Relationships between climate and the net exchange of carbon dioxide (CO2) between the atmosphere and biosphere on yearly to decadal scales are poorly known. This is a critical knowledge gap for models used to estimate long-term climate change impacts on both the biosphere and the rate of change of CO2 in the atmosphere. A pilot study, based on large databases from more than 100 observational sites over 6 continents with a total of 583 site-years of observations, suggests that the net flow of carbon into or out of ecosystems is highly correlated with: (1) mean annual temperature at mid- and high-latitudes, (2) water stress at mid- and low-latitudes, and (3) both temperature and water stress around the mid-latitudinal belt. On average, the influence of water stress on terrestrial ecosystem CO2 uptake exceeds the influence of temperature at mean annual temperatures above 16 C. This project will explore the ecological and physical mechanisms behind these initial results and develop a clearer understanding of the relative importance of temperature and water availability on carbon sequestration. This research is essential to understanding how future climate change is likely to alter the exchange of CO2 between the biosphere and the atmosphere.
The consensus of science represented by the Intergovernmental Panel on Climate Change (IPCC) is that over the 21st century warming will be greatest at high northern latitudes, while projected decreases in precipitation are likely over much of the terrestrial subtropical zone. Results of this project will provide an empirical model based on real-world data of how the most likely future climate change scenarios would affect the potential capacity of terrestrial CO2 uptake in high latitudes and low latitudes. The analysis and synthesis of information proposed here is based on a large dataset provided by more than 100 research groups around the world. Collaboration, communication, and co-authorship will be established among a large number of scientists who collect these data. Two lectures will be developed for a non-major course that serves >250 students, and will incorporate basic concepts of physiological ecology and climatology based on this research. The lectures will bring current research into a classroom with perhaps the most ethnically diverse student body in the nation.
Chuixiang Yi (PI), Queens College, City University of New York The consensus of science represented by the IPCC (2007) is that over the 21st century warming will be greatest at high northern latitudes, while projected decreases in precipitation are likely over much of the terrestrial subtropical zone. The goal of this project is to provide an empirical model from real-world data of how the most likely future climate change scenarios would limit the potential capacity of terrestrial CO2 uptake in high latitudes and low latitudes. The Principal Investigator with his students and colleagues have analyzed and synthesized data from more than 100 research groups around the world and found that temperature is the most important control on carbon flow from the atmosphere to terrestrial ecosystems in high latitudes, whereas water is the most important control for carbon movement in low latitudes. The sensitivity of carbon flows to annual mean temperature broke down at a threshold value of 16 oC, above which land-atmosphere carbon flows were controlled by water availability rather than by temperature. Yi et al. (2010) predicted that as climate warms, carbon flow from the atmosphere into ecosystems will be strengthened in high latitudes, but will decrease in low latitudes. The significance of this outcome is shown by the fact that this paper was awarded the World Meteorological Organization’s 2012 Norbert Gerbier-MUMM International Award . This paper has established extensive collaboration among 151 co-authors from 116 institutions throughout the world. Another outcome of this project is that Yi et al. (2012) developed a novel technique, called the "perfect-deficit" approach that assigns maximum growth observed in each day-of-the-year (DOY) over a period of 10 or more years, thus synthesizing a "perfect" annual growth curve that can be compared to other years. The difference between the 'perfect curve' and the curve of any other year shows a deficit in plant growth and that deficit is highly correlated to weather, particularly to extreme weather. This "perfect-deficit" approach was derived from ground-tower observations and remote satellite data and can be used to identify the relationship between extreme weather and ecosystem production loss. Since the warming associate extreme weather is becoming more frequent and severe, the development of this approach is timely to explore the effect of extreme weather events on the carbon-storage capacity of the terrestrial biosphere. Key publications for the findings: Yi, C., et al., Climate control of terrestrial carbon exchange across biomes and continents, Environmental Research Letters, 5, doi: 10.1088/1748-9326/5/3/034007, 2010. Yi, C., et al., Climate extremes and grassland potential productivity, Environmental Research Letters, 7, 035703 (6pp) doi:10.1088/1748-9326/7/3/035703, 2012.
