Detecting climate impacts with oceanic fish and fisheries data

Anthropogenic climate change is affecting the environment of all oceans, modifying ocean circulation, temperature, chemistry and productivity. While evidence for changes in physical signals is often distinct, impacts on fishes inhabiting oceanic systems are not easily identified, and therefore, quantification of responses is less common. Correctly attributing changes associated with a changing climate from other drivers is important for the implementation of effective harvest and management strategies and for addressing associated socio-economic impacts, particularly for countries highly dependent on oceanic resources. Data supporting investigation of responses of oceanic species to climate impacts include fisheries catch, fisheries-independent surveys, and conventional and electronic tagging data. However, there are a number of challenges associated with detecting climatic responses with these data, including (i) data collection costs (ii) small sample sizes (iii) limited time series relative to temporal scales at which environmental variability occurs, (iv) changing fisher and fisheries behavior due to non-climate drivers and (v) changes in population dynamics due to natural climate variability and non-climate drivers. We highlight potential biases and suggest strategies that should be considered when using oceanic fish and fisheries data in the evaluation of climate change impacts. Consideration of these factors is important when assessing variability in exploited species and designing management responses to climate or fisheries threats.     

Modeling the Influence of Topographic Barriers on Treeline Advance at the Forest-Tundra Ecotone in Northwestern Alaska

The response of terrestrial ecosystems to climate warming has important implications to potential feedbacks to climate. The interactions between topography, climate, and disturbance could alter recruitment patterns to reduce or offset current predicted positive feedbacks to warming at high latitudes. In northern Alaska the Brooks Range poses a complex environmental and ecological barrier to species migration. We use a spatially explicit model (ALFRESCO) to simulate the transient response of subarctic vegetation to climatic warming in the Kobuk/Noatak River Valley (200 × 400 km) in northwest Alaska. The model simulations showed that a significantly warmer (+6 °C) summer climate would cause expansion of forest through the Brooks Range onto the currently treeless North Slope only after a period of 3000–4000 yr. Substantial forest establishment on the North Slope didnot occur until temperatures warmed 9 °C, and only following a 2000 yr time lag. The long time lags between change in climate and change in vegetation indicate current global change predictions greatly over-estimate the response of vegetation to a warming climate in Alaska. In all the simulations warming caused a steady increase in the proportion of early successional deciduous forest. This would reduce the magnitude of the predicted decrease in regional albedo and the positive feedback to climate warming. Simulation of spruce forest refugia on the North Slope showed forest could survive with only a 4 °C warming and would greatly reduce the time lag of forest expansion under warmer climates. Planting of spruce on the North Slope by humans could increase the likelihood of large-scale colonization of currently treeless tundra. Together, the long time lag and deciduous forest dominance would delay the predicted positive regional feedback of vegetation change to climatic warming. These simulated changes indicate the Brooks Range would significantly constrain regional forest expansion under a warming climate, with similar implications for other regions possessing major east-west oriented mountain ranges.     

Effects of observed and experimental climate change on terrestrial ecosystems in northern Canada: results from the Canadian IPY program

Tundra and taiga ecosystems comprise nearly 40?% of the terrestrial landscapes of Canada. These permafrost ecosystems have supported humans for more than 4500?years, and are currently home to ca. 115,000 people, the majority of whom are First Nations, Inuit and Métis. The responses of these ecosystems to the regional warming over the past 30?C50?years were the focus of four Canadian IPY projects. Northern residents and researchers reported changes in climate and weather patterns and noted shifts in vegetation and other environmental variables. In forest-tundra areas tree growth and reproductive effort correlated with temperature, but seedling establishment was often hindered by other factors resulting in site-specific responses. Increased shrub cover has occurred in sites across the Arctic at the plot and landscape scale, and this was supported by results from experimental warming. Experimental warming increased vegetation cover and nutrient availability in most tundra soils; however, resistance to warming was also found. Soil microbial diversity in tundra was no different than in other biomes, although there were shifts in mycorrhizal diversity in warming experiments. All sites measured were sinks for carbon during the growing season, with expected seasonal and latitudinal patterns. Modeled responses of a mesic tundra system to climate change showed that the sink status will likely continue for the next 50?C100?years, after which these tundra systems will likely become a net source of carbon dioxide to the atmosphere. These IPY studies were the first comprehensive assessment of the state and change in Canadian northern terrestrial ecosystems and showed that the inherent variability in these systems is reflected in their site-specific responses to changes in climate. They also showed the importance of using local traditional knowledge and science, and provided extensive data sets, sites and researchers needed to study and manage the inevitable changes in the Canadian North.     

Indications of a climate effect on Mediterranean fisheries

Using the Food and Agriculture Organization’s (FAO) Mediterranean capture fisheries production dataset in conjunction with global and Mediterranean sea surface temperatures, we investigated trends in fisheries landings and landings per unit of effort of commercially important marine organisms, in relation to temperature oscillations. In addition to the overall warming trend, a temperature shift was detected in the Mediterranean Sea in the late 1990s. Fisheries landings fluctuations were examined for the most abundant commercial species (59 species) and showed significant year-to-year correlations with temperature for nearly 60 % of the cases. From these, the majority (~70 %) were negatively related and showed a reduction of 44 % on average. Increasing trends were found, mainly in the landings of species with short life spans, which seem to have benefited from the increase in water temperature. Τhe effect of oceanic warming is apparent in most species or groups of species sharing ecological (e.g. small and medium pelagic, demersal fish) or taxonomic (e.g. cephalopods, crustaceans) traits. A landings-per-unit-of-effort (LPUE) proxy, using data from the seven Mediterranean European Union member states, also showed significant correlation with temperature fluctuations for six out of the eight species examined, indicating the persistence of temperature influence on landings when the fishing effect is accounted for. The speed of response of marine landings to the warming of the Mediterranean Sea possibly shows both the sensitivity and the vulnerable state of the fish stocks and indicates that climate should be examined together with fisheries as a factor shaping stock fluctuations.     

The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly”

Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.     

Biophysical indicators and Indigenous and Local Knowledge reveal climatic and ecological shifts with implications for Arctic Char fisheries

Managing Arctic marine resources to be resilient to environmental changes requires knowledge of how climate change is affecting marine food webs and fisheries. Changes to fishery resources will have major implications for coastal Indigenous communities whose livelihoods, health, and cultures are strongly connected to fisheries. Understanding these broad social-ecological changes requires a transdisciplinary approach bringing together contrasting and complementary disciplines and ways of knowing. Here, we examine climatic proxies, ecological, and fishery indicators (stable isotopes, fish condition, and lipid content), and interviews with Inuit fishers to assess how marine ecosystem changes have influenced Arctic Char (Salvelinus alpinus) ecology and fisheries over a 30-year time period (1987–2016) in the Kitikmeot region of the Canadian Arctic. Inuit fishers reported several observations of environmental changes, including longer ice-free seasons, warmer ocean temperatures, and the arrival of new marine species. Biophysical data revealed important changes toward earlier dates of ice breakup (>12 days in some areas) and a shift in isotopic niche reflecting a changing Arctic Char diet, with increased contribution of pelagic carbon and higher trophic level prey. Fish condition was improved in years with earlier ice breakup, as observed by both Inuit fishers and biophysical indicators, while lipid content increased through time, suggesting that longer ice-free seasons may have a positive effect on Arctic Char quality as reflected by both fish condition and lipid content. Long-term impacts of continuing climate change, however, such as the northward expansion of boreal species and increasing ocean temperatures, could have negative effects on fisheries (e.g., physiological impairment in fish if temperatures exceed their thermal range). Continuous community-based monitoring that directly informs fisheries management could help communities and managers adaptively, and sustainably, manage in the face of multiple interacting changes in Arctic marine systems.     

Northward range shifts in Korean butterflies

Northward shifts due to global warming are apparent in various organisms in the Northern Hemisphere such as insects, fish, birds, and plants. However, these findings were mainly reported in Europe and North America. Therefore, such range shifts should be examined in other regions such as Asia to confirm global northward shifts in the Northern Hemisphere. In South Korea, we tested whether the distribution margins of Korean butterflies shifted northward or southward. We used occurrence data from two Korean butterfly atlases (1938-1950 and 1996-2011). The margin (northern or southern) shifts were evaluated using both latitudinal shifts of margin records (direct evaluation) and the intercept shift in the regression equation between the margin shift and the change in occurrence (intercept evaluation). Northern margins of southern species shifted northwards, whereas southern margins of northern species shifted southwards due to habitat enlargement (national reforestation in South Korea). The annual northward shift of northern margins of 10 Korean southern species was 1.6 km for 60 years, which is similar to the Korean isothermal shift (1.5 km per year).     

Changes of atmospheric water vapor budget in the Pearl River basin and possible implications for hydrological cycle

In this study, we thoroughly analyzed abrupt behaviors, trends, and periodicity properties of water vapor flux and moisture budget entering and exiting the four edges of the Pearl River basin based on the NCAR/NCEP reanalysis dataset by using the continuous wavelet transform and the simple two-phase linear regression technique. Possible implications for hydrological cycle and water resource management of these changes are also discussed. The results indicate that: (1) the water vapor propagating through the four edges of the Pearl River basin is decreasing, and it is particularly true for the changes of the water vapor flux exiting from the north edge of the study river basin. The transition point from increase to decrease occurs in the early 1960s; (2) The wavelet transform spectra indicate that the monthly water vapor flux through the north edge decreases and this decrease is mainly reflected by intermittent distribution of the wavelet power spectra after early 1980s. The periodicity properties of the water vapor flux through the north edge imply that the northward propagation of water vapor flux decreases after the 1980s; (3) close relations between water vapor flux, precipitation and streamflow implies that the altered hydrological cycle in the Pearl River basin is mainly manifested by seasonal shifts of water vapor flux after early 1960s. One of the direct consequences of these changes of water vapor flux is the seasonal transition of wet and dry conditions across the Pearl River basin. Regional responses of hydrological cycle to climate variation/change could be different from one river basin to another. Hydrological responses of the Pearl River basin to the global warming are mainly demonstrated by seasonal shifts of precipitation changes: winter comes to be wetter and summer tends to be dryer. The finding of the seasonal transition of precipitation in the Pearl River basin is of great scientific and practical merits in basin scale water resource management in the Pearl River basin under the changing climate and global warming in particular.     

Ungulate herbivory modifies the effects of climate change on mountain forests

Recent temperature observations suggest a general warming trend that may be causing the range of tree species to shift to higher latitudes and altitudes. Since biotic interactions such as herbivory can change tree species composition, it is important to understand their contribution to vegetation changes triggered by climate change. To investigate the response of forests to climate change and herbivory by wild ungulates, we used the forest gap model ForClim v2.9.6 and simulated forest development in three climatically different valleys in the Swiss Alps. We used altitudinal transects on contrasting slopes covering a wide range of forest types from the cold (upper) to the dry (lower) treeline. This allowed us to investigate (1) altitudinal range shifts in response to climate change, (2) the consequences for tree species composition, and (3) the combined effect of climate change and ungulate herbivory. We found that ungulate herbivory changed species composition and that both basal area and stem numbers decreased with increasing herbivory intensity. Tree species responded differently to the change in climate, and their ranges did not change concurrently, thus causing a succession to new stand types. While climate change partially compensated for the reductions in basal area caused by ungulate herbivory, the combined effect of these two agents on the mix of the dominant species and forest type was non-compensatory, as browsing selectively excluded species from establishing or reaching dominance and altered competition patterns, particularly for light. We conclude that there is an urgent need for adaptive forest management strategies that address the joint effects of climate change and ungulate herbivory.     

Ecological responses of plant species and communities to climate warming: upward shift or range filling processes?

The fate of alpine species in response to climate warming is still unclear. We analyze effects of climate warming on the composition of alpine plants communities and unravel the range filling of communities within a belt from long-term true upward shift processes. In the European Alps we re-sampled in 2003 the vegetation at sites studied in 1953 and analyzed the changes at intra- and inter-community level. Since 1953 all communities experienced a high species turnover, leading to an overall increase in species richness as new species exceeded species losses. The dominant species mainly declined allowing the potential expansion of competitors and/or of new species. The main recruitment sources are neighbor communities within the same elevation belt performing biotic exchanges with other plant communities in the same altitudinal belts. The changes of species distribution curves with elevation emphasized that more than half of the most widespread persisting species exhibited downward shifts instead of upward shifts. Upward shifts from lower elevation belts and of nonnative species were very limited. One third of the persisting species declined and could be used as a proxy to measure the extinction debt. Therefore the fate of plant communities will depend on the ability of the original species to persist and fill the available ecological gaps. Species persistence may be crucial in developing adaptation and environmental protection strategies.     

气候变化对我国小麦地理分布的潜在影响

根据GCM模拟结果，分析了CO2增加对我国小麦生产地理分布的潜在影响。结果表明:在加倍CO2气候下，我国小麦生产区将进一步向北和向西扩展，小麦栽培特点和品种类型也有较大变化。气候增暖可能对东北地区产生有利影响，但在中部和南部则可能产生高温应力。小麦生长期间平均温度的升高，特别是收获前的高温可能会增加对更早熟、更耐热品种的需求。     

A Modeling Study of Climate Change and Its Implication for Agriculture in China Part II: The Implication of Climate Change for Agriculture in China

The potential CO2-induced impacts on the geographical shifts of wheat growth zones in China were studied from seven GCMs outputs. The wheat growth regions may move northward and westward under the condition of a doubling CO2 climate. The wheat cultivation features and variety types may also assume significant changes. Climatic warming would have a positive influence in Northeast China, but high temperature stress may be produced in some regions of central and southern China. Higher mean air temperatures during wheat growth, particularly during the reproductive stages, may increase the need for earlier-maturing and more heat-tolerant cultivars.     

Harnessing scientific and local knowledge to face climate change in small-scale fisheries

Small-scale fisheries in developing regions are particularly vulnerable to climate change, but the assessment of climate-induced changes and impacts are often hampered by the data poor-situation of these social-ecological systems. Based on 40 years of scientific and local ecological knowledge, we provide a coherent narrative about the effects of a marine hotspot of climate change on a small-scale fishery across different geographical and temporal scales. We applied a mixed-methods approach to assess biophysical changes, social-ecological impacts, and the incremental spectrum of actions implemented at multiple levels to increase the adaptive capacity of a small-scale clam fishery. The warming hotspot here analyzed was the fastest-warming region in the South Atlantic Ocean. Long-term changes in wind intensity and direction were also noticeable at a regional scale. Both sea surface temperature and winds showed a clear shifting pattern in the late 1990 s. These climate-related stressors determined ecosystem and targeted population changes (e.g. clam mass mortalities, slow stock recovery rates after ecological shocks, habitat narrowing), and favored harmful algal bloom-forming organisms. Climate-induced drivers also affected the human component of the social-ecological system, preventing fishers from securing a fulltime livelihood and limiting the fishery economic potential. Adaptive responses at multiple levels provided some capacity to address climate change effects, and transformative pathways are being taken to adapt to climate-induced changes over the long-term. Transformative changes were fostered by the local perception of environmental change, shared narratives, sustained scientific monitoring programs, and the interaction between knowledge systems, facilitated by a bridging organization within a broader process of governance transformation. The combination of autonomous adaptations (based on linking social capital and fishery leaders agency) and government-led adaptations were essential to face the challenges imposed by climate change. Our results serve as a learning platform to anticipate threats and envision solutions to a wide range of small-scale fisheries in fast-warming regions worldwide.     

Nonlinear precipitation response to El Niño and global warming in the Indo-Pacific

Precipitation changes over the Indo-Pacific during El Niño events are studied using an Atmospheric General Circulation Model forced with sea-surface temperature (SST) anomalies and changes in atmospheric CO₂ concentrations. Linear increases in the amplitude of the El Niño SST anomaly pattern trigger nonlinear changes in precipitation amounts, resulting in shifts in the location and orientation of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). In particular, the maximum precipitation anomaly along the ITCZ and SPCZ shifts eastwards, the ITCZ shifts south towards the equator, and the SPCZ becomes more zonal. Precipitation in the equatorial Pacific also increases nonlinearly. The effect of increasing CO₂ levels and warming SSTs is also investigated. Global warming generally enhances the tropical Pacific precipitation response to El Niño. The precipitation response to El Niño is found to be dominated by changes in the atmospheric mean circulation dynamics, whereas the response to global warming is a balance between dynamic and thermodynamic changes. While the dependence of projected climate change impacts on seasonal variability is well-established, this study reveals that the impact of global warming on Pacific precipitation also depends strongly on the magnitude of the El Niño event. The magnitude and structure of the precipitation changes are also sensitive to the spatial structure of the global warming SST pattern.     

Northward migration under a changing climate: a case study of blackgum (Nyssa sylvatica)

Species are predicted to shift their distribution ranges in response to climate change. Region-wide, empirically-based studies, however, are still limited to support these predictions. We used a model tree species, blackgum (Nyssa sylvatica), to study climate-induced range shift. Data collected from two separate sampling periods (1980s and 2007) by the USDA’s Forestry and Inventory Analysis (FIA) Program were used to investigate changes in abundance and dominance, and shifts in distribution, of blackgum in four ecoregions of the eastern United States. Our results indicated new recruitment of blackgum in the northern portion of its range, along with increases in both density and annual rates of change in importance value (IV). Conversely, declines in recruitment were found in the southern portion of blackgum’s range, along with decreases in density and IV. The center portion of blackgum’s range had mixed patterns of change (i.e., both increases and decreases) throughout. A northward range expansion was also detected by comparing blackgum’s historic range to where it was detected during our two more-recent sampling periods. Our findings suggest that blackgum is migrating north in response to climate change. Our study also suggests two broader implications about tree migration patterns in response to climate change: (1) species can respond to changing climate in relatively short time periods, at least for generalist species such as blackgum, and (2) climate-induced vegetation dynamic patterns can be detected at the regional level, but are inherently complex.     

Climate Change Scenarios for the Hudson Bay Region: An Intermodel Comparison

General circulation models (GCMs) are unanimous in projecting warmer temperatures in an enhanced CO₂ atmosphere, with amplification of this warming in higher latitudes. The Hudson Bay region, which is located in the Arctic and subarctic regions of Canada, should therefore be strongly influenced by global warming. In this study, we compare the response of Hudson Bay to a transient warming scenario provided by six-coupled atmosphere-ocean models. Our analysis focuses on surface temperature, precipitation, sea-ice coverage, and permafrost distribution. The results show that warming is expected to peak in winter over the ocean, because of a northward retreat of the sea-ice cover. Also, a secondary warming peak is observed in summer over land in the Canadian and Australian-coupled GCMs, which is associated with both a reduction in soil moisture conditions and changes in permafrost distribution. In addition, a relationship is identified between the retreat of the sea-ice cover and an enhancement of precipitation over both land and oceanic surfaces. The response of the sea-ice cover and permafrost layer to global warming varies considerably among models and thus large differences are observed in the projected regional increase in temperature and precipitation. In view of the important feedbacks that a retreat of the sea-ice cover and the distribution of permafrost are likely to play in the doubled and tripled CO₂ climates of Hudson Bay, a good representation of these two parameters is necessary to provide realistic climate change scenarios. The use of higher resolution regional climate model is recommended to develop scenarios of climate change for the Hudson Bay region.     

Potential overwintering boundary and voltinism changes in the brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis>, in China in response to global warming

The brown planthopper Nilaparvata lugens (Stål) is a major rice insect pest in China and other Asian countries. This study assessed a potential northward shift in the overwintering boundaries and changes in the overwintering areas and voltinism of this planthopper species in China in response to global warming. Temperature data generated by 15 Global Circulation Models (GCMs) from 2010 to 2099 were employed to analyze the planthopper’s overwintering boundaries and overwintering areas in conjunction with three Special Report on Emissions Scenarios (SRES). Planthopper voltinism from 1961 to 2050 was analyzed in scenario A2 using degree-day models with projections from the regional circulation model (RCM) Providing Regional Climates for Impacts Studies (PRECIS). In both analyses, 1961–1990 served as the baseline period. Both the intermittent and constant overwintering boundaries were projected to shift northward; these shifts were more pronounced during later time periods and in scenarios A2 and A1B. The intermittent overwintering area was modeled to increase by 11, 24 and 44 %, and the constant overwintering area, by 66, 206 and 477 %, during the 2020s, 2050s and 2080s, respectively. Planthopper voltinism will increase by <0.5, 0.5–1.0 and 1.0–1.4 generations in northern, central and southern China, respectively, in 2021–2050. Our results suggest that the brown planthopper will overwinter in a much larger region and will produce more generations under future climate warming scenarios. As a result, the planthopper will exert an even greater threat to China’s rice production in the future.     

基于卫星遥感的植被NDVI对气候变化响应的研究进展

回顾了以往植被对气候响应的有关研究,从此类研究常使用的数据、方法及获取的结论3个方面进行了分析,重点阐述了归一化植被指数（Normalized Difference Vegetation Index,NDVI）对降水、温度和辐射等气候因子的响应特征,并探讨了未来的发展趋势。结果表明,植被NDVI对降水的显著响应往往出现在干旱半干旱地区和干湿季气候差异明显地区,且具有一定的滞后特征,滞后的时间尺度与局地条件关系密切;温度成为植被NDVI 控制因子的情况常出现在温带或寒温带地区,与对降水的滞后响应相比,植被对于温度的滞后响应并不是特别明显;辐射对于植被的主导影响主要出现在低纬度的部分区域、高云量区域和高纬度地区的特定时间段内。认为量化人类在植被对气候变化响应过程中的作用,全球变暖情形下植被对气候响应特征的深入分析,以及植被受气候影响的多尺度特征可能是以后此类研究的发展方向。     

Lags in vegetation response to greenhouse warming

Fossil pollen in sediments documents vegetation responses to climatic changes in the past. Beech (Fagus grandifolia), with animal-dispersed seeds, moved across Lake Michigan or around its southern margin, becoming established in Wisconsin about 1000 years after populations were established in Michigan. Hemlock (Tsuga canadensis), with wind-dispersed seeds, colonized a 50,000 km² area in northern Michigan between 6000 and 5000 years ago. These tree species extended ranges northward at average rates of 20–25 km per century. To track climatic changes in the future, caused by the greenhouse effect, however, their range limit would need to move northward 100 km per °C warming, or about 300 km per century, an order of magnitude faster than range extension in the past. Yet range extension in the future would be less efficient than in the past, because advance disjunct colonies have been extirpated by human disturbance, and because the seed source is reduced due to reductions in tree populations following logging. Many species of trees may not be able to disperse rapidly enough to track climate, and woodland herbs, which have less efficient seed dispersal mechanisms, may be in danger of extinction.     

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.