World threat as efforts to cut carbon emissions fail
The latest report from the world's leading climate science body, the Intergovernmental Panel on Climate Change or IPCC, warns that world emissions of greenhouse gases will have to peak soon and fall by up to 70% by 2050 - and then drop close to zero by 2100 - to keep global temperatures below two degrees Celsius.
This is the temperature governments have agreed to maintain but, on present trends, it looks to be a hopeless task given that such cuts are far deeper than most governments are planning or seemingly prepared to take.
The IPCC's Working Group III report is the third and final volume in the current IPCC Fifth Assessment Report.
Emission reduction suggestions
Released in Berlin last week, it warns that energy efficiency improvements have not kept up with economic growth and delaying action until 2030 could force reliance on undeveloped technologies to extract greenhouse gases from the air.
Drawing on almost 10,000 research papers to describe the changes to past, present and future greenhouse emissions, the report suggests possible ways of reducing emissions.
"We have a window of opportunity for the next decade, and maximum the next two decades, to act at moderate costs," said Professor Ottmar Edenhofer, co-chair of the IPCC's Berlin meeting.
"I'm not saying it's costless. I'm not saying climate policy is a free lunch, but it's a lunch worthwhile to buy."
Edenhofer, an economist at the Potsdam Institute for Climate Impact Research, said the world would need "a broad portfolio of options" if it was going to make deep enough emissions cuts to meet the internationally agreed target of limiting long-term warming to two degrees Celsius.
Those options include market-based solutions such as carbon pricing, moves towards renewable energies and other alternatives such as nuclear power, and other technological fixes that have yet to be widely deployed, including carbon capture and storage.
Limiting warming and economic growth
But the IPCC's calculations indicate that limiting global warming to two degrees Celsius is likely to stunt world economic growth by between 1% and 5%, relative to its current rate.
Swapping fossil fuels for plant material, and then burying the resulting carbon dioxide to avoid it entering the atmosphere could help put world greenhouse emissions into reverse, Edenhofer said.
Two lead authors of chapters in the report, Associate Professor Frank Jotzo and Professor David Stern, say that per capita emissions remain very unequal globally: people in high-income countries are responsible for nine times more greenhouse emissions on average than those in the poorest countries.
"Therefore, under a 'business as usual' scenario - in which no new policies or technological breakthroughs emerge to help reduce emissions - we can expect a lot of catch-up growth in emissions as developing economies grow," they say.
"This means we need to switch to low-carbon energy sources as soon as possible, because the majority of emissions are derived from energy use."
But the authors say that simply improving energy efficiency is unlikely to be enough because the data show this tactic has historically been insufficient to offset growth in income per capita, let alone population growth.
Stabilising atmospheric greenhouse gas levels by significantly reducing emissions, however, will have "relatively modest financial costs".
Global gross domestic product would be 2% to 6% lower in 2050 than it would otherwise have been. Meanwhile, under business as usual, global income per capita is expected to double by 2050.
Taking strong action on climate change would, therefore, only delay that doubling by one to three years.
In a commentary published in The Conversation, Jotzo and Stern say that while many of the report's modelling scenarios find the cost of emissions cuts is low, they do so by "overshooting" the atmospheric concentration of greenhouse gases.
"The concentration of greenhouse gases in the atmosphere first exceeds the level that would limit the temperature to two degrees Celsius but then emissions must become negative in the second half of the century.
"That means taking large amounts of carbon dioxide out of the atmosphere, perhaps by using biomass energy along with carbon capture and storage (referred to as BECCS) to replace the use of coal, oil and gas."
The researchers warn there is considerable uncertainty about whether this could be made to work in practice, both technically and economically. If such options were not available, the cost of emissions reductions would be near the higher end of the 2% to 6% range.
They note that for the first time, an IPCC report explicitly looks at the ethics of climate change, and its connection to the values that individuals and societies hold:
"In deciding whether and by how much to cut greenhouse gas emissions, today's governments are in part shaping the well-being of future generations. Does the welfare of people in the future count for less, purely because they live in the future? Should it count for less because people in the future are expected to be richer than we are?"
The report's modelling shows that developing nations need to act soon and decisively, if climate change is going to be held in check. But who should pay for the costs, and how should we compare the costs and benefits of climate change action across rich and poor societies? Jotzo and Stern ask.