State of the Carbon Cycle - Consequences of Rising Atmospheric CO2

The rise of atmospheric CO2, largely attributable to human activity through fossil fuel emissions and land-use change, has been dampened by carbon uptake by the ocean and terrestrial biosphere. We outline the consequences of this carbon uptake as direct and indirect effects on terrestrial and oceanic systems and processes for different regions of North America and the globe. We assess the capacity of these systems to continue to act as carbon sinks. Rising CO2 has decreased seawater pH; this process of ocean acidification has impacted some marine species and altered fundamental ecosystem processes with further effects likely. In terrestrial ecosystems, increased atmospheric CO2 causes enhanced photosynthesis, net primary production, and increased water-use efficiency. Rising CO2 may change vegetation composition and carbon storage, and widespread increases in water use efficiency likely influence terrestrial hydrology and biogeochemical cycling. Consequences for human populations include changes to ecosystem services including cultural activities surrounding land use, agricultural or harvesting practices. Commercial fish stocks have been impacted and crop production yields have been changed as a result of rising CO2. Ocean and terrestrial effects are contingent on, and feedback to, global climate change. Warming and modified precipitation regimes impact a variety of ecosystem processes, and the combination of climate change and rising CO2 contributes considerable uncertainty to forecasting carbon sink capacity in the ocean and on land. Disturbance regime (fire and insects) are modified with increased temperatures. Fire frequency and intensity increase, and insect lifecycles are disrupted as temperatures move out of historical norms. Changes in disturbance patterns modulate the effects of rising CO2 depending on ecosystem type, disturbance frequency, and magnitude of events. We discuss management strategies designed to limit the rise of atmospheric CO2 and reduce uncertainty in forecasts of decadal and centennial feedbacks of rising atmospheric CO2 on carbon storage

Indicate separate contributions of long-lived and short-lived greenhouse gases in emission targets

European Union funding: 821205, 821003, 820829. Wellcome Trust: 205212/Z/16/

Indicate separate contributions of long-lived and short-lived greenhouse gases in emission targets

European Union funding: 821205, 821003, 820829. Wellcome Trust: 205212/Z/16/

Air flow regime from 1999 to 2005 at the University of Michigan Biological Station and its relation to variability in net carbon dioxide flux and tropospheric ambient ozone; Summer 2006 analysis.

The purpose of this study is to better understand the typical air flow regime and environmental conditions of the University of Michigan Biological Station (UMBS), and determine the seasonal and year-to-year variability from 1999-2005. Calculating back-trajectories of air parcels arriving at the station exposes the history of the air mass flow, which helps in the assessment of air quality. South and southwesterly flow will be compared to tropospheric ambient ozone levels to see if pollution is transported to UMBS by air mass flow. The analysis of the air flow regime will ultimately by compared to the year-to-year variability in net carbon dioxide flux at UMBS, to determine if there is a correlation with air quality. Other variables that will be compared to air mass flow and net carbon dioxide flux are ambient temperature, light intensity, soil moisture, soil temperature, precipitation, maximum leaf area index, and photosynthetic photon flux density. The conclusion in the air flow regime was that from 1999-2005, 11.4%+/-1.83 of the total air flow was westerly, 30.3%+/_2.11 was north and northwesterly, 3.4%+/_1.11 was northeasterly, 4.5%+/-0.95 was east and southeasterly, 23.1%+/-1.33 was south and southeasterly, and 27.3%+/-1.78 the flow regime was indeterminate. (The +/- value is the variablility in the flow regime throughout all the years, e.g. a greater value means more variability from year-to-year.)http://deepblue.lib.umich.edu/bitstream/2027.42/55114/1/3559.pdfDescription of 3559.pdf : Access restricted to on-site users at the U-M Biological Station

Contrasting features of scattering and absorbing aerosol direct radiative forcings and climate responses

Human activities have greatly increased the amount of aerosols in the atmosphere since the Industrial Revolution. Anthropogenic aerosols are comprised of optically scattering and absorbing particles, with the principal concentrations located in the Northern Hemisphere. This thesis investigates the contrasting features between scattering and absorbing aerosol radiative forcings and the accompanying climate responses by employing the GFDL CM2.1 global climate model. Anthropogenic sulfate and black carbon aerosols are used as examples of a strong scatterer and strong absorber, respectively. Model aerosol distributions are evaluated by comparing optical properties with ground-based, aircraft, and satellite measurements. Geographical forcing distributions of absorbing and scattering aerosols show approximately similar magnitudes with opposite signs, and an interhemispheric forcing asymmetry, in complete contrast to long-lived greenhouse gases. Uncertainties in the forcings are addressed by examining the quantitative roles of cloud coverage, surface albedo, relative humidity, and mixing state in governing the magnitudes; clouds and high-albedo surfaces weaken sulfate forcing and strengthen black carbon forcing. Sulfate forcing is strengthened by hygroscopic growth. Black carbon forcing is strengthened by internal mixing. The contrast in climate responses to scattering and absorbing aerosol features (including the influence on clouds) is analyzed by employing different aerosol forcing configurations in preindustrial to present-day climate simulations. This thesis goes beyond the analysis of the typical temperature response by investigating important hydrological and dynamical climate responses, such as precipitation, atmospheric circulation, and heat transport. Aerosol responses are also contrasted to the long-lived greenhouse gases' climate response. Aerosol climate responses are governed by the sign of the forcing and the interhemispheric forcing asymmetry. Precipitation, atmospheric circulation, and heat transport responses are anti-correlated for scattering and absorbing aerosols. Compared to the interhemispherically symmetric long-lived greenhouse gas forcing effects, aerosols induce asymmetric patterns of changes in precipitation north and south of the equator accompanied by cross-equatorial heat fluxes in the atmosphere and ocean. Because responses to scattering and absorbing aerosols are opposite in sign and occur simultaneously, there is a significant dilution of their individuality in the net aerosol effect on climate. The findings are relevant for future climate changes and aerosol emission policy decisions

Distortion of sectoral roles in climate change threatens climate goals

The longstanding method for reporting greenhouse gas emissions—carbon dioxide equivalence (CO2e)—systematically underestimates methane-dominated economic sectors' contributions to warming in the coming decades. This is because it only calculates the warming impact of a pulse of emissions over a 100-year period. For short-lived climate forcers that mostly influence the climate for a decade or two, like methane, this method masks their near-term potency. Assessing the impacts of future greenhouse gas emissions using a simple climate model reveals that midcentury warming contributions of sectors dominated by methane—agriculture, fossil fuel production and distribution, and waste—are two times higher than estimated using CO2e. The CO2e method underemphasizes the importance of reducing emissions from these sectors, and risks misaligning emissions targets with desired temperature outcomes. It is essential to supplement CO2e-derived insights with approaches that convey climate impacts of ongoing emissions over multiple timescales, and to never rely exclusively on CO2e

Wide range in estimates of hydrogen emissions from infrastructure

Hydrogen holds tremendous potential to decarbonize many economic sectors, from chemical and material industries to energy storage and generation. However, hydrogen is a tiny, leak-prone molecule that can indirectly warm the climate. Thus, hydrogen emissions from its value chain (production, conversion, transportation/distribution, storage, and end-use) could considerably undermine the anticipated climate benefits of a hydrogen economy. Several studies have identified value chain components that may intentionally and/or unintentionally emit hydrogen. However, the amount of hydrogen emitted from infrastructure is unknown as emissions have not yet been empirically quantified. Without the capacity to make accurate direct measurements, over the past two decades, some studies have attempted to estimate total value chain and component-level hydrogen emissions using various approaches, e.g., assumptions, calculations via proxies, laboratory experiments, and theory-based models (simulations). Here, we synthesize these studies to provide an overview of the available knowledge on hydrogen emissions across value chains. Briefly, the largest ranges in estimated emissions rates are associated with liquefaction (0.15% to 10%), liquid hydrogen transporting and handling (2% to 20%), and liquid hydrogen refueling (2% to 15%). Moreover, present and future value chain emission rate estimates vary widely (0.2% to 20%). Field measurements of hydrogen emissions throughout the value chain are critically needed to sharpen our understanding of hydrogen emissions and, with them, accurately assess the climate impact of hydrogen deployment

Acting rapidly to deploy readily available methane mitigation measures by sector can immediately slow global warming

Methane mitigation is essential for addressing climate change, but the value of rapidly implementing available mitigation measures is not well understood. In this paper, we analyze the climate benefits of fast action to reduce methane emissions as compared to slower and delayed mitigation timelines. We find that the scale up and deployment of greatly underutilized but available mitigation measures will have significant near-term temperature benefits beyond that from slow or delayed action. Overall, strategies exist to cut global methane emissions from human activities in half within the next ten years and half of these strategies currently incur no net cost. Pursuing all mitigation measures now could slow the global-mean rate of near-term decadal warming by around 30%, avoid a quarter of a degree centigrade of additional global-mean warming by midcentury, and set ourselves on a path to avoid more than half a degree centigrade by end of century. On the other hand, slow implementation of these measures may result in an additional tenth of a degree of global-mean warming by midcentury and 5% faster warming rate (relative to fast action), and waiting to pursue these measures until midcentury may result in an additional two tenths of a degree centigrade by midcentury and 15% faster warming rate (relative to fast action). Slow or delayed methane action is viewed by many as reasonable given that current and on-the-horizon climate policies heavily emphasize actions that benefit the climate in the long-term, such as decarbonization and reaching net-zero emissions, whereas methane emitted over the next couple of decades will play a limited role in long-term warming. However, given that fast methane action can considerably limit climate damages in the near-term, it is urgent to scale up efforts and take advantage of this achievable and affordable opportunity as we simultaneously reduce carbon dioxide emissions

Biogeochemical Effects of Rising Atmospheric CO2 on Terrestrial and Ocean Systems

Rising carbon dioxide (CO2) has decreased seawater pH at long-term observing stations around the world, including in the open ocean north of Oahu, Hawaii, near Alaska's Aleutian Islands, the Gulf of Maine shore, and on Gray's Reef in the southeastern United States. This ocean acidification process has already affected some marine species and altered fundamental ecosystem processes, and further effects are likely. While atmospheric CO rises at approximately the same rate all over the globe, its non-climate effects on land vary depending on climate and dominant species. In terrestrial ecosystems, rising atmospheric CO concentrations are expected to increase plant photosynthesis, growth, and water-use efficiency, though these effects are reduced when nutrients, drought or other factors limit plant growth. Rising CO would likely change carbon storage and influence terrestrial hydrology and biogeochemical cycling, but concomitant effects on vegetation composition and nutrient feedbacks are challenging to predict, making decadal forecasts uncertain. Consequences of rising atmospheric CO are expected to include difficult-to-predict changes in the ecosystem services that terrestrial and ocean systems provide to humans. For instance, ocean acidification resulting from rising CO has decreased the supply of larvae that sustains commercial shellfish production in the northwestern United States. In addition, CO fertilization (increases) plus warming (decreases) are changing terrestrial crop yields. Continued persistence of uptake of carbon by the land and ocean is uncertain. Climate and environmental change create complex feedbacks to the carbon cycle and it is not clear how feedbacks modulate future effects of rising CO on carbon sinks. These are several mechanisms that could reduce future sink capacity