Biogeosciences News

Report Addresses Timeline for Cutting Greenhouse Gas Emissions

Levels of greenhouse gas emissions need to be limited by midcentury to keep within a 2°C increase, a new United Nations report states.


A new report states that “global carbon neutrality” needs to be achieved by 2055–2070 to limit global temperature rise to a 2°C increase relative to the preindustrial period. The report was released a few weeks prior to the United Nations (UN) Climate Change Conference, which will be held on 1–12 December in Lima, Peru.

The Emissions Gap Report 2014, issued by the United Nations Environment Program (UNEP) on 19 November, also states that total global greenhouse emissions need to shrink to net zero between 2080 and 2100 to keep within that 2°C limit.

Under a carbon neutral scenario with net zero emissions of carbon dioxide (CO2), emissions could be compensated by CO2 uptake through reforestation or techniques such as carbon capture and storage, according to the report.

Limiting Global Temperature Rise

To limit global temperature rise to 2°C, the total maximum amount of CO2 that could be emitted to the atmosphere from the 19th century onward needed to be kept to about 2900 gigatons (Gt), notes the report, which builds on the Fifth Assessment Report by the Intergovernmental Panel on Climate Change. However, much of that emissions “budget” already is used up, and to limit temperature rise to 2°C, the maximum amount of emissions since 2012 now must be kept at just 1000 Gt, according to the UNEP report.

The estimated gap for 2020 between emissions levels that are consistent with the 2°C limit and the levels expected if country climate change pledges and commitments are met is 52–54 Gt of CO2, whereas the emissions gap for 2030 is estimated at 14–17 Gt of CO2, the report states.

At a news briefing to release the report, Achim Steiner, UN ­under-​­secretary-​­general and UNEP executive director, said that continued emissions present an enormous risk in terms of global warming, particularly under a ­business-​­as-​­usual scenario. However, he also pointed to positive parts of the report, including its emphasis on the amount of emission reductions that could be gained through energy efficiency measures and a greater reliance on renewable energy.

In addition, he said that the 12 November ­U.S.-​­China announcement to limit greenhouse gas emissions—and other measures, including a recent commitment by the European Union to reduce greenhouse gas emissions by 40%—are indications that “the world is, in fact, moving to accelerating to action” to cut emissions.

Some Evidence of Moving in the Right Direction

At the briefing, Andrew Steer, president and CEO of the World Resources Institute (WRI), said that “on the one hand, we are way off track” in cutting emissions and that with every year that passes, the world is falling further from the least cost solution to climate change. “On the other hand, there is increasing evidence that this can be done much more cheaply than had originally been estimated.” WRI is part of a consortium of organizations involved in producing the UNEP report.

The report’s emission gap figures do not yet incorporate potential emissions reductions that could result from the ­U.S.-​­China announcement because it is too recent, Steiner said. However, former U.S. Senator Tim Wirth, vice chair of the United Nations Foundation, suggested at the briefing that reductions could be significant, including possibly a 2–6 Gt reduction with just the ­U.S.-​­China agreement.

Retaining the 2°C Limit

Some scientists recently suggested that the 2°C limit should be abandoned because it might be unrealistic, but Steiner dismissed the notion. “We don’t have that choice. It is an unethical choice, it is an irresponsible choice, and it is an unnecessary choice.”

“You simply first of all cannot defend a set of decisions being deferred for another 20–30 years that lock in generations for 2000 years,” he said. “Everything that we are discussing here is not a matter of saying you have the luxury to choose not to act. The question is how do we enable one another to act faster.”

Steiner added, “With every year that passes, being able to meet that 2° threshold gets more difficult, more expensive, and riskier because you are relying on more dramatic actions, you are relying on more unproven technologies, and you are relying essentially on moments of catharsis where people suddenly have to jump” to act.

Randy Showstack, Staff Writer


Citation: Showstack, R. (2014), Report addresses timeline for cutting greenhouse gas emissions, Eos Trans. AGU, 95(48), 446–447, doi:10.1002/2014EO480002.

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