In this blog post, we’ll examine the causes of global warming and its resulting ecological, environmental, economic, and social impacts, and explore the efforts being made by the international community and individuals to mitigate global warming.

What is global warming, and why does it occur?

The Earth’s annual average temperature has fluctuated over long periods due to natural climate variability. However, since the Industrial Revolution, the average global temperature has been rising rapidly as greenhouse gas emissions from human activities have increased. This phenomenon—a long-term rise in the average temperature of the atmosphere near the Earth’s surface and the oceans—is known as global warming. It is important to distinguish between short-term temperature fluctuations and long-term climate change. Temperatures can fluctuate easily depending on the weather from day to day, and short-term temperature increases can occur, such as when the seasons change from spring to summer. However, when examining long-term trends, the Earth’s average temperature has been on a general upward trajectory, and as this change persists, various problems are arising. In the past, based on previous assessment reports from the Intergovernmental Panel on Climate Change (IPCC), a temperature rise of 1.1–6.4°C was predicted between 1990 and 2100; however, the current IPCC Sixth Assessment Report projects that, depending on greenhouse gas emission scenarios, the global average temperature between 2081 and 2100 will rise by approximately 1.4–4.4°C compared to the pre-industrial period of 1850–1900. In other words, the extent of future temperature increases could vary significantly depending on how greenhouse gas emissions change going forward. So why is global warming occurring, and what are the problems caused by it? Let’s also take a closer look at the methods and efforts being undertaken to mitigate global warming.
First, the most significant cause of global warming is the increase in greenhouse gases resulting from human activities and the consequent intensification of the greenhouse effect. The Earth’s climate system consists of various components—including the atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere—and these components interact with one another to maintain the current climate. Most of the energy driving the climate system comes from the Sun. The energy that enters the Earth is transformed into various forms within the climate system and is ultimately released into space as long-wave radiation from the Earth. Greenhouse gases play a crucial role in this process. Carbon dioxide, methane, and water vapor in the atmosphere are representative greenhouse gases, and there are also various other greenhouse gases, such as nitrous oxide and chlorofluorocarbons (CFCs). Among these, the greatest contributor to current global warming is the increase in greenhouse gases—including carbon dioxide—emitted as a result of human activities. Greenhouse gases allow most of the relatively short-wavelength radiation from the Sun to pass through the Earth’s atmosphere, but they absorb and re-emit the long-wavelength infrared radiation that the Earth attempts to release into space. This process keeps the Earth’s surface and atmosphere warm; this is known as the greenhouse effect. While the greenhouse effect itself is a natural phenomenon essential for life on Earth, the massive emissions of greenhouse gases resulting from the use of fossil fuels and changes in land use since the Industrial Revolution have increased their concentration in the atmosphere. Consequently, global warming—characterized by a rise in the Earth’s average temperature—is underway.
Meanwhile, hypotheses have been proposed in the past suggesting that solar radiation and sunspot activity on the Sun’s surface could influence the Earth’s temperature rise. Solar activity can indeed influence Earth’s climate, and the amount of solar radiation fluctuates in cycles of approximately 11 years. However, based on accumulated observations and research findings to date, global warming over the past few decades cannot be explained by solar activity alone. In particular, while there has been no clear long-term upward trend in the energy received by Earth from the Sun since the 1950s, the Earth’s average temperature has risen significantly. Furthermore, if solar activity were the primary cause of global warming, all layers of the atmosphere would be warming together; however, actual observations show that while the Earth’s surface and the troposphere are warming, the stratosphere is cooling. This is consistent with the phenomenon in which heat emitted from Earth into space is absorbed more by the atmosphere due to the increase in greenhouse gases. Furthermore, ozone layer depletion is not a major factor explaining current global warming; while changes in the ozone layer may influence the climate, they cannot be considered the primary cause of the recent rise in surface temperatures.

What problems does global warming cause?

Let’s take a look at the problems caused by global warming. The issues stemming from global warming are vast and span ecosystems, the physical environment, the economy, and society, and they are closely interrelated. The rise in temperature due to global warming causes thermal expansion of seawater and the melting of glaciers and ice sheets, which in turn leads to sea-level rise. In fact, the global average sea level rose by approximately 0.20 meters from 1901 to 2018, and the rate of sea-level rise is accelerating over time. Consequently, the risk of inundation and flooding is increasing in densely populated low-lying and coastal areas. As temperatures rise, changes are also occurring in the polar ice sheets, including those in the Arctic and Antarctic. Since Arctic sea ice is mostly ice floating on the ocean, its melting does not significantly raise sea levels on its own; however, the melting of land-based ice sheets—such as the Greenland and Antarctic ice sheets—and mountain glaciers directly contributes to sea-level rise. In particular, if land-based ice sheets undergo significant and prolonged reduction, sea levels could rise substantially. Such a rise in sea level can lead to various environmental problems, including not only coastal flooding but also saltwater intrusion and ocean acidification. As glaciers in the polar regions and mountain glaciers on continents melt, they cause changes in nearby lakes and water resources; additionally, the thawing of permafrost can weaken ground stability.
Global warming is also causing changes in precipitation amounts and patterns. Precipitation may increase or decrease depending on the region, and the risk of drought may rise, particularly in dry seasons and regions. At the same time, a global trend toward increased frequency and intensity of heavy precipitation events is being observed, raising the possibility of greater flood damage caused by extreme precipitation such as localized downpours. In other words, global warming does not uniformly increase or decrease precipitation across all regions; rather, it affects the hydrological cycle by altering the amount and form of precipitation depending on the region and season. Furthermore, climate change influences atmospheric and oceanic circulation, which may lead to an increased risk of extreme weather events—such as heat waves, droughts, and torrential downpours—in specific regions.
Furthermore, global warming affects the economy and society, as well as tourism, agriculture, livestock farming, and fisheries. In Europe and other regions, rising temperatures are causing flowering and sowing dates to occur earlier, shifting the emergence of insects, and altering crop growing seasons. Conversely, extreme weather events can damage crops, and changes in the marine environment can impact fisheries and aquaculture. Furthermore, climate change causes shifts in supply and demand in both domestic and international markets and can have negative impacts on vulnerable sectors within various industries. Climate-sensitive industries, such as energy and transportation, may face increased operating costs or a higher risk of damage due to extreme weather events and rising temperatures. In the tourism and leisure sectors, extreme weather events such as wildfires and hurricanes can destroy tourist facilities, leading to massive losses. Furthermore, a decrease in naturally occurring snowfall affects ski tourism. In regions with insufficient natural snow, the need to produce artificial snow can lead to increased costs. As such, climate change is affecting not only the natural environment but also human life and economic activities in general in various ways.

What efforts are being made to prevent global warming?

To mitigate global warming, which causes numerous problems across many sectors, humanity is implementing various measures. First, many countries have sought to reduce greenhouse gas emissions and jointly address climate change by enacting international agreements. A prime example is the Kyoto Protocol. Prior to the Kyoto Protocol, the United Nations Framework Convention on Climate Change (UNFCCC) was established as an international environmental agreement to curb greenhouse gas emissions, which are the primary cause of climate change. This convention aims to stabilize the concentration of greenhouse gases in the atmosphere and emphasized that measures to prevent global warming should not be delayed merely because there is insufficient scientific certainty regarding climate change. It also established as fundamental principles the implementation of precautionary measures to predict and prevent climate change, as well as ensuring sustainable growth for all nations, and was officially adopted at the Rio Earth Summit in June 1992. Subsequently, the Kyoto Protocol was established to address the fact that the greenhouse gas reduction obligations under the UNFCCC lacked sufficient legal enforceability. The Kyoto Protocol stipulated that developed countries—which have historically been major emitters of greenhouse gases—must collectively reduce their emissions by at least 5% below 1990 levels during the first commitment period (2008–2012). It also introduced the Kyoto Mechanisms to enable countries with greenhouse gas reduction obligations to fulfill them in a cost-effective manner. Examples include the Joint Implementation (JI) mechanism, under which a developed country’s investment in greenhouse gas reduction projects in another developed country results in the emission reductions being credited toward the investing country’s reduction targets, and the Clean Development Mechanism (CDM), under which emission reductions achieved by a developed country through greenhouse gas reduction projects in a developing country are credited toward the developed country’s reduction targets. In addition, an emissions trading system was established, under which countries with greenhouse gas reduction obligations are allocated emission allowances and permitted to trade those allowances among themselves. The first commitment period of the Kyoto Protocol has already ended, and the international community’s response to climate change is now centered on the Paris Agreement, which was adopted in 2015 and entered into force in 2016. The primary objective of the Paris Agreement is to keep the global average temperature rise well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C.
At the Bali Climate Conference held in Bali, Indonesia, in 2007, discussions took place to strengthen international cooperation in addressing climate change and to set the direction for future negotiations. At that conference, discussions focused on strengthening international efforts to address climate change—including greenhouse gas reduction, adaptation, technology transfer, and financial support—and the Bali Action Plan was adopted based on these discussions. At the time, securing the participation of countries experiencing rapid increases in greenhouse gas emissions due to rapid industrialization, as well as the world’s major greenhouse gas emitters, emerged as a critical challenge for the international community. In 2007, United Nations Secretary-General Ban Ki-moon also urged major countries, including the United States and China, to take proactive measures to address climate change and to engage in international cooperation. Subsequently, the international community continued negotiations to address the limitations of the Kyoto Protocol and establish a new climate change response framework involving a broader range of countries, which culminated in the adoption of the Paris Agreement in 2015.

What can we do at home?

So, what are some simple steps we can take at home? You can save energy by unplugging appliances from outlets when not in use or turning off the lights when you leave the house. It’s also a good idea to use electronic devices for as long as possible and, when they can no longer be used, dispose of them in a recyclable manner so that the resources can be reused. In addition to recycling, you can also choose eco-friendly products by considering their environmental impact when making purchases. It helps to use products with a lower environmental impact rather than those that are harmful to the environment, and to avoid single-use items as much as possible. It is also effective to cook only as much food as you need to reduce unnecessary food waste. In this way, consistently practicing small actions in daily life—such as conserving energy and resources and reducing unnecessary consumption and waste—can be one way to address global warming.