Role of winter temperature and climate change on the survival and future range expansion of the hemlock woolly adelgid (Adelges tsugae) in eastern North America

Global climate change has already affected the abundances, range limits, and interactions of many species. The hemlock woolly adelgid (Adelges tsugae), an invasive insect introduced to eastern North America from Japan, has decimated stands of eastern hemlock (Tsuga canadensis) and Carolina hemlock (T. caroliniana) from Georgia to Connecticut. However, its spread across central and northern New England has been slowed substantially by its inability to tolerate cold winter temperatures. Using data from previous lab and field studies collected over the past 17 years, including adelgid spread and overwintering mortality, we first characterize the temperature conditions that may limit adelgid spread. We then show how, in the future, rising winter temperatures due to climate change are likely to remove the conditions currently limiting adelgid spread, and facilitate the northward expansion as more suitable habitat becomes available.     

Sensitivity of future ozone concentrations in the northeast USA to regional climate change

An air quality modeling system was used to simulate the effects on ozone concentration in the northeast USA from climate changes projected through the end of the twenty-first century by the National Center for Atmospheric Research’s (NCAR’s) parallel climate model, a fully coupled general circulation model, under a higher and a lower scenario of future global changes in concentrations of radiatively active constituents. The air quality calculations were done with both a global chemistry-transport model and a regional air quality model focused on the northeast USA. The air quality simulations assumed no changes in regional anthropogenic emissions of the chemical species primarily involved in the chemical reactions of ozone creation and destruction, but only accounted for changes in the climate. Together, these idealized global and regional model simulations provide insights into the contribution of possible future climate changes on ozone. Over the coming century, summer climate is projected to be warmer and less cloudy for the northeast USA. These changes are considerably larger under the higher scenario as compared with the lower. Higher temperatures also increase biogenic emissions. Both mean daily and 8-h maximum ozone increase from the combination of three factors that tend to favor higher concentrations: (1) higher temperatures change the rates of reactions and photolysis rates important to the ozone chemistry; (2) lower cloudiness (higher solar radiation) increases the photolysis reaction rates; and (3) higher biogenic emissions increase the concentration of reactive species. Regional model simulations with two cumulus parameterizations produce ozone concentration changes that differ by approximately 10%, indicating that there is considerable uncertainty in the magnitude of changes due to uncertainties in how physical processes should be parameterized in the models. However, the overall effect of the climate changes simulated by these models – in the absence of reductions in regional anthropogenic emissions – would be to increase ozone concentrations.     

Climate Change Projections for the United States Midwest

Environmental and societal factors such asair quality, water quality andavailability, land use changes andexpanding urbanization are alreadyaffecting human health and welfare,agriculture, and natural ecosystems in theMidwestern United States. Over thiscentury, these existing stresses willlikely be exacerbated by climate changesresulting from human activities. It isessential that policy decisions aimed atpreserving the well-being of a region beinformed by a good understanding of theregion's climate, how climate might change,and the uncertainties inherent in futureprojections. Recent updates in climatemodeling expertise and an expanded view ofpossible non-intervention emissionscenarios have narrowed the range of changethat can be expected over the Midwestthroughout the next century in some ways,while broadening it in others. In contrastto previous studies, which generallyconsider a mid-range scenario for futureemissions, this study presents the range ofchange that would result from low to highscenarios for climate change. In this waywe account for uncertainties inanthropogenic forcing on climate change inthe region and quantify the potentialeffects of human actions on future climate.This analysis also combines the latestclimate model projections with historicalrecords of observed climate over the pastcentury, effectively placing potentialchanges in extreme event frequencies suchas heavy rainfall events and temperaturethreshold exceedances within the context ofobserved variability over the past century.The purpose of this study is to provide anupdated picture of the potential impacts ofclimate change on the Midwest to inform theimpact assessment and policy developmentcommunity. From the magnitude of thechanges projected by this study, it isclear that these must be included in futurepolicy decisions in order to ensure thesuccessful adaptation and survival ofexisting human and natural systems in theMidwest.     

Projected change in climate thresholds in the Northeastern U.S.: implications for crops, pests, livestock, and farmers

Most prior climate change assessments for U.S. agriculture have focused on major world food crops such as wheat and maize. While useful from a national and global perspective, these results are not particularly relevant to the Northeastern U.S. agriculture economy, which is dominated by dairy milk production, and high-value horticultural crops such as apples (Malus domestica), grapes (Vitis vinifera), sweet corn (Zea mays var. rugosa), cabbage (Brassica oleracea var. capitata), and maple syrup (sugar maple, Acer saccharum). We used statistically downscaled climate projections generated by the HadCM3 atmosphere–ocean general circulation model, run with Intergovernmental Panel on Climate Change future emissions scenarios A1fi (higher) and B1 (lower), to evaluate several climate thresholds of direct relevance to agriculture in the region. A longer (frost-free) growing season could create new opportunities for farmers with enough capital to take risks on new crops (assuming a market for new crops can be developed). However, our results indicate that many crops will have yield losses associated with increased frequency of high temperature stress, inadequate winter chill period for optimum fruiting in spring, increased pressure from marginally over-wintering and/or invasive weeds, insects, or disease, or other factors. Weeds are likely to benefit more than cash crops from increasing atmospheric carbon dioxide. Projections of thermal heat index values for dairy cows indicate a substantial potential negative impact on milk production. At the higher compared to lower emissions scenario, negative climate change effects will occur sooner, and impact a larger geographic area within the region. Farmer adaptations to climate change will not be cost- or risk-free, and the impact on individual farm families and rural communities will depend on commodity produced, available capital, and timely, accurate climate projections.     

Regional climate change projections for the Northeast USA

Climate projections at relevant temporal and spatial scales are essential to assess potential future climate change impacts on climatologically diverse regions such as the northeast United States. Here, we show how both statistical and dynamical downscaling methods applied to relatively coarse-scale atmosphere-ocean general circulation model output are able to improve simulation of spatial and temporal variability in temperature and precipitation across the region. We then develop high-resolution projections of future climate change across the northeast USA, using IPCC SRES emission scenarios combined with these downscaling methods. The projections show increases in temperature that are larger at higher latitudes and inland, as well as the potential for changing precipitation patterns, particularly along the coast. While the absolute magnitude of change expected over the coming century depends on the sensitivity of the climate system to human forcing, significantly higher increases in temperature and in winter precipitation are expected under a higher as compared to lower scenario of future emissions from human activities.     

Global change: state of the science

Only recently, within a few decades, have we realized that humanity significantly influences the global environment. In the early 1980s, atmospheric measurements confirmed basic concepts developed a decade earlier. These basic concepts showed that human activities were affecting the ozone layer. Later measurements and theoretical analyses have clearly connected observed changes in ozone to human-related increases of chlorine and bromine in the stratosphere. As a result of prompt international policy agreements, the combined abundances of ozone-depleting compounds peaked in 1994 and ozone is already beginning a slow path to recovery. A much more difficult problem confronting humanity is the impact of increasing levels of carbon dioxide and other greenhouse gases on global climate. The processes that connect greenhouse gas emissions to climate are very complex. This complexity has limited our ability to make a definitive projection of future climate change. Nevertheless, the range of projected climate change shows that global warming has the potential to severely impact human welfare and our planet as a whole. This paper evaluates the state of the scientific understanding of the global change issues, their potential impacts, and the relationships of scientific understanding to policy considerations.     

Potential climate change impacts on Atlantic cod (Gadus morhua) off the northeastern USA

We examined the potential impacts of future climate change on the distribution and production of Atlantic cod (Gadus morhua) on the northeastern USA’s continental shelf. We began by examining the response of cod to bottom water temperature changes observed over the past four decades using fishery-independent resource survey data. After accounting for the overall decline in cod during this period, we show that the probability of catching cod at specified locations decreased markedly with increasing bottom temperature. Our analysis of future changes in water temperature was based on output from three coupled atmosphere–ocean general circulation models under high and low CO₂ emissions. An increase of <1.5°C is predicted for all sectors under the low emission scenario in spring and autumn by the end of this century. Under the high emission scenario, temperature increases range from ～2°C in the north to >3.5°C in the Mid-Atlantic Bight. Under these conditions, cod appear vulnerable to a loss of thermal habitat on Georges Bank, with a substantial loss of thermal habitat farther south. We also examined temperature effects on cod recruitment and growth in one stock area, the Gulf of Maine, to explore potential implications for yield and resilience to fishing. Cod survival during the early life stages declined with increasing water temperatures, offsetting potential increases in growth with warmer temperatures and resulting in a predicted loss in yield and increased vulnerability to high fishing mortality rates. Substantial differential impacts under the low versus high emission scenarios are evident for cod off the northeastern USA.     

Potential effects of climate change and rising CO2 on ecosystem processes in northeastern U.S. forests

Forest ecosystems represent the dominant form of land cover in the northeastern United States and are heavily relied upon by the region’s residents as a source of fuel, fiber, structural materials, clean water, economic vitality, and recreational opportunities. Although predicted changes in climate have important implications for a number of ecosystem processes, our present understanding of their long-term effects is poor. In this study, we used the PnET-CN model of forest carbon (C), nitrogen (N) and water cycling to evaluate the effects of predicted changes in climate and atmospheric carbon dioxide (CO₂) on forest growth, C exchange, water runoff, and nitrate ( $ {\text{NO}}^{ - }_{3} $ ) leaching at five forest research sites across the northeastern U.S. We used four sets of statistically downscaled climate predictions from two general circulation models (the Hadley Centre Coupled Model, version 3 and the Parallel Climate Model) and two scenarios of future CO₂ concentrations. A series of model experiments was conducted to examine the effects of future temperature, precipitation, CO₂, and various assumptions regarding the physiological response of forests to these changes. Results indicate a wide range of predicted future growth rates. Increased growth was predicted across deciduous sites under most future conditions, while growth declines were predicted for spruce forests under the warmest scenarios and in some deciduous forests when CO₂ fertilization effects were absent. Both climate and rising CO₂ contributed to predicted changes, but their relative importance shifted from CO₂-dominated to climate-dominated from the first to second half of the twenty-first century. Predicted runoff ranged from no change to a slight decrease, depending on future precipitation and assumptions about stomatal response to CO₂. Nitrate leaching exhibited variable responses, but was highest under conditions that imposed plant stress with no physiological effects of CO₂. Although there are considerable uncertainties surrounding predicted responses to climate change, these results provide a range of possible outcomes and highlight interactions among processes that are likely to be important. Such information can be useful to scientists and land managers as they plan on means of examining and responding to the effects of climate change.