Final answer:
Today's average global temperature has risen by more than 1°C in the last 100 years, a much more rapid increase compared to the minor fluctuations seen over the previous millennia, including the Medieval Climate Anomaly. This temperature rise is attributed to the significant warming trend observed since the late 19th century, with projections indicating even greater increases by 2100.
Step-by-step explanation:
The student is inquiring about the state of today's average global temperature compared to that of the past 1000 years. Records such as Hansen et al. (2006) data and other historical indicators reveal that for the 4,000 years prior to the Industrial Revolution, global temperatures were relatively constant with minor fluctuations. However, over the past 100 years, a significant increase in global surface temperatures has been observed. This warming trend, as depicted in the graph from Figure 24.9.3, shows a consistent rise in temperatures from the late 19th century onward, with a noticeable acceleration in recent decades.
During the Medieval Climate Anomaly, also known as the Medieval Warm Period (900-1300 AD), slightly warmer weather conditions prevailed, with average temperature changes around 0.10 °C to 0.20 °C above the norm. This is contrasted with the current average global temperature, which has increased by more than 1°C in the last century, according to NOAA and NASA data. This indicates a much more rapid increase in temperature than during previous anomalies.
Furthermore, projections state that by 2100, the global average temperature is expected to warm at least twice as much as it has during the last 100 years. The speed of this temperature rise is much faster than historical climate changes, challenging the adaptability of many species and ecosystems.