Prof. Baldwin and Sue Wing Forecast U.S. CO2 Emissions to Exceed Official Estimates in Recent Journal of Regional Science Paper
Recent developments in U.S. climate change policy have seen the first tentative steps toward legislating a binding aggregate emission cap and implementing curbs on GHGs at the state and regional levels.1 This state and regional level policy action has been identified as both a critical element in U.S. emissions reductions and as a force to shape national climate change mitigation policy (Byrne et al., 2007; Lutsey and Sperling, 2008; Rabe, 2008). Consequently, the resulting economic effects of these policies is the subject of intense recent interest (Grainger and Kolstad, 2009; Hassett et al., 2009; Sue Wing, 2010). The first step in making any such assessment, and one incorporated or mandated in all state climate action plans (EPA, 2012), is to forecast how states’ baseline emissions are likely to evolve. Prerequisite to such projections is the ability to characterize the geographic variations in the precursors of GHGs—particularly CO2—based on an understanding of their historical evolution.
In this paper we investigate how the driving forces behind U.S. carbon dioxide emissions have evolved over the period 1963–2008. We take an explicitly spatial approach, quantifying in detail the interregional variations in CO2 precursors that are largely absent in the literature. While several recent papers have exploited state-level databases on the prices and quantities of fuel use, their focus has been quantifying the aggregate effects of drivers such as income and prices.2 The unfortunate consequence is that the substantial interregional heterogeneity underlying these results, which is interesting in its own right, has largely been ignored. An important exception to this general trend is Metcalf’s (2008) inquiry into the drivers of the energy intensity of U.S. states, which he disaggregates into intrasectoral changes in energy efficiency and intersectoral changes in the structure of economic activity. This paper’s key feature is the use of index number decomposition analysis, which is a popular technique for apportioning the time-evolution of a composite variable into contributions associated with movements in its constituent factors.3 We build on this approach, developing an extended decomposition framework which attributes the evolution of CO2 emissions over space and time to five precursors: the emissions intensity of energy use, the energy intensity of economic activity, the composition of states’ output, per capita income and population. Click to read entire paper…
Assistant Professor Dana Bauer and colleagues at the University of Maine and Bowdoin College received funding from the National Science Foundation’s Couple Natural and Human Systems program to study the role and management of vernal pools in urbanizing landscapes. Vernal pools are small natural features that are far more important for maintaining biodiversity and providing ecosystem services than one would expect based on their size. The interdisciplinary project team will explore the biophysical and socioeconomic components of vernal pool ecology and management as a coupled-systems model and develop strategies that improve management of these resources and other analogous systems around the globe, from prairie potholes in mid-western North America to desert springs in southern Africa.
For more information on Dana Bauer and her work, visit her website.
Previous studies have highlighted the occurrence and intensity of El Niño–Southern Oscillation as important drivers of the interannual variability of the atmospheric CO2 growth rate, but the underlying biogeophysical mechanisms governing such connections remain unclear. Here we show a strong and persistent coupling (r2 ≈ 0.50) between interannual variations of the CO2 growth rate and tropical land–surface air temperature during 1959 to 2011, with a 1 °C tropical temperature anomaly leading to a 3.5 ± 0.6 Petagrams of carbon per year (PgC/y) CO2 growth-rate anomaly on average. Analysis of simulation results from Dynamic Global Vegetation Models suggests that this temperature–CO2 coupling is contributed mainly by the additive responses of heterotrophic respiration (Rh) and net primary production (NPP) to temperature variations in tropical ecosystems. However, we find a weaker and less consistent (r2 ≈ 0.25) interannual coupling between CO2 growth rate and tropical land precipitation than diagnosed from the Dynamic Global Vegetation Models, likely resulting from the subtractive responses of tropical Rh and NPP to precipitation anomalies that partly offset each other in the net ecosystem exchange (i.e., net ecosystem exchange ≈ Rh − NPP). Variations in other climate variables (e.g., large-scale cloudiness) and natural disturbances (e.g., volcanic eruptions) may induce transient reductions in the temperature–CO2 coupling, but the relationship is robust during the past 50 y and shows full recovery within a few years after any such major variability event. Therefore, it provides an important diagnostic tool for improved understanding of the contemporary and future global carbon cycle. Click for complete PNAS article…
Prof. Myneni’s recent paper in NATURE on asymmetric daytime and night-time warming on vegetation growth
Temperature data over the past five decades show faster warming of the global land surface during the night than during the day1. This asymmetric warming is expected to affect carbon assimilation and consumption in plants, because photosynthesis in most plants occurs during daytime and is more sensitive to the maximum daily temperature, Tmax, whereas plant respiration occurs throughout the day2 and is therefore influenced by both Tmax and the minimum daily temperature, Tmin. Most studies of the response of terrestrial ecosystems to climate warming, however, ignore this asymmetric forcing effect on vegetation growth and carbon dioxide (CO2) fluxes3, 4, 5, 6. Here we analyse the interannual covariations of the satellite-derived normalized difference vegetation index (NDVI, an indicator of vegetation greenness) with Tmax and Tmin over the Northern Hemisphere. After removing the correlation between Tmax and Tmin, we find that the partial correlation between Tmax and NDVI is positive in most wet and cool ecosystems over boreal regions, but negative in dry temperate regions. In contrast, the partial correlation between Tmin and NDVI is negative in boreal regions, and exhibits a more complex behaviour in dry temperate regions. We detect similar patterns in terrestrial net CO2 exchange maps obtained from a global atmospheric inversion model. Additional analysis of the long-term atmospheric CO2 concentration record of the station Point Barrow in Alaska suggests that the peak-to-peak amplitude of CO2 increased by 23 ± 11% for a +1 °C anomaly in Tmax from May to September over lands north of 51° N, but decreased by 28 ± 14% for a +1 °C anomaly in Tmin. These lines of evidence suggest that asymmetric diurnal warming, a process that is currently not taken into account in many global carbon cycle models, leads to a divergent response of Northern Hemisphere vegetation growth and carbon sequestration to rising temperatures. Click for complete article…