Media playback is unsupported on your device Media caption Clip courtesy The Royal Channel on YouTube

The Prince of Wales has warned of the "catastrophic" consequences of inaction on issues such as climate change, at a UN sustainability conference in Brazil.

Prince Charles said he had "watched in despair" at the slow pace of progress on the "critical issues of the day," in a pre-recorded video address in Rio.

He urged world leaders to adopt a more integrated approach to issues such as climate change and food security.

Waiting for the worst to happen would be "too late to act at all", he said.

Rio+20, the United Nations Conference on Sustainable Development, is attended by heads of state and representatives from governments, non-governmental organisations and the private sector.

In his address, the prince said scientific evidence showed the potential consequences of ignoring the risks.

'Sceptical reluctance'

"Like a sleepwalker, we seem unable to wake up to the fact that so many of the catastrophic consequences of carrying on with 'business-as-usual' are bearing down on us faster than we think, already dragging many millions more people into poverty and dangerously weakening global food, water and energy security for the future," he said.

"One thing is clear. We need to be much more informed about the actual state of the planet.

It is, perhaps, a trait of human nature to act only when the worst happens, but that is not a trait we can afford to rely on here Prince of Wales

"We do not have nearly enough knowledge on which to base the decisions that will be the best for the long term.

"Until we do, we expose ourselves to the mounting danger of major shifts in policy that are not well conceived, but come as panicked responses to crises that could have been avoided."

He said the "outright, sceptical reluctance" by some to engage with these issues had often slowed progress "to a standstill".

Pointing to the work of his International Sustainability Unit, a foundation set up to campaign on global sustainability, the prince said a better picture of environmental problems was needed before effective policy could be implemented.

'Don't have long'

He said data on energy, water, biodiversity, forestry and soil, which is collected separately, needed to be combined and analysed as a whole.

"If this could happen, at least then we would know what the state of the planet actually is - and then plan accordingly," he said.

He went on: "We do not have long to capture such a comprehensive picture, and so I would appeal to you as you meet here in Rio to make an even greater and concerted effort to persuade policy and decision-makers to act before it is finally too late.

"It is, perhaps, a trait of human nature to act only when the worst happens, but that is not a trait we can afford to rely on here.

"Once the worst does happen, I am afraid that this time around it will be too late to act at all."

The conference marks the 20th anniversary of the 1992 United Nations Conference on Environment and Development, in Rio de Janeiro, Brazil's second largest city.