What is the Hothouse Earth trajectory, and can we avoid it?

This article was originally published in February 24, 2024, and updated on September 29, 2026, with new research.

The Hothouse Earth trajectory is a term coined in an August 2018 paper by Johan Rockström, Katherine Richardson, and Hans Joachim Schellnhuber, describing a possible future scenario in which human-caused climate change sets Earth on a warming path that would be difficult or impossible for us to control or correct. In February 2026, the authors of the original paper, along with additional scientists, published new work suggesting that, as warming reaches the 1.5°C threshold, the changes that cause Hothouse Earth are beginning, increasing the risk of reaching this trajectory.

As the Hothouse Earth trajectory becomes more likely, it is increasingly important for everyone, including those outside the scientific community, to understand what drives Hothouse Earth, how close we are to the trajectory, and what’s at stake for our climate and everyday life if we do.

What is the Hothouse Earth trajectory?

In the Hothouse Earth trajectory, human-caused climate change initiates mechanisms in Earth’s systems that push the global climate into continued, self-perpetuating warming. That warming would continue even if humans were to stop adding more greenhouse gas emissions to the atmosphere. Once the climate is on the Hothouse Earth trajectory, in theory, we would not be able to slow, stop, or reverse it.

How does the Hothouse Earth trajectory work?

The mechanisms that would initiate the Hothouse Earth trajectory are positive climate feedback loops and the crossing of key climate tipping points. Some of these processes are already underway. 

Climate feedback loops

Warmer atmospheric temperatures could initiate positive climate feedback loops in Earth’s climate that generate warming in response to warming, growing stronger over time. Positive climate feedback loops warm the planet by either adding heat-trapping greenhouse gases to the atmosphere or increasing how much heat the earth’s surface absorbs and retains from the sun.

An example of a positive climate feedback loop is albedo loss, in which warmer global temperatures cause snow and ice to melt. Less snow and ice lowers Earth’s ability to reflect sunlight back into space, causing the earth to absorb more heat and creating more warming and ice melt in a looped cycle. 

Current warming levels have already initiated positive climate feedback loops that are adding to global warming, shown by the acceleration in Earth’s energy imbalance, a measure of the exchange of energy between Earth and space. There are climate feedback loops around the world that can add to warming in either small or large amounts, engaging the next important action in activating Hothouse Earth: crossing key climate tipping points.

Climate tipping points

A climate tipping point is a critical threshold in an Earth system, past which the system reinforces its own change until it enters a new state. This change may be rapid or gradual, and could be irreversible. Any component of an Earth system can cross a tipping point, from a single glacier to a system as complex as the Atlantic Meridional Overturning Circulation (AMOC). 

Crossing certain tipping points could drastically impact Earth’s warming trajectory. For example, if rising global average temperatures prompt the Amazon rainforest to cross a tipping point, past which the rainforest continues to degrade, the Amazon could change from absorbing greenhouse gases to emitting greenhouse gases. This emissions source would continue to raise global temperatures even if human emissions stopped completely. 

Another important tipping point could be the loss of a critical amount of mass in the Greenland Ice Sheet, which currently helps to cool the planet by reflecting sunlight and heat back into space. If rising temperatures caused the Greenland Ice Sheet to shrink by this critical amount, that ice loss would cause further ice loss and the ice sheet would continue to shrink until eventually it disappears, a process that would raise sea levels and drastically change ocean temperatures, disrupting crucial ocean currents like the AMOC that help to regulate global weather conditions. 

Crossing tipping points like these could generate enough additional warming to activate other feedback loops and initiate the crossing of more tipping points, generating even more warming. This cascading chain of impacts could keep the climate on an accelerating warming path, even if humans stop our own greenhouse gas emissions.

How close are we to activating Hothouse Earth?

Scientists do not know the precise temperature at which the planet and its atmosphere would transition into a Hothouse Earth trajectory. 

There is evidence that a Hothouse Earth trajectory is becoming more likely. According to a January 2026 report from Berkeley Earth, Global temperatures from 2023, 2024, and 2025 averaged more than 1.5°C above the pre-industrial baseline, and, as of early 2026, the planet is on track to surpass 2°C of warming as early as the 2030s. 

The February 2026 article by Johan Rockström et al. posits that as we reach 1.5°C of warming, we are closer than ever to triggering a Hothouse Earth trajectory. The authors write that we are on a path to overshoot 1.5°C, and that the longer and higher warming overshoots that 1.5°C threshold, the greater the risk of committing the planet to a Hothouse Earth trajectory. Specifically, climate models indicate that exceeding that threshold could increase this risk by 72%, compared to staying below it. A 2026 report by the United Nations Environment Programme concluded that global warming will exceed 1.5°C.

This does not necessarily mean that we are guaranteed to enter the Hothouse Earth trajectory, but the probabilities are rising. According to the authors, there is growing evidence that the Greenland Ice Sheet is losing structural stability and potentially set to collapse well before 2050, increasing the chances of crossing this tipping point and initiating cascading impacts in the near future. 

What happens if we activate the Hothouse Earth trajectory?

While there are aspects of the Hothouse Earth trajectory we can’t predict, here’s what could happen if we activate the Hothouse Earth trajectory.

Losing control

Until recently, human activity adding greenhouse gases to the atmosphere was the only force driving climate change. If we activate a Hothouse Earth trajectory, the planet would be warming itself via a series of cascading feedback loops. This additional self-generated warming would be out of our control, even if we stop activities that emit greenhouse gases. 

If humans are driving the car of climate change, initiating Hothouse Earth would be like losing control of the steering wheel, the accelerator, and the brakes. Because feedback loops amplify whatever warming level the planet is at, they grow more powerful over time, meaning that as we warm the planet further, our chances of controlling a potential Hothouse Earth trajectory reduce.

Major and irreversible change

According to the authors of the 2018 paper, planetary conditions on the Hothouse Earth trajectory would eventually “resemble planetary states…last seen several million years ago.” It is likely that many of the things that make our planet recognizable to us—plants, animals, and other organisms—would be unable to adapt to a rapid trajectory of continuous warming.

The changes described above, like the loss of the Amazon rainforest or the Greenland Ice Sheet, would be irreversible on time scales that matter to humans, and it would take millennia for the planet to return to a climate similar to the stable one of the Holocene, if ever.

Can we avoid Hothouse Earth

Our best chance of avoiding Hothouse Earth starts with reducing and stopping greenhouse gas emissions in order to slow, weaken, or prevent climate feedback loops and potentially avoid crossing crucial tipping points.

If emissions continue, it may be the case that the only way to avoid, prevent, or control crucial feedback loops and tipping points would be to directly manipulate aspects of Earth’s systems to intervene in the climate. However, there is not currently technology available to us that could prevent a Hothouse Earth once we are on the trajectory.