An anonymous reader quotes a report from USA Today: World leaders from 175 countries signed the historic Paris climate accord Friday, using Earth Day as a backdrop for the ceremonial inking of a long-fought deal that aims to slow the rise of harmful greenhouse gases. The deal sets a target of limiting global warming by 2100 to "well below" 2 degrees Celsius (3.6 degrees F), as compared to pre-industrial levels. To accomplish that, each nation sets its own target for reducing emissions and updates that mark each year. Friday's signing sets a record for the number of countries signing an agreement on the first available day, the Associated Press reported. The old record goes back to the Law of the Sea in Montego Bay, which was signed by 119 countries in 1982, according to AccuWeather. Signing the accord is only one step in the process. The leaders must now go back to their home countries' governments to ratify and approve the agreement, which could take months or years. The deal goes into effect once 55 countries representing at least 55% of global emissions formally join.