Humanity's emissions of greenhouse gases must peak within the next decade for the world to meet the goals of the Paris climate agreement, according to a new study published Thursday. Hitting that mark would require strong growth in renewable energy and rapid deployment of emissions-capturing technologies, the authors said.
Ultimately, fossil fuels will need to supply less than a quarter of global energy by 2100. They currently provide about 90 percent.
In a press release, the lead author called the goal ambitious but not impossible. But it added that continued reliance on fossil fuels and growth rates of only 2 to 3 percent in renewables would mean carbon emissions would peak toward the end of the century, with global temperatures rising about 3.5 degrees Celsius by then.
The findings were published in the journal Nature Communications.
The Paris Agreement, signed in 2015, was intended to keep warming to less than 2 degrees by 2100, with a goal of limiting it to 1.5 degrees. In order to do so, negotiators estimated that global emissions would have to reach net zero sometime in the second half of the century. At the time, it was widely acknowledged that nations would have to strengthen their efforts and reduce emissions faster than they promised during the talks.
The new study, led by researchers at the International Institute for Applied Systems Analysis, a research institute in Austria, shows the net zero goal would have to come before 2040 in order to limit warming to 1.5 degrees. To reach net zero, all emissions would be offset by the ability to remove them from the atmosphere, either through natural systems or carbon capture technology.
The authors used modeling to project emissions and warming under a range of scenarios. One assumes continued growth in the use of fossil fuels throughout the century. Another is a business-as-usual scenario with fossil fuel use peaking around 2055. Two others assume growth in renewable energy, one moderate and one rapid.
The modeling suggested that the business-as-usual scenario would lead to 3.1 to 3.3 degrees of warming by 2100. Even under the more aggressive renewable scenario, which assumes annual growth of 5 percent leading to a peak in fossil fuel use around 2022, the planet would warm 2.5 to 2.6 degrees by 2100 without extensive use of carbon capture and sequestration technology.
Limiting warming to 1.5 degrees, the authors found, would require both fast growth in renewables and full deployment of carbon capture technology across the global energy infrastructure. That would mean 34 percent annual growth in the amount of carbon sequestered from 2016 through 2040, with continued growth through the century.
Those steps would require a stark break from current trends. While the authors said the renewable energy goals are realistic, carbon capture technology has lagged, plagued by high costs. There is one opportunity for improvement, the authors note: greater potential for land use and agriculture to sop up more carbon dioxide than their models considered.