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Roz Pidcock

03.12.2012 | 5:15pm
ScienceCan we still limit warming to two degrees?
SCIENCE | December 3. 2012. 17:15
Can we still limit warming to two degrees?

Without a new “radical plan”, the world is unlikely to meet the target of two degrees of warming, according to a new study. As energy secretary Ed Davey joins negotiators at the UN climate talks in Doha, he seems optimistic that mustering enough political could still put the world back on track. But the new research suggests that two degree target is moving further out of reach.

Two degrees of warming

The official target of the United Nations Framework Convention on Climate Change (UNFCCC) is that to avoid serious climate change, global mean temperature rise should not exceed two degrees Celsius above pre-industrial levels.

But a new study in Nature Climate Change yesterday says that without a radical overhaul of emission reduction policies, it’s very unlikely we’ll hit that two degree target.

The researchers plotted carbon dioxide emissions since 1980 against the emissions scenarios the Intergovernmental Panel on Climate Change (IPCC) uses to estimate how fast greenhouse gas emissions could rise in the future.

The analysis included the most recent set of scenarios – called Representative Concentration Pathways (RCPs) – which are the basis for the next round of projections in 2013.

Falling off course

The research shows carbon dioxide emissions increased from 6.1 billion tonnes in 1990 to 9.5 billion tonnes in 2011 – an increase of 25 per cent. The rate of increase is growing too – from 1.9 per cent per year in the 1980s to 3.1 per cent per year since 2000. The researchers estimate emissions in 2012 will be 2.6 per cent above 2011 levels, 58 per cent higher than in 1990.

All of this means that current emissions are tracking the most pessimistic IPCC scenarios. The highest RCP – known as RCP8.5 – suggests four degrees warming by 2100. We wrote more about what a four degree world could look like here.

Limiting warming to two degrees needs “immediate significant and sustained global mitigation”, the researchers say. This echoes the conclusions of three recent reports from the United Nations Environment Programme, the World Bank and the World Meteorological Organisation.

Le Quere _RCPs

Current emissions are tracking the IPCC scenarios that lead to the most warming. RCP8.5 (red) is the most pessimistic of the new RCP scenarios, which projects four degree warming by 2100. Source: Peters et al. (2012)

Media coverage

The release of this new study coincides with UN climate talks in Doha. There, negotiators are discussing a replacement for the Kyoto Protocol that will legally oblige all nations to curb greenhouse gas emissions.

But media coverage of the new study suggests that hopes aren’t high. The BBC, Metro and The Guardian all report the concerns of co-author of the study Corinne Le Quéré, director of the Tyndall Centre for Climate Change Research. She says:

“[W]ith emissions continuing to grow, it’s as if no-one is listening to the scientific community…I am worried that the risks of dangerous climate change are too high on our current emissions trajectory. We need a radical plan.”

Ahead of his arrival in Doha today, the UK energy and climate change secretary Ed Davey sounded hopeful. He told the Independent:

“Two degrees is still within reach if we can muster the political will.”

So where do we go from here?

Staying below two degrees is unlikely but not impossible, says the new study. The most ambitious of the new IPCC scenarios (RCP3-PD) suggests it’s possible to limit warming to 1.5 degrees Celsius.

This scenario will depend on technologies that permanently remove carbon dioxide from the atmosphere – resulting in negative emissions. Such technologies could include carbon capture and storage (CCS) from fossil fuels and biomass.

But relying on negative emissions is risky because it depends on the large-scale roll out of emerging CCS technologies, say the researchers. One of the less ambitious scenarios – called RCP4.5 – suggests that the two degrees could be hit without negative emissions, relying instead on changes in fuel use and energy efficiency.

As the study highlights, some developed countries have successfully reduced their carbon output this way. The UK, Denmark and the US have had several periods since the 1970s in which they reduced emissions by one to two percent per year by substituting gas for coal or oil. Belgium, France and Sweden reduced emissions by 4-5 per cent over a ten year period by moving from oil to nuclear.

Big emitters, big responsibility

But a two degree temperature rise is still at the optimistic end of RCP4.5 and would require early action by the biggest emitters to work, says the new study. Together the US, China, the European Union and India are responsible for nearly half of all global emissions. As Le Quéré told the Telegraph:

“China is dominating the global rise in emission that’s for sure. The rich countries on the other side are decreasing a little bit – one to three per cent per year – but not enough to offset the growth in the developing world”

The Global Energy Assessment ( GEA), released last week by the International Institute for Applied Systems Analysis in Austria, echoes the need for technological innovations in energy efficiency and carbon capture, as well shifts in energy sources. The GEA also highlights the success of bottom-up initiatives like Sustainable Energy For All, which are helping developing countries move away from burning biomass toward less polluting energy sources.

Kickstarting mitigation

The message from the new study is the biggest emitters should lead by example and kickstart global mitigation, encouraging other nations to follow suit. As the researchers say in the study:

“If similar energy transitions are repeated over many decades in a broader range of developed and emerging economies, the current emissions trend could be pulled down”.

So current negotiations don’t look on track to deliver the emissions targets necessary to limit warming to the two degree target, unless radical changes are set in motion – a sentiment Ed Davey echoed as he set off for Doha. But are they right to emphasise the top-down negotiations? As the GEA highlights, mobilising bottom-up commitments to developing new energy pathways could play a significant role in limiting global emissions.



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