Tropical Forests in a Co2-Rich World

Tropical forests resemble, besides their enormous genetic diversity, the single largest biomass carbon pool in the world. Only a small annual increase of this pool could trap the current surplus of atmospheric CO₂. The fact that this is not happening already today (after the world has seen a 27% increase in atmospheric CO₂ in only 150 years) sets the boundaries of the likely trends to be expected in the future. In contrast to the possibly small overall responses of the tropical forest carbon pool, individual plant responses to CO₂ enrichment will be significant. Since species and their genotypes will not respond in identical ways, selective processes will be induced which will lead to new community structures and alterations of numerous plant-plant, plant-animal and plant-microbe interactions. Examples are provided for such subtile CO₂ effects, measured both in the greenhouse and in the field. From what is known currently it is concluded that in closed humid tropical forests leaf area index is unlikely to increase, mineral nutrient and water demand may (at least temporarily) become reduced, and leaf tissue quality plus associated consumer behavior will be altered. The big unknown is the behavior of tropical soils and their microflora and fauna. There is a realistic possibility that carbon turnover will be increased in tropical forests in a CO₂-enriched world, which would have substantial implications for nutrient cycling.     

Sensitivity of terrestrial carbon storage to CO2-induced climate change: Comparison of four scenarios based on general circulation models

The potential impacts of CO₂-induced climate change on terrestrial carbon storage was estimated using the Holdridge Life-Zone Classification and four climate change scenarios derived from general circulation models. Carbon values were assigned to life-zones and their associated soils from published studies. All four scenarios suggest an increase in area occupied by forests although details of predicted patterns vary among the scenarios. There is a poleward shift of the forested zones, with an increase in the areal extent of tropical forests and a shift of the boreal forest zone into the region currently occupied by tundra. Terrestrial carbon storage increased from 0.4% (8.5 Gt) to 9.5% (180.5 Gt) above estimates for present conditions. These changes represent a potential reduction of 4 to 85 ppm on elevated atmospheric CO₂ levels.     

Effects of Climate Change on Carbon Storage in Boreal Forests of China: A Local Perspective

The BIOME3 model was used to simulate the distribution patterns and carbon storage of the horizontal, zonal boreal forests in northeast and northwest China using a mapping system for vegetation patterns combined with carbon density estimates from vegetation and soils. The BIOME3 prediction is in reasonable good agreement with the potential distribution of Chinese boreal forests. The effects of changing atmospheric CO₂ concentration had a nonlinear effect on boreal forest distribution, with 3.5–10.8% reduced areas for both increasing and decreasing CO₂. In contrast, the increased climate together with and without changing CO₂ concentration showed dramatic changes in geographic patterns, with 70% reduction in area and disappearance of almost boreal forests in northeast China. The baseline carbon storage in boreal forests of China is 4.60 PgC (median estimate) based on the vegetation area of actual boreal forest distribution. If taking the large area of agricultural crops into account, the median value of potential carbon storage is 6.92 PgC. The increasing (340–500 ppmv) and decreasing CO₂ concentration (340–200 ppmv) led to decrease of carbon storage, 0.33 PgC and 1.01 PgC respectively compared to BIOME3 potential prediction under present climate and CO₂ conditions. Both climate change alone and climate change with CO₂ enrichment (340–500 ppmv) reduced largely the carbon stored in vegetation and soils by ca. 6.5 PgC. The effect of climate change is more significant than the direct physiological effect of CO₂ concentration on the boreal forests of China, showing a large reduction in both distribution area and carbon storage.     

Respiration of Recently-Fixed Plant Carbon Dominates Mid-Winter Ecosystem CO2 Production in Sub-Arctic Heath Tundra

Arctic ecosystems could provide a substantial positive feedback to global climate change if warming stimulates below-ground CO₂ release by enhancing decomposition of bulk soil organic matter reserves.Ecosystem respiration during winter is important in this context because CO₂ release from snow-covered tundra soils is a substantial component of annual net carbon (C) balance, and because global climate models predict that the most rapid rises in regional air temperature will occur in the Arctic during winter. In this manipulative field study, the relative contributions of plant and bulk soil organic matter C pools to ecosystem CO₂ production in mid-winter were investigated. We measured CO₂ efflux rates in Swedish sub-arctic heath tundra from control plots and from plots that had been clipped in the previous growing season to disrupt plant activity. Respiration derived from recently-fixed plant C (i.e., plant respiration, and respiration associated with rhizosphere exudates and decomposition of fresh litter) was the principal source of CO₂ efflux, while respiration associated with decomposition of bulk soil organic matter was low, and appeared relatively insensitive to temperature. These results suggest that warmer mid-winter temperatures in the Arctic may have a much greater impact on the cycling of recently-fixed, plant-associated C pools than on the depletion of tundra bulk soil C reserves, and consequently that there is a low potential for significant initial feedbacks from arctic ecosystems to climate change during mid-winter.     

Modeling responses of the meadow steppe dominated by Leymus chinensis to climate change

Grassland is one of the most widespread vegetation types worldwide and plays a significant role in regional climate and global carbon cycling. Understanding the sensitivity of Chinese grassland ecosystems to climate change and elevated atmospheric CO₂ and the effect of these changes on the grassland ecosystems is a key issue in global carbon cycling. China encompasses vast grassland areas of 354 million ha of 17 major grassland types, according to a national grassland survey. In this study, a process-based terrestrial model the CENTURY model was used to simulate potential changes in net primary productivity (NPP) and soil organic carbon (SOC) of the Leymus chinensis meadow steppe (LCMS) under different scenarios of climatic change and elevated atmospheric CO₂. The LCMS sensitivities, its potential responses to climate change, and the change in capacity of carbon stock and sequestration in the future are evaluated. The results showed that the LCMS NPP and SOC are sensitive to climatic change and elevated CO₂. In the next 100 years, with doubled CO₂ concentration, if temperature increases from 2.7-3.9˚C and precipitation increases by 10% NPP and SOC will increase by 7-21% and 5-6% respectively. However, if temperature increases by 7.5-7.8˚C and precipitation increases by only 10% NPP and SOC would decrease by 24% and 8% respectively. Therefore, changes in the NPP and SOC of the meadow steppe are attributed mainly to the amount of temperature and precipitation change and the atmospheric CO₂ concentration in the future.     

Tropical Forests in a Future Climate: Changes in Biological Diversity and Impact on the Global Carbon Cycle

Tropical forest ecosystems are large stores of carbon which supply millions of people with life support requirements. Currently tropical forests are undergoing massive deforestation. Here, I address the possible impact of global change conditions, including elevated CO₂, temperature rise, and nitrogen deposition on forest structure and dynamics. Tropical forests may be particularly susceptible to climate change for the following reasons: (1) Phenological events (such as flowering and fruiting) are highly tuned to climatic conditions. Thus a small change in climate can have a major impact on the forest, its biological diversity and its role in the carbon cycle. (2) There are strong coevolutionary interactions, such as pollination seed dispersal, with a high degree of specialization, i.e., only certain animals can effect these activities for certain species. Global change can decouple these tight coevolutionary interactions. (3) Because of high species diversity per unit area, species of the tropical rain forest must have narrow niches. Thus changes in global climate can eliminate species and therefore reduce biological diversity. (4) Deforestation and other forms of disturbance may have significant feedback on hydrology both regionally and globally. The predicted decline in the rainfall in the Amazon Basin and the intensification of the Indian monsoon can have a large effect on water availability and floods which are already devastating low-lying areas. It is concluded that tropical forests may be very sensitive to climate change. Under climatic change conditions their structure and function may greatly change, their integrity may be violated and their services to people may be greatly modified. Because they are large stores of great biological diversity, they require immediate study before it is too late. The study requires the collaboration of scientists with a wide range of backgrounds and experiences including biologists, climate modellers, atmospheric scientists, economists, human demographers and sociologists in order to carry out holistic and urgently needed work. Global climatic change brings a great challenge to science and to policy makers.     

Simulated changes in vegetation distribution, land carbon storage, and atmospheric CO2 in response to a collapse of the North Atlantic thermohaline circulation

It is investigated how abrupt changes in the North Atlantic (NA) thermohaline circulation (THC) affect the terrestrial carbon cycle. The Lund–Potsdam–Jena Dynamic Global Vegetation Model is forced with climate perturbations from glacial freshwater experiments with the ECBILT-CLIO ocean–atmosphere–sea ice model. A reorganisation of the marine carbon cycle is not addressed. Modelled NA THC collapses and recovers after about a millennium in response to prescribed freshwater forcing. The initial cooling of several Kelvin over Eurasia causes a reduction of extant boreal and temperate forests and a decrease in carbon storage in high northern latitudes, whereas improved growing conditions and slower soil decomposition rates lead to enhanced storage in mid-latitudes. The magnitude and evolution of global terrestrial carbon storage in response to abrupt THC changes depends sensitively on the initial climate conditions. These were varied using results from time slice simulations with the Hadley Centre model HadSM3 for different periods over the past 21 kyr. Changes in terrestrial storage vary between −67 and +50 PgC for the range of experiments with different initial conditions. Simulated peak-to-peak differences in atmospheric CO₂ are 6 and 13 ppmv for glacial and late Holocene conditions. Simulated changes in δ¹³C are between 0.15 and 0.25‰. These simulated carbon storage anomalies during a NA THC collapse depend on their magnitude on the CO₂ fertilisation feedback mechanism. The CO₂ changes simulated for glacial conditions are compatible with available evidence from marine studies and the ice core CO₂ record. The latter shows multi-millennial CO₂ variations of up to 20 ppmv broadly in parallel with the Antarctic warm events A1 to A4 in the South and cooling in the North.     

Boreal forest and tundra ecosystems as components of the climate system

The effects of terrestrial ecosystems on the climate system have received most attention in the tropics, where extensive deforestation and burning has altered atmospheric chemistry and land surface climatology. In this paper we examine the biophysical and biogeochemical effects of boreal forest and tundra ecosystems on atmospheric processes. Boreal forests and tundra have an important role in the global budgets of atmospheric CO₂ and CH₄. However, these biogeochemical interactions are climatically important only at long temporal scales, when terrestrial vegetation undergoes large geographic redistribution in response to climate change. In contrast, by masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests have a significant impact on the seasonal and annual climatology of much of the Northern Hemisphere. Experiments with the LSX land surface model and the GENESIS climate model show that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all times of the year compared to simulations in which the boreal forest is replaced with bare ground or tundra. These effects are greatest in arctic and sub-arctic regions, but extend to the tropics. This paper shows that land-atmosphere interactions are especially important in arctic and sub-arctic regions, resulting in a coupled system in which the geographic distribution of vegetation affects climate and vice versa. This coupling is most important over long time periods, when changes in the abundance and distribution of boreal forest and tundra ecosystems in response to climatic change influence climate through their carbon storage, albedo, and hydrologic feedbacks.     

Assessment of Major Pools and Fluxes of Carbon in Indian Forests

The major pools including phytomass, soil, litter, and fluxes of carbon (C)due to litterfall and landuse changes were estimated for Indian forests. Basedon growing stock-volume approach at the state and district levels, the Indianforest phytomass was estimated in the range of 3.8–4.3 PgC. The totalsoil organic pool in the top 1m depth was estimated as 6.8 PgC, usingestimated soil organic carbon densities and Remote Sensing (RS) based area byforest types. Based on 122 published Indian studies and RS-based forest area,the total litterfall carbon flux was estimated as 208.8 MgCha^–1 yr^–1.The cumulative net carbon flux (1880–1996) from Indian forests(1880–1996) due to landuse changes (deforestation, afforestation andphytomass degradation) was estimated as 5.4 PgC, using a simple book-keepingapproach. The mean annual net C flux due to landuse changes during1985–1996 was estimated as 9.0 TgC yr^–1. For the recentperiod, the Indian forests are nationally a small source with some regionsacting as small sinks of carbon as well. The improved quantification of poolsand fluxes related to forest carbon cycle is important for understanding thecontribution of Indian forests to net carbon emissions as well as theirpotential for carbon sequestration in the context of the Kyoto protocol.     

An estimate of equilibrium sensitivity of global terrestrial carbon cycle using NCAR CCSM4

Increasing concentrations of atmospheric CO₂ influence climate, terrestrial biosphere productivity and ecosystem carbon storage through its radiative, physiological and fertilization effects. In this paper, we quantify these effects for a doubling of CO₂ using a low resolution configuration of the coupled model NCAR CCSM4. In contrast to previous coupled climate-carbon modeling studies, we focus on the near-equilibrium response of the terrestrial carbon cycle. For a doubling of CO₂, the radiative effect on the physical climate system causes global mean surface air temperature to increase by 2.14 K, whereas the physiological and fertilization on the land biosphere effects cause a warming of 0.22 K, suggesting that these later effects increase global warming by about 10 % as found in many recent studies. The CO₂-fertilization leads to total ecosystem carbon gain of 371 Gt-C (28 %) while the radiative effect causes a loss of 131 Gt-C (~10 %) indicating that climate warming damps the fertilization-induced carbon uptake over land. Our model-based estimate for the maximum potential terrestrial carbon uptake resulting from a doubling of atmospheric CO₂ concentration (285–570 ppm) is only 242 Gt-C. This highlights the limited storage capacity of the terrestrial carbon reservoir. We also find that the terrestrial carbon storage sensitivity to changes in CO₂ and temperature have been estimated to be lower in previous transient simulations because of lags in the climate-carbon system. Our model simulations indicate that the time scale of terrestrial carbon cycle response is greater than 500 years for CO₂-fertilization and about 200 years for temperature perturbations. We also find that dynamic changes in vegetation amplify the terrestrial carbon storage sensitivity relative to a static vegetation case: because of changes in tree cover, changes in total ecosystem carbon for CO₂-direct and climate effects are amplified by 88 and 72 %, respectively, in simulations with dynamic vegetation when compared to static vegetation simulations.     

Annual CO2 Flux in Dry and Moist Arctic Tundra: Field Responses to Increases in Summer Temperatures and Winter Snow Depth

We examined the annual exchange of CO₂ between the atmosphere and moist tussock and dry heath tundra ecosystems (which together account for over one-third of the low arctic land area) under ambient field conditions and under increased winter snow deposition, increased summer temperatures, or both. Our results indicate that these two arctic tundra ecosystems were net annual sources of CO₂ to the atmosphere from September 1994 to September 1996 under ambient weather conditions and under our three climate change scenarios. Carbon was lost from these ecosystems in both winter and summer, although the majority of CO₂ evolution took place during the short summer. Our results indicate that (1) warmer summer temperatures will increase annual CO₂ efflux from both moist and dry tundra ecosystems by 45–55% compared to current ambient temperatures; (2) deeper winter snow cover will increase winter CO₂ efflux in both moist and dry tundra ecosystems, but will decrease net summer CO₂ efflux; and (3) deeper winter snow cover coupled with warmer summer temperatures will nearly double the annual amount of CO₂ emitted from moist tundra and will result in a 24% increase in the annual CO₂ efflux of dry tundra. If, as predicted, climate change alters both winter snow deposition and summer temperatures, then shifts in CO₂ exchange between the biosphere and atmosphere will likely not be uniform across the Arctic tundra landscape. Increased snow deposition in dry tundra is likely to have a larger effect on annual CO₂ flux than warmer summer temperatures alone or warmer temperatures coupled with increased winter snow depth. The combined effects of increased summer temperatures and winter snow deposition on annual CO₂ flux in moist tundra will be much larger than the effects of either climate change scenario alone.     

Sensitivity of carbon budget to historical climate variability and atmospheric CO2 concentration in temperate grassland ecosystems in China

Chinese temperate grasslands play an important role in the terrestrial carbon cycle. Based on the parameterization and validation of Terrestrial Ecosystem Model (TEM, Version 5.0), we analyzed the carbon budgets of Chinese temperate grasslands and their responses to historical atmospheric CO₂ concentration and climate variability during 1951–2007. The results indicated that Chinese temperate grassland acted as a slight carbon sink with annual mean value of 7.3 T?g C, ranging from -80.5 to 79.6 T?g C yr^-1. Our sensitivity experiments further revealed that precipitation variability was the primary factor for decreasing carbon storage. CO₂ fertilization may increase the carbon storage (1.4 %) but cannot offset the proportion caused by climate variability (-15.3 %). Impacts of CO₂ concentration, temperature and precipitation variability on Chinese temperate grassland cannot be simply explained by the sum of the individual effects. Interactions among them increased total carbon storage of 56.6 T?g C which 14.2 T?g C was stored in vegetation and 42.4 T?g C was stored in soil. Besides, different grassland types had different responses to climate change and CO₂ concentration. NPP and R_H of the desert and forest steppes were more sensitive to precipitation variability than temperature variability while the typical steppe responded to temperature variability more sensitively than the desert and forest steppes.     

Climate-related uncertainties in projections of the twenty-first century terrestrial carbon budget: off-line model experiments using IPCC greenhouse-gas scenarios and AOGCM climate projections

A terrestrial ecosystem model (Sim-CYCLE) was driven by multiple climate projections to investigate uncertainties in predicting the interactions between global environmental change and the terrestrial carbon cycle. Sim-CYCLE has a spatial resolution of 0.5°, and mechanistically evaluates photosynthetic and respiratory CO₂ exchange. Six scenarios for atmospheric-CO₂ concentrations in the twenty-first century, proposed by the Intergovernmental Panel on Climate Change, were considered. For each scenario, climate projections by a coupled atmosphere–ocean general circulation model (AOGCM) were used to assess the uncertainty due to socio-economic predictions. Under a single CO₂ scenario, climate projections with seven AOGCMs were used to investigate the uncertainty stemming from uncertainty in the climate simulations. Increases in global photosynthesis and carbon storage differed considerably among scenarios, ranging from 23 to 37% and from 24 to 81 Pg C, respectively. Among the AOGCM projections, increases ranged from 26 to 33% and from 48 to 289 Pg C, respectively. There were regional heterogeneities in both climatic change and carbon budget response, and different carbon-cycle components often responded differently to a given environmental change. Photosynthetic CO₂ fixation was more sensitive to atmospheric CO₂, whereas soil carbon storage was more sensitive to temperature. Consequently, uncertainties in the CO₂ scenarios and climatic projections may create additional uncertainties in projecting atmospheric-CO₂ concentrations and climates through the interactive feedbacks between the atmosphere and the terrestrial ecosystem.     

The Potential Response of Terrestrial Carbon Storage to Changes in Climate and Atmospheric CO2

We use a georeferenced model of ecosystem carbon dynamics to explore the sensitivity of global terrestrial carbon storage to changes in atmospheric CO₂ and climate. We model changes in ecosystem carbon density, but we do not model shifts in vegetation type. A model of annual NPP is coupled with a model of carbon allocation in vegetation and a model of decomposition and soil carbon dynamics. NPP is a function of climate and atmospheric CO₂ concentration. The CO₂ response is derived from a biochemical model of photosynthesis. With no change in climate, a doubling of atmospheric CO₂ from 280 ppm to 560 ppm enhances equilibrium global NPP by 16.9%; equilibrium global terrestrial ecosystem carbon (TEC) increases by 14.9%. Simulations with no change in atmospheric CO₂ concentration but changes in climate from five atmospheric general circulation models yield increases in global NPP of 10.0–14.8%. The changes in NPP are very nearly balanced by changes in decomposition, and the resulting changes in TEC range from an increase of 1.1% to a decrease of 1.1%. These results are similar to those from analyses using bioclimatic biome models that simulate shifts in ecosystem distribution but do not model changes in carbon density within vegetation types. With changes in both climate and a doubling of atmospheric CO₂, our model generates increases in NPP of 30.2–36.5%. The increases in NPP and litter inputs to the soil more than compensate for any climate stimulation of decomposition and lead to increases in global TEC of 15.4–18.2%.     

Tropical Forests Under the Climates of the Last 30,000 Years

Vegetational history can help us to predict future environments by providing data for testing AGCMs, for indicating the vegetational response to rapid warming and changing CO₂ concentrations, and for mathematical modelling of vegetation. Most of the data are palynological, and there are well over 100 pollen diagrams from tropical regions. Maps are presented showing summarized pollen diagrams from the lowlands of South-East Asia and the West Pacific, Tropical Latin America and Tropical Africa. In all these regions there is some evidence suggesting that at the LGM lowland forests were somewhat restricted in area and included montane elements. This is consistent with cooler and drier climate at the LGM. From the montane and lowland areas of these three regions, the pollen evidence is summarized in altitudinal diagrams. These suggest considerable depression of altitudinal zones at the LGM, suggesting temperatures c. 5–10°C cooler than now. These results conflict with earlier oxygen isotope data from marine foraminifera, but do not conflict with more recent oxygen isotope measurements from tropical corals. It is also suggested that altitudinal movements may be partly controlled by CO₂ concentration and ultraviolet light.     

Changes in Heat Index Associated with CO2-Induced Global Warming

Changes in Heat Index (a combined measure of temperature and humidity) associated with global warming are evaluated based on the output from four extended integrations of the GFDL coupled ocean-atmosphere climate model. The four integrations are: a control with constant levels of atmospheric carbon dioxide (CO₂), a second integration in which an estimate of the combined radiative forcing of greenhouse gases and sulfate aerosols over the period 1765–2065 is used to force the model, and a third (fourth) integration in which atmospheric CO₂$ increases at the rate of 1% per year to double (quadruple) its initial value, and is held constant thereafter. While the spatial patterns of the changes in Heat Index are largely determined by the changes in surface air temperature, increases in atmospheric moisture can substantially amplify the changes in Heat Index over regions which are warm and humid in the Control integration. The regions most prone to this effect include humid regions of the Tropics and summer hemisphere extra-tropics, including the southeastern United States, India, southeast Asia and northern Australia.     

The warming of the industrialized middle latitudes 1985–2050: Causes and consequences

The dominant influence on global climate for the indefinite future is expected to be a warming in the middle and high latitudes of both hemispheres. The speed of the warming is uncertain. The warming in winter may exceed 1.0 degree per decade. The warming in summer is expected to be less. The cause is the accumulation of infra-red absorptive gases, especially CO₂ and CH₄, in the atmosphere. The sources are the combustion of fossil fuels, the destruction of forests and their soils, and, possibly, the warming itself, which can be expected to stimulate decay of organic matter in soils. The warming in these latitudes is expected to be accompanied by increased precipitation as climatic zones migrate generally poleward. A 1 °C change in mean temperature is equivalent to a change in latitude of 100–150 km. The changes expected are rapid enough to exceed the capacity of forests to migrate or otherwise adapt. Forest trees will die at their warmer and drier limits of distribution more rapidly than forests can be regenerated in regions where climates become favorable. The destruction of forests will add further to the releases of C to the atmosphere. There is no equivalent countervailing storage that has been identified. The result suggests that a significant enhancement of the warming beyond current predictions is to be expected. An open-ended, accelerating warming of the Earth at rates that bring rapid changes in climatic zones, drive forests to impoverishment, and raise sea level rapidly is beyond the limits of simple adjustments of the human enterprise. Steps to stabilize the atmospheric composition seem inevitable. Because the total emissions of C to the atmosphere are not known, the current rate of transfer from the atmosphere to the oceans is uncertain. But whatever the current total release to the atmosphere, the annual atmospheric increase is about 3.0 G-tons of C as CO₂. At least three possibilities exist for reducing or eliminating the imbalance and moving toward long-term stability:

1. a reduction in the use of fossil fuels globally, now estimated as the source of about 5.6 G-tons of C annually;
2. a reduction or cessation of deforestation, now estimated as releasing 1–3 G-tons annually;
3. a vigorous program of reforestation that would remove from the atmosphere into storage in plants and soils about 1 G-ton of C annually for each 2 × 10⁶ km² tract reforested.

Further adjustments in emissions will be appropriate as experience accumulates. Such steps are appropriate now and possible. They will bring widespread ancillary benefits to the human enterprise.     

RESPONSES OF A GLOBAL CGCM TO CO2 INCREASE

The responses of the climate system to increase of atmospheric carbon dioxide(CO₂)arestudied by using a new version of the Bureau of Meteorological Research Centre(BMRC)globalcoupled general circulation model(CGCM).Two simulations are run:one with atmospheric CO₂concentration held constant at 330 ppm,the other with a tripling of atmospheric CO₂(990 ppm).Results from the 41-year control coupled integration are applied to analyze the mean state,seasonal cycle and interannual variability in the model.Comparisons between the greenhouseexperiment and the control experiment then provide estimations of the influence of increased CO₂on climate changes and climate variability.Especially discussed is the question on whether theclimate changes concerned with CO₂ inerease will impact interannual variability in tropical Pacific,such as ENSO.     

Detecting a Terrestrial Biosphere Sink for Carbon Dioxide: Interannual Ecosystem Modeling for the Mid-1980s

There is considerable uncertainty as to whether interannual variability in climate and terrestrial ecosystem production is sufficient to explain observed variation in atmospheric carbon content over the past 20–30 years. In this paper, we investigated the response of net CO₂ exchange in terrestrial ecosystems to interannual climate variability (1983 to 1988) using global satellite observations as drivers for the NASA-CASA (Carnegie-Ames-Stanford Approach) simulation model. This computer model of net ecosystem production (NEP) is calibrated for interannual simulations driven by monthly satellite vegetation index data (NDVI) from the NOAA Advanced Very High Resolution Radiometer (AVHRR) at 1 degree spatial resolution. Major results from NASA-CASA simulations suggest that from 1985 to 1988, the northern middle-latitude zone (between 30 and 60°N) was the principal region driving progressive annual increases in global net primary production (NPP; i.e., the terrestrial biosphere sink for carbon). The average annual increase in NPP over this predominantly northern forest zone was on the order of +0.4 Pg (10¹⁵ g) C per year. This increase resulted mainly from notable expansion of the growing season for plant carbon fixation toward the zonal latitude extremes, a pattern uniquely demonstrated in our regional visualization results. A net biosphere source flux of CO₂ in 1983–1984, coinciding with an El Niño event, was followed by a major recovery of global NEP in 1985 which lasted through 1987 as a net carbon sink of between 0.4 and 2.6 Pg C per year. Analysis of model controls on NPP and soil heterotrophic CO₂ fluxes (R_h) suggests that regional warming in northern forests can enhance ecosystem production significantly. In seasonally dry tropical zones, periodic drought and temperature drying effects may carry over with at least a two-year lag time to adversely impact ecosystem production. These yearly patterns in our model-predicted NEP are consistent in magnitude with the estimated exchange of CO₂ by the terrestrial biosphere with the atmosphere, as determined by previous isotopic (¹³C) deconvolution analysis. Ecosystem simulation results can help further target locations where net carbon sink fluxes have occurred in the past or may be verified in subsequent field studies.