Mr Ban said that all countries are threatened by climate change
UN chief Ban Ki-moon has warned a climate change conference in India that failure to tackle the issue will lead to global economic upheaval.
He appealed to nations to reach agreement on carbon emission cuts.
Mr Ban is attending the Delhi Sustainable Development Summit which, organisers say will press for cuts in carbon emissions.
He is also expected to discuss with India the attacks in Mumbai (Bombay) last year which killed 170 people.
"Deserts are spreading. Water scarcity is increasing. Tropical forests are shrinking. Our once prolific fisheries are in danger of collapse," said Mr Ban at the start of the conference in Delhi.
Mr Ban is attending a climate change conference in Delhi
"Failure to combat climate change will increase poverty and hardship. It will destabilise economies, breed insecurity in many countries and undermine our goals for sustainable development."
He said that all countries must work towards a "conclusive carbon emissions reduction" deal at an international climate change conference in Copenhagen in December which will debate initiatives when the Kyoto Protocol expires in 2012.
"Copenhagen must clarify commitments of developed countries to reduce their emissions," said Mr Ban.
"We must also achieve clarity on what mitigation actions developing countries will be prepared to make. In Copenhagen we must now bring all this all together in an ambitious, comprehensive and ratifiable agreement."
India faces the "challenges of poverty eradication, sustaining the rapid economic growth and dealing with the global threat of climate change", Rajendra Pachauri, head of the UN's 2008 Nobel prize-winning climate panel and one of summit organisers, told the AFP news agency.
Mr Ban arrived in India from Afghanistan and Pakistan.
In Pakistan - his first visit to the country since taking office in 2007 - Mr Ban announced that the UN would launch "very shortly" an independent inquiry into the killing of former Pakistani Prime Minister Benazir Bhutto.
Ms Bhutto was killed in an attack on a rally in 2007.
Mr Ban was due to meet the Indian foreign minister and Congress Party chief Sonia Gandhi to discuss the Mumbai attack later on Thursday.
The UN leader began his regional visit on Wednesday in Afghanistan, where he said the country would be a priority for the UN in 2009.
His visit to Pakistan later on Wednesday came amid growing unrest in Pakistan's border areas, with Taleban rebels attacking Nato supply routes into Afghanistan while government forces engage the Taleban in the Swat valley of North West Frontier Province.
Mr Ban called for the "immediate and safe release" of John Solecki, the head of the UN refugee agency (UNHCR) in the city of Quetta, who was snatched at gunpoint on Monday. His driver was killed.