The global response to climate change has gained momentum since the 2015 Paris Agreement, but it remains insufficient to meet the scale of the challenge. This agreement sets the objective of keeping global warming well below 2°C and continuing efforts to limit it to 1.5°C. To achieve this, greenhouse gas emissions should peak and decline as soon as possible.

The latest reports from United Nations Environment ProgramTHE International Energy AgencyAnd others have suggested that we are on the verge of peaking global emissions. However, stopping the increase in annual emissions is only the first step. The failure to act sooner and more decisively to bring emissions to net zero has made limiting global warming to 1.5°C an uncomfortably close call.

THE IPCC examined the “pathways” to keeping the temperature within 1.5°C within reach. In almost all of these countries, temperature rises will exceed 1.5°C, after which warming will be reversed by humanity removing more carbon from the atmosphere than it emits. This temporary excess of 1.5°C for at least a few decades is called “overshoot”.

In a recent study published in the journal Naturewe discuss the pitfalls of excessive optimism about the feasibility and safety of such temperature exceedance scenarios. Excessive confidence could lead to underestimating the risks associated with exceeding 1.5°C, even temporarily.

There is a need to be clear about what climate science knows and what it does not know about exceedance, and to plan accordingly. This means that while some risks can be directly reduced by global climate action, others may require additional measures. A responsible strategy to limit short- and long-term climate risks requires both stringent short-term emissions reductions and the development of large-scale carbon removal capacity.

What if the planet warms more than expected?

Even if warming falls below 1.5°C after this exceedance, the impacts of climate change will not automatically and uniformly reverse. Exceedance leads to irreversible consequences on populations and ecosystems, such as disappearance of speciesand the world we return to will be different from the one we failed to save.

We cannot be sure how much warming a given amount of greenhouse gas emissions will cause, and projections of exceedances are often based on the best estimate. The IPCC, for example, speaks of high exceedances exceeding 1.5°C “from 0.1 to 0.3°C”.

But these numbers represent only the middle of a wide range of possible outcomes. In reality, uncertainty about how certain features of the Earth system will respond to warming, such as the carbon cycle, means that the peak warming could be considerably higher – up to 1°C or more. We can’t even rule out continued warming after achieving net zero carbon emissions. Every fraction of a degree of warming counts: exceeding 1.5°C by a maximum of 1°C additional would have serious repercussions.

A capacity to remove several hundred billion tonnes of CO₂ over the course of this century may be needed to guard against the risks of high warming and to ensure that we can reduce warming to 1.5°C once this threshold is reached. exceeds.

In fact, our results imply that we may need almost 10 billion tonnes of CO₂ removal per year after 2050 (around 25% of current annual emissions). This would require a massive effort, but could be possible with rapid scale-up of a range of methods.

These include well-known strategies such as forest and wetland restoration and better land management. But it also includes new methods such as direct air capture technologyin which carbon would be sucked straight from the sky, or bioenergy and carbon capture and storage, which involves extracting CO₂ from the atmosphere and storing it underground.

Some of these methods may not work as intended due to technological, economic, social or sustainability limitations. But even if they don’t work on the scale envisioned, or at all, we should still try.

Limit climate risks in the short and long term.

Since we cannot know exactly how much the climate will warm, we will need to limit the risks as much as possible.

First, we must reduce emissions as quickly as possible to slow the rise in Earth’s temperature, limit peak warming, and reduce our reliance on removing large amounts of CO₂ to reach net zero emissions. .

THE Paris Agreement adapts to such a temperature inversion. Even if the temperature exceeds 1.5°C, countries are obliged to keep maximum temperatures “well below 2°C” and aim for a long-term drop in temperatures.

However, each fraction of warming will disproportionately cause even greater hardship for poor and vulnerable people. This is why delaying drastic emissions reductions is not a resilient strategy. The urgency to reduce emissions now should guide the next set of national emissions reduction targets, expected early next year.

Second, we should consider guarding against the high-risk consequences of high warming by strengthening our ability to remove carbon and reverse warming. Just as governments hold strategic reserves of food and water to deal with unexpected disruptions, the world must develop the capacity to remove large amounts of carbon from the atmosphere. But given the potential limits to how much carbon we can eventually increase, we also can’t afford to waste this capacity on emissions that could be avoided in the first place.

Investing in this type of removal capacity, in addition to pursuing the most ambitious emissions reductions possible, is a no-regrets strategy. If we were certain that a happier climate outcome would materialize, being able to remove this amount of carbon would allow us to bring temperatures down more quickly. And if the warmer side of our projections comes true, we will have put ourselves in a position in which we are best equipped to bring temperatures down again.

Achieving a long-term drop in temperatures would limit long-term climate impacts. For example, in our study we showed that falling temperatures could reduce global sea level rise by around 40 cm (and potentially up to 1.5 meters) by 2300. This could mean the difference between having or not having a future for entire nations. This can also limit the risks of triggering tipping points in the Earth system, such as the collapse of the Greenland ice sheet or currents in the Atlantic Ocean.

The high-risk consequences of exceeding 1.5°C mean we need to do more, not less, now – and focus on bring temperatures below 1.5°C in the long term.

This article was originally published on The conversation by Joeri Rogelj of Imperial College London, Gaurav Ganti of the University of Berlin and Carl-Friedrich Schleussner of the International Institute for Applied Systems Analysis (IIASA). Read the original article here.