Capping global warming at 2 degrees Celsius would require 40%-70% cut in heat-trapping gasses by 2050 from 2010 levels, which would require tripling renewables share, nuclear power, carbon-capture and storage, finds draft of unreleased UN report

PARKTOWN, South Africa , January 19, 2014 () – Most scenarios that meet the 2ºC cap on global warming that world leaders endorse require a 40 percent to 70 percent reduction in heat-trapping gases by 2050 from 2010 levels, according to the third instalment of the UN's biggest-ever study of climate change. The world would need to triple the share of renewables, nuclear power and carbon-capture and storage to meet that.

"This report shows that 2ºC is still technically possible and ought to remain the primary policy target" for climate negotiations that intend to produce a global agreement next year, Bob Ward, the policy director at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics (LSE), said.

A draft of the study was obtained by Bloomberg from a person with access to the documents who asked not to be identified because it hadn't been published. A spokesman for the panel declined to comment on the document.

The research is important because it's intended to influence the direction of UN negotiations involving more than 190 countries on how to combat global warming.

The discussions have been beset by wrangles between developing and industrialised nations over who should bear the cost of tackling climate change.

Countries are trying to divide up by next year the burden of emissions limits needed to stave off the worst effects of climate change, including rising sea levels and more frequent droughts.

"Without explicit efforts to reduce greenhouse gas emissions, the fundamental drivers of emissions growth are expected to persist," according to the study by the UN's Intergovernmental Panel on Climate Change (IPCC). Reaching the needed levels "will require large-scale changes of the global energy system as well as cuts in greenhouse gas emissions over the coming decades."

Delaying action to curtail greenhouse gases through 2030 would reduce options to stabilise the gases, require much more rapid scale-up of low-carbon technologies and rely more on techniques that take carbon dioxide out of the atmosphere, such as combining burning biomass with carbon capture and storage, the researchers wrote.

The findings are the third instalment of three reports summarising the IPCC's work. The first study was published on September 27. The second and third parts, to be published in March and April, are still subject to line-by-line revision by governments. A final document synthesising the three is scheduled for completion in October.

"It's a work in progress, and we look forward to discussing it when it's been finalised in April," Jonathan Lynn, a spokesman for the panel, said on Thursday.

The researchers examined the policies and technologies necessary to cut emissions, including a global carbon price and more extensive use of renewable energy. Their cost estimates don't consider the benefits of slower climate change, such as improved health, and the reduction in impacts of warming.

The researchers found that all scenarios that stabilise the concentration of greenhouse gases in the atmosphere at or below 480 parts per million (ppm) of carbon dioxide are "likely" to contain the temperature gain to below 2ºC. Some scenarios that peak above 530ppm before coming down to a range of 480 to 530ppm would also achieve that.

Containing the concentration to 480ppm "would entail global consumption losses" of 1 percent to 4 percent in 2030. That range would rise to 2 percent to 6 percent in 2050 and then to as much as 12 percent in 2100 when compared with scenarios that don't involve fighting climate change, according to the document. The current concentration is about 400ppm.

"The majority of scenarios reaching these atmospheric concentration levels are characterised by a tripling to almost a quadrupling of the share of zero- and low-carbon energy supply," the researchers wrote.

At the upper end of those ranges, the cost of fighting climate change could outstrip the cost of dealing with the effects of climate change, according to data in the draft of the second instalment of the UN report, which hasn't yet been finalised.

That document said that a temperature increase of 2.5ºC since industrialisation may lead to losses of as much as 2 percent of global economic output. At the same time, it warned that "aggregate impacts hide large differences between and within countries".

"Beyond 2ºC you risk potentially catastrophic impacts such as a destabilisation of the polar land-based ice sheets that would have very severe economic consequences which are not present in the economic models," Ward at LSE said. "Gross domestic product (GDP) does not tell the whole story.

"You could tell the story of World War II just through GDP, but it wouldn't tell you about the millions of people who died," he said. "The losses of livelihoods a result of climate change impacts are not captured by the GDP story."

Small island states have argued that even an increase of 2ºC may threaten the existence of some of their countries because of the encroachment of rising seas on land and water reservoirs.

A widely-cited report in 2006 for the UK government led by former World Bank chief economist Nicholas Stern calculated lower costs for mitigation and higher costs for inaction. It said the impacts of global warming could cost the world as much as 20 percent of economic output, compared with the 1 percent cost of containing the problem.

Other findings detailed in the UN study include:

l Greenhouse gas emissions grew by an average 2.2 percent per year between 2000 and 2010. Global emissions since 1970 outstrip those for the preceding 220 years.

l Just 10 nations accounted for 70 percent of emissions in 2010.

l Industrial emissions from developing nations now exceed those from industrialised ones, though high income nations are net importers of carbon dioxide emissions embedded in goods from abroad.

l Pledges for emissions cuts by 2020 that were made by the biggest emitters in 2010 don't correspond to the ''lowest cost" emissions reduction trajectory and would lead to greenhouse gas concentrations of as much as 650ppm by 2100.

l The lowest-cost global efforts to fight climate change involve making the majority of investments in developing nations.

The first instalment of the IPCC's report, dealing with the observed effects of global warming, was published on September 27. A draft of the second summary, detailing the costs of climate change, was leaked online in November. A final version isn't due until March. The final version of Thursday's summary is due for publication in April. - Bloomberg

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