"Today, the world has officially crossed the threshold for the Paris agreement to take effect," Obama said.
In December 2015, some 200 delegates at a United Nations climate conference in Paris committed to limiting increases in global average temperatures to no more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.
The Paris agreement was designed to take effect one month after being ratified by 55 signatories representing 55 percent of worldwide greenhouse-gas emissions.
On Wednesday, enough countries have submitted their instrument to formally join the agreement, according to the US Department of State.
On Tuesday, the European Parliament ratified the agreement on behalf of the European Union’s 28 members. The deal is intended to limit the rise in global average temperatures and reduce countries’ emissions of pollutants that contribute to planetary warming.