DOI: 10.5063/aa/dpennington.361.2
title: IPCC Climate Change Data: GFDL99 A2a Model: 2020 Precipitation

description: The experiments with the GFDL model used here were performed using the coupled ocean-atmosphere model described in Manabe et al. (1991) and Stouffer et al., (1994) and references therein. The model has interactive clouds and seasonally varying solar insolation. The atmospheric component has nine finite difference (sigma) levels in the vertical. This version of the model was run at a rhomboidal resolution of 15 waves (R15) yielding an equivalent resolution of about 4.5 degrees latitude by 7.5 degrees longitude. The model has global geography consistent with its computational resolution and seasonal (but not diurnal) variation of insolation. The ocean model is based on that of Byan and Lewis (1979) with a spacing between gridpoints of 4.5 degrees latitude and 3.7 degrees longitude. It has 12 unevenly spaced levels in the vertical dimension. To reduce model drift, the fluxes of heat and water are adjusted by amounts which vary seasonally and geographically, but do not change from one year to another. The model also includes a dynamic sea-ice model (Bryan, 1969) which allows the system additional degrees of freedom. The 1000-year unforced simulation used here is described in Manabe and Stouffer (1996). The drift in global-mean temperature during this unforced simulation is very small at about -0.023 degrees C per century. The two GFDL-R15 climate change experiments used here use the IS92a scenario of estimated past and future greenhouse gas (GGa1) and combined greenhouse gas and sulphate aerosol (GSa1) forcing for the period 1765-2065 (Haywood et al., 1997). For the GGa1 experiment only the 100-year segment from 1958-2057 are available through the IPCC DDC. The radiative effects of all greenhouse gases is represented in terms of an equivalent CO2 concentration, and the direct radiative sulphate aerosol forcing is parameterised in terms of specified spatially dependent surface albedo changes (following Mitchell et al., 1995). Results from these climate change experiments are discussed in Haywood et al. (1997). The model's climate sensitivity is about 3.7 degrees C.For the A2 emissions scenario the main emphasis is on a strengthening of regional and local culture, with a "return to family values" in many regions. The A2 world "consolidates" into a series of roughly continental economic regions, emphasizing local cultural roots. In some regions, increased religious participation leads many to reject a materialist path and to focus attention on contributing to the local community. Elsewhere, the trend is towards increased investment in education and science and growth in economic productivity. Social and political structures diversify, with some regions moving towards stronger welfare systems and reduced income inequality, while others move towards "lean" government. Environmental concerns are relatively weak, although some attention is paid to bringing local pollution under control and maintaining local environmental amenities. The A2 world sees more international tensions and less cooperation than in A1 or B1. People, ideas and capital are less mobile so that technology diffuses slowly. International disparities in productivity, and hence income per capita, are maintained or increased. With the emphasis on family and community life, fertility rates decline only slowly, although they vary among regions. Hence, this scenario family has high population growth (to 15 billion by 2100) with comparatively low incomes per capita relative to the A1 and B1 worlds, at US$7,200 in 2050 and US$16,000 in 2100. Technological change is rapid in some regions and slow in others as industry adjusts to local resource endowments, culture, and education levels. Regions with abundant energy and mineral resources evolve more resource intensive economies, while those poor in resources place very high priority on minimizing import dependence through technological innovation to improve resource efficiency and make use of substitute inputs. The fuel mix in different regions is determined primarily by resource availability. And divisions among regions persist in terms of their mix of technologies, with high-income but resource-poor regions shifting toward advanced post fossil technologies (renewables in regions of large land availability, nuclear in densely populated, resource poor regions) and low-income resource-rich regions generally relying on older fossil technologies. With substantial food requirements, agricultural productivity is one of the main focus areas for innovation and RD efforts in this future. Initially high levels of soil erosion and water pollution are eventually eased through the local development of more sustainable high-yield agriculture. Although attention is given to potential local and regional environmental damage, it is not uniform across regions. For example, sulfur and particulate emissions are reduced in Asia due to impacts on human health and agricultural production but increase in Africa as a result of the intensified exploitation of coal and other mineral resources. The A2 world sees high energy and carbon intensity, and correspondingly high GHG emissions. Its CO2 emissions are the highest of all four scenario families.