PwC report: current government ambitions won’t stop temperature rise
Greenhouse gas emissions aren’t falling fast enough to seriously address climate change, according to a new report by consultancy PricewaterhouseCoopers (PwC). Its analysis suggests that global greenhouse gas emissions associated with economic activity need to fall by more than 5 per cent each year to 2050 to reach the two degree target. Compared to recent reductions of just 0.8 per cent, this level of decarbonisation looks “highly unrealistic”.
The report led to a number of headlines claiming world temperatures may rise six degrees without greater efforts to mitigate climate change. We take a look at its modelling, and find that although it might be a bit simplified, its main conclusion stands – current efforts to mitigate climate change simply aren’t enough.
Current state of affairs
The report, called the Low Carbon Economy Index, analyses the amount of carbon emitted per unit of Gross Domestic Product (GDP) – a measure called carbon intensity. It concludes that to stand a 50 per cent chance of limiting temperature rise to two degrees celsius, carbon intensity needs to fall by more than 5 per cent per year. If that weren’t hard enough, the world’s major economies would need to repeat this feat every year until 2050.
Over the last decade or so, carbon intensity has been falling by about 0.8 per cent per year. According to the analysis by PwC, if the rates of decarbonisation don’t improve the world will be a long way off meeting its two degree target. Two degrees is a limit adopted by the European Union, based on IPCC findings, beyond which it becomes unlikely that serious negative effects can be avoided.
With no change by 2020, PwC estimates the emissions gap (between what is needed and what is being realised) could be about 12 gigatonnes of carbon dioxide. By 2030, the gap is expected to widen to around 30 gigatonnes. By 2050, it would be just less than 70 gigatonnes.
Modelling the future
It’s hard to appreciate what this all means when talking about gigatonnes and gross domestic product. But translated into temperature rise, the importance of decarbonisation becomes clearer.
Based on figures from the Intergovernmental Panel on Climate Change, PwC worked out the rate of decarbonisation needed to limit concentrations of greenhouses gases and, in turn, temperature rises.
Image - PWC (note)
Source: PricewaterhouseCoopers
The analysis suggests that reducing carbon intensity by 5.1 per cent per year would lead to a two degrees temperature rise, a reduction of three per cent per year would lead to a four degree rise, and a 1.6 per cent reduction per year would lead to a six degree rise. With just a 0.8 per cent reduction over the last decade, PwC’s figures suggest governments really need to up their game.
Caveats
It seems pretty straightforward, but the analysis has been simplified somewhat, and a lot of the complexity that climate models have to grapple with isn’t really considered here.
PwC worked out how the decarbonisation would give rise to certain greenhouse gas concentrations, but the rest comes from here.
Image - Screen Shot 2012-11-05 At 15.54.19 (note)
This table, which comes from the IPCC’s Fourth Assessment Report, gives a best guess at the temperature rise that will result from given levels of emissions. We’ve highlighted in grey the figures PwC use to make life a bit easier.
It shows that greenhouse gases will probably lead to temperature rise somewhere within a set range. A best guess is useful, but it’s not explicit. A best guess has a good chance of being realised, but isn’t certain. It also shows that the range of temperature rise gets bigger with higher concentrations of greenhouse gases, so there’s less certainty there.
These figures from the IPCC are themselves not a perfect prediction, and come from a series of basic assumptions rather than a climate model. On top of this, PwC acknowledges they don’t take into account climate feedback systems or the way carbon sinks like the ocean may change.
Taking all this into account, the PwC analysis might be oversimplified and its figures on decarbonisation may not limit temperature rise exactly as suggested. But the main point it makes probably still holds true – current efforts to decarbonise aren’t doing enough to mitigate climate change. Limiting temperature rise to two degrees is looking more unlikely by the day.