New reports detail how to limit global warming, warn of ‘existential’ risk from not acting soon

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Two new studies released during the United Nations’ Climate Week find that global temperature increases can be limited to the Paris Agreement goal of 2 degrees Celsius above pre-industrial levels, but cutting back carbon dioxide emissions alone will not be sufficient – and the stakes are as high as they come.

The paired reports, “Well under 2 degrees Celsius: fast action policies to protect people and the planet from extreme climate change,” written by a team of 33 prominent scientists and policy experts chaired by Veerabhadran Ramanathan and Nobel Laureate Mario Molina of UC San Diego with Durwood Zaelke of the Institute for Governance and Sustainable Development, and “Well below 2°C: Mitigation strategies for avoiding dangerous to catastrophic climate changes” by Yangyang Xu and Ramanathan published in the Proceedings of the National Academy of Sciences, detail a three-pronged approach to keep global warming below the 2-degree limit.

In addition to decarbonizing the global energy system, drastically reducing emissions of short-lived super climate pollutants (HFCs, methane, and black carbon), and atmospheric carbon extraction will also be necessary – and action needs to begin without delay to avoid potentially catastrophic risk.

Without a carbon-neutral energy system by 2050 and a severe reduction in short-lived super climate pollutants by 2020, exceeding the 2-degree limit is likely, and with that comes an increasing risk to humanity.

“The world has cumulatively emitted about 2.2 trillion tons of CO2 to date, and policymakers have previously assumed that we could emit up to 3.7 trillion tons and remain below dangerous levels,” said Ramanathan. “We show in our paper, however, that there is a 1 in 20 chance that emission beyond the current 2.2 trillion tons presents catastrophic and perhaps even an existential risk.”

Risks include exposing roughly 7 billion people to deadly heat stress, increased spread of diseases including Zika, and the possible extinction of close to 20 percent of species on earth — and that includes humans.

“How many of us would choose to buckle our grandchildren to an airplane seat if we knew there was as much as a 1 in 20 chance of the plane crashing? With climate change that can pose existential threats, we have already put them in that plane,” said Ramanathan.

While the conclusions of the reports are alarming, there is good news: Solutions already exist that will deliver benefits in the near-term, placing the world on a path to achieving the long-term targets of the Paris Agreement and near-term sustainable development goals.

"This report shines a bright light on the existential threat that climate change presents to all humanity," said California Governor Jerry Brown. "Scientists have many ideas about how to reduce emissions, but they all agree on the urgency of strong and decisive action to remove carbon from the economy."