- Countries have debated how to combat climate change since the early 1990s. These negotiations have produced several important accords, including the Kyoto Protocol and the Paris Agreement.
- Governments generally agree on the science behind climate change but have diverged on who is most responsible, how to track emissions-reduction goals, and whether to compensate harder-hit countries.
- Experts say the Paris Agreement is not enough to prevent the global average temperature from rising 1.5°C. When that happens, the world will suffer devastating consequences, such as heat waves and floods.
Over the last several decades, governments have collectively pledged to slow global warming. But despite intensified diplomacy, the world is already facing the consequences of climate change, and it is expected to get worse.
Through the Kyoto Protocol and the Paris Agreement, countries agreed to reduce greenhouse gas emissions, but the amount of carbon dioxide in the atmosphere keeps rising, heating the Earth at an alarming rate. Scientists warn that if this warming continues unabated, it could bring environmental catastrophe to much of the world, including staggering sea-level rise, record-breaking droughts and floods, and widespread species loss.
Since the Paris accord was signed in 2015, many countries have strengthened their climate commitments during the annual UN climate conferences known as COPs. At the end of the 2021 gathering, countries said they would come to the next year’s conference, COP27 in Egypt, with even more ambition. Still, experts say the current pledges are not enough to prevent catastrophic warming or adapt to its consequences.
What are the most important international agreements on climate change?
Montreal Protocol, 1987. Though not intended to tackle climate change, the Montreal Protocol [PDF] was a historic environmental accord that became a model for future diplomacy on the issue. Every country in the world eventually ratified the treaty, which required them to stop producing substances that damage the ozone layer, such as chlorofluorocarbons (CFCs). The protocol has succeeded in eliminating nearly 99 percent of these ozone-depleting substances. In 2016, parties agreed via the Kigali Amendment to also reduce their production of hydrofluorocarbons (HFCs), powerful greenhouse gases that contribute to climate change.
UN Framework Convention on Climate Change (UNFCCC), 1992. Ratified by 197 countries, including the United States, the landmark accord [PDF] was the first global treaty to explicitly address climate change. It established an annual forum, known as the Conference of the Parties, or COP, for international discussions aimed at stabilizing the concentration of greenhouse gases in the atmosphere. These meetings produced the Kyoto Protocol and the Paris Agreement.
Kyoto Protocol, 2005. The Kyoto Protocol [PDF], adopted in 1997 and entered into force in 2005, was the first legally binding climate treaty. It required developed countries to reduce emissions by an average of 5 percent below 1990 levels, and established a system to monitor countries’ progress. But the treaty did not compel developing countries, including major carbon emitters China and India, to take action. The United States signed the agreement in 1998 but never ratified it and later withdrew its signature.
Paris Agreement, 2015. The most significant global climate agreement to date, the Paris Agreement requires all countries to set emissions-reduction pledges. Governments set targets, known as nationally determined contributions (NDCs), with the goals of preventing the global average temperature from rising 2°C (3.6°F) above preindustrial levels and pursuing efforts to keep it below 1.5°C (2.7°F). It also aims to reach global net-zero emissions, where the amount of greenhouse gases emitted equals the amount removed from the atmosphere, in the second half of the century. (This is also known as being climate neutral or carbon neutral.)
Every five years, countries are supposed to assess their progress toward implementing the agreement through a process known as the global stocktake; the first is planned for 2023. Countries set their own targets, and there are no enforcement mechanisms to ensure they meet them.
The United States, the world’s second-largest emitter, was the only country to withdraw from the accord, a move by former President Donald Trump that took effect in November 2020. However, President Joe Biden reentered the United States into the agreement during his first months in office. A few countries have not formally approved the agreement: Eritrea, Iran, Libya, and Yemen.
Is there a consensus on the science of climate change?
Yes, there is a broad consensus among the scientific community, though some deny that climate change is a problem, including politicians in the United States. When negotiating teams meet for international climate talks, there is “less skepticism about the science and more disagreement about how to set priorities,” says David Victor, an international relations professor at the University of California, San Diego. The basic science is that:
- the Earth’s average temperature is rising at an unprecedented rate;
- human activities, namely the use of fossil fuels—coal, oil, and natural gas—are the primary drivers of this rapid warming and climate change; and,
- continued warming is expected to have harmful effects worldwide.
Data taken from ice cores shows that the Earth’s average temperature is rising more now than it has in eight hundred thousand years. Scientists say this is largely a result of human activities over the last 150 years, such as burning fossil fuels and deforestation. These activities have dramatically increased the amount of heat-trapping greenhouse gases, primarily carbon dioxide, in the atmosphere, causing the planet to warm.
The Intergovernmental Panel on Climate Change (IPCC), a UN body established in 1988, regularly assesses the latest climate science and produces consensus-based reports for countries.
Why are countries aiming to keep global temperature rise below 1.5°C?
Scientists have warned for years of catastrophic environmental consequences if global temperature continues to rise at the current pace. The Earth’s average temperature has already increased approximately 1.1°C above preindustrial levels, according to a 2021 assessment [PDF] by the IPCC. The report, drafted by more than two hundred scientists from over sixty countries, predicts that the world will reach or exceed 1.5°C of warming within the next two decades even if nations drastically cut emissions immediately.
An earlier, more comprehensive IPCC report summarized the severe effects expected to occur when the global temperature warms by 1.5°C:
Heat waves. Many regions will suffer more hot days, with about 14 percent of people worldwide being exposed to periods of severe heat at least once every five years.
Droughts and floods. Regions will be more susceptible to droughts and floods, making farming more difficult, lowering crop yields, and causing food shortages.
Rising seas. Tens of millions of people live in coastal regions that will be submerged in the coming decades. Small island nations are particularly vulnerable.
Ocean changes. Up to 90 percent of coral reefs will be wiped out, and oceans will become more acidic. The world’s fisheries will become far less productive.
Arctic ice thaws. At least once a century, the Arctic will experience a summer with no sea ice, which has not happened in at least two thousand years. Forty percent of the Arctic’s permafrost will thaw by the end of the century.
Species loss. More insects, plants, and vertebrates will be at risk of extinction.
The consequences will be far worse if the 2°C threshold is reached, scientists say. “We’re headed toward disaster if we can’t get our warming in check and we need to do this very quickly,” says Alice C. Hill, CFR senior fellow for energy and the environment.
Which countries are responsible for climate change?
The answer depends on who you ask and how you measure emissions. Ever since the first climate talks in the 1990s, officials have debated which countries—developed or developing—are more to blame for climate change and should therefore curb their emissions.
Developing countries argue that developed countries have emitted more greenhouse gases over time. They say these developed countries should now carry more of the burden because they were able to grow their economies without restraint. Indeed, the United States has emitted the most of all time, followed by the European Union (EU).
However, China and India are now among the world’s top annual emitters, along with the United States. Developed countries have argued that those countries must do more now to address climate change.
In the context of this debate, major climate agreements have evolved in how they pursue emissions reductions. The Kyoto Protocol required only developed countries to reduce emissions, while the Paris Agreement recognized that climate change is a shared problem and called on all countries to set emissions targets.
Are the commitments made under the Paris Agreement enough?
Most experts say no. Countries’ pledges are not ambitious enough and will not be enacted quickly enough to limit global temperature rise to 1.5°C. Policies as of late 2021 could result in a 2.7°C (4.9°F) rise by 2100, according to the Climate Action Tracker compiled by Germany-based nonprofits Climate Analytics and the NewClimate Institute.
“The Paris Agreement is not enough. Even at the time of negotiation, it was recognized as not being enough,” says CFR’s Hill. “It was only a first step, and the expectation was that as time went on, countries would return with greater ambition to cut their emissions.”
Since 2015, dozens of countries—including the top emitters—have submitted stronger pledges. For example, President Biden announced in 2021 that the United States will aim to cut emissions by 50 to 52 percent compared to 2005 levels by 2030, doubling President Barack Obama’s commitment. The following year, the U.S. Congress approved legislation that could get the country close to reaching that goal. Meanwhile, the EU pledged to reduce emissions by at least 55 percent compared to 1990 levels by 2030, and China said it aims to reach peak emissions before 2030.
But the world’s average temperature will still rise 2.1°C (3.8°F) by 2100 even if countries fully implement their pledges for 2030 and beyond. If the more than one hundred countries that have set or are considering net-zero targets follow through, warming could be limited to 1.8˚C (3.2°F), according to the Climate Action Tracker.
What are the alternatives to the Paris Agreement?
Many experts foresee the most meaningful climate action happening outside of the Paris Agreement. Some call for the creation of a climate club—an idea championed by Yale University economist William Nordhaus—that would penalize countries that do not meet their obligations or do not join. Others propose new agreements [PDF] that apply to specific emissions or sectors to complement the Paris accord.
“Progress is going to happen not globally with all countries joined together, but in smaller groups and by sector,” says Victor. In the past few years, there have been more examples of this. In 2021, Group of Twenty (G20) countries pledged to stop financing new coal-fired power plants abroad, and dozens of countries committed to collectively reduce emissions of methane, a potent greenhouse gas, by 30 percent by 2030. In 2022, countries in the International Civil Aviation Organization set a goal of achieving net-zero emissions for commercial aviation by 2050. Meanwhile, cities around the world have made their own pledges. In the United States, more than six hundred local governments [PDF] have detailed climate action plans that include emissions-reduction targets.
Companies are a large source of emissions, and many big firms have said they will try to reduce their emissions. Some have pledged to go carbon neutral, while others have said they will be carbon negative, meaning they would remove more carbon from the atmosphere than they release. During COP26, hundreds of financial institutions joined the Glasgow Financial Alliance for Net Zero (GFANZ) and pledged to achieve net-zero emissions by 2050. However, some firms have since threatened to back out, while others haven’t published plans for how they will reach that goal. This has led critics to accuse some of these companies of greenwashing, or marketing themselves as eco-conscious while continuing harmful practices.
Although moves by corporations are important for raising awareness and reducing some emissions, “it’s all pretty small relative to governments around the world setting a forceful climate policy,” Michael Greenstone, an economics professor at the University of Chicago, tells CFR’s Why It Matters podcast.
This In Brief lays out what to expect at COP27.
This timeline tracks UN climate talks since 1992.
CFR’s World101 library explains everything to know about climate change.
Climate Action Tracker assesses countries’ updated NDCs under the Paris Agreement.
CFR’s Alice C. Hill and Madeline Babin unpack the successes and failures of the 2022 U.S. climate bill.
In this series on climate change and instability by the Center for Preventive Action, CFR’s Michelle Gavin looks at the consequences for the Horn of Africa and the National Defense University’s Paul J. Angelo for Central America.
For Foreign Affairs, Yale University’s William Nordhaus unpacks why climate policy has failed and how governments can do better.