Three years separate us from a no-turning-back point in global warming, experts have warned. But there’s still time to prevent that dangerous scenario, as long as significant reductions are made in greenhouse gas emissions by 2020.

Against a blustery political context and just a few days away from the G20 summit (7-8 July) in Germany, a group of eminent scientists and policymakers released a statement in the journal Nature calling for a coordinated effort from governments and the scientific community to get climate change under control while there’s time.

The group, led by former UN climate chief Christiana Figueres, who was one of the people responsible for negotiating the Paris climate agreement, argues that the next three years will be determinant. If the world doesn’t drastically lower carbon dioxide emissions by 2020, climate change could be impossible to stop.

“When it comes to climate, timing is everything”, writes Figueres and other five co-authors, including scientists Hans Joachim Schellnhuber and Stefan Rahmstorf of the Postdam Institute for Climate Research. Citing a report published in April, they added: “Should emissions continue to rise beyond 2020, or even remain level, the temperature goals set in Paris become almost unattainable.”

The consequences of global warming caused by human activity are already visible. Ice sheets melting in Greenland and Antartica, summer sea ice disappearing in the Arctic and coral reefs dying from heat stress, are only some of the ecosystems starting to collapse after a 1ºC rise in temperatures since the late 19th Century. And as warming continues, its effects such as droughts, sea-level rise, and intensified heatwaves, will worsen and “affect the poorest and weakest first”.

“Should emissions continue to rise beyond 2020, or even remain level, the temperature goals set in Paris become almost unattainable.”

But there are still reasons to have hope. While temperatures have risen in the last decades, global carbon dioxide emissions from fossil fuels have stayed flat in the past three years, thanks to a decline of coal burning by China and the United States, and the exponential growth in clean energy worldwide. This is already a good sign, but not enough to prevent the world from warming to dangerous levels.

Our budget for carbon dioxide emissions for the whole century—the amount of the gas that can be released before the temperature limit is breached—will soon be over. Right now, these experts calculate, humanity has a mean budget of around 600 billion tonnes left to emit if we want to hold temperature increase within the Paris limit of 1.5º C to 2ºC. Past that point, the planet would run a growing risk of crossing critical tipping points where irreversible changes to the Earth system would be triggered.

But at the current emission rate of 41 billion of tonnes every year, we would exhaust that budget in only 15 years. Which means that if these levels continue, once that 15-year timespan is over emissions would necessarily have to drop to zero overnight.

This is why bending the curve of emissions downwards at the latest by 2020 is so important, according to the paper’s authors, who have launched Mission 2020 campaign to encourage action. “Lowering emissions globally is a monumental task, but research tells us that it is necessary, desirable and achievable”, they wrote.

“Recent political events have thrown the future of our world into sharp focus. But as before Paris, we must remember that impossible is not a fact, it’s an attitude.”

Timing is crucial in physics as it is in politics. Hence the moment of the statement’s release, intentionally aimed at influencing the upcoming G-20 summit in Hamburg, Germany. The group behind it wants to call on world leaders to acknowledge the importance of the 2020 climate turning point, urging them to “stand up for science” and use it “to guide decisions and set targets”.

French President Emmanuel Macron’s Make Our Planet Great Again Campaign is referred to in the article as a “compelling example” in the efforts being made to deliver on the Paris agreement. In contrast, it also notes Donald Trump’s announcement that the US will withdraw from the Paris agreement in 2020, the date when it is legally able to do so.

“Recent political events have thrown the future of our world into sharp focus. But as before Paris, we must remember that impossible is not a fact, it’s an attitude”, they said.

Hoping to find an echo in the G20 meeting, the paper’s authors set out six milestones for 2020. These include the increase in renewable energy up at least 30% of the world’s electricity supply; initiating plans to fully decarbonize cities by 2050; an increase in electric vehicles up to 15% of new car sales (the current market share is 1%); land-use policies that reduce deforestation; a gas emissions cut by half in industry well before 2050; and the investment of at least USD 1 trillion a year for climate change deployed by the financial sector.

“Cities and provincial governments must help to drive the ambition of national governments on climate change, particularly through smart infrastructure and transport policy.”

They also stress the importance of local leadership in addressing climate change, pointing to international initiatives such as C40 Cities—a network of megacities that adopted Deadline 2020 strategy to align emissions with the Paris target—and the Global Covenant of Mayors for Climate and Energy. “Cities and provincial governments must help to drive the ambition of national governments on climate change, particularly through smart infrastructure and transport policy.”

Endorsed by more than 60 co-signers, including scientists, business leaders, economists, and NGOs representatives, the statement ends with an appeal: “There will always be those who hide their heads in the sand and ignore global risks of climate change,” they wrote. “But there are many more of us committed to overcoming this inertia. Let us stay optimistic and act boldly together”.

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