So far, 96 countries, accounting for just over two-thirds of the world's greenhouse gas emissions, have formally joined the accord, which seeks to limit global warming to 2 degrees Celsius (3.6 degrees Fahrenheit).
Many more countries are expected to come aboard in the coming weeks and months.
UN spokesman Stephane Dujarric said Secretary-General Ban Ki-moon plans to commemorate "this historic day for both the people and the planet" by holding a conversation with civil society organizations about how they can contribute to the objectives of the Paris agreement.
"His push for action was backed by government officials, scientists, faith leaders, business executives and civil society activists around the world who understood that the future of our common home is at stake. They made today possible."
Scientists praised the speed at which the agreement, signed by 192 parties last December in Paris, has come into force, saying it underscores a new commitment by the international community to address the problem which is melting polar ice caps, sending sea levels rising and transforming vast swaths of arable land into desert.
"While the real effect of the agreement after it goes into effect is still uncertain, it is a simple sign that the international society is much more open to alter economic and political behavior to control climate change, which is by all means positive."
But scientists and policy makers say the agreement entering into force is just the first step of a much longer and complicated process of transitioning away from fossil fuels, which currently supply the bulk of the planet's energy needs and also are the primary drivers of global warming.
While the Paris agreement is legally binding, the emissions reductions that each country has committed to are not. Instead, the agreement seeks to create a transparent system that will allow the public to monitor how well each country is doing at meeting its goals in hopes that this will motivate them to transition more quickly to clean, renewable energy like wind, solar and hydropower.
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