Major Greenhouse Gas Reductions Needed by 2050: IPCC

Emissions of greenhouse gases grew at a faster rate over the decade from 2000 to 2010 than they did over the previous three decades, reaching the highest levels in human history, despite efforts to limit them, according to the last installment of the latest report from the Intergovernmental Panel on Climate Change, released Sunday.

Projections of global mean temperature anomalies over the 21st century relative to 1986–2005 from the combination of the computer models with process-based models, for greenhouse gas concentration scenarios. The assessed likely range is shown as a shaded band. The assessed likely ranges for the mean over the period 2081–2100 for all scenarios are given as coloured vertical bars, with the corresponding median value given as a horizontal line.

Click image to enlarge. Credit: IPCC Working Group I

This final installment, focused on mitigating climate change, says that in order to keep warming under the 2°C (3.6°F) threshold agreed on by the world’s governments at a 2009 meeting in Copenhagen, greenhouse gas emissions in 2050 will have to be 40 to 70 percent lower than what they were in 2010. By the end of the century, they will need to be at zero, or could possibly even require taking carbon dioxide out of the atmosphere, a controversial proposition.

The scientists who wrote the report examined about 1,000 scenarios for limiting greenhouse gas emissions through combinations of renewable energy development, increased energy efficiency, technologies that would capture and store carbon underground, and reforestation efforts. How to do this while limiting the impact to economic growth and poverty reduction is a key question, and the efforts necessary would likely differ from region to region, country to country, and state to state, the report said.

But the authors of the report, speaking to reporters in advance of the release, made one thing clear: “The longer we wait, the costlier it will be,” said Charles Kolstad, an environmental economist at the University of California, Santa Barbara, and a lead author of the report.

Half of all the greenhouse gas emissions from humans were emitted within the past 40 years, growing 2.2 percent per year over the past decade, compared to 0.4 percent per year over the previous three decades. This boost has come from two primary sources: “Emissions are increasing along with economic growth and population,” said another study lead author, Robert Stavins, a Harvard economics and policy expert.

Climate change has already caused the planet’s average temperature to rise by 1.6°F since the beginning of the 20th century. That temperature rise could reach 2.7°F above pre-industrial levels by the end of the century (and possibly as high as about 8.5°F above 1986-2005 levels) if nothing is done to curb emissions, according to the first part of the IPCC’s fifth assessment on climate change, as the entire report is called.

“Things are going to have to change if we do want to control climate change,” said Leon Clarke, an IPCC author and research economist with the Pacific Northwest National Laboratory. “If we do nothing, temperatures will continue to rise.”

Rising temperatures are expected to causes major shifts in ecosystems and precipitation patterns — with some areas becoming more prone to droughts and others to flooding, as well as affecting human health, food security, and potentially taxing infrastructure with stronger storms. The second part of the IPCC report detailed changes like these that are already occurring and warned they would become worse if greenhouse gas emissions aren't brought under control.

Controlling emissions means “de-carbonizing” the global economy, both by reducing the demand for so much energy and by supplying energy that generates far fewer, or no greenhouse gases, the report says. In particular, the use of coal, one of the dirtiest fossil fuels, was a major contributor to the rise in emissions over the past decade with the huge growth of developing countries like China’s and India’s. Trends like this must be reversed, and if steps aren’t taken to remove carbon from the energy equation, greenhouse gas emissions could double or even triple by the middle of the century, the report says.

One way to de-carbonize energy production is through what IPCC author Benoit Lefevre, of the World Resources Institute, describes as “a fundamental shift in global investment from fossil fuel to renewable energy.”

The growth of renewables has been stronger than what was anticipated in the last IPCC report, though emissions increases negated any benefit there, said Bill Hare, a climate scientist who is CEO and managing director of Climate Analytics, a non-profit focused on climate research. The IPCC doesn’t make specific recommendations on how the switch to renewables should be achieved, though it discusses the direct investment in such technologies, as well as systems like a carbon tax that could push people away from more conventional energy sources.

Another way to pull carbon out of the energy system is to employ carbon capture and storage technology, which to date has been a controversial proposal. CCS, as it is called, has not been implemented on a large scale, and there are questions on whether carbon dioxide sequestered underground, for example, actually stays put over the long term.

CCS could become a key component of mitigation strategies depending on what level of carbon dioxide the world decides to try and stay below and which of the various mitigation pathways examined in the report it takes to get there. The longer we wait to begin reductions and the bigger the reduction it takes, the more likely it is that CCS comes into the picture.

“You can’t get to the lower pathways without it,” Hare told Climate Central.

The breakdown of total greenhouse gas emissions (converted to carbon dioxide equivalents) from 2010 by economic sector, with indirect emissions from electricity and heat production factored in. (AFOLU stands for Agriculture, Forestry and Other Land Use.)

Click image to enlarge. Credit: IPCC Working Group III

On the demand side of the equation, changing behaviors and building infrastructure that uses energy more efficienctly could lower the amount of energy needed. “Lifestyle and behavioral changes could reduce energy demand by up to 20 percent in the short term and by up to 50 percent of present levels by mid‐century,” the report says.

Infrastructure like buildings and transportation networks will become particularly important in the coming decades as more and more of the world’s population comes to live in cities. As of 2011, 52 percent of the world’s population lived in urban areas, and that percentage could increase to 70 percent by 2050 and urban land cover could increase by 50 to 300 percent by 2030.

With so much urban infrastructure to be built in these coming decades we have “a window of opportunity,” Lefevre said, to build infrastructure “in a smart way and in a low-carbon way.”

Economics and ethics are major considerations in making all of the decisions on how to mitigate global warming. Economics played a bigger role in this report than in previous iterations, in part because much more research has been done and was available for review. “This is really something new and very, very important,” Lefevre said, because it increases the relevance of the report to policymakers who will be the ones deciding how investment in renewables are made, for example, and who bears the burden of implementing such changes.

Under the auspices of the United Nations, hundreds of scientists contribute to each part of each IPCC report, which have been released every six to seven year and seek to review the latest research on the state of climate science, its impacts, and the possibilities for adapting to and mitigating climate change. The reviews are meant to benefit policymakers in charge of making decisions on dealing with climate change. Those policymakers are working toward a global, binding agreement on climate change at a 2015 meeting in Paris. “Scientists have done their job now,” Lefevre said. “They have outlined the roadmap . . . it’s really about having policymakers pick up those roadmaps and adapt them to their countries and implement them.”

Not everyone is optimistic that these countries will actually reach agreement.

“There won’t be any international agreement,” said Steven Cohen, executive director of the Earth Institute at Columbia University, citing the inherent tensions between the interests of developed and developing countries. Cohen, who was not involved with the IPCC report, is still optimistic that humans can solve the issue of climate change and limit warming, but he thinks that economic incentives are what will get the job done.

Scientists involved with the report are also optimistic that humans can take action and prevent the worst effects of climate change.

“You can still do it. We can still hold warming below 2 degrees,” Hare said, but he added: “Time is running out.”

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