According to measurements from the Mauna Loa Observatory in Hawaii the Earth's atmosphere is right about to reach 400 parts-per-million (ppm) of CO2, a level that was last seen 3 million years ago. From the chart below we can see that the CO2 level is steadily raising since 1958 when the observation began.
According to the author of the source:
"The last time CO2 reached the symbolic milestone of 400 parts per million in the atmosphere - in the Pliocene era - temperatures rose by between 3 and 4 degrees and sea levels were between five and 40 meters higher than today."
Our world is approaching the 450 ppm level soon which is considered to be the point at which the world has a 50% chance of avoiding dangerous climate change. Any higher and the odds of avoiding searing temperature rises of 4 or 5 degrees by the end of the century become prohibitively risky.