On 4 March 2025, we had the pleasure of co-hosting an event organised by IDDRI, Sciences Po’s Institute for Environmental Transformations, and the Centre for European Studies and Comparative Politics (CEE).

The conference featured an in-depth discussion on the legacy of COP21 and the Paris Agreement with Todd Stern (Former U.S. Special Envoy for Climate Change), who has just published a new book on the subject: “Landing the Paris Climate Agreement – How it happened, why it matters and what comes next.” This dialogue was followed by a roundtable discussion with insights from Laurence Tubiana (CEO, European Climate Foundation and key architect of the Paris Agreement) and Sébastien Treyer (Executive Director, IDDRI), chaired by Dr. Charlotte Halpern (Sciences Po, CEE and Director of the Institute for Environmental Transformations).

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Part 1: A Conversation with Todd Stern

Reflections on Two Decades of Climate Agreements

Todd Stern provided a historical perspective on global climate negotiations, highlighting the Kyoto Protocol’s shortcomings, particularly its rigid divide between developed and developing countries hindering its long-term effectiveness. This so-called “firewall” exempted developing nations from binding emissions cuts while placing the burden solely on industrialised countries —  a structure that ultimately proved unsustainable as major emerging economies also became significant emitters.  He emphasised the incremental yet transformative journey leading to the Paris Agreement (2015), contrasting it with the tumultuous Copenhagen COP (2009) — often perceived as a failure but which, in his view, not only helped dismantle the strict firewall between developed and developing nations but also suggested that incremental progress can be made without legally binding texts.

Stern also highlighted how the Kyoto Protocol’s legally binding nature posed a major obstacle, particularly for the United States, which had agreed to it at the UNFCCC level but faced constitutional constraints at home: any treaty commitment required a two-thirds majority in the Senate, making ratification politically unfeasible. As a result, both the U.S. and the global community recognised that a similarly binding agreement would be unlikely moving forward. A turning point came with the 2014 U.S.-China joint climate announcement, which signalled a new era of cooperation between the two largest emitters. This high-level political agreement played a pivotal role in convincing the global community that a successful agreement in Paris was possible.

The road to the Paris Agreement was therefore paved well in advance. A key factor in the success of the Paris Agreement was the shifting political and international dynamic that prioritised multilateralism and broadened engagement beyond national governments. Unlike previous COPs, non-state actors — including the private sector, cities, and NGOs — played a significant role, largely due to Laurence Tubiana’s efforts to extend climate action beyond state actors. The French presidency’s diplomatic approach was also crucial; they managed the process transparently, ensuring all countries felt heard, and fostering trust throughout the negotiations. The High Ambition Coalition — a mix of vulnerable, developing countries alongside progressive developed nations — also helped push for stronger commitments. By 2015, countries had moreover enough time to absorb key ideas, and after years of stalled negotiations, there was a collective sense that a global agreement simply had to succeed.

Key Achievements of the Paris Agreement

Stern remarked upon how the Paris Agreement is recognised as a landmark climate accord, with several defining characteristics:

• Universality: Every country now has obligations under the agreement, marking a departure from past agreements (such as the Kyoto Protocol) wherein developing countries notably were not called upon to cut greenhouse gas emissions. Nevertheless, the principle of ‘common but differentiated responsibilities’ is still respected, whereby obligations are based on national capacity.
• Durability: Designed as a permanent framework, ensuring long-term climate commitments.
• Innovative Structure: Combining bottom-up (non-legally binding) country pledges with top-down legally binding transparency and reporting mechanisms.
• Built-in Ambition: A five-year cycle to encourage countries to progressively increase national commitments.
• Two Ambitious Goals: 1) Limiting global temperature rise to well below 2°C, with an aspirational target of 1.5°C, and 2) Achieving net-zero emissions in the second half of the century after peaking greenhouse gas emissions as soon as possible.

Despite its success, Stern acknowledged that the Paris Agreement has an inherent challenge — it relies on the assumption that countries will continuously increase their ambition over time, creating a mutually reinforcing cycle where stronger commitments drive further action. However, in the years since Paris, progress has been mixed: while many countries have made net-zero pledges and strengthened their targets, implementation remains insufficient, and the world is not on track to meet its climate goals. Stern acknowledged this as a major challenge, and when asked if he had any regrets or thoughts on how to fix it, he admitted there is no clear solution, emphasising that the gap between ambition and action remains a critical issue for the future of global climate policy.

Challenges in the Post-Paris Climate Landscape

In the 10 years that have passed since the Paris Agreement, Stern discussed how the climate landscape has advanced and outlined three major challenges we are currently facing:

1. The Science Is Clearer, and Impacts Are Worse Than Expected: Climate change is accelerating faster than previously predicted, even as recently as 10 years ago.
2. Technological Progress Is Significant but Not Enough: While clean energy advancements are promising, they are not overcoming systemic obstacles quickly enough.
3. Fossil Fuel Interests Remain a Major Barrier: The entrenched power of the fossil fuel industry continues to obstruct progress, particularly in major economies like the U.S., China, India, and Brazil.

He warned that, unlike crises such as COVID-19, climate change is still not being treated with the urgency it demands, despite its potentially catastrophic long-term consequences.

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Part 2: Roundtable Discussion – The Future of Multilateral Climate Action

Todd Stern and Charlotte Halpern were then joined by Laurence Tubiana and Sébastien Treyer in a roundtable discussion that examined the current political and geopolitical challenges facing climate action and multilateralism.

Backlash Against Climate Policies and Political Realities

Laurence Tubiana addressed the rising backlash against climate policies, emphasising that opposition predates Trump but has intensified due to energy security concerns following the war in Ukraine. Fossil fuel industries have capitalised on geopolitical instability, promoting the false narrative that oil, gas, and coal are essential for national security. Disinformation campaigns have further politicised climate action, portraying it as an elitist agenda disconnected from ordinary citizens.

She argued that public buy-in is essential, as climate policies will struggle to advance without broad societal support. However, she warned that current political trends — such as Trump’s disinterest in climate action and the resurgence of fossil fuel influence — have created an adverse context for international climate cooperation.

Is the Paris Agreement Still the Best Framework?

Sébastien Treyer raised concerns about growing frustration among Global South nations. Many developing countries feel that the promises made in Paris have not been fulfilled, particularly regarding climate finance and adaptation support. He noted that some voices in Africa and India question whether the Paris Agreement is still viable, as rich countries have not delivered on their mitigation and financial commitments.

Two key challenges must be addressed:

1. Southern countries struggle to access climate finance, even when money is theoretically available.
2. The G20 — the biggest emitters — must take stronger action, as developing countries cannot be expected to cut emissions alone.

Treyer emphasised the need for new forms of multilateralism, including technical standards, trade agreements, and bilateral cooperation, to complement existing global frameworks.

Can Europe Still Lead?

Laurence Tubiana highlighted Europe’s role in maintaining climate leadership, despite growing political and economic pressures. She pointed to recent EU industrial policies aimed at preserving the Green Deal framework, though concerns remain about defence spending diverting resources away from climate action.

She argued that climate action cannot be separated from economic and trade policies, highlighting the need for new trade agreements that align with climate and biodiversity goals. While challenges persist, she expressed hope that Europe can continue to drive progress through innovative partnerships.

The Political Challenge: Winning “Hearts and Minds”

Todd Stern emphasised that climate action is no longer just a scientific or policy issue; it is now a political and cultural battle. He stressed that leaders often will only act if they fear losing power, citing the 1970 Earth Day movement as an example of how youth activism can create political pressure.

Stern’s key message, particularly to students and young people, who will face the impacts of climate change most acutely in the coming decades:

• Change will only happen when politicians believe inaction will cost them votes.
• The fight against climate change is not just about negotiations but about mobilising public support.
• Technological progress will continue, but speeding up implementation is critical.

Key Takeaways

1. The Need for Public Buy-In

Winning the hearts and minds of the public is as important as winning policy debates. Disinformation and political polarisation must be countered, and climate policies must be framed as benefiting all citizens and not just an elite agenda.

2. Governments Must Feel the Pressure

History shows that political leaders act when they believe inaction will cost them politically. Climate movements must increase pressure on governments to make climate action a political necessity rather than an optional commitment.

3. Brazil’s Key Role in COP30

With Brazil hosting COP30 in 2025, the country has a unique opportunity to restore trust between developed and developing nations. Climate finance will be central, and Brazil must start negotiations early to ensure meaningful outcomes rather than last-minute diplomatic struggles.

4. Reforming Climate Finance Is Crucial

Both Todd Stern and Laurence Tubiana stressed that the current international finance system is inadequate. They discussed several proposals that could generate much-needed climate finance without relying solely on government budgets, such as:

• Reforming multilateral development banks (MDBs) to mobilise hundreds of billions of dollars
• Implementing global levies on shipping or fossil fuels
• Eliminating fossil fuel subsidies (which amount to nearly $1 trillion annually)

Overall, the event highlighted both the successes and ongoing challenges of multilateral climate action. While the Paris Agreement remains a historic achievement, its implementation faces political, financial, and geopolitical hurdles. Future progress will depend on public engagement, political pressure, and creative approaches to finance and diplomacy.

With the window for meaningful action rapidly closing, the coming years will be decisive in determining whether the world can still meet the ambitious goals set in Paris.

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Watch the full replay of the event here: