Seminars with Video
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Climate Science Seminar: Scientific Uncertainty and the Risks of Climate Change
May 7, 2009 (10:00 - 11:30 a.m.)
Jay Gulledge (Pew Center on Global Climate Change)
Abstract: There are basic mechansisms and consequences of human-induced climate
change that are known with high confidence. Other aspects are either
fundamentally uncertain, such as the climate sensitivity, or will remain
uncertain for many years, such as the timing and magnitude of change in
a particular location. Policy decisions must therefore be taken under
uncertainty and these decisions must take into account the risks of
climate change, which include potential surprises with severe
consequences for society. For more information, see a related book chapter that is available at:
http://www.pewclimate.org/docUploads/Gulledge-Risks-Uncertainty-Aspen08.pdf
Climate Science Seminar: Climate Change and Its Causes: A Discussion about Some Key Issues
February 26, 2009
Nicola Scafetta (Duke University)
Abstract: A comparison of past and recent studies suggests that the problem of climate change is complex, as it is evident. Several key issues remain open and their solution may drastically change our understanding of the phenomenon. The crucial issue is: how is it possible to address a problem such a climate change where several crucial physical ingredients are still severely uncertain? In particular, some of the key issues he will address are: a) Did the total solar activity remain constant (as the IPCC and PMOD claim) or increase (as ACRIM claims) since 1980? b) Was the preindustrial temperature almost constant (The Hockey Stick graph) or did it experience a large change? c) What is the contribution of the GHG forcing on climate change, was it overestimated in some important past publications and might this have contributed to shape and bias the following debate? It is evident that solving the above issues in one way or in another is crucial for correctly interpreting climate change. He will propose a solution based on minimal physical assumptions that appear to have been confirmed by a large scientific empirical and theoretical literature. This solution suggests that a significant portion of climate change is natural and linked to changes of solar activity. He will also address the puzzling possibility that climate change might be partially driven by an additional natural forcing different from the radiative one that has not been identified yet. Finally, he will use these findings to attempt a climate prediction about the 21st century and discuss the possibility of an imminent global cooling.
Dr. Scafetta is a research scientist in the Department of Physics at Duke. He has about 40 papers in peer reviewed journals and two books in preparation.
Climate Science Seminar: Natural and Anthropogenic Influences on Earth’s Surface Temperature
January 28, 2009 (10:00 to 11:30 am)
Judith Lean (U.S. Naval Research Laboratory)
Abstract: There are many sources of climate variability, including anthropogenic gases, the El Nino Southern Oscillation (ENSO), volcanic aerosols and solar activity. Deciphering their concurrent impacts on Earth’s surface temperature is difficult because the solar activity cycle and volcanic cooling project onto each other, and both project onto ENSO. Longer-term solar changes may also project onto anthropogenic influences in the past century. A multivariate analysis is one approach for quantifying the natural and anthropogenic components of the surface temperature record simultaneously. Such an analysis, using the best available estimates of each together with the observed temperature, enables comparisons of the geographical distributions of surface temperature responses to the individual influences consistent with their global impacts from 1889 to 2006. The combined natural and anthropogenic influences (at appropriate lags) capture 76% of the variance in the monthly global surface temperature record, suggesting that much of the variability arises from processes that can be identified and their impact on the global surface temperature quantified by direct linear association with the observations. The response to solar forcing is quite different from that reported in several papers published recently: solar forcing produces a detectable 11-year cycle of amplitude 0.1K but contributed negligible long-term warming in the past 25 years and 10% of the warming in the past 100 years, not 69% as claimed elsewhere. Zonally averaged responses to both natural and anthropogenic forcings do not increase rapidly from mid to high latitudes, and therefore differ distinctly from those indicated by the IPCC, whose conclusions depended on model simulations. A recent paper co-authored by Dr. Lean on this subject can be found at Judith L. Lean and David H. Rind, "How Natural and Anthropogenic Influences Alter Global and Regional Surface Temperatures: 1889 to 2006, Geophysical Research Letters, Vol. 35, L18701, September 16, 2008. Dr. Lean is a Senior Scientist for Sun-Earth System Research in the Space Science Division of NRL. She is a member of the National Academy of Sciences and the author or co-author of over 100 papers in professional journals.
Climate Science Seminar: Global Warming: What Is It All About?
December 9, 2008 (1:30 to 3:00 pm)
Richard Lindzen (MIT)
Abstract: This is the first of three seminars on the science of global warming from widely different viewpoints. While global warming is frequently presented as a single phenomenon that one either believes in or denies, the real situation is, unsurprisingly, much more complex in the presenter's view. There are, in fact, certain aspects of the issue on which a substantial measure of agreement exists: namely, that global mean temperature has increased a few tenths of a degree since the 19th Century, and that increases in atmospheric CO2 have contributed some part of this warming. He examines some approaches to determining exactly how much of observed warming is actually due to anthropogenic greenhouse forcing, and how explicit feedbacks are involved in these results. However, the connection of this warming to catastrophic projections is extremely tenuous in his view. Moreover, proposed mitigation policies have little relevance to warming regardless of the level of warming expected. Understanding these ‘disconnects’ not only helps one to assess the overall situation rationally, but also permits one to see how the issue is being improperly exploited in Dr. Lindzen's view.
Dr. Lindzen is the Alfred P. Sloan Professor of Meteorology at MIT. He is a member of the National Academy of Sciences and has authored or co-authored over 200 professional journal articles.
Climate Science Seminar: Global Sea Level Rise
October 16, 2008
Carl Wunsch (MIT)
Abstract: Like many aspects of climate change, the problem of determining, describing, and understanding shifts in "sea level" proves to be far more complicated and interesting than summary sound bites suggest. Something is now known of the spatial patterns of sea level change and they are very complex, showing major regions of falling sea surface over large areas. Although the best estimates of the global average all show a positive rate of rise, partitioning the rise between heating/cooling and the addition/subtraction of fresh water lies at the very edge of modern oceanographic observational and modeling techniques. The eventual societal costs of sea level rise, whether accelerated or stable at present estimated rates, are huge and to a large extent appear inexorable.