Health and Environment: Human Impact on Climate Change and Human Health

The Second Assessment of the Intergovernmental Panel on Climate Change has just completed its final review as the member governments throughout the World approve the Policy Maker's Summaries for the three Working Groups. These assessments represent the current "state of knowledge" about the effects of human impacts on the global climate system.

The Science Assessment will report on the state of knowledge about the projected effects of emissions of greenhouse gases, aerosols and clouds on future climate changes. The Impacts, Mitigation and Adaptation assessment reviews how sources and sinks of greenhouse gases can be managed to reduce or offset emissions or technologies to adapt to climate change. The Economic Assessment, reviews the state of knowledge about effects of sociocultural changes and costs and benefits of mitigation and adaptation.

There are several sectors associated with the emission of greenhouse gases. These include energy production, energy demand, transportation, human communities, and agriculture and forestry. This brief overview, stemming from the Working Group II meeting in Montreal, Quebec, focuses on the sectors associated with the agricultural and forest industries. It is important to recognize that this includes more than just primary production. It includes the manufacture and delivery of goods and services; the systems of commodity production; and the storage, processing, transportation and marketing of the commodities.

The primary concern is on emissions of greenhouse gases from and the effects of climate changes on agriculture and forestry sectors. Policies will need to focus on mitigating the atmospheric composition of the greenhouse gases, that is to reduce emissions as well as to reduce the quantities in the atmosphere. Since the agricultural and forest sectors have the only economically feasible means for sequestering carbon at this time, implementing near term policy options are likely to receive positive consideration. Policy options, however, will also need to focus on adapting agriculture and forestry to climate change. The primary reason is that there will be a need to adapt to a future global atmospheric warming., short of implementing draconian measures - like an immediate decrease of over 60% in global emissions - which may be technically but not socially or economically feasible at this time.

The Science Assessment Report points out that greenhouse gas concentrations are still increasing. These increases will lead to a positive radiative forcing of climate, tending to warm the surface and to produce other climate changes. These trends can be attributed largely to human activities, mostly fossil fuel use and land use conversions between agriculture and forestry.

· The atmospheric concentration of carbon dioxide, methane, and nitrous oxide have grown significantly since pre-industrial times: by about 30%, 145% and 15% respectively.

· The growth rates of carbon dioxide, CH₄ and N₂O experienced large anomalous reductions in the late 1980s and early 1990s. Current data indicate that growth rates have returned to those resembling the long-term trends.

Many greenhouse gases remain in the atmosphere for a long time (for carbon dioxide and N₂O, many decades to centuries), hence they affect radiative forcing on long time-scales. Compared to human life spans the resulting radiative forcing from the long-lived gases will persist for long periods.

· If carbon dioxide emissions were maintained at or near today's levels, they would lead to a nearly constant rate of increase in atmospheric concentrations for at least two centuries, reaching about 500 ppmv (approaching twice the pre-industrial concentration of 280 ppmv) by the end of the 21st century.

· A stable level of carbon dioxide concentration at values up to 1000 ppmv could be maintained only with anthropogenic emissions that eventually drop below 1990 levels.

· To a first approximation the eventual stabilized concentration is governed more by the accumulated anthropogenic carbon dioxide emissions from now until the time of stabilization, and less by the exact path taken to reach stabilization. This means that, for a given stabilization scenario, - higher emissions in early decades imply lower emissions later on.

New information has now emerged regarding other anthropogenic factors that affect radiative forcing:

· Tropospheric aerosols (microscopic airborne particles) resulting from the combustion of fossil fuels, smelting, and biomass burning give rise to a negative radiative forcing over particular regions.

· The estimated net contribution of chloroflurocarbons to radiative forcing, while still positive, is less than originally believed because of the depletion of stratospheric ozone by the CFCs. Further, the growth rates of CFC concentrations have slowed to about zero and concentrations will start to decrease through implementation of the Montreal Protocol and its Amendments.

Climate has changed over the past century. At any one location, year-to-year variations in weather can be large, but analyses of meteorological and other data over large areas and over periods of decades or more have provided evidence for supporting some important changes.

· Global mean surface temperature has increased by between about 0.3 and 0.6°C since the late 19th century; the additional data available since 1990 and the re-analyses since then have not significantly changed this range of estimated increase.

· Recent years have been among the warmest since I860, the period of instrumental record.

· Night-time temperatures have generally increased more than daytime temperatures.

· Despite the cooling effect of the Mt. Pinatubo volcanic eruption, the years since 1990 have been some of the warmest in the instrumental record, as were many of the years in the 1980s.

· The limited available evidence suggests that 20th century global mean temperature is at least as warm as any other century since at least 1400 AD. Data prior to 1400 are too sparse to allow reliable estimates of global mean temperature.

· Global mean sea level has risen by between 10 and 25 cm over the past 100 years and it is likely that much of the rise has been related to the concurrent rise in global temperature.

Although it is not known whether climatic variability or the frequency of extreme events have increased or decreased over the 20th century on a world-wide scale, there have been significant changes in certain regions:

· The behavior of the El Nino-Southern Oscillation has been unusual since 1989.

· Antarctica has calved an iceberg half the size of Laborador this year, which is now free floating.

For the mid-range IPCC emission scenarios, models project an increase in global mean surface temperature, relative to the present, of 2°C by 2100 with the lowest estimate projecting a 1°C rise. A corresponding projection for the highest emissions scenario would lead to a warming of 3.5°C.

In all cases the average rate of warming would probably be greater than any seen in the last 10,000 years.

Sea level is projected to rise as a result of thermal expansion of oceans and melting of polar ice. For the mid-range scenario, models project a rise in sea level of about 50 cm by 2100 with the lowest estimate projecting a 15 cm rise by 2100. Sea level could continue to rise in the future centuries beyond 2100 even if concentrations of greenhouse gases were stabilized by that time.

Impending Impact of Erosion of Ozone Layer: New Estimates

Satellite measurements, taking cloud cover into account, predict ozone erosion will make increased UV radiation a peril in the lighter bands within the next 30 years. Lightest areas have already been affected.

SOURCE: New York Times, 11/21/95

Options To Reduce Emissions and Enhance The Sinks of Greenhouse Gases

Human activities are directly increasing atmospheric concentrations of several greenhouse gases. Significant reductions in net greenhouse gas emissions are technically possible and can be economically feasible. These reductions can be achieved by utilizing an extensive array of technologies, and policy measures that accelerate technology development, diffusion, and transfer in all sectors, including the energy, industry, transportation, residential/commercial, and agricultural/forestry sectors.

By 2100, the world's commercial energy system will in effect be replaced at least twice, offering opportunities to change the energy system without premature retirement of capital stock. Significant amounts of capital stock in the industrial, commercial, residential, and agricultural/forestry sectors will also be replaced. These cycles of capital replacement provide opportunities to utilize new, better performing technologies.

Energy Demand

Global energy demand has grown at an average annual rate of approximately 2% for almost two centuries, although energy demand growth varies considerably over time and between different regions. In the published literature, different methods and conventions are used to characterize energy consumption. However, based on aggregated national energy balances, 385 exajoules of primary energy was used in the world in 1990, resulting in the release of 6.0 Gt of carbon as carbon dioxide. Of this 279 exajoules were delivered to end users accounting for 3.7 Gt of carbon emissions as carbon dioxide at the point of consumption. The remaining 106 exajoules were used in energy conversion and distribution, accounting for 2.3 Gt of carbon emissions as carbon dioxide.

In 1990, the three largest sectors of energy consumption were industry - (43% of carbon dioxide releases, including energy conversion), residential/commercial buildings (28%) and transport (22%) with agriculture, forestry and other sectors accounting for 7%. Of these, transport sector energy use and related carbon dioxide emissions have been the most rapidly growing over the past two decades.

Numerous studies have indicated that 10-30% energy efficiency gains above present levels are feasible at little or not net cost in many parts of the world through technical conversion measures and improved management practices of the next two to three decades. Using technologies that presently yield the highest output of energy services for a given input of energy, efficiency gains for 50-60% would be technically feasible in many countries over the same time period. Achieving these potentials will depend on future cost reductions, financing and technology transfer, as well as measures to overcome a variety of non-technical barriers. Because energy use is growing world-wide, even replacing current technology with more-efficient technology could still lead to an absolute increase of carbon dioxide in the future.

In the industrial sector energy use in 1990 was estimated to be 98-117 exajoules. Without new greenhouse gas mitigation, this might grow to 140-242 exajoules in 2025. Countries differ widely in their current industrial energy-use and in the transportation sector, energy use in 1990 was estimated to be 61-65 exajoules. Without new greenhouse gas mitigation measures, this might grow to 90-140 exajoules in 2025. This could be reduced to 60-100 exajoules through the adoption of vehicles using very efficient drive-trains, light-weight construction and low-air-resistance design, without compromising comfort and performance. Further energy use reductions are possible through the use of smaller vehicles; altered land-use patterns, transport systems, mobility patterns and lifestyles; and shifting to less energy intensive transport modes. Greenhouse gas emissions per unit of energy used could be reduced through the use of alternative fuels and fuel cells and electricity from renewable sources.

The removal and storage of carbon dioxide from fossil fuel power-station stack gases is feasible but reduces the conversion efficiency and significantly increases the production cost of electricity. Another approach to decarbonization uses fossil fuel feedstock to make hydrogen rich fuels. The future availability of conversion technologies such as fuel cells that can efficiently use hydrogen would increase the relative attractiveness of the latter approach. Both approaches generate a by-product stream of carbon dioxide that can be stored, for example, in depleted natural gas fields. Alternative hydrogen sources which are highly attractive result from agricultural sources of generated methane or access to an hydrous ammonia.

Forest ecosystem models project that a sustained increase in the global mean temperature of 1°C is sufficient to cause changes in regional climates that will affect the growth and regeneration capacity of forests in many regions. In several instances this will alter the organization and composition of forests. Possible changes in temperature and water availability under doubled equivalent-carbon dioxide equilibrium conditions are projected to affect a substantial faction of the existing forested area of the world, primarily in the temperate and boreal regions. The regional changes are likely to entail broad vegetation type changed with shifting canopy and understory dominance. Climate change is expected to occur at a rapid rate relative to the speed at which forest species grow, reproduce, and reestablish themselves. For mid-latitude regions a global average warming of 1-3.5°C over the next 100 years would be equivalent to a poleward shift of the present isotherms by approximately 200-400 km or an altitude shift of about 300-500 meters. This compares to some past tree species migration that are believed to be in the order of 4-200 meters per century. Therefore, species composition of forests is likely to change. Given the ecologic amplitude and genetic plasticity of species, new assemblages of species and thus new ecosystem composition may be established.

Although net primary productivity could increase, the total standing biomass of forests may not, because of more frequent outbreaks and extended ranges of pests and pathogens, and increasing frequency and intensity of fires. Large pulses of carbon could be released into the atmosphere during transition from one forest type to another due to fire and mortality of existing canopy. There would, however, be subsequent rapid uptake of carbon as new species take over a community and dominate the canopy.

In tropical rangelands, mean temperature increases should not lead to major alterations in productivity and species composition, but rainfall amount and seasonality and increased evapotranspiration will cause such changes. Increases in atmospheric carbon dioxide concentrations may raise the carbon to nitrogen ratio of forage for herbivores, thus reducing its food value. Shifts in temperature and precipitation in temperate rangelands may result in altered growing seasons and boundary shifts between grasslands, forests, and shrublands.

Crop yields and changes in productivity due to climate change will vary considerably across regions and among localities, thus changing the patterns of production. Productivity is projected to increase in some areas and decrease in others, especially the tropics and subtropics. However, existing studies show that on the whole, global agricultural production could be maintained relative to baseline production in the face of climate change modeled by general circulation models it doubled equivalent carbon dioxide equilibrium. Regional effects would vary widely. This conclusion takes into account the beneficial effects of carbon dioxide fertilization but does not allow for changes in agriculture and the possible effects of changing climatic variability.

Focusing on global agricultural production does not address the potentially serious consequences of large differences at local and regional scales, even at mid-latitudes. There may be increased risk of hunger and famine in some locations; many for the world's poorest people - particularly those living in subtropical and tropical areas and dependent on isolated agricultural systems in semi-arid and arid regions - are most at risk of increased hunger. Many of these at-risk populations are found in Sub-Saharan Africa; South, East and Southeast Asia; and tropical areas of Latin America, as well as some Pacific Island nations.

Adaptation - such as changes in crops and crop varieties, improved water management and irrigation systems, and changes in planting schedules and tillage practices - will be important in limiting negative effects and taking advantage of beneficial changes in climate. The extent of adaptation depends on the affordability of such measures, particularly in developing countries; access to know-how and technology; the rate of climate changes; and biophysical constraints such as water availability, soil characteristics, and crop genetics. The incremental costs of adaptation strategies would create a serious burden for developing countries; adaptation strategies may result in cost savings for some countries. There are significant uncertainties about the capacity of different regions to adapt successfully to projected climate change.

SOURCE: Gary R. Evans, Special Assistant/Global Change Issues, USDA, Washington, D.C., USA