This December – just 100 days from now – the UN climate change talks in Copenhagen will begin. There’s a lot of expectation around this meeting because world leaders have committed to agreeing a historic treaty to tackle the biggest crisis facing humanity.

The meeting is expected to draft and ratify a new treaty to replace the Kyoto Protocol, which will expire in 2012. Simply put, the outcome of these talks will determine the future of our planet.

We are already experiencing climate change. Floods, droughts, hurricanes, sea-level rise, and seasonal unpredictability – hallmarks of climate change – are affecting people’s rights to life, security, food, water, health, shelter and culture in all corners of the world today. Already – with an average temperature rise of less than 1C – climate change kills more than 300,000 people each year.

With this in mind, the clear reason for the expectation around Copenhagen is that if the right deal is struck, we can halt the worst of climate change before everybody is affected. Plus, we can fight the downturn by creating green jobs and building access to renewable energy for all. We can improve the world we live in, instead of consigning millions to homelessness and poverty – or worse.

Because of the potential of this deal, an unprecedented alliance of organisations – including faith and youth groups, unions, environmental and development NGOs, such as WWF, Oxfam International, Consumers International and Kofi Annan’s Global Humanitarian Forum, plus a number of high-profile supporters– have come together under the TckTckTck campaign. We believe that only by working together in a broad alliance will we have the size, power and influence to ensure a good deal in Copenhagen.

Now is the time for world leaders to give this crisis their attention. They must commit now to attending the talks in Copenhagen where they must sign a deal that is fair, ambitious and binding and that reflects the latest science. Governments must get behind a treaty that reduces developed country emissions by at least 40% by 2020.

Tackling climate change is an issue of justice. Rich countries have been responsible for the vast majority of greenhouse gas emissions and therefore must take responsibility for dealing with crisis in a fair and equitable way. The deal must therefore enable and support poor countries to adapt to the worst consequences of the climate crisis, as well as reducing their emissions. The deal must protect marginalised communities in rich and poor countries.

The Copenhagen deal should be ambitious and ensure that global greenhouse emissions peak no later than 2017. It must create a pathway to clean jobs and clean energy for all and establish necessary conditions for a sustainable and prosperous future for people, flora and fauna. It must be binding and must be able to be verified and enforced.

With just 100 days to go until the meeting begins, and with climate scientists painting a bleaker future at even 2C of warming, time is running out.

But it is not yet too late. There is still time to build a greener safer world, but the clock is ticking.

Kumi Naidoo chairs TckTckTck and is honorary president of CIVICUS: World Alliance for Citizen Participation.