It’s exactly two decades since the first scientific warning in 1989 that global warming should be limited to no more than one or two degrees. Every year since then, the scientific evidence for climate change has become firmer and the message that greenhouse gas emissions have to be reduced substantially to avoid unmanageable changes has become more urgent (for examples, see here and here in the 1990s, and here, here and here in recent years).
The European Union announced as early as 1996 that the ultimate goal of global climate change agreements should be to limit global warming to two degrees Celsius relative to pre-industrial levels. Given that the Earth has already warmed 0.74 degrees over the past 100 years, this leaves very limited room to manoeuvre and is the basic reason why global and comprehensive actions to reduce greenhouse gas emissions are now urgent.
Over the last few years, an increasing number of governments agreed to this long-term target (this includes the G8, ie, the eight most influential industrialised nations, which collectively are responsible for almost 30% of global greenhouse gas emissions). The recent Major Economies Forum has also ‘recognised the scientific view’ that warming ought not to exceed two degrees. The countries represented in this forum make up about 70% of global emissions.
The assessment of climate change science by the Intergovernmental Panel on Climate Change (IPCC) in 2007 found that global greenhouse gas emissions would need to peak before 2020 and be reduced to less than 50% of their 1990 levels by the year 2050 if we want about a 50/50 (or even lesser) chance of limiting warming to two degrees. Beyond 2050, emissions of long-lived greenhouse gases such as carbon dioxide have to fall close to zero by the end of the 21st century. Taking the uneven levels of development of different countries into account, these global emissions reduction targets imply that developed countries as a group would have to reduce their emissions by 25 to 40% by 2020, and by 80 to 95% by 2050 (relative to 1990 levels). Developing countries as a group would need to reduce their emissions by 10 to 30% below business as usual by 2020 — the most advanced developing countries such as China, South Korea and Mexico would need to reduce their emissions significantly more.
These numbers and timeframes are not political negotiating cards — they simply follow from the lifetime of greenhouse gases in the atmosphere, and the time it takes to replace long-lived carbon-intensive infrastructure with new low- or zero-carbon technology. If we are serious about a target of two degrees, this is what needs to be done. If we delay emissions reductions while waiting for a new miracle technology, but meanwhile continue to build coal-fired power plants, these plants will continue to emit carbon dioxide for many decades into the future and thus accumulate a stock of carbon dioxide in the atmosphere that will make it next to impossible to keep warming to two degrees Celsius.
So far the cold facts. Recent assessments of how real actions measure up against the goal of two degrees are sobering and can make you rather hot under the collar. A recent study found that based on all the emissions reduction pledges by both industrialised and developing countries in the lead-up to the climate change negotiations in Copenhagen, the probability that warming will remain below two degrees is extremely small. The best estimate for future warming is closer to four degrees. And that’s using the optimistic interpretations of what the various pledges really mean. This is not just a matter of a couple of degrees more — it’s the difference between changes that are (barely) manageable and a train wreck. Facing up to the reality, a scientific conference in Oxford this week is exploring what a world that is four degrees warmer might look like. It’s not a pretty picture.
Perhaps even more tellingly, another study estimated that the costs of achieving these (insufficient) reduction targets are also predictably miniscule for industrialised countries — they amount on average to less than 0.1% of GDP in the year 2020, with no country facing a cost of more than 0.6% of GDP. Given that the GDP of industrialised countries is expected to grow on average by about 42% between 2009 and 2020, these costs are nothing but trivial. And yet, the costs of mitigation are persistently the most widely used reason for not implementing stronger mitigation actions.
In a forthcoming blog I will look at how the pledges and costs of emissions reductions for different countries compare (including New Zealand), and the possible reasons behind the differences. Regardless of those details though — we are serious about limiting warming to two degrees, aren’t we? Yeah right!