Global warming policies we set today will determine the next 10,000 years

The decisions made in the next couple of decades about reducing greenhouse gas emissions will determine the severity of global warming — including potentially catastrophic sea level rise — for the next 10,000 years, according to a provocative statement by prominent climate scientists. 

The research, published Monday in the journal Nature Climate Change, examines the "deep time" implications of emissions of global warming pollutants such as carbon dioxide. 

The study vividly demonstrates how the lag effects that are inherent in the climate system affect policy decisions that today's leaders must make through the middle of this century. 

These lag effects — namely the ability of carbon dioxide to remain in the air for thousands of years, and the high sensitivity and long memory of global ice sheets to this temperature increase — will ensure that today's policy choices will play out on a stage longer than the history of human civilization. 

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"If carbon dioxide emissions continue unchecked, the carbon dioxide released during this century will commit Earth and its residents to an entirely new climate regime," the study states. 

The study reviews evidence from ice cores, tree rings and other sources showing the past 20,000 years of the Earth's climate history, including how sea levels fell during the last ice age and rose as the climate entered a new, more stable and mild period known as the Holocene. 

The study also notably details projections for the next 10,000 years based on different scenarios of rising greenhouse gas emissions from burning fossil fuels such as coal and oil. 

It does not base its results on the highest emissions scenario, also known as a worst-case scenario, but the results are sobering nonetheless.

For example, the study shows that future rates of sea level rise due to melting ice caps and warming, expanding seas, could be on the order of up to 4 meters, or 13.1 feet, per century, which would be unprecedented in more than 8,000 years. 

Image: Climate Central

To compare this with more commonly cited projections through 2100, most assessments project up to around 1 meter, or 3.3 feet, of sea level rise during that period.

In total, the study projects a global mean sea level rise of between 25 to 52 meters, or 82 to 171 feet within the next 10,000 years, noting that at least 1.2 to 2.2 meters of that is already virtually guaranteed, due to emissions-to-date. 

"Even if emissions were capped or reduced to some lower rate, we would still be committed to global mean sea level rise that is substantially larger than that experienced over much of recorded human civilization," the study states. 

The only way to avoid such a scenario would be to drive emissions down to zero, or even into negative territory, in which the environment is taking out more carbon than is being added to it. 

"This research is a deeply urgent wake-up call to become much more ambitious," wrote study co-author Benjamin Strauss of the research and journalism organization Climate Central.

Sea level rise commitment

Based on the sea level rise projections, the study calculated the parts of the world that would be most directly impacted. The world population on land below the level of projected sea level rise is 1.3 billion, or 19% of the 2010 global population, the study found. 

A 30-meter, or 98-foot, rise in sea level along the U.S. East Coast would inundate nearly all of New York City, Boston, Miami (along with the rest of South Florida), and coastal Louisiana, among other areas.

Image: Climate central

A total of 122 countries would see at least 10% of their current population in areas that would be directly submerged, the study found, with 25 coastal megacities seeing half their population submerged, based on current population levels. 

Anders Levermann, a study co-author and researcher at the Potsdam Institute for Climate Impacts Research in Germany, told Mashable in an email that the study shows how current emissions are creating a new era in geological time, which many scholars have now termed the "Anthropocene" for the human influence on the Earth. 

"I think a very interesting perspective (but not the only one) is to say that this paper really says that humans are creating a new geological epoch. What we are doing now in a very brief moment in history is changing the Earth for millennia to come," Levermann wrote. 

"The Anthropocene will be at least as long as the Holocene," he added, referring to the geological epoch during which time human civilization became established and flourished.

Discounting the future 

Policy makers and economists often discount the future cost of choices made today, which can result in a lack of consideration for future generations when setting climate policies. The authors of the study designed this research to show how problematic this is. 

"No generation has ever had such an opportunity to help or harm so many hundreds of generations coming after it," Strauss said. "We have the chance to build a legacy as the most hated or the greatest generation for 10,000 years."

Studies including this new research have shown that unless greenhouse gas emissions are reduced significantly through the middle of this century, we will be locked into a rate and magnitude of global warming that human civilization has never experienced before, with profound consequences particularly for low-lying and poor nations around the world.

This was acknowledged by diplomats at the Paris Climate Summit in December, but the deal struck there only covers emissions through the year 2030, with a fuzzy long-term emissions target of peaking global emissions by an unspecified date.

While the agreement struck in Paris was historic, it would still allow for global emissions to increase through the year 2030. Based on the emissions pledges submitted to the U.N., which are also known as Intended Nationally-Determined Contributions, or INDCs, the world is in for around 3 degrees Celsius, or 5.4 degrees Fahrenheit, of warming through 2100.

That's is enough warming to set in motion a cascade of impacts for centuries to come, according to the new study, 

"The eventual magnitude as well as the rate of change is still in our hands," Levermann said. "The more we emit, the more and the faster we change."