Top scientists say the danger from greenhouse gases is no longer in doubt. The IPCC’s 2023 synthesis estimates human-caused warming at about 1.1°C above preindustrial during 2011–2020 [1]. The WMO reports atmospheric CO2 near 420 ppm in 2023, roughly a 10% rise over two decades [2]. A 135-page National Academies review deems climate change “beyond scientific dispute,” urging retention of EPA’s 2009 endangerment finding [4]. Eleven researchers told AP there is no possible world in which greenhouse gases are not a threat to public health and welfare [5].

Key Takeaways

– Shows human-driven warming reached about 1.1°C in 2011–2020, necessitating rapid, deep cuts and net-zero CO2 by mid-century to blunt severe climate risks. – Reveals atmospheric CO2 hit ~420 ppm in 2023, roughly a 10% rise over two decades, while methane and nitrous oxide also set new records. – Demonstrates a 135-page National Academies review (Sept. 2025) deemed climate change beyond scientific dispute and urged retaining EPA’s 2009 endangerment finding. – Indicates 11 leading scientists say greenhouse gases clearly threaten public health and welfare, with attribution analyses linking more extreme events directly to emissions. – Suggests widespread misestimates of greenhouse gas emissions jeopardize 2030 NDCs, requiring accurate accounting plus behavioral and policy interventions to avoid high-emitter lock-in.

What the science says about greenhouse gases

Decades of observations now point to the same conclusion: human-caused greenhouse gas emissions are the dominant driver of observed warming [1]. The IPCC’s 2023 Synthesis Report estimates the global surface temperature was about 1.1°C higher than preindustrial levels over 2011–2020, with increased frequency and intensity of extremes and rising sea levels already apparent [1]. The authors call for rapid, deep, and sustained emissions cuts across all sectors, and net‑zero CO2 by around mid‑century to contain risks that mount with each additional fraction of a degree [1].

Put simply, the world is already in a riskier climate at current warming levels. With roughly 1.1°C of warming, the IPCC links higher chances of extreme heat, heavier precipitation, drought in some regions, and compounding hazards for communities and infrastructure [1]. The synthesis emphasizes that delaying emissions cuts locks in greater damages, while faster action limits medium‑ and long‑term risks—underscoring that policy timelines directly influence future climate outcomes and societal costs [1].

Record concentrations: greenhouse gases hit 420 ppm CO2

The atmosphere’s composition reflects the accelerating pressure from greenhouse gases. According to the WMO, CO2 concentrations reached about 420 parts per million in 2023, marking a roughly 10% increase over two decades and continuing a long‑running upward trend [2]. Methane and nitrous oxide also hit record levels in 2023, extending multi‑year gains that add to near‑term warming and complicate mitigation strategies across sectors [2]. WMO Secretary‑General Celeste Saulo warned that without swift reductions in emissions, these trends make achieving the Paris Agreement’s temperature goals unlikely [2].

The WMO also linked recent pollutant increases to fossil fuel use and widespread fires, pointing to identifiable, persistent drivers behind the record readings [2]. The implication is straightforward: stabilizing temperature outcomes requires bending the concentration curve quickly, and the longer greenhouse gases rise, the more stringent—and costly—the emissions cuts needed later to keep within internationally agreed limits [2].

Evidence of impacts is now beyond scientific dispute

In a sweeping 135-page review released on September 17, 2025, the National Academies concluded that climate change is “beyond scientific dispute,” finding the evidence for greenhouse gas‑driven warming overwhelming and impacts in the United States already worsening [4]. The report urged policymakers to retain the EPA’s 2009 endangerment finding on greenhouse gases, warning that public health, the economy, and infrastructure face escalating harms without swift mitigation and adaptation [4].

This national conclusion mirrors international assessments. The IPCC’s latest synthesis underscores increased risks from extreme events and accelerating sea‑level rise, and ties those rising hazards to the level and duration of greenhouse gas emissions [1]. Aligning U.S. policy with the best available evidence, the Academies’ panel highlights that timely action reduces cumulative harm—especially for frontline communities that are most exposed to climate‑related stresses [4].

Public health and welfare risks tied to greenhouse gases

Scientists consulted by AP were blunt about the stakes: “There is no possible world in which greenhouse gases are not a threat to public health,” said one of 11 experts interviewed in a February 2025 assessment of the evidence [5]. They pointed to the rapidly expanding body of peer‑reviewed studies and attribution analyses that link more frequent and severe extremes—heat waves, intense rainfall, and other hazards—to rising greenhouse gas concentrations [5].

These scientists emphasized that the threat encompasses both immediate and longer‑term public welfare impacts, arguing that the evidence base already justifies regulatory action by agencies tasked with protecting health and safety [5]. Their warnings align with the National Academies’ call for policy continuity and strengthened safeguards, given the clear causal chain from emissions to risks faced by communities and critical systems across the country [4].

Emissions accounting errors are a hidden roadblock

Sound climate policy depends on sound numbers. Yet a 2024 study in Nature Climate Change found widespread public and institutional misestimates of greenhouse gas emissions across countries, undermining mitigation competence [3]. The authors documented systematic underestimation of emissions, which can skew policy design, delay effective action, and mask where reductions are most urgent across sectors and regions [3].

The study concludes that accurate accounting is essential to meet 2030 nationally determined contributions (NDCs) and avoid lock‑in risks from continued high emissions [3]. It calls for targeted behavioral and policy interventions to improve understanding and reporting accuracy, warning that mismeasurement today can create costly course corrections tomorrow—especially as deadlines for near‑term targets draw closer [3].

Timelines: what cuts are needed by 2030 and mid-century

The scientific guidance on timelines is unequivocal: achieving net‑zero CO2 by around mid‑century, preceded by rapid and deep reductions this decade, is needed to limit escalating risks [1]. The IPCC notes that the window for limiting warming to safer levels narrows with continued emissions, and that each year of delay requires steeper, more disruptive cuts later to achieve the same temperature outcome [1].

Concentration data heighten the urgency. With CO2 near 420 ppm in 2023 and other greenhouse gases at record levels, the WMO cautions that Paris targets are unlikely without swift emission reductions [2]. Meeting 2030 NDCs also hinges on fixing emissions misestimates that impede effective policy design and progress tracking, the Nature Climate Change study warns [3]. The National Academies add that failure to act promptly will amplify health, economic, and infrastructure harms, reinforcing the need for consistent, durable policy signals [4].

What regulators and markets should do next

Policy clarity matters. The National Academies explicitly urged policymakers to retain the EPA’s 2009 endangerment finding, reaffirming greenhouse gases as a public health and welfare threat that warrants regulatory safeguards and consistent implementation [4]. The panel’s message is that losing this anchor would risk legal and policy uncertainty at a time when the science has only strengthened [4].

Scientists interviewed by AP advised that the EPA “just needs to look around the world” to see the growing dangers tied to greenhouse gas increases, pointing to the scale and pace of recent extremes and the weight of attribution evidence [5]. International monitoring underscores the same point: record‑high concentrations reported by the WMO, including ~420 ppm CO2 in 2023, require urgent, measurable declines in emissions to keep international goals within reach [2]. Closing accounting gaps that misstate emissions should be a near‑term priority for agencies and markets alike, as accurate inventories determine credible progress toward 2030 targets [3].

Sources:

[1] IPCC – Summary for Policymakers — AR6 Synthesis Report: Climate Change 2023: https://www.ipcc.ch/report/ar6/syr/longer-report/

[2] The Guardian (reporting WMO) – Planet-heating pollutants in atmosphere hit record levels in 2023: www.theguardian.com/environment/2024/oct/28/planet-heating-pollutants-in-atmosphere-hit-record-levels-in-2023″ target=”_blank” rel=”nofollow noopener noreferrer”>https://www.theguardian.com/environment/2024/oct/28/planet-heating-pollutants-in-atmosphere-hit-record-levels-in-2023 [3] Nature Climate Change – Widespread misestimates of greenhouse gas emissions suggest low carbon competence: www.nature.com/articles/s41558-024-02032-z” target=”_blank” rel=”nofollow noopener noreferrer”>https://www.nature.com/articles/s41558-024-02032-z

[4] Politico (reporting National Academies) – Climate change ‘beyond scientific dispute,’ National Academies report says: www.politico.com/news/2025/09/17/climate-change-beyond-scientific-dispute-national-academies-report-says-00568552″ target=”_blank” rel=”nofollow noopener noreferrer”>https://www.politico.com/news/2025/09/17/climate-change-beyond-scientific-dispute-national-academies-report-says-00568552 [5] PBS NewsHour (AP) – Scientists say EPA just needs to look around the world to see the growing dangers of climate change: www.pbs.org/newshour/science/scientists-say-epa-just-needs-to-look-around-the-world-to-see-the-growing-dangers-of-climate-change” target=”_blank” rel=”nofollow noopener noreferrer”>https://www.pbs.org/newshour/science/scientists-say-epa-just-needs-to-look-around-the-world-to-see-the-growing-dangers-of-climate-change

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