospheric circulation, affect weather conditions in various regions around the world. During past periods of strong El Niño events, floods occurred in countries such as China and India, while Indonesia and other regions experienced prolonged dry spells that led to severe droughts and wildfires. However, El Niño and global warming are not the same phenomenon, and the occurrence of El Niño does not mean that all weather-related disasters can be viewed as direct results of global warming. Global warming itself alters the risks associated with heat waves and torrential rains, and depending on the region and weather conditions, it can also influence the risks of droughts and wildfires. The economic costs of damage caused by climate change are also extremely high. When extreme weather occurs, agricultural and industrial activities are disrupted, residential areas and infrastructure are destroyed, and recovery and reconstruction require enormous costs. Furthermore, even for weather-related disasters of the same scale, the extent of damage can vary significantly depending on the economic conditions and social vulnerabilities of the affected regions. Therefore, global warming is not merely an environmental issue but a problem that affects human life and safety, economic activity, and the sustainability of society.
Another major concern is sea-level rise. One of the primary causes of sea-level rise is thermal expansion of the oceans. Since water expands in volume as its temperature rises, the volume of seawater increases as the oceans warm. Combined with the water from melting glaciers and ice sheets flowing into the oceans, this leads to a rise in the global average sea level. In the past, the change in volume resulting from a 1-degree Celsius rise in seawater temperature was sometimes explained using simple numerical values; however, since actual sea-level rise is influenced by various factors—such as seawater temperature, depth, salinity, ocean circulation, and changes in the mass of glaciers and ice sheets—it is impossible to calculate the total sea-level rise based solely on temperature changes at a specific depth. If global warming continues, sea-level rise is expected to persist over the long term.
Rising sea levels can pose significant problems, particularly in low-lying coastal areas, where the land is often fertile and ports and cities are well-developed, leading to high population densities. Delta regions are especially vulnerable; Bangladesh is a prime example. A significant rise in sea level can lead to coastal flooding, erosion, and saltwater intrusion, which can adversely affect agriculture, drinking water supplies, and living conditions. Countries with low average elevations across their entire territory, as well as island regions at low elevations, are also highly vulnerable to sea-level rise. The IPCC assesses that the scale of global average sea-level rise by 2100 could vary significantly depending on greenhouse gas emissions, and that the risk of long-term sea-level rise increases as global warming intensifies.
An even more serious concern is that global warming can be further amplified through various feedback loops. As surface temperatures rise, the amount of water vapor in the atmosphere can increase; since water vapor is a powerful greenhouse gas, this further intensifies the greenhouse effect. Furthermore, as snow and ice decrease, the albedo of the Earth’s surface decreases, allowing more solar energy to be absorbed. This process, in which various changes resulting from a warming climate further intensify global warming, is called climate feedback. Therefore, without efforts to curb the increase in emissions of greenhouse gases, including carbon dioxide, global warming is likely to become even more severe in the long term. In the past, there was a belief that since global warming was still in its early stages, large-scale and severe disasters might not occur during the current generation; however, today the impacts of climate change—such as heat waves, torrential rains, droughts, wildfires, and rising sea levels—are already evident in many regions. Most importantly, as global warming continues, some changes may become irreversible. Therefore, we must reduce greenhouse gas emissions as quickly as possible while simultaneously making efforts to adapt to the climate change that is already underway.
Since global warming is a global issue, international action is required. A prime example of international measures to address global warming is the United Nations Framework Convention on Climate Change (UNFCCC), adopted in 1992. The UNFCCC establishes a basic international framework for responding to climate change and requires countries to report on their greenhouse gas emissions and removals, as well as the status of policy implementation. Subsequently, the Kyoto Protocol was adopted, and the international framework for addressing climate change has evolved with the establishment of the Paris Agreement. The Kyoto Protocol set greenhouse gas reduction targets primarily for developed countries and proposed various policy measures, including improving energy efficiency, protecting forests and promoting afforestation and reforestation, developing and utilizing renewable energy and low-carbon technologies, and reducing emissions in the transportation sector. Meanwhile, the Montreal Protocol is an international agreement designed to regulate substances that deplete the ozone layer; while it is not directly equivalent to an agreement addressing climate change, it is related to climate issues in that some ozone-depleting substances have a strong greenhouse effect. Today, the international community’s response to climate change encompasses not only reducing greenhouse gas emissions but also adaptation to mitigate the impacts of climate change, as well as the development of clean energy, forest conservation, and improvements in energy efficiency. However, such international treaties and policies can easily feel distant to individuals. Readers may unconsciously assume that preventing global warming is the responsibility of large-scale organizations such as governments, corporations, and public institutions. However, since individual lifestyles also influence energy consumption and greenhouse gas emissions, changes in individual behavior are equally important. Walking or biking for short distances and using public transportation for longer ones can help reduce greenhouse gas emissions from the transportation sector. Since power generation produces not only carbon dioxide but also various other greenhouse gases, conserving electricity and improving energy efficiency can also be seen as a way to address global warming. However, individual efforts alone cannot solve the problem of climate change; it is crucial for governments, businesses, and the international community to work together to bring about structural change.
As science and technology have advanced, humanity has been able to enjoy a much more convenient lifestyle than in the past, but this has also led to increased use of fossil fuels and resource consumption, resulting in environmental degradation. Even if we do not adequately prepare for global warming, the current generation may not directly experience all the problems. However, the effects of climate change are already evident, and as global warming continues, the risks and costs that future generations will have to bear could grow even greater. Therefore, we have a responsibility to pass on an intact and livable Earth to future generations. It would be truly paradoxical if humanity—which has achieved remarkable scientific and civilizational progress—were to threaten its own livelihood by failing to properly preserve the environment. Let’s start by making small changes in our daily lives. At the same time, governments, businesses, and the international community must continue to implement practical policies and technologies to reduce greenhouse gas emissions and adapt to climate change. If small individual actions are combined with societal and international efforts, we can mitigate the risks of climate change and help protect the Earth for future generations.
