The new report from the Intergovernmental Panel on Climate Change shows that global greenhouse gas emissions have grown faster than ever over the last decade. Taking action to achieve the world’s goal of limiting global warming to 2°C will mean making dramatic cuts in emissions. This raises not just technical and economic challenges, but also profound questions of ethics and values – such as the responsibility we bear towards future generations, and our attitude to the risk of very severe climate change damages.
The Working Group 3 report – released today as the third and final volume in the current IPCC Fifth Assessment Report – assesses the options for mitigating climate change. It draws on almost 10,000 research papers to map out our knowledge about past, present and future greenhouse emissions, and sets out the ways in which we might attempt to reduce them.
Emissions have grown faster than ever
The report shows that since 2000, world greenhouse gas emissions have grown much more rapidly than in previous decades. This is mainly because of rapid growth in middle-income countries like China. However, 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. This means that we need to switch to low-carbon energy sources as soon as possible, because the majority of emissions are derived from energy use. Simply improving energy efficiency is unlikely to be enough, as the data show this tactic has historically been insufficient to offset growth in income per capita, let alone population growth.
On the other hand, the report finds that stabilising atmospheric greenhouse gas levels by significantly reducing emissions will have relatively modest financial costs. Global gross domestic product (GDP) would be 2-6% 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.
Overshoot: the negative emissions scenario
But many of the report’s modelling scenarios that find that the cost of emissions cuts is low, 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 2°C 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.
But there is considerable uncertainty about whether this could be made to work in practice, both technically and economically. If such options are not available, the cost of emissions reductions will be near the higher end of the 2-6% range.
And there is a big risk that future decision makers will not take the ambitious action that would be required when the time comes – even if today’s governments might assume they will.
Values, ethics and risk
For the first time, the report also explicitly looks at the ethics of climate change, and its connection to the values that we hold as individuals and societies.
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?
Knowing the price of everything?
Judgements about value also come into the complex debate about future economic costs and damages from climate change.
All too often, analyses focus purely on the anticipated economic damage, using lower estimates as a rationale for less action on climate change. This is a simplistic view, as it misses three crucial points.
First, as humans we care about things that are not valued in economic markets. Most Australians care far more about the Great Barrier Reef than its (nevertheless impressive) tourism revenues would suggest. Most of us also care about species going extinct, on an emotional level quite separate from the environmental and health benefits of species diversity. Ignoring these concerns means ignoring many of the values that societies hold.
Second, climate effects will vary greatly across different regions and social groups, and this is usually not reflected in simple economic cost estimates. It is often the poor who are most at risk from climate change, and will find it harder to adapt or recover. If a citizen of an Australian beach suburb loses a A$2 million house, should this be counted as 200 times worse than a Vietnamese peasant losing their A$10,000 home?
Finally, and crucially, climate change is about risks. There is a risk – perhaps small, but we do not know how small – of catastrophic impacts. Should we ignore the risk of very bad outcomes for future generations, or should we give extra weight to them?
The IPCC’s report does not provide the answers, because the IPCC is not policy prescriptive. It aims to give decision-makers the latest reliable information, and a compass to navigate their way through decisions that should be based on deeper considerations than short-term economics or electoral tactics.
Frank Jotzo and David Stern are both authors of the IPCC Fifth Assessment Report, Working Group III on Mitigation. David is a lead author of Chapter 5 on emissions trends and Frank is a lead author of Chapter 3 on ethics and economics and of the report’s technical summary. Both work at the Crawford School of Public Policy at the Australian National University.