China's urban planning experts Monday called for a substantial implementation of low carbon concept in city development strategy to avoid environmental crisis amid rapid urbanization.

It will be hard for the country to achieve its goal of sustainable development if measures were not taken to improve energy efficiency and to cut carbon emission, the experts warned, citing the fact that a 75 percent of urbanization by 2050 means much more energy consumption and carbon dioxide emission.

They sounded the alarm in a report, China's Low Carbon Eco-city Development Strategy, which was launched here Monday based on a research by the Chinese Society for Urban Studies (CSUS).

The report predicted that even in the best "low-carbon development" scenario, the rise of the emission of carbon dioxide, a major greenhouse gas (GHG), would likely be halted only by 2035.Cities will be the dominant energy consumer and GHG emitter.

By 2050, between 70 percent and 75 percent of the Chinese will live in cities, while the urban economy contributes 90 percent of the national economy, according to the report.

Li Xun, CSUS's senior urban planner, said the fast urbanization put great strain on China's sustainable development.

"Even though China adopts the strict emission standard, the situation is still not optimistic," Li said.

The "low-carbon development" scenario requires China, now the world's third largest economy, to raise the use of renewable energy from about 9 percent of total energy use at present to 30 percent in the next 20 years. The efficiency of energy use in power plants must be improved by 20 percent in the same period and "strict" energy-saving policies must be adopted.

The report cited undated United Nations figures as saying that urban residents currently accounted for only half of the world's population, but cities emit 75 percent of the world's total CO2.

Yang Fuqiang, director of Global Climate Solutions, a program sponsored by World Wide Fund for Nature (WWF), said the low carbone co-city development strategy is a must-do option for China, a country facing multiple challenges of city sprawling, energy strain and fast economic growth.

"Lacks of clear goal and evaluation criteria also hinder the building of low carbon eco-cities," Yang said.

The report listed the vision of policy makers, technology support and fiscal stimulation as major solutions. It will be eventually provided to lawmakers and government officials in some 600 Chinese cities.

According to the report, city planners should set clear vision on urban functions in light with the city's capacity for environmental sustainability. Integrated public transport systems, green building technology and clean production technology are among options to promote low-carbon cities.

Besides calling for developing and applying energy-efficiency technology, it also suggests greater fiscal stimulation to local governments in the development of clean energy programs.

"The goal is a tough task to achieve, but it gives constructive suggestions," Li said.

"China's urbanization will have a defining impact on this century's human development," Li said. "It is inevitable to embrace low-carbon concept if we want the urbanization more sustainable."