Temperatures have been slowly rising for a number of years. In the charts below you can see that the late 19th and early 20th century were quite cool relative to the rest of the time period, 1880-2016. Temperatures on average continued to rise throughout the 20th century. Notice that there were fewer and fewer instances of below average temperatures. In fact, the last month the world saw below average temperatures was December 1984. Temperature increases really accelerated in the 21st century. December 2015 was the first time world temperatures were more than one degree Celsius or about 1.8 degrees Fahrenheit above average. This started a streak of five straight such months. If this doesn't sound like much, consider that such a rise in your body temperature would likely leave you quite sick.
Carbon dioxide, a potent greenhouse gas, was first consistently measured beginning in 1958 by Charles Keeling at the Mauna Loa Observatory in Hawaii. Notice that carbon dioxide levels fluctuate with the seasons, with levels tending to drop during the northern hemisphere's summer as its greater plant mass peaks then. However, the long term trend has shown consistently rising CO2 levels. Carbon Dioxide levels passed 400 parts per million for a given month in 2014 with the long term trend passing 400 parts per million in 2015. CO2 levels have not been this high in millions of years when temperatures were even warmer than they currently are.
Each colored bar represents one month of temperature anomalies or CO2 levels in the atmosphere. Monthly temperature anomaly measurements date from 1880. Measurements of CO2 levels in the atmosphere were first measured on a monthly basis in March of 1958. Hover over a bar to see the anomaly/CO2 levels for that month. Scroll down to see how temperatures and CO2 levels increase over time. Temperature anomalies are based on climate normals for the 20th century.