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Transition into the Anthropocene: learning about the climate system from the 19th and early 20th century

Final Report Summary - TITAN (Transition into the Anthropocene: learning about the climate system from the 19th and early 20th century)

The TITAN (transition into the Anthropocene) project determined the causes of climate variations and change from the Industrial Revolution to the present time. It found that the cold conditions in the early 19th century were largely caused by volcanic eruptions. The 'year without a summer' 1816 in Europe was greatly influenced by the eruption of Mount Tambora. From this active volcanic period climate rebounded to warmer conditions over the 19th century, by the end of which greenhouse warming can be detected in longterm trends. We found that the exceptionally cold conditions in the South Atlantic during the beginning of the 20th century, which spread northward, enhance the slope of the warming trend into the early 20th century warming. That warming culminated in an unusually warm North Atlantic in the 1940s, which TITAN found was involved in setting the stage for the dry springs and record hot summers in the Great Plains of the US. We found that climate models do not reproduce these record heat waves under 'standard' climate boundary conditions, but can simulate similar heat waves if accounting for the removal vegetation associated with the dustbowl droughts and agricultural crisis.
TITAN also investigated the origin of climate variability which cause increases or decreases in the rate of warming, such as the slowdown of warming that ended recently. It found that climate models simulate such periods, but that for the longest and strongest periods, large volcanic eruptions are a pace-setter. An apparent mismatch of the response to volcanoes in models and data was attributed to coincidence with El Nino events. TITAN also showed that global warming influences precipitation patterns in similar ways in models and data, when using long island stations, and that global warming enhances the contrast between wet and dry regions of the planet, while volcanic eruptions decrease that contrast. The warming since industrialisation can be used to constrain the future warming response, although not very tightly as uncertainty in the cooling caused by aerosol pollution is considerable.