Topic Brief: Beyond Net Zero

Reaching net zero faster has benefits for many generations to come

Net zero carbon emissions are achieved if the amount of greenhouse gases released into the atmosphere by humans is balanced by what is removed through human activities, such as boosting ‘carbon sinks’ – e.g. through tree planting or wetlands restoration – and developing new technologies that support the extraction of carbon from the air.

The removal of atmospheric greenhouse gases beyond what is emitted is called ‘net negative’ carbon emissions; this is only possible through carbon dioxide (CO₂) removal techniques, which encompass a variety of approaches to actively remove CO₂ from the atmosphere and store it long-term.

The impacts of fossil fuels

Greenhouse gas emissions are at record levels. The continuous expansion of fossil carbon projects and land-use change means we are failing to reduce emissions meaningfully. And we are entering a new era where global warming is guaranteed to surpass 1.5°C.

To assess climate risks, climate scientists often use ‘future scenarios’, which are plausible pathways that combine socioeconomic trends with greenhouse gas emission trajectories to project future climate conditions and their impacts. These scenarios cover a wide range of possible emissions futures. In the past, the focus has been on high-emission pathways; going forward, it is equally important to focus on more policy-relevant pathways that reach net zero emissions.

In all scenarios, the Arctic and Antarctica will warm more than the tropics, and continued warming will result in summers without sea ice in the Arctic. All this will have consequences for the global climate.

Carbon dioxide (CO₂)

Carbon dioxide (CO₂) is a gas that lingers in the atmosphere for centuries, trapping heat near the Earth’s surface. Its naturally long-lasting presence means that emissions from this year contribute to warming for years to come. Therefore, the extent of long-term warming is significantly influenced by the balance of emission and removals.

Under all ‘plausible future’ scenarios (from low to high emissions), reaching net zero faster is better. Halting CO₂ emissions will lead to declining CO₂ concentrations, as natural land and ocean carbon sinks absorb and store the atmospheric CO₂.

Unlike CO₂, greenhouse gases like methane (CH₄) are short-lived and stay in our atmosphere for roughly a decade, but they have a much stronger warming influence than CO₂. Therefore, rapid reductions in CH₄ emissions can lead to near-term cooling and support mitigation efforts.

It is imperative to reach net zero, despite locked-in impacts

The reality is that even after we reach net zero, we will still face long-term consequences due to the inherent inertia of climate systems. Any delays in emissions reduction will have dire consequences.

For example, even after reaching net-zero, the average temperature of the ocean – not just on the surface, but throughout its entire depth – will continue to warm. The rise in ocean heat for centuries to come will put many marine species at severe risk, particularly in the Southern Ocean.

This ocean warming will cause sea ice around the Antarctic to continue to melt. This sea ice reflects, rather than absorb, radiation from the sun, and protects ice sheets. The loss of these ice sheets will contribute to rising global sea level, putting low-lying areas at severe risk.

Some parts of the world may experience continued warming, including possibly more frequent and intense heatwaves. Key climate patterns, like El Niño Southern Oscillation and the Atlantic Ocean currents, may also shift in ways that we don’t yet fully understand.

Alarmingly, changes to several crucial parts of the Earth system, such as the Boreal permafrost, the Atlantic Meridional Overturning Circulation and the Arctic and Antarctic ice sheets, may be triggered at higher levels of warming, starting irreversible and potentially catastrophic chain reactions.

Despite the locked-in and potentially irreversible impacts, many of these changes are likely to be incrementally worse if we delay halting our emissions. Reaching net zero targets as soon as possible is an imperative.

We can limit further damage

Not all is lost. By reaching net zero, we will stop further warming. However, sea level rise, ocean acidification, and some ice sheet loss will continue for centuries. Reaching “net-negative” emissions – removing carbon from the atmosphere at a greater rate than we emit it – can help bring the global average temperature down. 

Weather resources, like wind and solar, are supporting the electrification of the energy network. These technological advances have resulted in a reduction in annual coal emissions.

In many parts of the world, cutting fossil fuels also involves cutting aerosols such as sulphates, which currently have a cooling effect on the planet. Cutting rapid aerosol emissions without also reducing greenhouse gases may lead to a short-term rise in warming. However, the long-term benefits – such as better air quality and health improvements – far outweigh this temporary effect. Short-term adaptation strategies are critical to address the removal of this masking effect of aerosols, and halting emissions early is necessary to limit the impacts of the short-term warming spike.

In tandem with emissions cuts, we need to plan for continuously changing climate risks to develop smart adaptation strategies. Since many climate change impacts are likely to persist even beyond net zero, adaptation strategies will play a major role to limit risks. However, they will not eliminate all risks, especially for low-lying islands, coral reefs and the biodiversity of our planet.

Early action to halt emissions is critical to reduce the adaptation burden on our communities. It also means fewer long-term adaptation costs and persistent climate impacts for future generations. The scale of impacts will depend strongly on how quickly we cut emissions today.

Download a PDF copy of the topic brief here.

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