With researchers warning that limiting global warming to 1.5 °C is fast slipping from our grasp, we know it will take a mammoth effort to reach. But the scale of emissions reductions required is actually something we have already achieved before – quite recently and rather by accident.

In 2020, global carbon dioxide (CO2) emissions fell by 6.3 percent or some 2,200 metric tons (MtCO2), a new study in Nature Geoscience reports.

That reduction "is the largest absolute annual decline in emissions, larger than the emissions decrease of the 2009 financial crisis (380 MtCO2) and even larger than the decrease reconstructed at the end of World War II (814 MtCO2)," Tsinghua University Earth system scientist Zhu Liu and colleagues wrote in their paper.

Of course, we all know that was due to the massive disruption to our economies and way of life wrought by the deadly and ongoing COVID-19 pandemic – not something we want to repeat.

But if we made equivalent changes in a targeted and controlled manner, it is technically possible to achieve these emissions reductions, and with far fewer negative impacts to boot.

For instance, the researchers found the biggest single factor in reducing emissions, accounting for almost a third of the drop, was the massive decrease in ground transport – cars and trucks. If, instead of stopping a lot of this transport, we switched to powering it with renewable energy, we could achieve sizeable cuts without the crippling consequences.

"It's a great demonstration that it is possible to reduce our emissions, we just need to choose the way we're going to do that," Australian National University climate scientist Nerilie Abram, who was not involved in the study, told the Australian Broadcasting Corporation.

"It's not just individuals doing their part to reduce how much they travel – those sorts of things are not the solutions. We need a planned transition across society to implement the changes that are needed."

It would be a herculean effort, but the benefits would be massive.

Limiting warming to 1.5 °C would reduce risks to humans by around 40 percent compared to a 2 °C scenario, and up to 85 percent compared to a 3.66 °C scenario, found another study also published this week in Climatic Change. University of East Anglia environmental scientist Rachel Warren and colleagues used 21 types of climate models to consider water scarcity, heat stress, diseases, flooding, drought, and economic impacts.

They concluded hundreds of millions of additional people will be exposed to severe drought with each level of warming. But sticking to 1.5 °C could reduce global economic impacts by 20 percent compared to a 2 °C future, and even reduce the number of people exposed to malaria and dengue fever by 10 percent.

Since the lockdowns, CO2 emissions have returned to 2019 levels, Liu and team report. They suggest orienting stimulus packages for pandemic recovery towards mitigation strategies, but point out the finances for such supports are still dominated by fossil fuel investments.

These are the sorts of systemic problems that must be shifted to get lasting results, and those changes are already underway.

Unfortunately, overshooting 2 °C would cost life on Earth dearly – with "waves of irreversible extinctions and lasting damage to tens of thousands of species," University of Cape Town ecologist Joanne Bentley and colleagues wrote for The Conversation. Their new research attempts to understand the scale of damage this would cause the ecosystems we depend on.

"The effort to stop temperatures rising isn't an abstract attempt at bending curves on a graph: it's a fight for a livable planet."

Even if the 1.5 °C target slips away, every fraction of a degree of warming matters. The 1.5 °C goal was always just meant to provide something tangible to aim for, it's not a magic scientific number.

What's more, we have already avoided some of the worst scenarios we were previously heading for and researchers agree we still have a decent shot at limiting our warming to below 2 °C.

"If we end up at 1.6 °C, that's better than 1.7 °C; if we end up at 1.7 °C, that's a lot better than 2 °C. If we ended up at 2 °C, that's a lot better at where we were heading 20 years ago, which was 5 °C," climate scientist Katharine Hayhoe from Texas Tech University told New Scientist.

"Every bit of warming matters. Every year matters, every choice matters, every action matters."

The new studies were published in Nature Geoscience, Climatic Change and Philosophical Transactions of the Royal Society B.