Greenhouse-gas emissions must fall dramatically below 2010 levels in the next 35 years and to virtually zero by 2100 if the world wants to take a least-cost approach to combating human-triggered climate change, according to a new report from the Intergovernmental Panel on Climate Change.
Governments approved the report at the end of a week-long IPCC meeting in Copenhagen last week. It's the final installment in periodic sets of reports the IPCC produces on climate change, the range of current and projected effects, and the likely effect of actions ranging from business as usual to rigorous efforts to reduce greenhouse-gas emissions – mainly carbon dioxide from using fossil fuel and from land-use changes.
Known as the synthesis report, the summary for policymakers release today and the larger volume it draws represent a concise presentation of the state of the climate, the consequences of various actions or inaction, and the options available for reducing emissions and adapting to global warming – information contained in the three, much-larger main volumes the IPCC has released since September 2013.
In climate talks over the past five years, countries have agree to work toward holding the increase in global average temperatures to 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels by 2100. Countries settled on this as a level that would avoid what the Framework Convention on Climate Change terms “dangerous anthropogenic interference” with Earth's climate.
The window is rapidly closing for taking action in cost-effective ways in order to meet that objective, according to the report's authors.
“We're either going to have to be lucky and discover that the climate is less sensitive than we think it is, or we're going to have to be lucky with new technological developments falling into our laps, or we're going to have to act very fast to avoid the 2-degree warming,” says Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University and one of the report's authors. “Frankly, with the fate of the planet at stake, we shouldn't have to lean too much on luck to get this problem solved.”
Research, development, and deployment of new technologies is important, Dr. Oppenheimer says, but the response time for uncovering and fielding these technologies may be too slow if we don’t act quickly to curb emissions with existing approaches.
The final installment in the latest set of IPCC climate assessment reports comes at a time when countries are preparing to meet in Lima, Peru, in hopes of hammering out a draft for a new global climate treaty, one that engages developed as well as developing countries. The goal is to have a new agreement ready for approval at climate talks in Paris at the end of 2015
“The IPCC synthesis report delivers a critical message at a critical moment,” said Bob Perciasepe, who heads the Center for Climate and Energy Solutions in Arlington, Va., in a prepared statement. “The core findings aren’t new, but the report makes them clearer than ever, and they are worth underscoring.”
Warming, especially since the 1950s, “is unequivocal,” the report reiterates, adding that it's “extremely likely” that greenhouse-gas emissions from burning fossil fuel and from land-use changes have been the dominant cause of warming since the '50s.
Left to business as usual, which already accounts for the natural tendency of economies to use energy more efficiently as new technologies emerge, emissions continue to rise to levels that lead to global average temperatures of at least 4 degrees C. above pre-industrial levels by the end of the century. The latest report on current emissions from the Global Carbon Project shows emissions rising, closely tracking this business-as-usual scenario. This, despite the growing number of countries adopting climate-related policies and a global economic slowdown.
Based on a range of modeling studies on which the IPCC drew, to stand a better-than-even chance of achieving the 2-degree goal, greenhouse-gas emissions need to peak within the next six years and decline by 40 to 70 percent by 2050. Greenhouse-gas emissions must fall essentially to zero by 2100.
“We do have a range of options to reduce emissions substantially – those are both policy options and technology options. So there is a way to do this,” says Leon Clarke, a senior scientist with the Joint Global Change Research Institute in College Park, Md., and another of the report's authors.
Still, “that's going to require a pretty serious transformation of the energy system, potentially reducing emissions from the electricity sector all the way down towards zero in the next 35 years,” he adds.
Efficiency improvements will help, as will changes to forest- and farm-management practices to help sequester CO2 naturally.
Still, by 2050, renewable sources, including bioenergy, plus nuclear energy and carbon capture and storage, collectively would need to grow from 30 percent today in a world with 7.2 billion people to 80 percent in a world with 9.6 billion to help provide the emissions reductions needed to stay on the 2-degree path.
Nuclear energy faces stiff political resistance in many countries, as well as stiff economic competition from natural gas. Carbon capture and storage, which would extract carbon dioxide from power-plant emissions and pump the CO2 into rock formations deep underground, faces its own set of issues.
The IPCC acknowledges that as currently understood, there are biological and geological limits to wholesale use of carbon capture and storage around the world. And it's difficult to estimate how much impact it could have on emissions over the course of a century.
Still carbon capture and storage is seen as a key piece of the puzzle whose role in principle can be kept relatively small during the second half of the century only if countries make the emission reductions needed during the next few decades.
Although the task appears daunting, hiking the 2-degree trail can be accomplished at a relatively low cost, the study argues, especially compared with the cost of doing nothing and having to cope with the effects of a substantially warmer world.
Annual mitigation costs 0.06 percent of global gross domestic product.
“This translates into delayed, but not foregone, growth,” said IPCC Chairman Rajendra Pachauri, during a press conference Sunday unveiling the report.
One of the key challenges to projecting the future of emissions and global warming is the inability to predict what people actually do, collectively or individually. The summary points out, for instance, that changes in an individual's consumption patterns, especially concerning energy use, changes in diet, and reducing food waste can help.
For the first time, the IPCC addresses the role changes in society have the potential to play in combating climate change, notes Dr. Oppenheimer, adding that sometimes, such shifts can be relatively quick.
One hint comes from emerging studies of “millennials” – the generation born between the 1980s and the early 2000s. These studies indicate that many millennials are moving to cities and forgoing car ownership, if not driving altogether, he says. This reduces emissions from transportation.
These offer additional glimmers of hope in dealing with global warming, he says.