Quantcast

Hothouse Earth: Here’s What the Science Actually Does – and Doesn’t – Say

Climate
MARK GARLICK / SCIENCE PHOTO LIBRARY / Getty Images

By Richard Betts

A new scientific paper proposing a scenario of unstoppable climate change has gone viral, thanks to its evocative description of a "Hothouse Earth."


Much of the media coverage suggests that we face an imminent and unavoidable extreme climate catastrophe. But as a climate scientist who has carried out similar research myself, I am aware that this latest work is a lot more nuanced than the headlines imply. So what does the hothouse paper actually say, and how did the authors draw their conclusions?

First, it's important to note that the paper is a "perspective" piece—an essay based on knowledge of the scientific literature, rather than new modeling or data analysis. Leading Earth System scientist Will Steffen and his 15 co-authors draw on a diverse set of literature to paint a picture of how a chain of self-reinforcing changes might potentially be initiated, eventually leading to very large climate warming and sea level rise.

One example would be the thawing of Arctic permafrost, which releases methane into the atmosphere. As methane is a greenhouse gas, this means the Earth retains more heat, causing more permafrost to thaw, and so on. Other possible self-reinforcing processes include the large-scale die-back of forests, the melting of sea ice, or the loss of ice sheets on land.

Global map of potential tipping cascades, with arrows showing potential interactions. Steffen et al / PNAS

Hothouse or Stabilized?

Steffen and colleagues introduce the term "Hothouse Earth" to emphasize that these extreme conditions would be outside those that have occurred over the past few hundred thousand years, which have been cycles of ice ages with milder periods in between. They also present an alternative scenario of a "Stabilized Earth" where these changes are not triggered, and the climate remains similar to now.

The authors make the case that there is a level of global warming which is a critical threshold between these two scenarios. Beyond this point, the Earth System might conceivably become set on a pathway that makes the extreme "hothouse" conditions inevitable in the long term. They argue—or perhaps speculate—that the process of irreversible self-reinforcing changes could in theory start at levels of global warming as low as 2°C above pre-industrial levels, which could be reached around the middle of this century (we are already at around 1°C). They also acknowledge large uncertainty in this estimate, and say that it represents a "risk averse approach".

A key point is that, even if the self-perpetuating changes do begin within a few decades, the process would take a long time to fully kick in—centuries or millennia.

Steffen and colleagues support their suggestion of a threshold at 2°C through reference to previously-published scientific work. These include other review papers which themselves drew on wider literature, and an "expert elicitation" study in which scientists were asked to estimate the levels of global warming at which "tipping points" for these key climate processes might be passed (I was one of those consulted).

The authors argue that 2°C can still be avoided if humanity takes concerted action to reduce its warming effect on the climate. In a similar way that the "Hothouse Earth" scenario involves huge changes in the climate system with multiple effects of one process leading to another, the concerted global action to avoid 2°C would, they suggest, also involve huge changes in the human system, again with several fundamental steps leading from one change to another.

Don't Ignore the Caveats

Personally, I found this an interesting and important think piece that was well worth reading. But since this is not actually new research, why is it getting so much coverage? I suspect that one reason is the use of the vivid "Hothouse Earth" term at a time when everyone's talking about heatwaves. Another is that it's clearly a dramatic narrative, and not surprisingly this has led to some sensationalist articles.

With some exceptions, much of the highest-profile coverage of the essay presents the scenario as definite and imminent. The impression is given that 2°C is a definite "point of no return", and that beyond that the "hothouse" scenario will rapidly arrive. Many articles ignore the caveats that the 2°C threshold is extremely uncertain, and that even if it were correct, the extreme conditions would not occur for centuries or millennia.

Some articles do however emphasise the more tentative nature of the work, and some push back against this overselling of the doomsday scenario, arguing that provoking fear or despair is counterproductive.

One thing that strikes me about the scientific literature on "tipping points" is that there are a lot of review papers like this that end up citing the same studies and each other – indeed, my colleagues and I wrote one a while ago. There is a great deal of interesting, insightful research going on using theoretical methods and calculations with large approximations. However, we have yet to see an equivalent level of research in the highly-complex Earth System Models which generate the kind of detailed climate projections used for addressing policy-relevant questions by the Intergovernmental Panel on Climate Change (IPCC).

Steffen and colleagues have made a good start at addressing such questions, going as far as they can on the basis of the existing literature, but their essay should motivate new research to help narrow down the huge uncertainties. This will help us see better whether "Hothouse Earth" is our destiny, or mere speculation. In the meantime, awareness of the risks—however tentative—can still help us decide how to manage our impact on the global climate.

Reposted with permission from our media associate The Conversation.

EcoWatch Daily Newsletter

Protesters gathered outside US Bank and Wells Fargo locations around the U.S. to protest investment in the Dakota Access Pipeline on Dec. 1, 2016. This photo is from a protest outside US Bank in south Minneapolis, Minnesota. Fibonacci Blue / CC BY 2.0

By Jake Johnson

As a growing number of states move to pass laws that would criminalize pipeline protests and hit demonstrators with years in prison, an audio recording obtained by The Intercept showed a representative of a powerful oil and gas lobbying group bragging about the industry's success in crafting anti-protest legislation behind closed doors.


Speaking during a conference in Washington, DC in June, Derrick Morgan, senior vice president for federal and regulatory affairs at the American Fuel & Petrochemical Manufacturers (AFPM), touted "model legislation" that states across the nation have passed in recent months.

AFPM represents a number of major fossil fuel giants, including Chevron, Koch Industries and ExxonMobil.

"We've seen a lot of success at the state level, particularly starting with Oklahoma in 2017," said Morgan, citing Dakota Access Pipeline protests as the motivation behind the aggressive lobbying effort. "We're up to nine states that have passed laws that are substantially close to the model policy that you have in your packet."


The audio recording comes just months after Texas Gov. Greg Abbott signed into law legislation that would punish anti-pipeline demonstrators with up to 10 years in prison, a move environmentalists condemned as a flagrant attack on free expression.

"Big Oil is hijacking our legislative system," Dallas Goldtooth of the Indigenous Environmental Network said after the Texas Senate passed the bill in May.

As The Intercept's Lee Fang reported Monday, the model legislation Morgan cited in his remarks "has been introduced in various forms in 22 states and passed in ... Texas, Louisiana, Oklahoma, Tennessee, Missouri, Indiana, Iowa, South Dakota, and North Dakota."

"The AFPM lobbyist also boasted that the template legislation has enjoyed bipartisan support," according to Fang. "In Louisiana, Democratic Gov. John Bel Edwards signed the version of the bill there, which is being challenged by the Center for Constitutional Rights. Even in Illinois, Morgan noted, 'We almost got that across the finish line in a very Democratic-dominated legislature.' The bill did not pass as it got pushed aside over time constraints at the end of the legislative session."

Reposted with permission from our media associate Common Dreams.

DESIREE MARTIN / AFP / Getty Images

Wildfires raging on Gran Canaria, the second most populous of Spain's Canary Islands, have forced around 9,000 people to evacuate.

Read More Show Less
Sponsored
Wolves in Mount Rainier, Washington. Ron Reznick / VW Pics / Universal Images Group via Getty Images

The last four members of an embattled wolf pack were killed in Washington State Friday, hours before the court order that could have saved them.

Read More Show Less
Aerial view of lava flows from the eruption of volcano Kilauea on Hawaii, May 2018. Frizi / iStock / Getty Images

Hawaii's Kilauea volcano could be gearing up for an eruption after a pond of water was discovered inside its summit crater for the first time in recorded history, according to the AP.

Read More Show Less
Plateau Creek near De Beque, Colorado, where land has been leased for oil and gas production. Helen H. Richardson / The Denver Post / Getty Images

By Randi Spivak

Slashing two national monuments in Utah may have received the most attention, but Trump's Interior Department and U.S. Forest Service have been quietly, systematically ceding control of America's public lands to fossil fuel, mining, timber and livestock interests since the day he took office.

Read More Show Less
Sponsored
Global SO2 Emission Hotspot Database / Greenpeace

A new report by Greenpeace International pinpointed the world's worst sources of sulfur dioxide pollution, an irritant gas that harms human health. India has seized the top spot from Russia and China, contributing nearly 15 percent of global sulfur dioxide emissions.

Read More Show Less
The huge surge this year in Amazon deforestation is leading some European countries to think twice about donations to the Amazon Fund. LeoFFreitas / Moment / Getty Images

By Sue Branford and Thais Borges

Ola Elvestrun, Norway's environment minister, announced Thursday that it is freezing its contributions to the Amazon Fund, and will no longer be transferring €300 million ($33.2 million) to Brazil. In a press release, the Norwegian embassy in Brazil stated:

Read More Show Less
Gina Lopez, the Philippine secretary of the environment, at a meeting with residents affected by a mine tailing disaster. Keith Schneider

Gina Lopez, a former Philippine environment secretary, philanthropist and eco-warrior, died on Aug. 19 from brain cancer. She was 65.

Read More Show Less