EARTH SYSTEM DYNAMICS. Earth’s climate history is one of extraordinary change. We use earth system models of past climates and compare them with the geological record to understand how and why Earth’s climate has varied in the past and what this might teach us about future climate change. We typically focus on extreme or transitional climates, and investigate the large-scale dynamics and physics that drive climate change. Some examples include:
- Greenhouse climate intervals. The Cretaceous (145-66 Ma) was an interval in Earth history of extreme warmth. As such, it represents an important case study for how the climate system operates under warm conditions like those we might face in the near future. The study of greenhouse climates is of particular importance because current earth system models fail to adequately simulate such fundamental features as the pole-to-equator thermal gradient.
- Ice ages. We currently live in an ice age, yet for most of the geological past, ice ages were rare. We are interested in explaining the factors that both gave rise to and ended these exceptionally cold periods.
- Transitions. Earth’s climate history is rich with change and punctuated with important transitions, such as Antarctic glaciation, the establishment of the tropical Pacific thermocline, or the onset of the monsoon system. The source of these transitions is uncertain. Some of these may be related to the evolution of life, such as the rise of terrestrial plants in the early Paleozoic or the expansion of C4 grasslands in the Miocene. Others are likely related to the movement of continents or variations in atmospheric composition. Our goal is to determine the cause of these large-scale transitions.
- Fiorella, R.P. and Poulsen, C.J. (2013). Dehumidification over Tropical Continents Reduces Climate Sensitivity and Inhibits Snowball Earth Initiation. Journal of Climate, 26, 9677-9695, doi:10.1175/JCLI-D-12-00820.1.
- Horton, D.E., Poulsen, C.J., and Pollard D., (2010). Influence of high-latitude vegetation feedbacks on late Palaeozoic glacial cycles, Nature Geoscience, 3, 572-577, doi:10.1038/NGEO922.
- Poulsen, C.J. and Zhou, J. (2013). Sensitivity of Arctic Climate Variability to Mean State: Insights from the Cretaceous. Journal of Climate, 26, 7003-7022, doi: 10.1175/JCLI-D-12-00825.1.