Background
Carbon dioxide (CO2) and other gases heat the planet through a process known as the greenhouse effect. When sunlight reaches the earth, it heats the surface. Some of that heat is released back into the atmosphere. Greenhouse gases trap some of that heat rather than allowing it to escape back into space, which warms the atmosphere further. Most greenhouse gases are released during the burning of fossil fuels such as coal, oil, and natural gas.
Although the concentration of greenhouse gases in the atmosphere has changed naturally in the past, the changes being observed now are much faster and much bigger [PDF] than previous changes. Carbon dioxide levels are now substantially higher than at any other point in millions of years. Careful analysis of the sources of carbon found in the atmosphere indicates that this rise is due to human activity.
As global temperatures rise, experts warn that extreme weather events including droughts and forest fires will occur more frequently. Consequently, major ecosystems will be threatened. Over the past decade, oceans have warmed faster than expected, and drought and monsoon cycles have intensified. In recent years, global average temperatures have continued to reach ever-higher records. Climate-related wildfires have raged in Australia, the Amazon Rainforest, the Arctic, and California. In the United States alone, climate change contributed to twenty-eight separate disasters in 2023. These disasters included hurricanes, wildfires, and extreme storms that amounted to billions of dollars in damage. Some projections show that rising sea levels could flood populated coastal areas in the United States in the coming decades. Precise forecasts are difficult to make, but researchers estimate that, worldwide, climate change could force up to one billion people from their homes by 2050 if global temperatures are not moderated.
The over 190 countries that joined the 2015 Paris Agreement have agreed that in order to avoid catastrophic harm from climate change, temperature increases by 2100 should be kept below a maximum of 2°C, and preferably below 1.5°C relative to global average temperatures at the start of the Industrial Revolution. Yet little agreement exists on how to achieve this goal. Many policymakers question whether even a 2°C goal can be met.
Many countries are concerned that making the major, rapid reductions required to meet the targets in the Paris Agreement will be expensive, politically controversial, or both. Moreover, countries disagree as to who should bear the most responsibility for achieving that target. Governments of developing countries point out that developed countries bear the most cumulative responsibility for climate change mitigation. This is because developed countries have been emitting at high levels for the longest time. (For example, the United States is the largest overall emitter historically and the second-largest currently.) Governments of developed countries, on the other hand, note that emissions from developing countries are rising fast, and the majority of future emissions are likely to come from the developing world. (Indeed, China has already surpassed the United States and Europe in CO2 emissions.)
Despite these challenges, addressing climate change has been a prominent international concern since the 1980s. In 1992, the United States and 164 other countries signed the UN Framework Convention on Climate Change (UNFCCC). The goal of this framework was to stabilize greenhouse gases at a level that would prevent dangerous changes in the climate. The convention did not set specific targets for countries. Instead, it established the principle of “common but differentiated responsibilities and respective capabilities” among countries, placing higher expectations on developed countries. Those countries pledged to voluntarily reduce emissions and make regular reports on their progress. These reports showed little progress in subsequent years toward meeting the voluntary reductions.
The UNFCCC also established a Conference of the Parties (COP), which called treaty signatories to an annual meeting to discuss the agreement’s implementation and make any changes they thought necessary. In 1997, the parties agreed on a change in the agreement. This was known as the Kyoto Protocol, which mandated that thirty-seven industrialized countries reduce their greenhouse gas emissions by 5 percent below 1990 levels between 2008 and 2012. The protocol had limited results: developing countries faced no required emissions cuts, and the United States, the largest greenhouse gas emitter among developed countries, never ratified the treaty. The treaty failed to decrease reliance on fossil fuels and brought about only modest cuts in greenhouse gas emissions. Despite its limitations the Kyoto Protocol laid the framework for other, more robust climate agreements, including the Paris accord.
In December 2015, the UNFCCC convened a major summit in Paris. The goal was to negotiate a successor agreement to the Kyoto Protocol. Over the course of 2015, countries were asked to submit pledges to the UNFCCC, known as intended nationally determined contributions (INDCs). (Now that the deal has come into force, these are referred to as nationally determined contributions [NDCs].) These documents were requested from all member countries, rich and poor. These documents outlined what each country intended to do to reduce its current emissions or limit future emissions growth. Most pledges involved reducing CO2 emissions. Some NDCs also addressed issues such as adopting renewable energy sources, reducing coal use or storing related emissions underground through a process known as carbon capture and sequestration, and preserving or restoring forests. Independent assessments of the pledges found that, collectively, they would reduce emissions significantly if fulfilled, but not by enough to reach the 2°C target recommended by the IPCC.
At the summit, negotiators also debated whether and how to monitor countries’ progress toward fulfilling their pledges and how to make pledges more stringent over time. Policymakers also discussed whether and how to provide financial support to help poor countries adapt to the changing climate and reduce their own emissions. The final agreement called on countries to make new emissions reduction pledges every five years, beginning in 2023, with the hope that they would increase their reduction targets each time. Wealthy countries also pledged additional money to help poor, vulnerable countries adapt to the effects of climate change. The degree to which the agreement is successful in mitigating climate change will only be seen over time. However, most analysts agree that the Paris summit produced the most important global climate agreement since the Kyoto Protocol.
The Paris Agreement came into force in 2016. In 2017, however, then-President Donald Trump announced his intention to withdraw the United States from the agreement. In response, China, India, the European Union, and many other signatories reaffirmed their commitments. The United States’ withdrawal from the agreement became effective in late 2020. However, shortly after the inauguration of President Joe Biden in January 2021, the United States rejoined the Paris Agreement.
Though the commitments that countries made under the Paris Agreement have resulted in some emissions reduction, pledges that countries made still amount to less than what is needed to achieve the agreement’s goals. Furthermore, most countries are not actually on track to meet the commitments they made in Paris. If current trends continue, climate models predict that temperatures will more likely rise by 2.7°C. Such a rise in temperature would increase the risk of catastrophic harm from climate change.
Several countries have made historic investments in green initiatives in recent years. The 2022 U.S. Inflation Reduction Act, for instance, included $370 billion for climate-related projects, making it the largest climate investment in the country’s history. European countries, most notably France and Germany, have made large-scale investments in climate initiatives as well. Still the vast majority of countries continue to lag behind on climate spending, making pledges more difficult to fulfill.