The carbon dioxide/climate controversy: Some personal comments on two recent publications

The pervasive opinion on the relationship between the state of the climate and the increasing concentration of CO₂ is that a general global warming will occur with social, economical and environmental corollaries that may be adverse. However, there exist a number of dissenting arguments that call for a much smaller increase in global temperature or even an induced global cooling. Furthermore, the positive biological effects of a greater atmospheric CO₂ loading are emphasized.The difference of opinion is highlighted in two recent publications: CO ₂, Friend or Foe by Sherwood Idso and Carbon Dioxide: A Second Assessment by the National Academy of Science CO₂/Climate Review Committee. Using the two publications as focal points, some personal remarks are made regarding the controversy and the relative merits of the scientific arguments.     

Solar,volcanic, and CO2 forcing of recent climatic changes

The climate, as represented by the mean Northern Hemisphere temperature, has shown substantial changes within the past century. The temperature record is utilized as a means of elucidating the relative importance of anthropogenic CO₂ increase, volcanic aerosols, and possible solar insolation variations in externally forcing climate changes. Solar luminosity variations, suggested by observed solar radius variations on an ≈ 80 yr time scale, allow a self-consistent explanation of the hemispheric temperature trends. Evidence for solar influences on the climate is also found on the shorter 11 and 22 yr time scales present in solar activity cycles. The author is a staff scientist at the High Altitude Observatory, P.O. Box 3000, Boulder, CO 80307, of the National Center for Atmospheric Research. This work was completed while the author was a postdoctoral fellow in the Advanced Study Program of NCAR. Any opinions, findings and conclusions or recommendations expressed in this paper are those of the author and do not necessarily reflect the views of the National Science Foundation. The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Comments on ‘solar,volcanic and CO2 forcing of recent climatic changes’

The various limitations of a recent analysis of climatic variations in terms of solar volcanic and carbon dioxide forcing have been examined in more detail. In particular, the possibility of additional CO₂ release from forest clearing greatly increases the very large statistical uncertainties in the original analysis. While the inclusion of the various forcing terms is a highly desirable approach, the uncertainties in the data used mean that it is not appropriate to suggest that the surface warming due to the greenhouse effect has now been roughly determined.     

A robust sequential CO2 emissions strategy based on optimal control of atmospheric CO2 concentrations

This paper formally introduces the concept of mitigation as a stochastic control problem. This is illustrated by applying a digital state variable feedback control approach known as Non-Minimum State Space (NMSS) control to the problem of specifying carbon emissions to control atmospheric CO₂ concentrations in the presence of uncertainty. It is shown that the control approach naturally lends itself to integrating both anticipatory and reflexive mitigation strategies within a single unified framework. The framework explicitly considers the closed-loop nature of climate mitigation, and employs a policy orientated optimisation procedure to specify the properties of this closed-loop system. The product of this exercise is a control law that is suitably conditioned to regulate atmospheric CO₂ concentrations through assimilating online information within a 25-year review cycle framework. It is shown that the optimal control law is also robust when faced with significant levels of uncertainty about the functioning of the global carbon cycle.     

A load-based CO2 cap in the power sector

Oregon's governor has proposed a load-based cap and trade programme that limits carbon dioxide (CO₂) emissions to 10% below 1990 levels by 2020. A load-based programme is different from the source-based European Union Emissions Trading Scheme (EU ETS), as it regulates emissions sources, located outside the state, that serve Oregon's electricity load. This article describes the stakeholder process that developed the legislative proposal for the load-based cap. The Oregon Clean Energy Planning Model©, a modified capacity expansion model of annual load resource balances, is used to estimate programme costs. The net present value of the climate policy to Oregon ranges from a $518 million benefit to a $414 million cost under various load growth scenarios. Programme benefits are possible under low and medium load growth because the societal returns of energy efficiency exceed its cost over the life of the programme. CO₂ allowance prices in 2017–2020 are estimated in the medium case at approximately $21 per tonne. Low energy efficiency deployment could raise allowance costs to $36, while an aggressive efficiency programme could reduce them to $13.50. Competition for Northwest renewable resources could increase allowance prices in final phase to $37, indicating the interdependence in programme design among state climate policies.     

基于生产与消费视角的CO2环境库茨涅兹曲线的实证研究

 基于生产和消费视角,对人均GDP和单位GDP的CO₂排放之间的内在关系进行了实证分析。对1990-2004年44个国家的人均GDP与生产型和消费型的单位GDP的CO₂排放进行面板数据的单位根检验和协整分析,在此基础上,对CO₂环境库茨涅兹曲线（EKC）进行模拟。结果显示：无论是从生产视角还是从消费视角,单位GDP的CO₂排放量都具有显著的倒"U"形状,符合环境库茨涅兹曲线特征。但对于多数发展中国家,消费型单位GDP的CO₂排放量总是低于生产型单位GDP的CO₂排放量,表明多数发展中国家在国际贸易中存在着内涵CO₂排放的净出口,这对从生产角度核算国家温室气体排放体系提出了挑战。最后,分析了CO₂环境库茨涅兹曲线对中国应对气候变化的启示。     

Effect of increasing CO2 on the stratospheric level of CO and O3

Production and destruction processes of carbon monoxide (CO) and ozone (O3) are examined in the light of increasing amount of atmospheric carbon dioxide (CO2). It is found that doubling of CO2 will increase the stratospheric concentration of CO and will have positive effect on O3 concentration.     

A Method for Estimating the Cost of CO2 Mitigation through Afforestation

The Kyoto Protocol allows Annex I countries to use afforestation (theconversion of non-forest landto forest) to meet emissions reduction targets. We present a new method forestimating the cost of CO₂mitigation through afforestation based on econometric models of land use. Landuse models are developed from dataon observed land allocation decisions and quantify the relationship betweenthe share of land in forest and the netreturns to forestry, among other land use determinants. The econometricapproach measures the actual responsesby landowners to observed changes in net returns, in contrast to earlierstudies in which landowner responses aredictated by the researcher. Models are estimated for Maine, South Carolina,and Wisconsin. The estimated modelsare used to simulate subsidies for afforestation, which imply increases inforest area and net reductions inatmospheric CO₂ concentrations. Average cost measures – totalsubsidies divided by total carbon sequestered –are derived for afforestation programs with and without timber harvesting. Theuse of econometric land use modelsin integrated assessments of climate change is explored. We model the effectson land use patterns and the costsof CO₂ mitigation of changes in the net returns to agricultureinduced by climate change.