segunda-feira, abril 07, 2008

Dangerous assumptions

We also use the emissions-scenario building blocks in our analysis, but adopt a frozen-technology baseline to reveal the full challenge of decarbonization. Using this baseline also reveals the huge amount of emissions-reducing technological change built into the 2000 Special Report on Emission Scenarios (SRES) and similar scenarios.

Most SRES scenarios also predict a rapid decline in energy intensity (exceeding 1.0% per year), which may be neither realistic nor achievable. To achieve a century-long 1.0% annual rate of energy intensity decline requires very large increases in energy efficiency. Even with a substantial policy effort this would be very difficult to achieve. Only about 20% (plusminus 10%) of global energy intensity decline can be expected from sectoral shifts in economic activity, such as from manufacturing to services. The rest must come from improved efficiencies in individual energy-using sectors, requiring either technology changes or new technologies.

One reason for the current rise in global energy and carbon intensities is the economic transformation taking place in the developing world, especially in China and India. As development proceeds, rural populations move to high-rise buildings that consume energy and energy-intensive materials. This process is likely to continue, not only in these countries, but all over populous south Asia, and eventually Africa, until well beyond 2050. An analysis of China's carbon-dioxide emissions estimated them to be rising at a rate of between 11% and 13% per year for the period 2000–2010, which is far higher than that assumed by the SRES scenarios for Asian emissions (2.6–4.8% per year).

Because of these dramatic changes in the global economy it is likely that we have only just begun to experience the surge in global energy use associated with ongoing rapid development. Such trends are in stark contrast to the optimism of the near-future IPCC projections and seem unlikely to alter course soon. The world is on a development and energy path that will bring with it a surge in carbon-dioxide emissions — a surge that can only end with a transformation of global energy systems. We believe such technological transformation will take many decades to complete, even if we start taking far more aggressive action on energy technology innovation today. A range of 'built-in' emissions reductions (blue) in the scenarios used by the Intergovernmental Panel on Climate Change (IPCC). Total cumulative emissions to 2100 associated with a frozen-technology baseline are shown for: six individual scenarios, the means of these scenarios (n=6), and for all 35 IPCC scenarios, and the median of the scenario set (AR4). Additional reductions will have to be achieved by climate policy (red), assuming carbon-dioxide stabilization at about 500 parts per million (p.p.m.), leaving allowed emissions for this stabilization target (yellow).

Dangerous assumptions (Nature article)

WIGLEY: Well, in the past, energy efficiency has improved. If you look at the records over the last number of decades, even over the last century, in terms of the emissions of carbon dioxide per unit of energy, we're improving the way we produce energy. But what is a little alarming is that if you look at just the last five to ten years, those changes have gone in the other direction. Now, if you make assumptions that the changes that occurred up to say the year 2000 are going to continue in the future, and you look at what's happened over the last five years or so, that change towards greater efficiency has not continued. Dangerous IPCC Assumptions (Insnet)
Dangerous Assumptions (Living on Earth)