A debate exists over whether tropical troposphere temperature trends in climate models are incons... more A debate exists over whether tropical troposphere temperature trends in climate models are inconsistent with observations (Karl et al. 2006, IPCC (2007), Douglass et al 2007, Santer et al 2008). Most recently, Santer et al (2008, herein S08) asserted that the Douglass et al statistical methodology was flawed and that a correct methodology showed there is no statistically significant difference
In a recent paper 1 (herein MM03), we developed an updated version of the climate proxy data set ... more In a recent paper 1 (herein MM03), we developed an updated version of the climate proxy data set used by Mann et. al. 2 (MBH98) to compute a Northern Hemisphere (NH) temperature index. The most significant changes were the replacement of obsolete versions of proxy data used in MBH98 with current versions from the World Data Center for Paleoclimatology (WDCP) and the use of conventional principal component analysis (PCA) to reduce networks of tree ring chronologies to regional aggregates using the maximum period in which all sites were available. Applying the methodology of MBH98 to the new data yielded an NH temperature index in which the values in the 15 th century exceeded those in the late 20 th century, thereby contradicting the conclusions in MBH98 of a unique 20 th century climate warming. In their response, 3 Mann et. al. highlighted the influence of three (of 22) proxy series in their data that extend back to 1400. The three proxies are: a ring width series from the site at Twisted Tree Heartrot Hill (TTHH) in northern Canada; the first principal component (PC1) of
Proceedings of the National Academy of Sciences, 2009
Mann et al. (1) present two paleoclimate reconstruction methods [''error-in-variables'' (EIV) and... more Mann et al. (1) present two paleoclimate reconstruction methods [''error-in-variables'' (EIV) and ''composite plus scale'' (CPS)], claiming statistically significant skill for both. Their figure 3 reveals that from approximately 750 to 1100, the CPS 95% confidence interval excludes the EIV 95% confidence interval and vice versa. This is evidence not of skill, but of inconsistency. Contrary to assurances (1), archived Mann et al. source code did not show how they calculated their figure 3 confidence intervals, which are unjustifiably narrow. Paleoclimate reconstructions are an application of multivariate calibration, which provides a theoretical basis for confidence interval calculation (e.g., refs. 2 and 3). Inconsistency among proxies sharply inflates confidence intervals (3). Applying the inconsistency test of ref. 3 to Mann et al. A.D. 1000 proxy data shows that finite confidence intervals cannot be defined before Ϸ1800. Numerous other problems undermine their conclusions. Their CPS reconstruction screens proxies by calibration-period correlation, a procedure known to generate ''hockey sticks'' from red noise (4). The proportion of proxies with ''significant'' correlation to gridcell temperature is overestimated by comparison to two (not one) gridcells, inclusion of ''proxies'' incorporating instrumental temperatures, and underadjustment for autocorrelation. Their non-dendro network uses some data with the axes upside down, e.g., Korttajarvi sediments, which are also compromised by agricultural impact (M. Tiljander, personal communication), and uses data not qualified as temperature proxies (e.g., speleothem ␦ 13 C). Although Mann et al. purport to ''follow the suggestions'' of ref. 5, they employed ''strip-bark'' dendrochronologies despite the recommendation of ref. 5 that these chronologies be ''avoided'' and fail to observe the caveats of ref. 5 that negative CE statistics indicate unreliable results.
This paper applies principal component analysis to investigate the linkages, or dominant co-fluct... more This paper applies principal component analysis to investigate the linkages, or dominant co-fluctuation patterns, of per capita carbon dioxide emissions across countries for the time period 1950-2000. Energy resource world markets are investigated as an offsetting mechanism possibly coordinating emission fluctuations between countries. The results of the analysis provide evidence that world energy resource markets are acting as a coordinating mechanism for emission fluctuations in most cases. The results also suggest that until recently the dominant emission co-fluctuation pattern for developed countries differs from the dominant emission co-fluctuation pattern for developing countries. The common fluctuation pattern found in the 1984-2000 time period suggests that an offsetting mechanism does exist and will help contain global per capita emissions into the future. The strong degree that emissions are linked between countries and energy markets acting as an offsetting mechanism suggests that to be successful a global agreement to address climate change must require emission reductions by all major emitters, not just the developed countries.
Overall climate sensitivity to CO2 doubling in a general circulation model results from a complex... more Overall climate sensitivity to CO2 doubling in a general circulation model results from a complex system of parameterizations in combination with the underlying model structure. We refer to this as the model's major hypothesis, and we assume it to be testable. We explain four criteria that a valid test should meet: measurability, specificity, independence, and uniqueness. We argue that temperature change in the tropical 200‐ to 300‐hPa layer meets these criteria. Comparing modeled to observed trends over the past 60 years using a persistence‐robust variance estimator shows that all models warm more rapidly than observations and in the majority of individual cases the discrepancy is statistically significant. We argue that this provides informative evidence against the major hypothesis in most current climate models.
Meyer (Environ Econ Policy Stud, 2022) questions a number of assumptions behind the social cost o... more Meyer (Environ Econ Policy Stud, 2022) questions a number of assumptions behind the social cost of carbon (SCC) calculations in Dayaratna et al. (Environ Econ Policy Stud 22:433–448, 2020), especially the CO2 fertilization benefit and the climate sensitivity estimate. He recommends against increasing the CO2 effect and suggests applying a recent climate sensitivity estimate in Lewis, Clim Dyn (2022), but did not calculate the resulting SCC distribution. Herein we critically assess his recommendations and compute the SCC distribution they imply. It has a median SCC value in 2050 of $3.39 and implies a 33.4 percent probability of the optimal carbon tax being negative. While a bit higher than the results in Dayaratna et al. (Environ Econ Policy Stud 22:433–448, 2020), they are not materially different for the purposes of setting optimal climate policy.
Some externalities, such as global warming, involve complex and uncertain relationships between e... more Some externalities, such as global warming, involve complex and uncertain relationships between emissions and the environment, with effects acting over lags the lengths of which are themselves subject to uncertainty. Optimal pricing rules can be derived in principle, but application is often controversial due to the necessity of assuming key model parameters which are imprecisely known. Bayesian learning methods may help reduce uncertainty, but only with time lags that preclude immediate policy guidance. This paper argues that the situation giving rise to a complex intertemporal externality also yields an observable state variable that can, under a simple transformation, yield an approximation to the optimal externality price. I outline the assumptions necessary to derive the transformation, and present numerical examples that illustrate its ability to follow linear and nonlinear first-best price paths. A specific application to greenhouse gases is proposed.
There was a small mistake in the command file used to compute the results in our paper [McKitrick... more There was a small mistake in the command file used to compute the results in our paper [McKitrick and Michaels 2004].1 The formula for computing cosine of absolute latitude (COSABLAT) takes the angle in radians but our data were entered in degrees. We have corrected this and produced new versions of the affected Tables. Table 4 below, showing the central results of the paper, displays the original and corrected columns side-by-side for ease of comparison. Tables 5—8 are presented in corrected versions only. As is evident in Table 4, except for the impacts on the COSABLAT variable itself, the changes are very small. The principal effect of the correction is a reduced weight on the constant term and an increased weight on the COSABLAT variable itself. Indeed the correction improves the overall fit and removes the anomalously small cosine-latitude effect. The socioeconomic variables remain significant and the effects carry over from the station data to the gridded data as before. Becau...
We explore the implications of recent empirical findings about CO2fertilization and climate sensi... more We explore the implications of recent empirical findings about CO2fertilization and climate sensitivity on the social cost of carbon (SCC) in the FUND model. New compilations of satellite and experimental evidence suggest larger agricultural productivity gains due to CO2growth are being experienced than are reflected in FUND parameterization. We also discuss recent studies applying empirical constraints to the probability distribution of equilibrium climate sensitivity and we argue that previous Monte Carlo analyses in IAMs have not adequately reflected the findings of this literature. Updating the distributions of these parameters under varying discount rates is influential on SCC estimates. The lower bound of the social cost of carbon is likely negative and the upper bound is much lower than previously claimed, at least through the mid-twenty-first century. Also the choice of discount rate becomes much less important under the updated parameter distributions.
Comparisons of trends across climatic data sets are complicated by the presence of serial correla... more Comparisons of trends across climatic data sets are complicated by the presence of serial correlation and possible step-changes in the mean. We build on heteroskedasticity and autocorrelation (HAC) robust methods, specifically the Vogelsang-Franses (VF) nonparametric variance estimator, to allow for a step-change in the mean at a known or unknown date. The VF method provides a powerful multivariate trend estimator robust to unknown serial correlation up to but not including unit roots. We show that the critical values change when the mean shift occurs at a known or unknown date. We derive an asymptotic approximation that can be used to simulate critical values, and we outline a simple bootstrap procedure that generates valid critical values and p-values. Our application builds on the literature comparing simulated and observed trends in the tropical lower-and midtroposphere since 1958. The method identifies a shift in observations relative to models in 1977, coinciding with the Pacific Climate Shift. Allowing for a level shift causes apparently significant observed trends to become statistically insignificant. Model over-estimation of warming is significant whether or not we account for a level shift, although null rejections are much stronger when the level shift is included.
Inference regarding trends in climatic data series, including comparisons across different data s... more Inference regarding trends in climatic data series, including comparisons across different data sets as well as univariate trend significance tests, is complicated by the presence of serial correlation and step-changes in the mean. We review recent developments in the estimation of heteroskedasticity and autocorrelation robust (HAC) covariance estimators as they have been applied to linear trend inference, with focus on the Vogelsang-Franses (2005) nonparametric approach, which provides a unified framework for trend covariance estimation robust to unknown forms of autocorrelation up to but not including unit roots, making it especially useful for climatic data applications. We extend the Vogelsang-Franses approach to allow general deterministic regressors including the case where a step-change in the mean occurs at a known date. Additional regressors change the critical values of the Vogelsang-Franses statistic. We derive an asymptotic approximation that can be used to simulate critical values. We also outline a simple bootstrap procedure that generates valid critical values and p-values. The motivation for extending the Vogelsang-Franses approach is an application that compares climate model generated and observational global temperature data in the tropical lowerand mid-troposphere from 1958 to 2010. Inclusion of a mean shift regressor to capture the Pacific Climate Shift of 1977 causes apparently significant observed trends to become statistically insignificant, and rejection of the equivalence between model generated and observed data trends occurs for much smaller significance levels (i.e. is more strongly rejected).
Canadian Journal of Agricultural Economics/Revue canadienne d'agroeconomie, 2005
Scientific assessment panels are playing increasingly influential roles in national and internati... more Scientific assessment panels are playing increasingly influential roles in national and international policy formation. Although they typically appeal to the standard of journal peer review as their quality control criterion, there seems to be confusion about what peer review actually does. It is, at best, a necessary condition of reliability, but not a sufficient condition. There is also the problem that assessment panels may be biased in favor of one side or another when evaluating areas in which the science is unclear. In this paper I argue that additional checks and balances are needed on the information going into scientific assessment reports when it will be used to justify major policy investments. I propose two new mechanisms to bias-proof the outcome: an Audit Panel and a Counterweight Panel. The need for such mechanisms is discussed with reference to the "hockey stick" debate in climate change. Les comités scientifiques d'évaluation jouent des rôles de plus en plus influents dans la formulation des politiques nationales et internationales. Bien que pour les revues scientifiques, la révision par les pairs représente un critère pour assurer le contrôle de la qualité, la confusion semble régner quant au rôle de cette révision par les pairs. Elle est, au mieux, une condition nécessaire pour assurer la fiabilité, sansêtre toutefois une condition suffisante. Il y a aussi le fait que les comités d'évaluation peuvent avoir un parti pris pour un aspect ou un autre lorsqu'ilsévaluent des domaines où la science n'est pas claire. Dans le présent article, nous avons maintenu que l'information publiée dans les rapports d'évaluation scientifique devrait faire l'objet de vérifications supplémentaires lorsqu'elle est utilisée pour justifier d'importants investissements en matière de politique. Nous avons proposé deux mécanismes pour vérifier et contre-vérifier les résultats: créer un comité de vérification et un comité de contre-vérification. Nous avons discuté de la nécessité d'instaurer ce genre de mécanismes en faisant référence au débat sur les changements climatiques.
Integrated Assessment Models (IAMs) require parameterization of both economic and climatic proces... more Integrated Assessment Models (IAMs) require parameterization of both economic and climatic processes. The latter includes Equilibrium Climate Sensitivity (ECS), or the temperature response to doubling CO2 levels, and Ocean Heat Uptake (OHU) efficiency. ECS distributions in IAMs have been drawn from climate model runs that lack an empirical basis, and in Monte Carlo experiments may not be constrained to consistent OHU values. Empirical ECS estimates are now available, but have not yet been applied in IAMs. We incorporate a new estimate of the ECS distribution conditioned on observed OHU efficiency into two widely-used IAMs. The resulting Social Cost of Carbon (SCC) estimates are much lower than those from models based on simulated parameters. In the DICE model the average SCC falls by 30-50% depending on the discount rate, while in the FUND model the average SCC falls by over 80%. The span of estimates across discount rates also shrinks substantially.
Canadian economists, politicians and even environmentalists are lining up enthusiastically behind... more Canadian economists, politicians and even environmentalists are lining up enthusiastically behind pricing carbon as the solution to controlling greenhouse gas emissions in this country. Pricing carbon (or, more accurately, pricing carbon dioxide) is not just a fashionable policy approach; it is the most efficient way we have to ration emissions, as it allows emitters — businesses and consumers — to make the most rational decisions about where it makes economic sense to curtail carbon and where it does not. Painfully costly command-and-control reductions make little sense in Canada, given our marginal contribution to global emissions. When practiced globally, a carbon price deals with Canadian emitters as fairly as it does others. However, a beneficial outcome is not guaranteed: certain rules must be observed in order for carbon pricing to have its intended effect of achieving the optimal balance between emission reduction and economic growth. First and foremost, carbon pricing only ...
Major insurance and reinsurance firms have expressed concern that global warming poses economic t... more Major insurance and reinsurance firms have expressed concern that global warming poses economic threats to the industry due to increased risk of extreme weather events. Past studies have examined the connection between global warming trends and the value of insured damages. In principle, if weather-related threats are increasing, insurance firms may face higher payouts, but they may also enjoy an expanded market for insurance products. If they are able to price the new risks appropriately they may even end up better off. This study examines whether climatic variations have historically been connected to the profitability of insurance firms. We form a portfolio of insurance firms and then estimate a three-factor model augmented with climate variables of interest. Short-run relationships between climatic variables and insurance firms indicate that temporary deviations have small but likely beneficial effects on insurance firms. Overall, our results suggest that the past increases in extreme weather conditions have not had a negative effect on the market value of insurance firms.
The IPCC has drawn attention to an apparent leveling-off of globally-averaged temperatures over t... more The IPCC has drawn attention to an apparent leveling-off of globally-averaged temperatures over the past 15 years or so. Measuring the duration of the hiatus has implications for determining if the underlying trend has changed, and for evaluating climate models. Here, I propose a method for estimating the duration of the hiatus that is robust to unknown forms of heteroskedasticity and autocorrelation (HAC) in the temperature series and to cherry-picking of endpoints. For the specific case of global average temperatures I also add the requirement of spatial consistency between hemispheres. The method makes use of the Vogelsang-Franses (2005) HAC-robust trend variance estimator which is valid as long as the underlying series is trend stationary, which is the case for the data used herein. Application of the method shows that there is now a trendless interval of 19 years duration at the end of the HadCRUT4 surface temperature series, and of 16-26 years in the lower troposphere. Use of a simple AR1 trend model suggests a shorter hiatus of 14-20 years but is likely unreliable.
The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, “MBH98” hereafter... more The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, “MBH98” hereafter) for the estimation of temperatures from 1400 to 1980 contains collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects. We detail these errors and defects. We then apply MBH98 methodology to the construction of a Northern Hemisphere average temperature index for the 1400–1980 period, using corrected and updated source data. The major finding is that the values in the early 15th century exceed any values in the 20th century. The particular “hockey stick” shape derived in the MBH98 proxy construction – a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 — is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal comp...
Physical, mathematical and observational grounds are employed to show that there is no physically... more Physical, mathematical and observational grounds are employed to show that there is no physically meaningful global temperature for the Earth in the context of the issue of global warming. While it is always possible to construct statistics for any given set of local temperature data, an infinite range of such statistics is mathematically permissible if physical principles provide no explicit basis for choosing among them. Distinct and equally valid statistical rules can and do show opposite trends when applied to the results of computations from physical models and real data in the atmosphere. A given temperature field can be interpreted as both "warming" and "cooling" simultaneously, making the concept of warming in the context of the issue of global warming physically ill-posed.
A debate exists over whether tropical troposphere temperature trends in climate models are incons... more A debate exists over whether tropical troposphere temperature trends in climate models are inconsistent with observations (Karl et al. 2006, IPCC (2007), Douglass et al 2007, Santer et al 2008). Most recently, Santer et al (2008, herein S08) asserted that the Douglass et al statistical methodology was flawed and that a correct methodology showed there is no statistically significant difference
In a recent paper 1 (herein MM03), we developed an updated version of the climate proxy data set ... more In a recent paper 1 (herein MM03), we developed an updated version of the climate proxy data set used by Mann et. al. 2 (MBH98) to compute a Northern Hemisphere (NH) temperature index. The most significant changes were the replacement of obsolete versions of proxy data used in MBH98 with current versions from the World Data Center for Paleoclimatology (WDCP) and the use of conventional principal component analysis (PCA) to reduce networks of tree ring chronologies to regional aggregates using the maximum period in which all sites were available. Applying the methodology of MBH98 to the new data yielded an NH temperature index in which the values in the 15 th century exceeded those in the late 20 th century, thereby contradicting the conclusions in MBH98 of a unique 20 th century climate warming. In their response, 3 Mann et. al. highlighted the influence of three (of 22) proxy series in their data that extend back to 1400. The three proxies are: a ring width series from the site at Twisted Tree Heartrot Hill (TTHH) in northern Canada; the first principal component (PC1) of
Proceedings of the National Academy of Sciences, 2009
Mann et al. (1) present two paleoclimate reconstruction methods [''error-in-variables'' (EIV) and... more Mann et al. (1) present two paleoclimate reconstruction methods [''error-in-variables'' (EIV) and ''composite plus scale'' (CPS)], claiming statistically significant skill for both. Their figure 3 reveals that from approximately 750 to 1100, the CPS 95% confidence interval excludes the EIV 95% confidence interval and vice versa. This is evidence not of skill, but of inconsistency. Contrary to assurances (1), archived Mann et al. source code did not show how they calculated their figure 3 confidence intervals, which are unjustifiably narrow. Paleoclimate reconstructions are an application of multivariate calibration, which provides a theoretical basis for confidence interval calculation (e.g., refs. 2 and 3). Inconsistency among proxies sharply inflates confidence intervals (3). Applying the inconsistency test of ref. 3 to Mann et al. A.D. 1000 proxy data shows that finite confidence intervals cannot be defined before Ϸ1800. Numerous other problems undermine their conclusions. Their CPS reconstruction screens proxies by calibration-period correlation, a procedure known to generate ''hockey sticks'' from red noise (4). The proportion of proxies with ''significant'' correlation to gridcell temperature is overestimated by comparison to two (not one) gridcells, inclusion of ''proxies'' incorporating instrumental temperatures, and underadjustment for autocorrelation. Their non-dendro network uses some data with the axes upside down, e.g., Korttajarvi sediments, which are also compromised by agricultural impact (M. Tiljander, personal communication), and uses data not qualified as temperature proxies (e.g., speleothem ␦ 13 C). Although Mann et al. purport to ''follow the suggestions'' of ref. 5, they employed ''strip-bark'' dendrochronologies despite the recommendation of ref. 5 that these chronologies be ''avoided'' and fail to observe the caveats of ref. 5 that negative CE statistics indicate unreliable results.
This paper applies principal component analysis to investigate the linkages, or dominant co-fluct... more This paper applies principal component analysis to investigate the linkages, or dominant co-fluctuation patterns, of per capita carbon dioxide emissions across countries for the time period 1950-2000. Energy resource world markets are investigated as an offsetting mechanism possibly coordinating emission fluctuations between countries. The results of the analysis provide evidence that world energy resource markets are acting as a coordinating mechanism for emission fluctuations in most cases. The results also suggest that until recently the dominant emission co-fluctuation pattern for developed countries differs from the dominant emission co-fluctuation pattern for developing countries. The common fluctuation pattern found in the 1984-2000 time period suggests that an offsetting mechanism does exist and will help contain global per capita emissions into the future. The strong degree that emissions are linked between countries and energy markets acting as an offsetting mechanism suggests that to be successful a global agreement to address climate change must require emission reductions by all major emitters, not just the developed countries.
Overall climate sensitivity to CO2 doubling in a general circulation model results from a complex... more Overall climate sensitivity to CO2 doubling in a general circulation model results from a complex system of parameterizations in combination with the underlying model structure. We refer to this as the model's major hypothesis, and we assume it to be testable. We explain four criteria that a valid test should meet: measurability, specificity, independence, and uniqueness. We argue that temperature change in the tropical 200‐ to 300‐hPa layer meets these criteria. Comparing modeled to observed trends over the past 60 years using a persistence‐robust variance estimator shows that all models warm more rapidly than observations and in the majority of individual cases the discrepancy is statistically significant. We argue that this provides informative evidence against the major hypothesis in most current climate models.
Meyer (Environ Econ Policy Stud, 2022) questions a number of assumptions behind the social cost o... more Meyer (Environ Econ Policy Stud, 2022) questions a number of assumptions behind the social cost of carbon (SCC) calculations in Dayaratna et al. (Environ Econ Policy Stud 22:433–448, 2020), especially the CO2 fertilization benefit and the climate sensitivity estimate. He recommends against increasing the CO2 effect and suggests applying a recent climate sensitivity estimate in Lewis, Clim Dyn (2022), but did not calculate the resulting SCC distribution. Herein we critically assess his recommendations and compute the SCC distribution they imply. It has a median SCC value in 2050 of $3.39 and implies a 33.4 percent probability of the optimal carbon tax being negative. While a bit higher than the results in Dayaratna et al. (Environ Econ Policy Stud 22:433–448, 2020), they are not materially different for the purposes of setting optimal climate policy.
Some externalities, such as global warming, involve complex and uncertain relationships between e... more Some externalities, such as global warming, involve complex and uncertain relationships between emissions and the environment, with effects acting over lags the lengths of which are themselves subject to uncertainty. Optimal pricing rules can be derived in principle, but application is often controversial due to the necessity of assuming key model parameters which are imprecisely known. Bayesian learning methods may help reduce uncertainty, but only with time lags that preclude immediate policy guidance. This paper argues that the situation giving rise to a complex intertemporal externality also yields an observable state variable that can, under a simple transformation, yield an approximation to the optimal externality price. I outline the assumptions necessary to derive the transformation, and present numerical examples that illustrate its ability to follow linear and nonlinear first-best price paths. A specific application to greenhouse gases is proposed.
There was a small mistake in the command file used to compute the results in our paper [McKitrick... more There was a small mistake in the command file used to compute the results in our paper [McKitrick and Michaels 2004].1 The formula for computing cosine of absolute latitude (COSABLAT) takes the angle in radians but our data were entered in degrees. We have corrected this and produced new versions of the affected Tables. Table 4 below, showing the central results of the paper, displays the original and corrected columns side-by-side for ease of comparison. Tables 5—8 are presented in corrected versions only. As is evident in Table 4, except for the impacts on the COSABLAT variable itself, the changes are very small. The principal effect of the correction is a reduced weight on the constant term and an increased weight on the COSABLAT variable itself. Indeed the correction improves the overall fit and removes the anomalously small cosine-latitude effect. The socioeconomic variables remain significant and the effects carry over from the station data to the gridded data as before. Becau...
We explore the implications of recent empirical findings about CO2fertilization and climate sensi... more We explore the implications of recent empirical findings about CO2fertilization and climate sensitivity on the social cost of carbon (SCC) in the FUND model. New compilations of satellite and experimental evidence suggest larger agricultural productivity gains due to CO2growth are being experienced than are reflected in FUND parameterization. We also discuss recent studies applying empirical constraints to the probability distribution of equilibrium climate sensitivity and we argue that previous Monte Carlo analyses in IAMs have not adequately reflected the findings of this literature. Updating the distributions of these parameters under varying discount rates is influential on SCC estimates. The lower bound of the social cost of carbon is likely negative and the upper bound is much lower than previously claimed, at least through the mid-twenty-first century. Also the choice of discount rate becomes much less important under the updated parameter distributions.
Comparisons of trends across climatic data sets are complicated by the presence of serial correla... more Comparisons of trends across climatic data sets are complicated by the presence of serial correlation and possible step-changes in the mean. We build on heteroskedasticity and autocorrelation (HAC) robust methods, specifically the Vogelsang-Franses (VF) nonparametric variance estimator, to allow for a step-change in the mean at a known or unknown date. The VF method provides a powerful multivariate trend estimator robust to unknown serial correlation up to but not including unit roots. We show that the critical values change when the mean shift occurs at a known or unknown date. We derive an asymptotic approximation that can be used to simulate critical values, and we outline a simple bootstrap procedure that generates valid critical values and p-values. Our application builds on the literature comparing simulated and observed trends in the tropical lower-and midtroposphere since 1958. The method identifies a shift in observations relative to models in 1977, coinciding with the Pacific Climate Shift. Allowing for a level shift causes apparently significant observed trends to become statistically insignificant. Model over-estimation of warming is significant whether or not we account for a level shift, although null rejections are much stronger when the level shift is included.
Inference regarding trends in climatic data series, including comparisons across different data s... more Inference regarding trends in climatic data series, including comparisons across different data sets as well as univariate trend significance tests, is complicated by the presence of serial correlation and step-changes in the mean. We review recent developments in the estimation of heteroskedasticity and autocorrelation robust (HAC) covariance estimators as they have been applied to linear trend inference, with focus on the Vogelsang-Franses (2005) nonparametric approach, which provides a unified framework for trend covariance estimation robust to unknown forms of autocorrelation up to but not including unit roots, making it especially useful for climatic data applications. We extend the Vogelsang-Franses approach to allow general deterministic regressors including the case where a step-change in the mean occurs at a known date. Additional regressors change the critical values of the Vogelsang-Franses statistic. We derive an asymptotic approximation that can be used to simulate critical values. We also outline a simple bootstrap procedure that generates valid critical values and p-values. The motivation for extending the Vogelsang-Franses approach is an application that compares climate model generated and observational global temperature data in the tropical lowerand mid-troposphere from 1958 to 2010. Inclusion of a mean shift regressor to capture the Pacific Climate Shift of 1977 causes apparently significant observed trends to become statistically insignificant, and rejection of the equivalence between model generated and observed data trends occurs for much smaller significance levels (i.e. is more strongly rejected).
Canadian Journal of Agricultural Economics/Revue canadienne d'agroeconomie, 2005
Scientific assessment panels are playing increasingly influential roles in national and internati... more Scientific assessment panels are playing increasingly influential roles in national and international policy formation. Although they typically appeal to the standard of journal peer review as their quality control criterion, there seems to be confusion about what peer review actually does. It is, at best, a necessary condition of reliability, but not a sufficient condition. There is also the problem that assessment panels may be biased in favor of one side or another when evaluating areas in which the science is unclear. In this paper I argue that additional checks and balances are needed on the information going into scientific assessment reports when it will be used to justify major policy investments. I propose two new mechanisms to bias-proof the outcome: an Audit Panel and a Counterweight Panel. The need for such mechanisms is discussed with reference to the "hockey stick" debate in climate change. Les comités scientifiques d'évaluation jouent des rôles de plus en plus influents dans la formulation des politiques nationales et internationales. Bien que pour les revues scientifiques, la révision par les pairs représente un critère pour assurer le contrôle de la qualité, la confusion semble régner quant au rôle de cette révision par les pairs. Elle est, au mieux, une condition nécessaire pour assurer la fiabilité, sansêtre toutefois une condition suffisante. Il y a aussi le fait que les comités d'évaluation peuvent avoir un parti pris pour un aspect ou un autre lorsqu'ilsévaluent des domaines où la science n'est pas claire. Dans le présent article, nous avons maintenu que l'information publiée dans les rapports d'évaluation scientifique devrait faire l'objet de vérifications supplémentaires lorsqu'elle est utilisée pour justifier d'importants investissements en matière de politique. Nous avons proposé deux mécanismes pour vérifier et contre-vérifier les résultats: créer un comité de vérification et un comité de contre-vérification. Nous avons discuté de la nécessité d'instaurer ce genre de mécanismes en faisant référence au débat sur les changements climatiques.
Integrated Assessment Models (IAMs) require parameterization of both economic and climatic proces... more Integrated Assessment Models (IAMs) require parameterization of both economic and climatic processes. The latter includes Equilibrium Climate Sensitivity (ECS), or the temperature response to doubling CO2 levels, and Ocean Heat Uptake (OHU) efficiency. ECS distributions in IAMs have been drawn from climate model runs that lack an empirical basis, and in Monte Carlo experiments may not be constrained to consistent OHU values. Empirical ECS estimates are now available, but have not yet been applied in IAMs. We incorporate a new estimate of the ECS distribution conditioned on observed OHU efficiency into two widely-used IAMs. The resulting Social Cost of Carbon (SCC) estimates are much lower than those from models based on simulated parameters. In the DICE model the average SCC falls by 30-50% depending on the discount rate, while in the FUND model the average SCC falls by over 80%. The span of estimates across discount rates also shrinks substantially.
Canadian economists, politicians and even environmentalists are lining up enthusiastically behind... more Canadian economists, politicians and even environmentalists are lining up enthusiastically behind pricing carbon as the solution to controlling greenhouse gas emissions in this country. Pricing carbon (or, more accurately, pricing carbon dioxide) is not just a fashionable policy approach; it is the most efficient way we have to ration emissions, as it allows emitters — businesses and consumers — to make the most rational decisions about where it makes economic sense to curtail carbon and where it does not. Painfully costly command-and-control reductions make little sense in Canada, given our marginal contribution to global emissions. When practiced globally, a carbon price deals with Canadian emitters as fairly as it does others. However, a beneficial outcome is not guaranteed: certain rules must be observed in order for carbon pricing to have its intended effect of achieving the optimal balance between emission reduction and economic growth. First and foremost, carbon pricing only ...
Major insurance and reinsurance firms have expressed concern that global warming poses economic t... more Major insurance and reinsurance firms have expressed concern that global warming poses economic threats to the industry due to increased risk of extreme weather events. Past studies have examined the connection between global warming trends and the value of insured damages. In principle, if weather-related threats are increasing, insurance firms may face higher payouts, but they may also enjoy an expanded market for insurance products. If they are able to price the new risks appropriately they may even end up better off. This study examines whether climatic variations have historically been connected to the profitability of insurance firms. We form a portfolio of insurance firms and then estimate a three-factor model augmented with climate variables of interest. Short-run relationships between climatic variables and insurance firms indicate that temporary deviations have small but likely beneficial effects on insurance firms. Overall, our results suggest that the past increases in extreme weather conditions have not had a negative effect on the market value of insurance firms.
The IPCC has drawn attention to an apparent leveling-off of globally-averaged temperatures over t... more The IPCC has drawn attention to an apparent leveling-off of globally-averaged temperatures over the past 15 years or so. Measuring the duration of the hiatus has implications for determining if the underlying trend has changed, and for evaluating climate models. Here, I propose a method for estimating the duration of the hiatus that is robust to unknown forms of heteroskedasticity and autocorrelation (HAC) in the temperature series and to cherry-picking of endpoints. For the specific case of global average temperatures I also add the requirement of spatial consistency between hemispheres. The method makes use of the Vogelsang-Franses (2005) HAC-robust trend variance estimator which is valid as long as the underlying series is trend stationary, which is the case for the data used herein. Application of the method shows that there is now a trendless interval of 19 years duration at the end of the HadCRUT4 surface temperature series, and of 16-26 years in the lower troposphere. Use of a simple AR1 trend model suggests a shorter hiatus of 14-20 years but is likely unreliable.
The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, “MBH98” hereafter... more The data set of proxies of past climate used in Mann, Bradley and Hughes (1998, “MBH98” hereafter) for the estimation of temperatures from 1400 to 1980 contains collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculation of principal components and other quality control defects. We detail these errors and defects. We then apply MBH98 methodology to the construction of a Northern Hemisphere average temperature index for the 1400–1980 period, using corrected and updated source data. The major finding is that the values in the early 15th century exceed any values in the 20th century. The particular “hockey stick” shape derived in the MBH98 proxy construction – a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 — is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal comp...
Physical, mathematical and observational grounds are employed to show that there is no physically... more Physical, mathematical and observational grounds are employed to show that there is no physically meaningful global temperature for the Earth in the context of the issue of global warming. While it is always possible to construct statistics for any given set of local temperature data, an infinite range of such statistics is mathematically permissible if physical principles provide no explicit basis for choosing among them. Distinct and equally valid statistical rules can and do show opposite trends when applied to the results of computations from physical models and real data in the atmosphere. A given temperature field can be interpreted as both "warming" and "cooling" simultaneously, making the concept of warming in the context of the issue of global warming physically ill-posed.
Uploads
Papers by Ross McKitrick