A large group of NGOs organized a Climate Change demonstration Saturday that mobilized as many as 100,000 participants to march from Copenhagen Cathedral in downtown Copenhagen to the Bella Center – the venue for COP15, the 15th United Nations Climate Change Conference.

The demonstration, organized under the theme "Planet first - People first," focused on the environmental and humanitarian aspects of climate change, and witnessed tens of thousands demanding a fair, ambitious and binding climate deal at COP15.

The head of the Anglican Communion, Archbishop of Canterbury Rowan Williams, spoke at the opening of the demonstration and called the march “the most important event that we’re likely to see in our life time.”

“Why is it important? It’s important because you are going to try to help our leaders lead in the world,” the archbishop stated.

“We have to make it the case that the people of our world are demanding justice in such a way that it’s impossible for our political leaders to deny it. That’s why we’re all here in Copenhagen. That’s what you’re marching for,” he continued.

According to the U.N. Framework Convention on Climate Change, 2009 is a crucial year in the international effort to address climate change.

Since Dec. 7 and until Dec. 18, national government delegations who agreed to shape an ambitious international response to climate change in 2007 have been meeting in Copenhagen to agree on a post-2012 climate agreement that will replace the current Kyoto Protocol.

Under Kyoto, 37 industrial countries are required to cut emissions a total 5 percent from 1990 by 2012, and based on the current declarations from wealthy countries, the World Wildlife Fund for Nature estimates the total emissions cut will amount to 10 percent by 2020.

Some scientists, however, say industrialized nations must cut emissions by 25 to 40 percent from 1990 levels by 2020 to prevent climate disasters, such as coastal flooding from rising sea levels, severe weather events, and variations in rainfall and temperatures that will affect agriculture and wipe out species of plants and animals.

Despite such claims, there is still notable disagreement over the exact causes of global climate change and its degree of devastation.

While climate change activists insist that humans are to blame for climate change, critics say global warming could be caused naturally by changes such as alternations in the Earth’s orbit and solar energy and solar wind output.

Some even argue that science, contrary to what many leading scientists claim, does not support the claim that increased CO2 in the atmosphere is having a negative effect on the earth.

They say no one currently really understands clearly how the earth is responding to the increase in the greenhouse gas and that cap and trade legislation – pollution control policy that sets a limit or cap on the amount of pollutants that can be emitted – could even do serious harm to the world’s poor without guaranteeing that global warming would decrease.

Despite the uncertainty, a number of prominent religious leaders and faith-based groups are attending the United Nations summit on climate change with the aim to persuade global leaders to support cuts in carbon emissions.

“[L]et’s give them (our leaders) opportunity in the days ahead to do what they need to do – not just for us, not even for just our children or grandchildren, but for a world given into our hands to treasure, to care, and to share,” Archbishop Williams told participants of Saturday's march.

Apart from the organizations’ activists, Saturday's demonstration was also joined by many of the city’s people, including a group of youth activists who the police said they rounded up from the tail end of the demonstration in a preventive action.

The climate summit in Copenhagen has drawn participants from 192 countries representing governments, the business community, and civil society. Organizers have anticipated approximately 15,000 participants.