UN Secretary-General Ban Ki-Moon said global warming was becoming the defining issue of the era and will hurt rich and poor alike.
"Our world is in the grip of a dangerous carbon habit," Ban said in a statement to mark World Environment Day, which is being marked by events around the globe and hosted by the New Zealand city of Wellington.
"Addiction is a terrible thing. It consumes and controls us, makes us deny important truths and blinds us to the consequences of our actions," he said in the speech to reinforce this year's World Environment Day theme of "CO2 Kick the Habit".
"Whether you are an individual, an organization, a business or a government, there are many steps you can take to reduce your carbon footprint. It is a message we all must take to heart," he said.
World Environment Day, conceived in 1972, is the United Nations' principal day to mark global green issues and aims to give a human face to environmental problems and solutions.
New Zealand, which boasts snow-capped mountains, pristine fjords and isolated beaches used as the backdrop for the "Lord of the Rings" film trilogy, has pledged to become carbon-neutral.
"We take pride in our clean, green identity as a nation and we are determined to take action to protect it. We appreciate that protecting the climate means behaviour change by each and every one of us," said New Zealand Prime Minister Helen Clark.
New Zealand, like many countries, staged art and street festivals to spread the message on how people can reduce carbon usage.
In Australia, Adelaide Zoo staged a wild breakfast for corporate leaders to focus on how carbon emissions threaten animal habitats.
In Bangladesh's capital Dhaka, people plan to clean up Gulshan Baridhara Lake that has become badly polluted, and in Kathmandu the Bagmati River Festival will focus on cleaning up the river there.
Many Asian cities, such as Bangalore and Mumbai, plan tree-planting campaigns, while the Indian town of Pune will open a "Temple of Environment" to help spread green awareness.
Global carbon emissions from burning fossil fuels are rising quickly and scientists say the world faces rising seas, melting glaciers and more intense storms, droughts and floods as the planet warms.
A summit of G8 nations in Hokkaido, Japan, next month, is due to formalise a goal agreed a year ago that global carbon emissions should be reduced by 50 percent below 1990 levels by 2050.
But some nations think the cuts should be deeper, leading to a reduction of 80 percent of carbon emissions by 2050 to try to stablise CO2 concentrations in the air to limit global warming.
Australian Prime Minister Kevin Rudd said climate change was already a reality.
"We have been experiencing the worst drought in living memory and our inland rivers are running dry," he said in a statement.
"We are committed to reducing greenhouse gas emissions by 60 per cent on 2000 levels by 2050. We will implement emissions trading as the primary mechanism for achieving this target," he said.
North Korean state media said the government was doing its bit for the environment, including updating existing thermal power plants, increasing hydro-power generating capacity, creating more forests and using more organic fertilisers.
The country's carbon output is already fairly small because it cannot afford large quantities of oil and relies heavily on hydro plants for power.
The UN Environment Programme said the cost of greening of the world's economy would cost as little as a few tenths of global GDP annually over 30 years and would be a driving force for innovation, new businesses and employment.