Final answer:
The warmest years in the history of weather instruments occurred in the 21st century, coinciding with a rise in carbon dioxide levels and a documented long-term warming trend. Option d) is correct.
Step-by-step explanation:
The warmest years in the history of weather instruments are in the 21st century. The average annual temperature on Earth has been rising for the past 100 years, particularly sharply since the late 1800s. Significant temperature anomalies have occurred throughout history, such as the Medieval Climate Anomaly or the Medieval Warm Period, and the Little Ice Age, but the 21st-century warming trend surpasses these past events.
The global land-ocean temperature index from 1880 to 2020 clearly indicates a long-term warming trend, with the most recent decades consistently warmer than the mid-20th-century baseline. This trend corresponds with rising levels of atmospheric carbon dioxide, suggesting a strong relationship between carbon dioxide concentration and temperature.