‘Window to avoid worst climate scenarios is rapidly shutting’

In 2023, scientists for the first time quantified nine planetary boundaries—aspects that affect the functioning of Earth systems, including climate change, ocean acidification and land-system change—and concluded that six of them have already been transgressed. This assessment is based on a framework put forth in 2009 by a team led by Johan Rockström, now director at Potsdam Institute for Climate Impact Research and professor of earth system science at the University of Potsdam, Germany. All the boundaries are under strain due to global warming, bringing us closer to irreversible climate tipping points, Rockström tells Shagun on the sidelines of the Food Planet Prize in Stockholm. Excerpts:

Shagun (S): Global temperatures have been rising steadily, driven by human activity. How have natural systems responded?

Johan Rockström (JR): Warming has been largely linear so far. The rise in temperature is already translating to more frequent and intense droughts, floods, heatwaves, wildfires, disease patterns and stronger, human-reinforced storms. This forms the basis for declaring a climate crisis. Now in that journey, the planet itself is governed by biological, chemical and physical processes that have been dampening the impact of this stress. For instance, the oceans absorb about 90 per cent of the excess heat generated by fossil fuel burning and around 25 per cent of the carbon dioxide. Forests and other terrestrial ecosystems take up another 25 per cent. Even the melting of ice in the Arctic, Antarctic and Himalayan glaciers consumes about 4 per cent of that heat. In fact, only about 1 per cent of the heat we produce remains in the atmosphere, which is driving the climate crisis. The key concern is, what happens if the planet is no longer dampening and reducing the impacts of climate change, but rather self-enforcing them—releasing more methane, nitrous oxide, carbon from trees and soils, or heat from oceans. This would be the “tipping point”, or the point at which we cross the critical threshold from where the planet shifts from helping to stabilise the climate to actually reinforcing the warming trend.

The Greenland ice sheet, the Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest currently play roles that help cool the planet. But if these systems cross a tipping point, their internal feedbacks reverse—instead of absorbing carbon or heat, they start emitting carbon or releasing heat, accelerating climate change.

S: How close are we to crossing tipping points, and what might happen if we do?

JR: What happens when you cross a tipping point is that the very functioning of the Earth’s system changes and it will be too late to make amends. It is very difficult to re-freeze the Greenland ice sheet or regrow the Amazon rainforest. There is no knowledge and no evidence that it is possible to do. So, these are hard lines in the sand that we do not want to cross.We are so close that we cannot rule out that we have crossed a few tipping points already, but it is inconclusive. Undoubtedly, if we continue on the path we are on right now and allow ourselves to permanently reach 1.5°C, then we would be in what I would call a high-risk terrain of crossing tipping points. 

A recent study suggests that we cannot rule out the shutdown of AMOC this century. Even if something like an AMOC collapse may take 100 years to fully occur, it would be unstoppable after it crosses the threshold. And there is more and more science showing that the Amazon rainforest may tip over into going from a rainforest to a savanna system, which would release massive amounts of carbon. We have more evidence that coral reef systems, the Greenland ice sheet, and the Siberian permafrost are all showing signs of either close to tipping, or possibly, already at a point where they will unstoppably release more carbon and methane than they hold. If that happens, warming accelerates, not just from our continued emissions, but because the planet itself starts emitting more greenhouse gases.

The window is still open to avoid those worst-case scenarios, but it is rapidly shutting. We are probably just years or potentially one or two decades away. We need to move fast.

S: Have governments meaningfully acknowledged these limits, in particular after the introduction of the Planetary Boundaries framework? Is there recognition of how narrow the window is, and an urgency to act? 

JR: Unfortunately, the level of political ignorance is still very high, and I’d say it dominates globally. Some governments do understand the risks, but in climate negotiations, there’s a huge disconnect between what science is telling us and how political leaders respond. Even in Europe, where leaders accept that climate change is real, they are still completely wrongly positioning the climate crisis as something that can be politically compromised as a trade-off with other areas like security, jobs and economic development, and are therefore putting a pause button on efforts on climate. But the reality is, the climate crisis underpins all other issues — food security, health, economy and even education. Solving it must be the foundation for everything else. 

Governments are not fully aligned with the scientific risk assessment. But I would also be self-critical here and say that I think we, in the scientific community, have failed to effectively communicate. Take the AMOC study, for example. Right now, the probability [of AMOC crossing the tipping point] is uncertain. Some studies say it is low, others say it is higher. But the impact is so severe that even a 5 per cent or 10 per cent chance is unacceptable. It’s like aviation: would you get on a plane if the pilot told you there’s a 10 per cent chance it won’t land safely? Of course not. But when it comes to the climate, we are playing Russian roulette with the planet. We urgently need to rethink how we talk about climate risk. It’s not just about probability — it’s about consequences we cannot afford.

S: A large portion of global food production today is actually dependent on practices that transgress planetary boundaries. What would this mean for our food systems? 

JR: The single largest cause for breaching planetary boundaries transgressions is, in fact, the unsustainable and unhealthy global food system. When you look at the assessment, six of the nine planetary boundaries have been breached. And when we look at each one of those, the food system is a major, if not the primary, contributor. Take climate change, for instance: the global food system accounts for 25-30 per cent of all greenhouse gas emissions. This is not just from carbon dioxide, but also methane and nitrous oxide. In terms of biosphere integrity (genetic diversity and energy available to ecosystems), again, food systems are the leading cause of biodiversity loss, primarily because of agricultural expansion into natural ecosystems. 

All of this shows that if we can transform the food system into one that is sustainable, circular and aligned with planetary boundaries, we can push the whole planet back into a resilient and healthier state. Alongside the energy transition, the food system transition is absolutely essential. The only reason we are currently able to produce enough food — despite the fact that nearly a billion people still go undernourished — is because we’re doing so at the expense of the planet. 

S: Food systems are protected and regulated at the national level. How do we overcome the political and structural barriers to achieve global food system transformation?

JR: We need to think of the food system as part of the global commons. It is so important to bring the food system agenda into climate and biodiversity negotiations, and to position it where it truly belongs. Yes, global coordination is very challenging. However, what we are beginning to see, particularly in the context of climate change, is that there is a win-win opportunity here. The planet-damaging way of producing food—the one we are stuck in for over 50 years—is also a very fragile system. It’s not very good at handling droughts, floods, or disease outbreaks. When you instead invest in zero-tillage systems and perennial crops with deeper root systems, more crop rotations, less ineffective use of nitrogen and phosphorus, for example, you build more resilient farming systems. So, shifting to a more sustainable model is not just good for the planet, it’s actually essential for food security and resilience in a rapidly changing climate.

Then there’s freshwater use — the food system is by far the largest consumer, whether it’s blue water (used for irrigation) or green water (rainfall used by crops). When we look at nutrient overloading, particularly nitrogen and phosphorus, it is again [linked with] agriculture. Industry plays a small part, but the massive overuse of fertilisers in food production is the dominant cause. The same goes for land system change: deforestation and degradation of ecosystems for farmland.

This interview was originally published in the August 16-31, 2025 print edition of Down To Earth