Just a few decades remain to halt global warming and head off its most catastrophic effects, says a new United Nations report that offers a sweeping menu of climate change fixes that would require global cooperation to implement.
The Intergovernmental Panel on Climate Change (IPCC) mitigation report, released Sunday in Berlin, explores some 1,200 scenarios to avert the worsening effects of global warming by 2100. The proposals range from planting more trees to relying much more on nuclear power. (Related: "Global Warming 101.")
"This report is a wake-up call about global economic opportunity we can seize today as we lead on climate change," said U.S. Secretary of State John Kerry in a statement. "This report makes very clear we face an issue of global willpower, not capacity."
Sunday’s report is the third in a series of UN reports on climate change released in the past year that paint a picture of "virtually certain" climate change, driven by increasing emissions—80 percent of them from the burning of fossil fuels—which is already melting the Arctic, acidifying oceans and harming crops. (See also: "New Climate Change Report Warns of Dire Consequences.")
The report urges global action before 2020. The alternative, it says, is paying more later when temperatures rise to dangerous levels, and running more severe risks of climate change, which include rising seas, acidified oceans, longer heat waves, and severe crop failures.
"The longer we wait, the more costly things will be," said Stanford University economist Charles Kolstad, a lead author of the IPCC report. "It is possible to cut back on greenhouse gas emissions, that's clear. But it will be a challenge."
Overall, global greenhouse gas emissions—largely caused by burning coal, oil and natural gas—need to be cut 40 to 70 percent by mid-century, the report says, for humanity to face better than 50-50 odds of dodging the worst effects of global warming. (Related: "Clean Coal Test: Power Plants Prepare to Capture Carbon.")
To hit those emission reduction goals, the report calls for a tripling or quadrupling of "low carbon" power sources such as nuclear, solar, or renewable energy around the world.
Many of the report's proposals involve "overshooting" emissions targets in early decades and turning to technologies that effectively remove carbon dioxide, the most significant greenhouse gas, from the atmosphere in later decades to have any realistic chances of working.
"One of the most important contributions of the report is simply in laying out a road map," said Kelly Levin of the World Resources Institute in Washington, D.C., a longtime IPCC report observer. "There are a ton of solutions."
Global Road Map
Since everyone shares the air and because everyone can pollute it, the report says that emissions policies need to involve the entire international community to be effective. But efforts in global cooperation on climate change, like the 1997 Kyoto Protocol, have produced mixed results at best
"None of that is going to happen on its own," said Harvard University's Robert Stavins, another IPCC report lead author, "so public policy is required at the international level."
A 1992 United Nations agreement broadly obligated the world to keep global warming temperature increases below "dangerous" levels, usually seen as 3.6°F (2°C), the point at which costly climate effects kick in.
The toll would be felt largely by poor farmers who live in dry and monsoon-dependent regions around the world that look to be hardest hit by warmer temperatures, and who have the fewest resources to deal with crop losses.
"The report makes clear a transition to clean energy and different behavior in how we use energy is needed to stay below that 2-degree [Celsius] increase," said Levin.
Without new power technologies spreading worldwide, avoiding the 3.6°F increase in temperatures over pre-industrial levels looks "very challenging," said report author Leon Clarke of the the Pacific Northwest National Laboratory's Joint Global Change Research Institute.
Two technologies in particular look promising. One is growing forests expressly to pull carbon out of the air, an idea known as afforestation.
The other idea is to generate electricity from burning renewable energy sources, such as sawgrass or genetically engineered algal fuels, and stuffing their greenhouse gas emissions underground, a technique known as bioenergy with carbon capture and storage.
Both technologies exist, but scaling them up for worldwide use looks daunting, Clarke said.
Even if the world aims for less ambitious emissions cuts and allows more global warming, Clarke added, people will have to turn to such technologies. Otherwise, temperatures will keep rising.
In any case, the world will have to shoot for zero greenhouse gas emissions by 2100, the report's analysis suggests.
The report also points to energy efficiency and changes in how cities are built and managed as ways to limit emissions. For instance, roofs could be painted to absorb less heat, and more mass transit systems could reduce the need for emissions-spewing vehicles.
Sponsored by the World Meteorological Organization and the UN Environment Programme (UNEP), the report comes amid a long-lasting slowdown in economic growth after 2008's recession that has raised questions about how the world might come together to tackle climate change.
In coming decades, China will overtake the United States, the biggest emitter historically, in total greenhouse gas emissions, said Harvard's Stavins.
That might create an opening for international agreements to go forward on limiting climate change, he suggested, as developing nations see they are bearing more responsibility for global warming.
Otherwise, Stavins sees small agreements on regional levels, among different cities, states, or provinces pursuing steps to cut emissions as the "de facto" world response to climate change. "There really is a lot of skepticism about a big world agreement," he said.
MIT economist John Reilly, who was not an author of the climate report, agreed: "It is too easy to wait and let someone else hurt their economy by going first."
The report is aimed largely at world leaders attending next year's international climate summit in Paris, which is expected to pick up the problems left unresolved at the last such global summit, in 2009 in Denmark, in particular, making climate mitigation plans for after 2030.
Written by more than 400 experts and reviewers from 57 nations over the past four years, the IPCC reports are essentially vast reviews of the latest climate research.
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