Continuing to emit carbon dioxide poses significant threats, including the risk of triggering tipping points that can lead to major disruptions such as the shutdown of critical ocean currents. Current modeling indicates that injecting aerosols into the stratosphere to reflect sunlight could mitigate this risk, though the effectiveness diminishes significantly if it is initiated much later, such as in 2080.

“My conclusion is that if we are genuinely committed to preventing climate change, we must take solar radiation management seriously. This includes exploring its potential advantages and drawbacks,” declared Claudia Winners from Utrecht University in the Netherlands.

A tipping point signifies changes that are irreversible for centuries, including the slowing or stopping of critical marine currents that distribute immense amounts of heat, impacting the global climate.

One such current is the Atlantic Meridional Overturning Circulation (AMOC), which transfers heat from the tropics to Europe. A collapse of this system could instigate rapid sea level rises in North America, severe temperature decreases in Northern Europe, and significant disruptions to the Asian monsoon.

Stratospheric aerosol injection represents a proposed geoengineering method that involves the dispersal of sun-reflective particles in the upper atmosphere via airplanes, balloons, or rockets.

According to the model employed by Winners’ team, the strength of AMOC could decrease by over 50% in the coming century under a worst-case emissions scenario. However, utilizing stratospheric aerosol injections to maintain global temperatures around 1.5°C could significantly mitigate current weakening, as Winners explained at the Exeter Climate Conference held in the UK last week.

Indeed, AMOC would not dip below this scenario under aggressive emissions reductions without geoengineering. “So, for at least the next 80 years, the effectiveness of stratospheric aerosol injections is higher than the mitigation from greenhouse gases,” Winners stated.

However, the model indicates that AMOC would fail to recover if aerosol injections are delayed until 2080, especially if they are employed to bring global temperatures back above 1.5°C after an overshoot, as suggested by the model.

The team also examined subpolar gyres in the North Atlantic, a circular current linked to AMOC that circulates around areas where cold, saline water sinks. If this sinking process halts because the oceans become fresher and warmer, it will significantly affect the climate in Europe.

In a worst-case scenario, the model predicts that sinking will cease and that commencing stratospheric aerosol injections in 2080 would not reactive the process. However, if injections start now, subsidence could be preserved in two out of the three crucial regions.

Nevertheless, these findings necessitate validation through numerous studies examining more realistic emission scenarios, as there are potential risks involved, according to Winners. “You can really mess it up too,” she cautioned.

For successful geoengineering, sustained global cooperation over centuries will be paramount. “You might say this is the largest governance challenge humanity has ever faced,” articulated ethicist Stephen Gardiner during another session at the conference from Washington University in Seattle.

For instance, if stratospheric aerosol injections are only conducted in one hemisphere without a global consensus, Winners warns that it could alter tropical rainfall patterns worldwide.

In a subsequent presentation, Jim Heywood from the University of Exeter discussed another geoengineering method, known as marine cloud brightening, which demonstrated that localized interventions could potentially incite global climatic changes.

With the risks now understood, they can be circumvented, said Haywood. “It’s merely a shift in strategy.” Yet, many researchers remain skeptical about the feasibility of managing geoengineering risks.

“Solar radiation management sounds entirely manageable. Shouldn’t we refer to it as solar radiation interference?” Stephen Rahmstorf questioned Winners after her presentation at the University of Potsdam in Germany.

There is also a concern that geoengineering could be perceived as an alternative to emission reductions. “We are not addressing the root causes of climate change,” stated Winners. “It’s merely a symptom management strategy; however, if the symptoms deteriorate excessively, it may complement a true solution.”

Due to these concerns, some climate scientists oppose even investigating the potential risks and advantages of geoengineering. The topic has become so contentious that participants at at least one meeting opted out of a session focused on it.

Winners is not the first to assert that geoengineering might need to commence immediately to avert tipping points. Last year, two independent teams concluded that solar radiation management could prevent the collapse of the West Antarctic ice sheet, another significant tipping point.

“It stands to reason that delaying increases the risk of irreversible changes,” Winners mentioned to New Scientist following her presentation. “I believe that’s quite clear.”