Papers by Robert Kaufmann
Rensselaer Polytechnic Institute Department of Economics Working Paper, May 1, 2004
The principal tools used to model future climate change are General Circulation Models which are ... more The principal tools used to model future climate change are General Circulation Models which are deterministic high resolution bottom-up models of the global atmosphere-ocean system that require large amounts of supercomputer time to generate results. But are these models a costeffective way of predicting future climate change at the global level? In this paper we use modern econometric techniques to evaluate the statistical adequacy of three general circulation models (GCMs) by testing three aspects of a GCM's ability to ...
Global and hemispheric temperatures, greenhouse gas concentrations, solar irradiance, and anthrop... more Global and hemispheric temperatures, greenhouse gas concentrations, solar irradiance, and anthropogenic sulfate aerosols all have increased during the last one hundred and fifty years. Classical linear regression techniques will indicate a positive relationship among such series whether or not such a relation exists. Such standard techniques cannot, therefore, show whether observed temperature increases are the result of anthropogenic climate change. However, recent developments in econometrics allow for the analysis of ...
This paper updates estimates of global anthropogenic sulfate emissions through 1993 and provides ... more This paper updates estimates of global anthropogenic sulfate emissions through 1993 and provides a time series of estimates for each year. We extend the methodology developed by Hameed and Dignon (1989) to include emissions from copper smelting and use estimates for US emissions between 1900 and 1940 which were not previously available. Emissions since 1986 show a slight rise due to an increase in the US followed by a slight decline and a continuing decline in emissions from the other OECD countries. Emissions from the rest of the world peak in 1989 and show a steep decline associated with recession and economic restructuring in Eastern Europe. The various emissions series are consistent with the historical record for the atmospheric concentration of non sea sulfates that is reconstructed from an ice core recovered from Greenland.
Journal of Geophysical Research: Atmospheres, 2002
We use cointegration procedures that are designed to estimate and test relations among integrated... more We use cointegration procedures that are designed to estimate and test relations among integrated time series to develop a model of the relation between surface temperature and the radiative forcing of solar irradiance, greenhouse gases, and tropospheric sulfates. We use this model to test some basic hypotheses regarding the relation between surface temperature and radiative forcing. We find that there is a statistically meaningful relation between surface temperature and changes in the radiative forcing associated with natural variability and human activity. We also find that hemispheric temperatures cannot be explained by hemispheric forcings alone: Hemispheric temperatures are linked. Differences in hemispheric temperatures are associated with differences in the hemispheric temperature effects of greenhouse gases, anthropogenic sulfur emissions, and solar irradiance. Estimates for the temperature sensitivity (ΔT2x) are consistent with the middle and lower range of values estimate...
Ecological Economics, 2000
Methods for investigating the role of energy in the economy involve aggregating different energy ... more Methods for investigating the role of energy in the economy involve aggregating different energy flows. A variety of methods have been proposed, but none has received universal acceptance. This paper shows that the method of aggregation has crucial effects on the results of the analysis. We review the principal assumptions and methods for aggregating energy flows: the basic heat equivalents approach, economic approaches using prices or marginal product for aggregation, emergy analysis, and thermodynamic approaches such as exergy. We argue that economic approaches such as the index or marginal product method are superior because they account for differences in quality among fuels. We apply various economic approaches in three case studies in the US economy. In the first, we account for energy quality to assess changes in the energy surplus delivered by the extraction of fossil fuels from 1954 to 1992. The second and third case studies examine the importance of energy quality in evaluating the relation between energy use and GDP. First, a quality-adjusted index of energy consumption is used in an econometric analysis of the causal relation between energy use and GDP from 1947 to 1996. Second, we account for energy quality in an econometric analysis of the factors that determine changes in the energy/GDP ratio from 1947 to 1996. Without adjusting for energy quality, the results imply that the energy surplus from petroleum extraction is increasing, that changes in GDP drive changes in energy use, and that GDP has been decoupled from between aggregate energy use. All of these conclusions are reversed when we account for changes in energy quality.
Energy Policy, Feb 1, 2009
Oil prices, inventory levels, and utilization rates are influenced by changes that are transmitte... more Oil prices, inventory levels, and utilization rates are influenced by changes that are transmitted horizontally and/or vertically through the energy supply chain. We define horizontal transmissions as changes that are generated by linkages among fuels at a similar stage of processing while vertical transmissions are changes that are generated by upstream/downstream linkages in the oil supply chain. Here, we investigate
RePEc: Research Papers in Economics, Mar 1, 1997
Several time series investigations of global climate change have been published, but the time ser... more Several time series investigations of global climate change have been published, but the time series properties of the variables has received little attention with a few exceptions in the case of global temperature series. We focus on the presence or absence of stochastic trends. We use three different tests to determine the presence of stochastic trends in a selected group of global climate change data for the longest time series available. The test results indicate that the radiative forcing due to changes in the atmospheric concentrations of CO 2 , CH 4 , CFCs, and N 2 O, emissions of SO X , CO 2 , CH 4 , and CFCs and solar irradiance contain a unit root while most tests indicate that temperature does not. The concentration of stratospheric sulfate aerosols emitted by volcanoes is stationary. The radiative forcing variables cannot be aggregated into a deterministic trend which might explain the changes in temperature. Taken at face value our statistical tests would indicate that climate change has taken place over the last 140 years but that this is not due to anthropogenic forcing. However, the noisiness of the temperature series makes it difficult for the univariate tests we use to detect the presence of a stochastic trend. We demonstrate that multivariate cointegration analysis can attribute the observed climate change directly to natural and anthropogenic forcing factors in a statistically significant manner between 1860 and 1994 1.
Energy Policy, 2007
This paper describes a structural econometric model of the world oil market intended to be used t... more This paper describes a structural econometric model of the world oil market intended to be used to assess oil price developments and to provide quantitative analyses of oil related risk assessments. In this model, oil demand is explained by behavioural equations that relate demand to domestic activity and the real price of oil. Oil supply for non-OPEC producers is derived from a competitive behaviour, taking into account the effect of geological and economic variables. Oil prices are defined by a "price rule" based on changes in market conditions and OPEC behaviour. In particular, OPEC acts according to a cooperative behaviour and ensures the global equilibrium at the price determined by the price rule. Insample simulation results show that the model satisfactorily reproduces past developments in oil markets. Policy simulations show that the responses of demand and non-OPEC supply are rather inelastic to changes in price. Finally, although OPEC is assumed to "close" the model by absorbing any excess in supply or demand, the model shows that OPEC decisions about quota and capacity utilisation have a significant, immediate impact on oil price.
Nature
The distribution of dryland trees and their density, cover, size, mass and carbon content are not... more The distribution of dryland trees and their density, cover, size, mass and carbon content are not well known at sub-continental to continental scales1–14. This information is important for ecological protection, carbon accounting, climate mitigation and restoration efforts of dryland ecosystems15–18. We assessed more than 9.9 billion trees derived from more than 300,000 satellite images, covering semi-arid sub-Saharan Africa north of the Equator. We attributed wood, foliage and root carbon to every tree in the 0–1,000 mm year−1 rainfall zone by coupling field data19, machine learning20–22, satellite data and high-performance computing. Average carbon stocks of individual trees ranged from 0.54 Mg C ha−1 and 63 kg C tree−1 in the arid zone to 3.7 Mg C ha−1 and 98 kg tree−1 in the sub-humid zone. Overall, we estimated the total carbon for our study area to be 0.84 (±19.8%) Pg C. Comparisons with 14 previous TRENDY numerical simulation studies23 for our area found that the density and ...
This paper updates estimates of global anthropogenic sulfate emissions through 1993 and provides ... more This paper updates estimates of global anthropogenic sulfate emissions through 1993 and provides a time series of estimates for each year. We extend the methodology developed by Hameed and Dignon (1989) to include emissions from copper smelting and use estimates for US emissions between 1900 and 1940 which were not previously available. Emissions since 1986 show a slight rise due to an increase in the US followed by a slight decline and a continuing decline in emissions from the other OECD countries. Emissions from the rest of the world peak in 1989 and show a steep decline associated with recession and economic restructuring in Eastern Europe. The various emissions series are consistent with the historical record for the atmospheric concentration of non sea sulfates that is reconstructed from an ice core recovered from Greenland.
This manuscript describes a new statistical technique applied to the glacial-interglacial problem... more This manuscript describes a new statistical technique applied to the glacial-interglacial problem. Obviously, the authors are not familiar with the subject of paleoclimatology and their premises are often quite shaky or even plainly wrong. The authors are also not familiar with climate dynamics and the set of "climate variables" that they choose and discuss in this paper is probably difficult to justify. I am furthermore not convinced at all that the statistical technique they are using can provides any new information to the problem of glacial cycles. A good illustration of their conclusions is given in Table 5: Ice volume is linked to southern insolation (South 70◦N) and sea level is linked to northern insolation (North 60◦N). This is in my opinion sufficient to illustrate how an uninformed use of paleoclimatic data, combined with poor climate physics can lead to
We test hypotheses about glacial dynamics by evaluating the ability of a linear statistical model... more We test hypotheses about glacial dynamics by evaluating the ability of a linear statistical model to simulate climate during the previous ~800,000 years. During this period, the linear model simulates the timing and magnitude of glacial cycles, including the saw-tooth pattern in which ice accumulates gradually and ablates rapidly, without falsely simulating an interglacial after each peak in obliquity. Conversely, the linear model fails to simulate experimental observations that are created by a nonlinear data generating process. Together, these (in)abilities suggest that nonlinearities, threshold effects, bifurcations, and/or phase-specific governing equations do not play a critical role in glacial cycles during the late Pleistocene. Furthermore, the model’s accuracy throughout the sample period suggests that changes in orbital geometry create the Mid-Brunhes event.
Economics of Energy & Environmental Policy, 2020
Motivations underlying the research Over the last several years, I have published papers that sho... more Motivations underlying the research Over the last several years, I have published papers that show arbitrage opportunities largely unify the world oil market and that they can account for much of the price differences among crude oils. Exceptions include crude oils that are especially heavy or originate in nations with poor governance. But my confidence in these results was limited by the sudden appearance of a large spread in the prices for Brent and WTI, which are two of the world's most important benchmark crude oils. As stated by the Morpheus character in the film The Matrix, "You don't know what it is, but it's there, like a splinter in your mind, driving you mad." My splinter, I had to understand why to crude oils from nations with relatively transparent governments and similar physical characteristics (both light and sweet), suddenly seemed to be priced by regionalized markets. This sudden separation in price also perplexed other researchers. They posited several possible explanations; the shale oil boom, imports from Canada, building inventories, the lifting of the US ban on crude oil exports, changes in transportation infrastructure, declining production of crude oils that make-up Brent, the collapse of Libyan production, and even exchange rates. But these efforts did not satisfy my curiosity. Often, authors examined only a subset of possible explanations, which raised the specter of omitted variable bias. In others, authors ignored the nonstationary nature of the data, which raised the possibility that the statistical results were spurious. Finally, many analyses implicitly assumed that the spread was caused by a sudden change in an explanatory variable and so looked for a change-point in the price spread, rather than focusing on the factors that influenced the price of Brent and WTI. Research performed Here, I try to solve these shorting-coming by estimating two cointegrating vector autoregression (CVAR) models for the price of Brent and WTI and analyzing their residuals to identify periods when the model fails in a statistically significant manner. A univariate model specifies only the price of Brent and WTI. This model likely suffers from omitted variable bias and so its residual should identify periods when the long-and short-term relations between the two prices change in a statistically significant fashion. The second CVAR model contains all possible explanary variables. If this expanded CVAR model includes the relevant variables, the residuals should not contain any structural changes and the long-and short-run relations should quantify the factors that open and close the price spread. After an initial period (1987-2010) when the price spread between Brent and WTI remains relatively constant, their prices move separately during three periods. Starting in 2011, the price spread expands suddenly. This spread narrows starting in 2014. But in 2017, the price spread widens again. The CVAR models identify the likely causes for the two later periods. In 2014, the price spread shrinks because investments in transportation infrastructure increase the flow of crude oil from the mid-continent to Texas. Expanding the market for WTI raises its price. The price spread expands when the US lifts the ban on exporting crude oil. The price of WTI falls because the existing infrastructure forces exporters to load their cargos onto smaller, higher cost vessels and introducing new customers to the physical characteristics of WTI forces exporters to offer price discounts. Conversely, the CVAR models do not clearly identify the causes for and the timing of the increase in the price spread between Brent and WTI that starts in 2011. Results suggest that increasing imports
Million barrels per day Cumulative production total: 1 trillion barrels Twin peaks: peak-oil supp... more Million barrels per day Cumulative production total: 1 trillion barrels Twin peaks: peak-oil supporters think we have already reached or will soon reach a historical maximum of oil production (red line); others argue that oil production will not peak until at least 2030 (blue lines).
Paleoceanography, 2016
We test competing forms of the Milankovitch hypothesis by estimating the coefficients and diagnos... more We test competing forms of the Milankovitch hypothesis by estimating the coefficients and diagnostic statistics for a cointegrated vector autoregressive model that includes 10 climate variables and four exogenous variables for solar insolation. The estimates are consistent with the physical mechanisms postulated to drive glacial cycles. They show that the climate variables are driven partly by solar insolation, determining the timing and magnitude of glaciations and terminations, and partly by internal feedback dynamics, pushing the climate variables away from equilibrium. We argue that the latter is consistent with a weak form of the Milankovitch hypothesis and that it should be restated as follows: internal climate dynamics impose perturbations on glacial cycles that are driven by solar insolation. Our results show that these perturbations are likely caused by slow adjustment between land ice volume and solar insolation. The estimated adjustment dynamics show that solar insolation affects an array of climate variables other than ice volume, each at a unique rate. This implies that previous efforts to test the strong form of the Milankovitch hypothesis by examining the relationship between solar insolation and a single climate variable are likely to suffer from omitted variable bias.
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Papers by Robert Kaufmann