The Kyoto Protocol will come into effect tomorrow, more than seven years after it was first adopted.
The protocol is the international treaty aimed at combating climate change.
Environmental campaigners have described it as an important first step towards dealing with global warming.
However, critics have warned that as long as the US, China and India refuse to sign up, Kyoto will change little.
The Kyoto Protocol was born in December 1997 in Japan's old imperial capital.
The aim is to reduce the burning of fuels, like oil and coal, because they produce gases which are warming the planet and risking catastrophic weather.
147 countries, accounting for 61% of greenhouse gas emissions, are now party to Kyoto, which will run until 2012.
For those who worked tirelessly for Kyoto to become operational, tomorrow will be a huge step forward. For them, the need to switch from fossil fuels to renewables quickly is unanswerable.
Increased flooding and adverse weather conditions are already hitting Ireland. It is hoped that Kyoto will be the beginning of the solution.
