In March 1958, Dr. Charles David Keeling began regularly measuring the amount of carbon dioxide in the atmosphere from the Mauna Loa Observatory in Hawaii. In the years that followed, his research revealed what is now called the Keeling curve: a graph of continuous recording. On October 11 and 12, Kissinger and Le Duc Tho agreed on a peace agreement, with both sides working to achieve this goal ahead of the US presidential election on November 7. President Thieu rejected the settlement and refused to accept a peace that left North Vietnamese forces in South Vietnam and legitimized the Communist shadow government controlled by Hanoi, the Provisional Revolutionary Government. His rejection forced Kissinger to resume negotiations with Duke Tho. Nixon asked prominent Asian-American politician Anna Chennault to be his « channel to Mr. Thieu »; Chennault agreed and regularly reported to John Mitchell that Thieu had no intention of attending a peace conference. On November 2, Chennault informed the South Vietnamese ambassador: « I just heard my boss in Albuquerque say that his boss [Nixon] is going to win. Thieu, reassured by a massive influx of U.S.
military aid and a combination of promises and threats from Nixon, reluctantly agreed to join. On January 27, 1973, the Agreement on the End of war and the restoration of peace in Vietnam was signed by representatives of the Communist forces of South Vietnam, North Vietnam, South Vietnam and the United States. A ceasefire would take effect the next morning in North and South Vietnam, and within 60 days, all U.S. forces would be withdrawn, all U.S. bases dismantled, and all prisoners of war released. The prisoner of war issue will remain controversial for decades, although there is no credible evidence that US prisoners of war were secretly detained in Vietnam after the signing of the Paris Agreement (see Box: Vietnam Prisoners of War and MIA). An international force would maintain peace, the South Vietnamese would have the right to determine their own future, and North Vietnamese troops would remain in the south but would not be strengthened. The 17th parallel was to remain the dividing line until the country could be reunified by « peaceful means. » Nixon`s plan worked, and in early January 1973, the Americans and North Vietnamese settled the final details of the settlement. All parties to the conflict, including South Vietnam, signed the final agreement in Paris on January 27. .