That 20% reduction by 2015 breaks down like this (see www.unep.org):
— 15% = reductions in the energy supply by using sustainable sources such as wind, biomass, solar and geothermal ... see low carbon power generation
— 2% = improvements in transport ... better public transport, increased cycle safety, congestion charges, green zones, parking restrictions, etc.
— 2% = energy management in public and private buildings, improved renovation techniques and low-energy building design
— 1% = further motivating and involving citizens

The 1973-4 world oil crisis was one of the catalysts for Danish investment in reducing the country's reliance on fossil fuel imports and reducing overall energy consumption. Another was economic recession. Temporary measures to save energy included banning driving on Sundays, turning off streetlights and lowering the heating temperature in schools and public buildings.

Even though the Danish economy has grown by 78% since 1980, energy consumption has hardly changed (www.kemin.dk). Ongoing measures, such as investment in low carbon power generation and district heating, have reduced its CO2 emissions by about one sixth since 1990. In a 2006 EU opinion poll, more Danes said they would be willing to pay higher prices for energy derived from clean sources than the citizens of any other country.

Recent national strategies include:
— New building codes that specify thicker insulation and better seals for windows (1979 onwards).
— Bringing the 2005 EU directive on greenhouse gas emissions into Danish law.
— The One Tonne Less campaign, encouraging citizens to reduce CO2 emissions by changing everyday habits (March 2007 - December 2009).
— The 2008 Energy Agreement, targeting at least 20% gross energy consumption in 2011 from renewable energy sources, and 30% in 2025.
— The decision that renewable energy generation should be generally carbon neutral and help reduce greenhouse gas emissions overall.
— A scheme that allows utilities not meeting government guidelines to buy energy credits from better-performing ones.

Denmark has developed a strategy for adapting to climate change (www.kemin.dk/klimatilpasningsstrategi_UK_web.pdf), and in 2007 it set up the Ministry of Climate & Energy to address climate and energy issues.

Between 1975 and 2001, Denmark achieved a 20% reduction in its heating bill, even though heated floor space increased by 30% in that time. Figures released in 2007 show that each citizen uses an average 6,600kWh of electricity per year, compared with 13,300kWh per person in the USA (http://online.wsj.com).

Copenhagen hopes to be the world's first Eco-Metropolis and already uses a significant proportion of low carbon power generation and has a city-wide district heating network. An integrated approach to transport has enabled a de-emphasis on car travel and a wide take-up of public systems and cycling. A large area of the central city has been pedestrianised.

According to EnergyMap, Copenhagen emits 2,590,000 tonnes of CO2 a year. Building-related emissions account for more than 30% of this, and over 20% is connected with traffic. One of the city's aims is a 35% reduction in CO2 emissions between 1990 and 2010.

There have been a number of notable renovation and construction schemes. The first new project completed to sustainable building standards is Stenurten day care centre for children under 6 years (June 2002). It received environmental certification (EMAS and ISO 14001) in August 2004. Another is the renovation of the 1880s Hedebygade housing block (1998-2002). Here the installation of a heliostat (mirror) to maximise natural light, plus solar panels, has resulted in a 58% reduction in electricity consumption against the Danish average and around a third less CO2 emissions, again against the national average.

On 19th February 2009, Copenhagen became the 100th participant to join the United Nations Environment Programme's Climate Neutral Network, connecting low carbon economies, societies and companies globally.

In September 2009, the city held a 100% carbon neutral music and arts festival, CO2PENHAGEN, powered entirely by renewable energy. In December of that year, the Danish government hosted the United Nations Climate Change Conference COP15, which was held in Copenhagen.

The continuing momentum of the benefits achieved so far should drive Copenhagen’s low carbon aspirations well into the century. The city has committed to increasing the market share of sustainable and renewable energy sources for its heat and power.

In March 2006, Copenhagen received the European Environmental Management Award. In 2008 it was dubbed Energy City of Denmark as well as being voted the World's Most Liveable City by Monocle magazine. In December 2009, Copenhagen was named as Europe's greenest major city in a study of 30 EU cities released by Siemans to coincide with COP15.

The beginning of the industrialization in Europe in around 1750, particularly in Britain, signalled the start of rapidly increasing CO2 emissions as a result of human endeavour. A dramatic illustration of the recent rise in CO2 emissions and where the concentrations are, can be seen in this time lapse video on YouTube.

Besides Copenhagen, various other cities and municipalities are aiming for carbon neutral status. In 2007, the City of Sydney declared itself the first carbon neutral local government in Australia. Also in Australia, Brisbane (the country's third largest city) has declared its aim to reach carbon neutrality by 2026. A number of cities have joined the Climate Neutral Network and set out their aims.

Several countries have pledged to reach carbon neutrality too. In mid 2010, the list included Cost Rica (aiming for 2021), Iceland, Maldives (by around 2020), New Zealand, Norway (by 2030), Tuvalu and Vatican City. Maldives is aiming to be the first country to reach the goal. Denmark is currently (2010) home to the largest carbon-neutral settlement in the world — the island of Samsø.

There are many individual initiatives around the world and the number is growing all the time. Individual companies, large and small, and individual construction projects, local authorities, towns and villages, and municipalities have plans and pledges in place — including many Danish or Denmark-connected organizations. The methods of achieving their aims range from energy efficiency measures and local renewable-energy power generation to carbon offset schemes and carbon taxes, depending on circumstances and location.