Speaker: Bharat Rastogi, assistant professor of physical geography, CU Boulder

Topic:  Atmospheric and space-based constraints on regional carbon fluxes: Case studies from Amazonia and the Western U.S.
 

Abstract
Terrestrial ecosystems offset roughly 30% total anthropogenic CO2 emissions annually, serving as critical carbon sinks that have kept pace with increasing emissions from burning of fossil fuels and land use change. The net ecosystem exchange (NEE) of terrestrial ecosystems also controls the inter-annual variability of the amount of CO2 that accumulates in the atmosphere, i.e., the atmospheric CO2 growth rate. However, the fate of this climate subsidy is unknown due to an incomplete understanding of carbon cycle processes. Terrestrial biosphere models encode ecological theory based on measurements at leaf and plot to km2 scales to provide biome wide fluxes, but state of the science inter-comparison projects repeatedly fail to converge on the magnitude and drivers of present-day NEE. This is largely due to missing constraints on regional-scale fluxes from diverse biomes. In this talk, I start with a presentation of constraints on regional and global carbon cycling and use measurements of in-situ and space-based observations of CO2 to quantify regional flux variability in two different biomes. First, we head to the Amazon, the largest region of intact forest globally, commonly known as the “lungs of the Earth” due to the highest observed rates of global photosynthesis and respiration. Here I present results from a high-resolution regional atmospheric inversion that is constrained by space-based observations of total column CO2 (XCO2).  Next, we head closer to home and examine flux variability in the semi-arid Western U.S., a contrasting biome that is characterized by low flux and high variability (e.g., to water stress). In both cases, I highlight the limitations of space-based XCO2, the implications of sub-ppm (parts per million) scale biases on Peta grams of Carbon (1015 g) and the importance of independent evaluation datasets.
 

Bio
Bharat Rastogi is an assistant professor in the Department of Geography at CU Boulder. Prior to this he was a postdoctoral associate and a research scientist at the Cooperative Institute of Research in Environmental Sciences (CIRES) and NOAA’s Global Monitoring Laboratory in Boulder where he worked in the Carbon Cycle Greenhouse Gasses Division. Bharat completed his PhD in the Department of Forest Ecosystems and Society at Oregon State University and an MA in geography from University of California, Santa Barbara. Bharat’s research primarily asks the question:  What is the impact of anthropogenic climate change on terrestrial ecosystems, and in turn how does large-scale plant-atmosphere exchange feedback on to the climate system? Bharat enjoys indoor racquet sports in his spare time. He is originally from India and continues to lament the inaccessibility of an edible stone fruit produced by the tropical tree: Magnifera indica.

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