This paper discusses the design of efficient environmental policies in general and reviews omissions and shortcomings of the presentation of the economic dimensions of climate change in the Intergovernmental Panel on Climate Change (IPCC) Working Group III's Report: "Climate Change 1995 Economic and Social Dimensions of Climate Change: Contribution of Working Group III to the Second Assessment Report of the Intergovernmental Panel on Climate Change" (Cambridge Univ. Press, Cambridge, UK, 1996). / Includes bibliographical references (p. 15-16). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

The Terrestrial Ecosystem Model (TEM, version 4.0) was used to estimate net primary production (NPP) in China for contemporary climate and NPP responses to elevated CO₂ and climate changes projected by three atmospheric general circulation models (GCMs): Goddard Institute for Space Studies (GISS), Geophysical Fluid Dynamic Laboratory (GFDL) and Oregon State University (OSU). For contemporary climate at 312.5 ppmv CO₂, TEM estimates that China has an annual NPP of 3,653 TgC/yr (10^12 gC/yr). Temperate broadleaf evergreen forest is the most productive biome and accounts for the largest portion of annual NPP in China. The spatial pattern of NPP is closely correlated to the spatial distributions of precipitation and temperature.Annual NPP of China is sensitive to changes in CO₂ and climate. At the continental scale, annual NPP of China increases by 6.0% (219 TgC/yr) for elevated CO₂ only (519 ppmv CO₂). For climate change with no change in CO₂, the response of annual NPP ranges from a decrease of 1.5% (54.8 TgC/yr) for the GISS climate to an increase of 8.4% (306.9 TgC/yr) for the GFDL-q climate. For climate change at 519 ppmv CO₂, annual NPP of China increases substantially, ranging from 18.7% (683 TgC/yr) for the GISS climate to 23.3% (851 TgC/yr) for the GFDL-q climate. Spatially, the responses of annual NPP to changes in climate and CO₂ vary considerably within a GCM climate. Differences among the three GCM climates used in the study cause large differences in the geographical distribution of NPP responses to projected climate changes. The interaction between elevated CO₂ and climate change plays an important role in the overall response of NPP to climate change at 519 ppmv CO₂. / Includes bibliographical references (p. 14-17). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/). / Supported by the National Aeronautics and Space Administration's Earth Observing System. NAGW-2669. Supported by the Dept. of Energy's National Institute for Global Environmental Change. 901214-HAR Supported by the Joint Program on Science and Policy of Global Change at MIT. CE-S-462041

The climatological impact of increases in greenhouse gas concentrations in the atmosphere, despite being a subject of intensive study in recent years, is still very uncertain. One major uncertainty affecting possible climate change that has not received enough attention is the uncertainty in heat uptake by the deep ocean. We analyze the influence of this process and its uncertainty on climate predictions by means of numerical simulations with a 2-dimensional climate model. In the case of high climate sensitivity, as a result of uncertainty in deep ocean heat uptake, there is more than a factor of two uncertainty in the predicted increase of surface temperature. The corresponding uncertainty in the sea level rise due to thermal expansion is much larger than the uncertainty in the predicted temperature change and is significant even in the case of low climate sensitivity. / Includes bibliographical references (p. 3). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

Policies under consideration within the Climate Convention would impose CO₂ controls on only a subset of nations. A model of economic growth and emissions, coupled to an analysis of the climate system, is used to explore the consequences of a sample proposal of this type. The results show how economic burdens are likely to be distributed among nations, how carbon "leakage" may counteract the reductions attained, and how policy costs may be influenced by emissions trading. We explore the sensitivity of results to uncertainty in key underlying assumptions, including the influence on economic impacts and on the policy contribution to long-term climate goals. / Includes bibliographical references (p. 16). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

In a partial factorial model experiment, we used the Terrestrial Ecosystem Model (TEM, version 4.0) to assess the relative roles of changes in CO2, temperature, precipitation and cloudiness in equilibrium responses of primary production and carbon storage. In the experiment, we used two levels of atmospheric CO2 concentration (315 and 522 ppmv CO2), contemporary climate and changes in temperature, precipitation and cloudiness as estimated by a 3-dimensional atmospheric general circulation model (Geophysical Fluid Dynamic Laboratory-GFDL) and a 2-dimensional climate model (Land-Ocean climate model at Massachusetts Institute of Technology) for doubled CO2. The results show that elevated CO2 and projected increases in temperature account for most of the overall equilibrium responses of NPP and carbon storage to changes in climate and CO2, while the projected changes in precipitation and cloudiness contribute least. This is partly attributable to the magnitudes of changes in CO2 and climate variables as projected by the climate models. The results also show that the interactions among changes in CO2 and climate variables play a significant role in the equilibrium responses of NPP and carbon storage to changes in CO2 and climate. Of all the interaction terms, the interaction between a change in CO2 and a change in temperature is the most significant. / Includes bibliographical references (p. 21-25). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

Emissions of carbon dioxide from combustion of fossil fuels, which may contribute to long-term climate change, are projected through 2050 using reduced form models estimated with national-level panel data for the period 1950-1990. We employ a flexible form for income effects, along with fixed time and country effects, and we handle forecast uncertainty explicitly. We find an "inverse-U" relation with a within-sample peak between carbon dioxide emissions (and energy use) per capita and per captia income. Using the income and population growth assumptions of the Intergovernmental Panel on Climate Change (IPCC), we obtain projections significantly and substantially above those of the IPCC. / Includes bibliographical references (p. 25-27). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/). / Supported by the U.S. Department of Energy, the MIT Center for Energy and Environmental Policy Research, the MIT Joint Program on the Science and Policy of Global Change, and the National Science Foundation.

This paper presents the probabilistic collocation method as a computationally efficient method for performing uncertainty analysis on large complex models such as those used in global climate change research. The collocation method is explained, and then the results of its application to a box model of ocean thermohaline circulation are presented. A comparison of the results of the collocation method with a traditional Monte Carlo simulation show that the collocation method gives a better approximation for the probability density function of the model's response with less than 20 model runs as compared with a Monte Carlo simulation of 5000 model runs. / Includes bibliographical references (p. 21). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

The authors used the terrestrial ecosystem model (TEM, version 4.0) to estimate global responses of annual net primary production (NPP) and total carbon storage to changes in climate and atmospheric CO2, driven by the climate outputs from the 2-dimensional MIT L-O climate model and the 3-dimensional GISS and GFDL-q atmospheric general circulation models (GCMs). For contemporary climate with 315 ppmv CO2, TEM estimates that global NPP is 47.9 PgC/yr and global total carbon storage is 1658 PgC: 908 PgC of vegetation carbon and 750 PgC of reactive soil organic carbon. For climate change associated with a doubling of radiative forcing and an atmospheric level of 522 ppmv CO2, the responses of global NPP are +17.8% for the MIT L-O climate, +18.5% for the GFDL-q climate and +20.6% for the GISS climate. The responses of global total carbon storage are +6.9% for the MIT L-O climate, +8.3% for GFDL-q climate and +8.7% for the GISS climate. Among the three climate change predictions, the changes in latitudinal distributions of cumulative NPP and total carbon storage along 0.5o latitudinal bands vary slightly, except in high latitudes. There are generally minor differences in cumulative NPP and total carbon storage for most of the 18 biomes, except for the responses of total carbon storage in boreal biomes for the 2-D MIT L-O climate change. The results demonstrate that the linkage between the TEM and the 2-D climate model is useful for impact assessment and uncertainty analysis within an integrated assessment framework at the scales of the globe, economic regions and biomes, given the compromise between computational efficiency in the 2-D climate model and more detailed spatial representation of climate fields in 3-D GCMs. / Includes bibliographical references (p. 13-16). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

A significant number of long-term climate change simulations are to be carried out in the Integrated Framework of the MIT Global Change Joint Program. Since Global Circulation Models (GCMs) require an enormous amount of computer time, the two-dimensional statistical-dynamic model developed by Stone and Yao was chosen to be used for the initial stage of the Joint Program. At MIT, the model has been modified to make it more suitable for the purposes of the Joint Program, including developing a new scheme for a surface flux calculation. A number of simulations with the modified version of the model have been performed in which a few schemes for cloud and ocean heat transport calculation have been tested. Comparisons of the results of the present climate simulations with observational data show that the model reasonably reproduces main features of zonally averaged atmospheric circulation. A climate sensitivity produced by the model coupled with a mixed layer ocean model in response to the doubling of the atmospheric CO2 concentration lies in the range of the results obtained with GCMs. The results of the simulations with a gradual increase of the greenhouse gas concentrations in the atmosphere, in which diffusion of heat into the deep ocean was taken into account, are also similar to those obtained in the analogous simulations with GCMs. As a whole, presented results demonstrate that the modified version of the two-dimensional model can be successfully used for climate change predictions in the Integrated Framework of the Joint Program. / Includes bibliographical references (p. 13-14). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).

Achieving agreement about whether and how to control greenhouse gas emissions would be difficult enough even if the consequences were fully known. Unfortunately, choices must be made in the face of great uncertainty, about both likely climate effects and the costs of control. Because several of the greenhouse gases have residence times of decades to centuries, any economic and environmental consequences are for practical purposes irreversible on those time scales. On the other hand, the commitment of resources to emissions control also has an irreversible aspect: investment foregone leaves a permanent legacy of reduced human welfare. Neither of the extreme positions, to take urgent action now or do nothing awaiting firm evidence, is a constructive response to the climate threat. Responsible treatment of this issue leads to a difficult position somewhere in between. / Includes bibliographical references (p. 32-34). / Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).