Nicholas Stern considers the implications of a new UN report warning that humanity has been too slow to cut emissions

The world must now face up to the fact that the increase in average global temperatures will surpass 1.5° Celsius, the more ambitious of the 2015 Paris climate agreement’s targets. That means devising a plan for managing the consequences—by increasing our focus on adaptation, loss and damage, and geoengineering—while redoubling our efforts to cut greenhouse-gas (GHG) emissions.

A sobering new report from the United Nations Environment Programme (UNEP) warns that even if governments deliver on all their existing climate pledges, global warming could reach 1.8°C later this century. Meanwhile, a continuation of current policies could produce warming of 2.6°C by 2100. Either way, overshooting 1.5°C will expose the world to serious costs, including more frequent and intense heatwaves and bouts of heavy rain in many places. It will also bring us closer to breaching climate thresholds (or “tipping points”) beyond which lie far greater risks—such as destabilization of the polar ice caps in Greenland and West Antarctica.

While the poorest countries will continue to be hit earliest and hardest, this summer has demonstrated that even rich countries like the United Kingdom are not prepared for the climate-driven risks that are already materializing, let alone the risks that await us. Temperatures will rise, and the negative effects of climate change will continue to mount until global GHG emissions are reduced to net zero and atmospheric concentrations stop growing. As long as they are still rising, so will the costs to us all. The net-zero target follows from physics, not ideology.

The effects of overshooting 1.5°C will require much larger investments in adaptation and resilience, ranging from higher sea defenses to the development of more drought-resistant crop varieties. Such investment will become a much higher priority, and overall investment needs will become much greater than would have been the case had we met the Paris target.

But there are limits to adaptation. Breaching major climate thresholds could lead to conditions so hostile that socioeconomic development itself would be reversed, forcing hundreds of millions of people to move despite whatever adaptation measures are in place.

The longer it takes us to reach net-zero emissions, the larger the costs will be. Minimizing those costs will require more investment in rapidly cutting emissions through the deployment of renewables and electric vehicles, while making more rapid progress in hard-to-abate sectors such as maritime shipping and air travel.

Although investment in the necessary technologies has been growing strongly, we still need a marked and sustained acceleration to phase out the polluting, inefficient practices that are making emissions rise further. Despite the International Energy Agency’s warning five years ago that limiting warming to 1.5°C would require that no new fossil fuel projects be launched, many producers have been expanding their exploitation of oil, gas, and coal reserves. As a result, managing climate change will require stranding even more fossil-fuel infrastructure, creating a real cost for investors who have backed dirty energy over renewables.

One must also acknowledge the high costs associated with depending on international hydrocarbon markets. The competition for fossil fuels drives violent conflict, and price volatility has repeatedly caused severe economic crises. And yet, in most of the world, clean energy is now cheaper than dirty alternatives. Investing in clean, efficient technologies and infrastructure offers developing countries the chance to generate strong, sustainable, and resilient economic growth while cutting emissions.

Nonetheless, the UNEP report points out that reversing the 1.5°C overshoot will require us to go beyond net zero to achieve negative emissions, meaning we will eventually need to remove much more carbon dioxide from the atmosphere than we add. Though we can and should expand natural carbon sinks, including forests, these are unlikely to offer the total capacity we will need. Closing the remaining gap therefore will require greater investment in artificial methods of extracting and storing billions of tons of atmospheric CO2.

We should also examine carefully the potential of other geoengineering solutions, including those designed to reduce the total amount of solar energy reaching the Earth’s surface. Further research is needed, however, because these options come with significant risks and ethical implications. For example, cooling the planet while leaving high levels of CO2 in the atmosphere would acidify our oceans, with potentially dangerous consequences.

The next few decades will be challenging. There will be many opportunities for investment and growth, but also serious dangers, owing to our hitherto slow response to the risks of climate change. We must come to grips with our new reality before we blow past yet another dangerous threshold.

*Nicholas Stern is Chair of the Grantham Research Institute on Climate Change and the Environment and the Global School of Sustainability at the London School of Economics and Political Science. This content is © Project Syndicate, 2026, and is here with permission.