1.5. 

Has a number ever contained more portent? 

In 2023, climate records were shattered month after month after month. Hurricanes intensified with record speed. Wildfires set records of scale. Air temperatures had never been so high. Antarctic winter sea ice levels had never been so low. The ocean was so overheated that it was said to be suffering a fever. Fuelled by the El Niño phenomenon, the global mean temperature in 2023 was the highest on record – reaching 1.498°C above pre-industrial levels and giving the world a glimpse of the implications of reaching and breaching the 1.5°C temperature limit set to safeguard humanity. 

In December, for the first time the UK’s Met Office predicted that the year ahead stands “a reasonable chance of a year temporarily exceeding 1.5°C”. Dr Nick Dunstone, who led the Met forecast, acknowledged that while such a temporary rise won’t mean a breach of the Paris Agreement, nevertheless, “…the first year above 1.5°C would certainly be a milestone in climate history”. 

So now here we are. Despite it all – after three decades of climate diplomacy, historic pledges made by almost all the world’s countries eight years ago, the surprisingly breakneck speed of technological progress, the advantageous economies of renewable energy, an ever-clearer understanding of how to contain global warming, and the shocking evidence before our own eyes of the destructive verdict of inaction – humanity arrives at this sober moment. A chief goal of the Paris Agreement is likely slipping beyond our grasp, according to “Ten New Insights from Climate Science 2023/2024”, a report to which SEI contributed. 

Experts who might previously have conceded their alarm only in private conversation now express their fears publicly, emphasizing that scientists cannot ignore the increasingly clear trends, and indicating that they feel a moral obligation to alert humanity to the realities of such threats. New research indicating that global warming is coming faster and may be worse than previously forecast now has scientists debating assumptions that underpin forecasts and the ethics of suggesting that geoengineering measures may be warranted. It is difficult to shrug off the unsettling words from James Hansen – director of the program on Climate Science Awareness and Solutions at Columbia University’s Earth Institute, and the former scientist with the US National Aeronautics and Space Administration whose 1988 climate forecast proved prescient. As he put it last year, “The 1.5–degree limit is deader than a doornail.” 

Reacting to the prospect of overshoot  

The question for 2024 and beyond concerns how the widely held view among key scientists – that “1.5°C is in the rearview mirror” – will influence attempts to achieve the Paris Agreement’s second-best option: limiting global warming to “well below 2°C”.  

Such beliefs will almost certainly steer and motivate international diplomacy, public policy and finance, industry and the wider private sector, civil society, and the psyches of us all – especially as we witness shocking climate-related disasters, suggesting that certain tipping points are imminent, or already here. 2023’s record-shattering temperatures may be a temporary, El Niño-powered surge, but emissions that are the chief propellent keep rising to new heights. Scientists may debate forecasting methodologies and underlying assumptions, but one need not be an expert on the details of computer-generated scenarios to take the pulse. Outlandish fires, storms, droughts, sea-level rise, and extinctions are coming faster than expected, rendering the gap between aims and actions and needed funding all the more alarming. Recent assessments suggest that the world’s remaining carbon budget will be spent in six years. 

The historic COP28 agreement for “transitioning away from fossil fuels in energy systems” leaves the world parsing the meaning of verb choices and prepositional phrases to decipher the implications for action. Contortions are evident. Key players at some level celebrate that the Conference of Parties has finally addressed the elephant in the room (bringing up fossil fuels, surprisingly, at an event led by an oil executive at an event in a petrostate). They also despair that, yet again, the progress made and actions pledged are far too inadequate (potentially on the way to 2.9°C). 

Science writer David Wallace-Wells suggested after COP28 that this may be a “period of normalization” in the era of climate reckoning. “…while there are surely reasons to move past apocalyptic politics toward something more pragmatic, one cost is a loss of perspective at negotiated, technocratic events like these”, he wrote. 

As a report by Chatham House and the Institute for Public Policy Research suggests, responses to the prospect of exceeding 1.5°C could veer towards one of two extremes. The world could enter a “doom loop” – swamping the ability of governments to respond, playing into the hands of defenders of the status quo, and leading to the use of controversial technologies, such as solar geoengineering technologies to manipulate the climate. Indeed, some argue that the world will need everything in its arsenal – including geoengineering – if it is to contain temperature rise. Alternatively, the likelihood of overshoot could jolt leaders into bold action. It could be a turning point, helping the world move away from empty promises and incremental measures. It could provide the sense of urgency needed to deliver thus-far elusive, transformational changes on the scales needed. 

The International Energy Agency forecasts that fossil fuel use will peak in 2030 thanks to the rocketing pace of technological advances. Still, it notes that this is far from enough. The most recent State of Climate Action reports that progress is failing across the board, with 41 of 42 indicators off track to achieve 2030 targets. More than half of these are so far off track that efforts “must accelerate twofold this decade”; some indicators are “heading in the wrong direction entirely”. For example, government financing for fossil fuels has increased sharply.  

Entering uncharted territory 

The situation has given rise to the creation of an international Climate Overshoot Commission, which has already outlined its strategies to address the prospect of breaching 1.5°C. Its recommendations include establishing international protocols to explore and regulate geoengineering through solar radiation modification – already the subject of a controversial experiment in Mexico to release sulphur dioxide particles into the earth’s upper atmosphere to reflect heat.  

The State of the Climate 2023 report puts a gravely succinct headline on the state of affairs: “Entering uncharted territory”.  

Climate forecasts inevitably involve uncertainty – to borrow a summary coined by former US Secretary of Defence Donald Rumsfeld, there are “known knowns, known unknowns and unknown unknowns”. The calculus is always in flux when it comes to writing the equation for what will be politically feasible, economically viable, technically possible, and socially acceptable. As experiences from both the pandemic crisis and the vanguard of technological frontier illustrate, things can change in unexpected ways and in an instant. Against this backdrop, the Emissions Gap Report 2023 concludes: “significantly ramping up implementation in this decade is the only way to keep the window open for limiting global warming to 1.5°C without significant overshoot”. 

The real power of 1.5°C is not in the digits themselves but in their symbolism. It is the goal the world’s leaders agreed to meet. It is the promise made to future generations. It is the rallying cry, the red line drawn to protect us all. What is the power in a number? We are about to find out.