Paris to Kyoto: The History of UN Climate Agreements

Introduction

Over the last several decades, governments have collectively pledged to slow global warming. Despite intensified diplomacy, the world is already facing the consequences of climate change, which are expected to get worse.

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The United States, the world’s second-largest emitter, is the only country to withdraw from the agreement, a move Trump made during his first administration in 2017. After former President Joe Biden rejoined the agreement, Trump again withdrew the United States on the first day of his second term in 2025. Three other countries have not formally approved the agreement: Iran, Libya, and Yemen.

Is there a consensus on the science of climate change?

There is a broad consensus among the scientific community that the climate is warming. However, some industry leaders and political groups deny the existence of climate change or the severity of its cascading effects, including several politicians in the United States. 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 show that the Earth’s average temperature is rising faster 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 the global temperature continues to rise at the current rate. In 2025, the World Meteorological Organization reported that the Earth’s average temperature had already reached about 1.55°C above preindustrial levels in 2024, which marked the hottest year on record for the tenth consecutive year.

Year-over-year record heat has had severe effects on the environment. A comprehensive IPCC report published in 2018 summarized the major climate events that have occurred as the global temperature warms and will continue as Earth breaches the 1.5°C threshold:

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.

“We’re headed toward disaster if we can’t get our warming in check.”

Alice C. Hill, CFR Senior Fellow for Energy and the Environment

Oceanic 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,” said 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 greenhouse gases of all, 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.

What progress have countries made since the Paris Agreement?

Every five years, countries are supposed to assess their progress toward implementing the Paris agreement through a process known as the global stocktake. The first of these reports, released in September 2023, warned governments that “the world is not on track to meet the long-term goals of the Paris Agreement.”

That said, countries have made some breakthroughs during the annual UN climate summits, such as the landmark commitment to establish the Loss and Damage Fund at COP27 in Sharm el-Sheikh, Egypt. The fund aims to address the inequality of climate change by providing financial assistance to poorer countries, which are often least responsible for global emissions yet most vulnerable to climate disasters. At COP28, countries decided that the fund will be initially housed at the World Bank, with several wealthy countries, such as the United States, Japan, the United Kingdom, and EU members, initially pledging around $430 million combined. At COP29, developed countries committed to triple their finance commitments to developing countries, totaling $300 billion annually by 2035.

Recently, there have been global efforts to reduce methane emissions, which account for more than half of human-made warming today because of their higher potency and heat trapping ability within the first few decades of release. The United States and EU introduced a Global Methane Pledge at COP26, which aims to slash 30 percent of methane emissions levels between 2020 and 2030. At COP28, oil companies announced they would cut their methane emissions from wells and drilling by more than 80 percent by the end of the decade. However, pledges to phase out fossil fuels were not renewed the following year at COP29.

Are the commitments made under the Paris Agreement enough?

Most experts say that countries’ pledges are not ambitious enough and will not be enacted quickly enough to limit global temperature rise to 1.5°C. The policies of Paris signatories as of late 2024 could result in a 2.6°C 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,” said 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 made stronger pledges that could potentially reduce emissions by 17 percent below 2019 levels, per an October 2025 UN report. For example, the EU pledged to reduce emissions by at least 55 percent compared to 1990 levels by 2030, and China committed to reduce net greenhouse gas emissions by 7–10 percent from peak levels by 2035. While the United States previously announced stronger efforts to reduce emissions under the Biden administration, Trump voided reduction targets for 2030, 2035, and 2050 by withdrawing from the Paris Agreement.

But the world’s average temperature will still rise more than 2°C (3.6°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?

Some experts foresee the most meaningful climate action happening in forums outside the United Nations. Yale University economist William Nordhaus has argued that purely voluntary international accords like the Paris Agreement promote free-riding and are destined to fail. The best way to cut global emissions would be to have governments negotiate a universal carbon price rather than focus on country emissions limits, he has argued. Others propose new agreements [PDF] that apply to specific emissions or sectors to complement the Paris Agreement.

In recent years, climate diplomacy has occurred increasingly through minilateral groupings. The Group of Twenty (G20), representing countries that are responsible for 80 percent of the world’s greenhouse gas pollution, has pledged to stop financing new coal-fired power plants abroad and agreed to triple renewable energy capacity by the end of this decade. However, G20 governments have thus far failed to set a deadline to phase out fossil fuels. 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.

Industry is also a large source of carbon pollution, and many firms have said they will try to reduce their emissions or become carbon neutral or carbon negative, meaning they would remove more carbon from the atmosphere than they release. The Science Based Targets initiative, a UK-based company considered the “gold standard” in validating corporate net-zero plans, says it has certified the plans of more than three thousand firms, and aims to more than triple this total by 2025. Still, analysts say that many challenges remain, including questions over the accounting methods and a lack of transparency in supply chains.