UN Report Declares 1.5C Warming Limit Unavoidable; Focus Shifts to Limiting 'Overshoot'

A United Nations climate report released on Wednesday indicates that the globe will inevitably surpass the Paris Climate Agreement's 1.5-degree Celsius warming target within the next few years. The primary objective now, according to the report, is to minimize the duration of this warming "overshoot" and subsequently bring global average temperatures back down.

The annual UN Emissions Gap report, intended to guide policymakers attending the upcoming COP31 climate talks in Turkey next month, has historically expressed skepticism about meeting the 1.5-degree target. However, this year's edition marks the first time its authors have declared that exceeding the target is "imminent and unavoidable." UN Environment Program Executive Director Inger Andersen stated in a call with reporters, "We are now saying this window has closed, but we can open it again by making the overshoot as brief as possible." She further elaborated, "This is about how to find a way back as shortly and as quickly as possible with as limited an overshoot as possible."

Previous reports concentrated on the disparity between countries' emissions reduction commitments and the actions needed to limit global warming to 1.5 C above preindustrial levels. This year's report redefines the "gap" by examining new emissions overshoot scenarios. It assesses what would be required to cap peak warming at 1.7 to 1.8 degrees C before reducing temperatures back to 1.5 C through emissions cuts and the deployment of carbon removal technologies.

The report emphasizes that every additional fraction of a degree of warming above 1.5 C "raises the risk of irreversible changes including in ice sheets, permafrost carbon, ocean circulation, and coral systems, along with devastating human impacts." Climate scientist Michael Mann of the University of Pennsylvania noted that each incremental increase in warming can have an "immense" impact in terms of "damage, cost and loss of lives." Mann was not involved in the UNEP report.

According to the UNEP, the least severe overshoot scenario projects peak warming between 1.7 and 1.8 degrees C, with a return to at or below 1.5 C by 2100. Achieving this pathway necessitates a far more substantial reduction in global greenhouse gas emissions than currently proposed for the COP31 talks. Specifically, it requires an 18% cut by 2030, a 45% cut by 2035, and a 69% cut by 2040, relative to 2025 levels. This scenario also calls for a tripling of renewable electricity capacity by 2035 and significant cuts to fossil fuels, including the phaseout of coal by 2040. Furthermore, it demands a large-scale implementation of carbon removal technologies, which have yet to be proven effective at such a massive scale.

In stark contrast, fulfilling existing emissions reduction pledges would only result in a 5-to-8% emissions cut by 2030 and an 11-to-15% reduction by 2035, leading to a peak warming of approximately 2.6 degrees C. If countries adhere to their current policies, warming could reach a peak of around 2.8 C, an increase from last year partly attributed to the United States' withdrawal from the Paris Agreement and its retracted emissions reduction commitments. Even with countries meeting their existing reduction commitments and net-zero pledges, warming is projected to peak at 2.1 C.

The report warns, "Without urgent action, the lowest possible 1.5 C overshoot pathway will quickly fade." It highlights that "Every five years of CO2 emissions at current levels pushes peak warming up by around 0.1 C." Mann added that an additional 0.1 C of global warming "Permanently cuts global GDP by roughly 1.2% (over $1.2 trillion annually) and pushes approximately 140 million more people into life-threatening, dangerously hot climates."

Climate scientist Kate Marvel of Project Drawdown, a climate research and solutions nonprofit, suggested that exceeding the 1.5-degree target is a milestone but not an outright failure of climate science and policy. "There’s nothing special about any given temperature threshold," she commented. "The right unit isn’t degrees, it’s tons — of carbon dioxide, methane and other greenhouse gases. If we want to avoid the worst impacts, our task is and has always been to reduce these emissions as quickly as possible." Marvel concluded, "Passing 1.5 degrees is a sign that we’re not moving fast enough, but it doesn’t mean we’re doomed."