Hothouse Earth: Runaway global warming threatens 'habitability of the planet for humans'

Doyle Rice | USA TODAY

Show Caption Hide Caption A record number of Americans now believe in global warming, poll says According to a new poll by University of Michigan's Center for Local, State, and Urban Policy, more Americans than ever now believe that global warming is occurring.

We've been warned.

Runaway global warming on our planet remains a distinct possibility in the decades and centuries ahead, scientists reported Monday in a new study, warning that a "hothouse Earth" threatens the very “habitability of the planet for human beings.”

Such a hothouse Earth climate would see global average temperatures some 6 to 8 degrees Fahrenheit higher than they are now, with sea levels 30 to 200 feet higher than today, the paper said.

In addition, even if the carbon emission reductions called for in the Paris Agreement are met – meaning a rise of no more than 3.6 degrees above preindustrial levels – that still may not be enough.

Scientists at the Stockholm Resilience Centre, the Australian National University and other institutions made their forecast by reviewing past reports on tipping points for climate change. They also looked back at what the Earth's climate was like millions of years ago, when carbon dioxide levels were higher than today, primarily due to volcanic activity.

Global warming is caused by the burning of fossil fuels such as oil, gas and coal, which release greenhouse gases like carbon dioxide into the atmosphere and oceans. Those gases have caused global temperatures to rise to levels that cannot be explained by natural causes.

The paper said that a hothouse Earth trajectory would almost certainly cause widespread river flooding, increase the risk of damage from coastal storms, and eliminate coral reefs (and all of the benefits they provide for societies) by the end of this century or earlier.

More: Global heat, fires and floods: How much did climate change fuel that hellish July?

More: Global warming risk: Rising temps from climate change linked to rise in suicides

Study lead author Will Steffen said "our study suggests that human-induced global warming of (3.6 degrees) may trigger other Earth system processes, often called ‘feedbacks,’ that can drive further warming – even if we stop emitting greenhouse gases."

The feedbacks include methane release from thawing permafrost, loss of snow cover in the Northern Hemisphere, loss of Arctic summer sea ice, and dramatic reduction of Antarctic sea ice and polar ice sheets.

“These tipping elements can potentially act like a row of dominoes," said study co-author Johan Rockstrom of the Stockholm Resilience Centre, an independent research institute that specializes in sustainable development and environmental issues.

"It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if 'hothouse Earth' becomes the reality,” he said.

Steffen added that these feedbacks would be difficult to influence by human actions. They could not be reversed, steered or substantially slowed.

The study "Trajectories of the Earth System in the Anthropocene" was published in the peer-reviewed journal Proceedings of the National Academy of Sciences.

As for what to do to prevent a hothouse Earth, it's easier said than done: Decarbonize the world economy, end deforestation, improve farming techniques and promote carbon-capture technologies, among other recommendations.

This can "only be achieved and maintained by a coordinated, deliberate effort by human societies to manage our relationship with the rest of the Earth system, recognizing that humanity is an integral, interacting component of the system," according to the study. "Humanity is now facing the need for critical decisions and actions that could influence our future for centuries, if not millennia."