Cooling the Planet: A Third Lever Popular

The climate debate has been built around a familiar objective: to reduce greenhouse-gas emissions to zero fast enough to stop further warming. Increasingly, carbon dioxide removal is being added as a second essential task. But the evidence on accelerating warming, Earth-system tipping points and locked-in climate change raises a harder question: will reducing emissions and removing carbon act quickly enough to prevent dangerous near-term warming?  The answer is no.

Climate risk is moving faster than policy

Recent climate extremes are not isolated events. They are occurring against a backdrop of accelerating, non-linear and abrupt change across the climate system. Scientists were shocked in 2023 when global average warming exceeded 1.5°C, ahead of their expectations. Yet now, as we charge towards a super El Niño, the forecast for 2027 is an astounding 1.75°C.

Our new briefing paper, A Safe Climate Means Cooling the Planet , points to growing evidence that tipping points can be triggered at lower temperatures than previously assumed, with some critical Earth systems already undergoing abrupt change at today’s level of warming. It argues that a warming world of around 1.5°C cannot reasonably be regarded as a safe-climate policy endpoint.

The implications are significant.

Protecting vulnerable communities, coastlines, ice sheets, coral reefs and major ecosystems ultimately requires more than stabilising the climate at its present level. The longer-term objective must be to restore atmospheric conditions closer to those under which human civilisation developed — the relatively stable Holocene climate — when atmospheric carbon dioxide remained below about 280 parts per million, before industrialisation.

That means climate strategy has to address both the cause of warming and the warming already embedded in the Earth system.

Reduce, remove and repair

The briefing proposes a three-lever framework.

Reduce: greenhouse-gas emissions must be driven towards zero at emergency speed.

Remove: excess carbon dioxide must be drawn out of the atmosphere and securely stored, ultimately bringing atmospheric concentrations back towards safer levels.

Repair: research is urgently needed into interventions capable of cooling the planet and protecting critical Earth systems, while emissions reduction and carbon removal have time to take full effect.

The first two levers remain fundamental. Emissions reduction tackles the continuing source of the problem, while carbon dioxide removal can begin reversing the accumulation of greenhouse gases already in the atmosphere.

But both face an unavoidable constraint: time.

The briefing paper says that even a rapid transition to zero emissions would not immediately stop warming. Earth’s current energy imbalance, existing greenhouse-gas concentrations and slow-moving feedbacks mean additional warming is already in the system. Large-scale carbon removal would then take considerable time to materially reduce atmospheric concentrations.

In that interval, further tipping points may be crossed.

That is the case for a third lever.

Why research into cooling matters

Climate interventions aimed at increasing the amount of sunlight reflected away from the Earth — broadly described as albedo modification — could, in principle, reduce temperatures much faster than carbon removal.

They would not replace emissions reduction. Nor would they remove carbon dioxide or address ocean acidification. Their potential role would instead be temporary, limiting peak warming while the underlying causes of climate change are addressed.

Several approaches are already under investigation.

• Marine cloud brightening seeks to increase the reflectivity of low-lying clouds using fine seawater spray. Research has included work examining whether the technique could help protect the Great Barrier Reef, especially during periods of marine heatwaves.
• Stratospheric aerosol injection would introduce reflective particles into the upper atmosphere, partly mimicking the temporary cooling effect observed after major volcanic eruptions. It is the most extensively studied form of albedo modification, although significant environmental, political and governance questions remain.
• Other possibilities range from increasing the reflectivity of buildings and surfaces to more speculative concepts involving cirrus-cloud modification and space-based systems.

These proposals vary enormously in maturity, effectiveness, risk and scalability.

That is precisely why research matters.

And for governments, it is a security issue, too. Sooner or later, with or without a global governance framework, a nation somewhere is likely to start an albedo modification program, especially at a time when unbearable climate extreme are hitting hard. It is important for governments to understand who is doing what, and plausible future scenarios.

The question is not intervention versus no intervention

Debate around climate intervention often frames the choice as one between deliberately altering the climate and leaving nature alone.

But the climate system has already been profoundly altered by human activity. A “hands off” strategy died long ago.

The more relevant comparison is between the risks and consequences of a particular intervention,  and the risks and consequences of allowing the planet to become substantially hotter without one.

As the briefing notes, there is no risk-free pathway out of climate disruption. The policy task is to develop the evidence needed to compare options, understand unintended consequences, establish appropriate governance and determine which approaches — if any — could provide a net social and environmental benefit.

This becomes particularly important if warming continues to accelerates faster than expected and more major climate systems approach irreversible thresholds.

From modelling to applied research

Much of the scientific understanding of solar climate intervention has so far come from modelling, laboratory work and observations of natural analogues such as volcanic eruptions.

Those tools are indispensable, but they cannot answer every question.

A systematic assessment of effectiveness, risks and unintended consequences will ultimately require carefully designed real-world research. That means transparent, independently-scrutinised field experiments conducted within credible governance frameworks — not premature deployment.

International activity is already beginning to move in this direction. Governments and research institutions in several countries are funding research into carbon drawdown, albedo modification and related climate interventions, while initiatives focused on governance and participation are also expanding.

The briefing argues that this effort needs to become far more deliberate and coordinated.

Governments, including the federal government in Australia,  should establish dedicated programs for applied cooling research, cooperate internationally, and ensure developing nations — many of which face the greatest climate risks — participate meaningfully in research and governance.

Keeping all three levers available

Reducing emissions remains indispensable. So does removing carbon dioxide already accumulated in the atmosphere. But if climate change is progressing more quickly than those measures can reverse it, responsible climate risk management requires asking what additional tools may be needed.

That does not mean assuming planetary cooling interventions will work, or that they should inevitably be deployed. But it does mean finding out.

The objective should be to build the knowledge, governance and technical capacity required to make informed decisions before the world confronts a climate emergency in which the available options are narrower, riskier and poorly understood.  The more governance procrastinate, the more difficult climate interventions become at higher levels of warming.

A safe-climate strategy therefore needs all three levers: reduce emissions, remove excess carbon, and investigating how critical climate systems might be protected and repaired.

The question is no longer whether cooling the planet should be part of serious climate research. It is whether that research can advance fast enough to inform the decisions a rapidly warming world may soon have to make.