What Can We Learn about the Climate of the Twenty-First Century from Historical Observations?

This talk will discuss how observations confirm and challenge climate models used to project future climate change. It will focus on two properties of the climate system which Susan Solomon’s work has been instrumental to point out and pin down:

The first example involves the timescale of the climate response. Two strong eruptions in the early 19^th century, Mount Tambora and an unknown eruption, perturbed the climate system and led to longterm cooling. Both climate models and observations including of glacier length illustrate that this cluster of eruptions caused not only shortterm climate anomalies such as those observed during the year without a summer, but also long-term cool conditions from which the climate system only recovered towards the middle of the 19^th century. In contrast, an absence of strong eruptions during the early part of the 20^th century contributed to that early warming.

The second example illustrates the coupled nature of the earth system and particularly, its role in extreme events. The dust bowl heatwaves in the US illustrate how change in vegetation as well as change in water availability played a large role in the record heat waves that occurred over this time. Moreover, the deviation of extreme temperatures from the mean shows promise as an emergent constraint on future change in temperature extremes, and is linked to simulations of the water budget. Hence in order to predict realistic change in summer heat waves, consideration of the water cycle and vegetation response to climate change is vital, and the historical example of the dust bowl heat waves illustrates that this coupled system may be subject to tipping point behaviour.