Cities are responsible for four fifths of all greenhouse emissions. That means that effective steps to cut emissions in urban areas can have profound effects on the environment. A new study based on the city of Munich shows how a major metropolitan area could make itself virtually carbon-free within a few decades. Most of the technology that’s needed is already available — and putting it to work would save money.
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Cities are attractive places to live. They promise work, a vibrant cultural life, and a host of leisure activities. All of which is very true of Munich, Bavaria's capital. From here, it's only a short hop to go climbing or skiing in the Alps, to reach crystal-clear lakes, or to drive to Italy and the Mediterranean. Little wonder then that Munich is one of the few cities in Germany that is set to grow in the coming decades. Although an exception in Germany, the city is, however, very much in line with the trend toward ever-larger metropolitan areas.
In the world's newly industrializing and developing countries people flock to cities in search of work and education and in hope of a better life. And last year a watershed was reached. In 2008, for the first time ever, half of the world's population lived in cities. By 2050 this figure is forecast to grow to 70 %. This will result in huge urban sprawls that consume resources and pollute environments.
Although metropolitan areas cover only 1 % of the earth's surface, they are responsible for 75 % of the world's energy consumption and 80 % of greenhouse gases, not least carbon dioxide (CO2). As such, they are storing up trouble for themselves, since experts expect cities to be seriously affected by climate change. Shanghai, for example, is likely to suffer from storms and heavy rains, and Germany's Federal Environment Agency predicts that by the end of the century Munich will see a significant increase in the number of hot days and "tropical" nights each year.
Is there any good news about cities? Well, yes. The very fact that they are not only the biggest culprits in climate change, but that they are so concentrated offers a good opportunity to tackle the problems they cause, since the key levers for climate protection have their biggest impact here. The major metropolitan areas of the world are thus in a unique position to lead the way to more environmentally- friendly modes of living and doing business.
How can a modern city, despite population growth, reduce carbon emissions without having to compromise on living standards or risking a slowdown in economic growth? This is the question that has occupied researchers from Germany's Wuppertal Institute for Climate, Environment and Energy with the support of Siemens. Their study "Munich — Paths toward a Carbon-free Future" presents a detailed look at what the city can do to minimize its environmental footprint between now and 2058. The study concludes that it is possible to transform a city like Munich into a practically carbon-free area. This, it says, will require close cooperation between municipal authorities, energy companies, and the population, along with a clear commitment to efficient technologies, ranging from energy-saving refrigerators to power plants, as well as a general willingness to invest in greater use of renewable energy sources such as wind, solar power, biomass, and geothermal energy.
Cutting CO2 by 80 to 90 %. The study sketches two alternative scenarios for Munich. The so-called "target scenario" adopts the very optimistic view that the vision of a carbon-free future can be more or less achieved over the 50-year span under consideration in the study.
Another scenario — the so-called bridge scenario — is somewhat more conservative and assumes, for example, that increased efficiency in power generation will be offset by rises in demand and that individual transportation will remain similar to its present-day form. Nevertheless, the results are impressive in both cases. The optimistic target scenario predicts that through the implementation of comprehensive efficiency measures the average CO2 emissions per inhabitant can be curbed by around 90 % to 750 kg per annum by the middle of the century.
The more conservative bridge scenario, on the other hand, results in a average CO2 reduction of almost 80 % to approximately 1.3 t. In comparison, on the basis of the IPCC World Climate Report of 2007, the European Union's environmental ministers came up with a target of reducing greenhouse gas emissions worldwide by over 50 % and thereby to an average figure of less than two metric tons per capita. Both of the Munich scenarios undercut this target substantially.
The Munich study analyzes in detail which measures will achieve the greatest reduction in CO2 emissions and whether they are economical. Almost half of Munich's CO2 emissions are the result of energy used to heat the city's homes and buildings. Improving the insulation of roofs, facades, and basements would thus yield significant savings. It is therefore crucial not to scrimp in this area. In fact, the study assumes that the refurbishment of existing housing in Munich will conform to the Passive House standard and that all future housing will also conform to this standard. This includes the use of not only the best insulation and vacuum-insulated windows but also ventilation systems that recover residual heat from the houses' exhaust air before it is blown outside.