The Pliocene Warm Interval: Is It An Analogue For Future Warming?

1. The Pliocene Warm Interval: Is It An Analogue For Future Warming? Abstract:The Pliocene Epoch (5.3 to 2.6 Ma) is the last “great global warming” before the beginning of the Pleistocene ice age. Paleoclimate proxy data, such as animal and plant fossils on land or in the ocean, suggest that the Earth was 2 to 3 degrees C warmer than present, with the most pronounced heating found in the polar regions. There may also have been a persistent El Niño-like feature, called El Padre, that led to increased warmth of tropical ocean surface waters. Despite these differences, the concentration of atmospheric CO2 during the Pliocene was similar to current day levels (380 ± 40 ppm). For this reason, climate researchers want to understand whether the Pliocene represents a warm world in an equilibrium state, a condition that we may eventually achieve in the near future even if CO2 emissions are stabilized. For our study, we used EdGCM/GISS GCM Model II to explore whether an El Padre could have contributed to the Pliocene global warming. We have also examined to what extent we can draw parallels between the regional climate impacts of an El Padre-driven Pliocene climate, and a strong modern El Niño, such as the 1997/1998 event, which has been projected to become a persistent feature of a future warm climate. We find that an El Padre/persistent El Niño could have played an important warming role for the Pliocene, and therefore has implications for our future climate. • Objectives • To determine if the Pliocene is a proper analog towards the future climate changes that have been projected by scientists. • Compare and contrast the characteristics of the Pliocene warm climate and possible forcings, such as the El Padre (persistent El Nino) effect, to our own modern day climate characteristics. • Results • In the predicted SST runs, we saw a greater increase in higher latitude temperatures when compared with the modern control run, consistent with Pliocene paleoclimate proxy data. • Our most extreme pSST run (425 ppm CO2) had a global average temperature increase of ~2 degrees Celsius compared to our modern control run. The polar regions showed a temperature increase of up to ~29 degrees Celsius. However, the mid-latitudes went through more warming in the northern hemisphere than in the southern hemisphere, most likely due to the distribution of land vs. ocean in the northern hemisphere vs. the southern hemisphere. • The equatorial regions did not change significantly in terms of temperature, with some areas even cooling (not by more than ~1 degree Celsius). • Global average precipitation is only slightly higher than that of the modern control run; however, many places undergo drastic increase or decreases. For example Central America, the Atlantic ocean, and the Asia-Pacific islands get significantly dryer than they are today (up to more than 3 mm/day less), whereas other places, such as Africa, South America, and the western Pacific ocean get a lot wetter (up to ~2.5 mm/day). • In the El Padre predicted SST runs, we saw a much warmer climate (> 3 degrees Celsius) than the modern control run; however, the maximum temperatures (present in Antarctica) remained the same as they did in the normal pSST runs. Surface air temperature-wise the El Padre runs simply showed more pronounced warming in the areas that where undergoing warming in the pSST runs. • Precipitation patterns in these runs do bare similarities to those regional patterns expected from Pliocene paleoclimate proxy data as well as with strong modern El Nino events. For example, we see a significant increase in precipitation in the equatorial west coast of South America, more precipitation in the Indian subcontinent (keep in mind there are also areas of decreased precipitation in the Indian subcontinent), decrease around the Japanese islands and a few areas of increased precipitation in Africa. • Importance of This Study • Understanding the factors and forcings that produced the Pliocene’s warm stable climate can help us understand what our world may become like in the near future, even if the CO2 emissions are stabilized at or near current levels. This is an anomaly map of our Pliocene control run minus out modern control run, showing us how different the Pliocene’s climate was from our own despite the similar forcings. Pliocene/ El Nino like Regional Impacts- this is a map of the temperature and precipitation during the Pliocene which is very similar to El Nino. What we think is that during the Pliocene there was a permanent El Nino. To differentiate the two we call this El Padre. • Methods • We used a software called EdGCM, which utilizes the NASA/GISS GCM Model II, to run all our climate simulations. • We first ran a series of sensitivity experiments using specified sea surface temperatures (SSTs) to examine the model’s response to certain forcings, such as greenhouse gas level changes. • We then ran a series of predicted SST experiments, in which the model’s ocean was allowed to respond to climate forcings set for each simulation. • We ran a total of four ensembles of runs, two with specified SSTs and two with predicted SSTs. For each ensemble, we changed the CO2 concentration in 5 ppm increments, from 380 ppm to 425 ppm. To one specified and one predicted SST ensemble, we also added the El Padre phenomenon by increasing tropical SSTs between 16N-16S. Pliocene El Padre Time Series Pliocene Time Series without El Padre Conclusions Our findings to date do suggest that an El Padre phenomenon, or persistent El Nino, did contribute to a global average increase in temperature during the Pliocene. Regional patterns of temperature and precipitation are also reasonably well reproduced by our Pliocene El Padre simulations although some differences remain. If the Pliocene does in fact represent a warm climate at equilibrium, it is very likely to be a good analog for our future warm world once our climate is no longer in transition. Sponsors: National Aeronautics and Space Administration (NASA) NASA Goddard Space Flight Center (GSFC) NASA Goddard Institute for Space Studies (GISS) NASA New York City Research Initiative (NYCRI) Contributors: Principal Investigator 1: Dr. Mark Chandler Principal Investigator 2: Dr. Linda Sohl Graduate Student: Sonali Shukla High School Teacher: Mohamed Shanap Undergraduate Student: Carimaxy Benitez NYCRI Apprentice: Francisco Benavides Surface Air Temperature- This map illustrates the similarities that the Pliocene/El Nino regional impact and our Pliocene maximum run minus our Pliocene control run. Precipitation- The arrows indicate where most of the precipitation is taking place, very similar to the regional precipitation shown above. This map is a Pliocene to its maximum 425 ppm minus our Pliocene control run 380 ppm. References Fedorov, A.V, Dekens, P.S, McCarthy, M, Ravelo, A.C, DeMenocal, P.B, Barreiro, M, Pacanowski, R.C, and Philander, S.G, 2006. The Pliocene Paradox (Mechanisms for a Permanent El Nino): Science, v.312, p.1485-1489, DOI: 10.1126/science.1122666. Molnar, P, and Cane, M.A, 2007. Early Pliocene (pre-Ice Age) El Nino-like Global Climate: Which El Nino?: Geosphere v.3, p.337-365, DOI:10.1130/ges00103.1.