The air in most Asian cities is getting more polluted and the rivers filthier, but experts say there are many reasons to believe in a green vision for the region as urbanisation powers ahead. From the putrid, ever-expanding slums in megalopolises such as Manila to the new Chinese industrial boomtowns, examples of environmental anarchy appear to be exploding across the region. Air pollution, already above World Health Organization standards in most cities, is worsening as car ownership surges, while factories required to drive unprecedented economic growth pump increasing amounts of waste into waterways. Meanwhile, the carbon and resource footprints of Asian cities are ballooning as hundreds of millions of people grow richer, consume more and depend largely on fossil-fuel driven economies to drive wealth creation. Nevertheless, urban planners and green activists point to many environmental success stories throughout Asia, as well as a growing awareness about the need to develop sustainably, as justification for hope. \"Many big picture trends in regards to the environment are getting worse but I also see the trends that are offering solutions,\" said Red Constantino, head of the Manila-based Institute for Climate and Sustainable Cities. \"Those (positive) trends are picking up steam. And you have to start somewhere. So I don\'t think doom and gloom scenarios are very helpful right now. It doesn\'t factor in the positive drivers that are out there.\" Constantino cited the stunning expansion of China\'s urban rail network as one of the most obvious examples of Asia beginning to move along a path of sustainable development. Professor Yeung Yue-man, emeritus professor of geography at the Chinese University of Hong Kong who has conducted in-depth research on Asian urbanisation, was even more upbeat. \"It doesn\'t look bad for cities in Asia,\" said Yeung, who is also an adviser to the Hong Kong government. \"In terms of what is needed for infrastructure and looking after their people, in many Asian cities, especially ones that are better off economically, they have embraced the concept of sustainable development.\" Yeung said Singapore, Taipei, Seoul and Hong Kong in particular offered many lessons to other Asian cities on how to develop sustainably as they expanded and their populations grew more wealthy. A report by the Economist Intelligence Unit released in February assessing the green credentials of 22 major cities in Asia similarly highlighted many positive environmental trends and models around the region. China\'s world-leading ambitions for renewable energy were praised, specifically the nation\'s biggest off-shore wind farms near Shanghai that are expected to provide electricity for four million households by 2020. On a more showcase level, it pointed to the 71-storey Pearl River Tower in Guangzhou, southern China, which is due for completion this year and intended to be one of the most environmentally friendly skyscrapers in the world. The Economist Intelligence Unit\'s Asian Green City Index report also highlighted the Tokyo government\'s implementation last year of Asia\'s first cap-and-trade system to curb greenhouse gas emissions. Under the scheme, the Japanese capital is aiming to cut its emissions of carbon dioxide and other gases blamed for global warming by 25 percent by 2020 from 2000 levels, as well as spur similar measures by the national government. Meanwhile, in Singapore, the city-state\'s chronic water shortages are being addressed by region-pioneering recycling technologies. Three litres of water out of every 100 that Singaporeans drink now comes from wastewater that has been filtered and purified. Nevertheless, the scale of environmental damage caused by fast-expanding cities cannot be glossed over, the Asian Development Bank warned in a major report on Asian urbanisation. It said the economic, health and other costs of environmental degradation were more than $2 billion a year in Bangkok and $1 billion annually in Jakarta. \"Costs in Asia\'s other large cities are comparable. They are rising as safety thresholds for a large number of pollutants and poisons are exceeded in increasingly large geographic areas,\" it said. And while recognising many positive trends, the ADB also emphasised that more needed to be done to convince authorities that caring for the environment would benefit their economies. \"City administrators need to believe in sustainable growth and reject the notion that they must choose between protecting the environment and promoting prosperity,\" the report said. \"There is a direct connection between environmental protection and wealth creation.\"