Office of Biological and Environmental Research Weekly Report

April 6, 2009

Using Analogue Past Climate to Understand Future Evolution of Current Climate:

Climate changes in the early Pliocene period (~3-5 million years ago) are often considered the closest analog to today’s global warming. It is believed that the external factors controlling the Pliocene climate system - the intensity of sunlight incident on Earth’s surface, global geography, and the atmospheric concentration of CO₂ (350-400 ppm) - were similar to present-day conditions. A recent study led by DOE-funded researcher, Professor Alexey Fedorov of Yale University create a reconstructed latitudinal distribution of sea surface temperatures for the Pliocene. This reconstruction shows that the difference in temperatures between the equator and subtropics was greatly reduced during this period, leading to a permanent El Nino-like state with global impacts on climate. In contrast, El Niño-like states only occur intermittently today during the warm phase of a quasi-periodic climate oscillation, that impacts weather and climate patterns worldwide every 4-5 years. The authors concluded that models simulating the early Pliocene climate may need to incorporate additional mechanisms for increased ocean heat uptake when simulating the early Pliocene climate to account for the permanent El Nino-like state during that period. These findings are relevant to current discussions about global warming due to the enormous impacts of changes in Earth’s warm pool, such as dramatic shifts in global precipitation patterns and cloud cover, and tentative evidence that the tropical belt has again been expanding poleward over the past few decades as it did during the Pliocene.

Reference:

Brierley, C.M. A.V. Fedorov, Z. Liu, T.D. Herbert, K.T. Lawrence and J.P. LaRiviere Greatly Expanded Tropical Warm Pool and Weakened Hadley Circulation in the Early Pliocene. Science (2009). Science Express, DOI: 10.1126/science.1167625

Media Interest: No

Contact: Anjuli Bamzai, SC-23.1, (301) 903-0294

Impacts of Aerosol Measurement Errors on Climate Change Studies. Scientists in DOE’s Atmospheric Radiation Measurement (ARM) Program used radiative transfer models to show that measurement errors in aerosol properties, typical of current best practices, result in large uncertainties (twenty to eighty percent) in modeling aerosol impacts on climate. The largest contributor to total uncertainty is in measuring the scattering versus absorbing properties of aerosols. The results provide specific information for each of the primary aerosol properties used as inputs to climate models. The information serves as a guide to reduce measurement errors for each aerosol property. This methodology will lead to an acceptable level of uncertainty in aerosol modeling and an identification of areas where measurements might be most improved.

Reference:

McComiskey, A., S. E. Schwartz, B. Schmid, H. Guan, E. R. Lewis, P. Ricchiazzi, and J. A. Ogren (2008), Direct aerosol forcing: Calculation from observables and sensitivities to inputs, J. Geophys. Res., 113, D09202, doi:10.1029/2007JD009170.

Media Interest: No

Contact: Kiran Alapaty, SC-23.1, (301) 903-3175

Climate-Relevant Isoprene Chemical Pathways Uncovered. In spite of their many positive attributes, including removing carbon from the atmosphere, some trees also contribute to the challenges of climate change. Many deciduous trees emit isoprene (2-methyl-1,3-butadiene, C5H8) during daylight hours, a major organic carbon compound accounting for up to 2% of the carbon fixed by those plants and about one third of total volatile organic compounds (VOC) emissions. DOE research has previously demonstrated that isoprene oxidation may contribute significantly to the global aerosol burden with impacts on climate forcing and ozone production. A recent study by this same group described isoprene photooxidation and developed a detailed mechanism, including branching ratios and yields, for the compounds identified. The authors summarize the most important features of this mechanism in a scheme appropriate for use in global chemical transport models. The impact of this chemistry is important in the light of the potential for significant changes in isoprene emissions caused by climate change and changes in land use.

Reference:

F. Paulot, J. D. Crounse, H. G. Kjaergaard, J. H. Kroll, J. H. Seinfeld, and P. O. Wennberg (2009), Isoprene photooxidation: new insights into the production of acids and organic nitrates, Atmos. Chem. Phys., 9, 1479–1501.

Media Interest: No

Contact: Ashley Williamson, SC-23.1, (301) 903-3120

LBNL Earth Scientist Named Geological Society Distinguished Lecturer. Dr. Susan Hubbard, a staff scientist in the Earth Sciences Division at Lawrence Berkeley National Laboratory, has been chosen to serve as the 2010 Geological Society of America's (GSA) Birdsall-Dreiss Lecturer. The endowed lectureship is made to one person annually by the GSA Hydrogeology Division based on two criteria. The nominee must be (1) a renowned scientist whose publication record and research have had national and international impact in the field of hydrogeology and (2) an outstanding speaker. Hubbard is the 32nd GSA Birdsall-Dreiss Lecturer, and the first from a DOE national laboratory. Hubbard has made major contributions to the field of Hydrogeophysics through her research which is sponsored by DOE’s Office of Biological and Environmental Research

Media Interest: No

Contact: David Lesmes, SC 23.1, (301) 903-2977.