Earth Systems

Abrupt shifts in 21st-century plankton communities

Abstract: Marine microbial communities sustain ocean food webs and mediate global elemental cycles. These communities will change with climate; such changes can be gradual or foreseeable, but likely have much more substantial consequences when sudden and unpredictable.

In a complex virtual marine microbial ecosystem, we find climate-change-driven shifts over the 21st century are often abrupt, large in amplitude and extent, and unpredictable using standard early warning signals. Phytoplankton with unique resource needs, especially fast-growing species such as diatoms, are more prone to abrupt shifts.

Abrupt shifts in biomass, productivity, and community structure are concentrated in Atlantic and Pacific subtropics. Abrupt changes in environmental variables such as temperature and nutrients rarely precede these ecosystem shifts, indicating that rapid community restructuring can occur in response to gradual environmental changes, particularly in nutrient supply rate ratios.

How predictable is plankton biogeography using statistical learning methods?

Abstract: Plankton play an important role in marine food webs, in biogeochemical cycling, and in moderating Earth's climate. Their possible responses to climate change are of broad scientific and social interest; yet observations are sparse, and mechanistic and statistical methods yield diverging predictions.

Here, we evaluate a statistical learning method using output from a 21st Century marine ecosystem model as a 'ground truth'. The model is sampled to mimic historical ocean observations, and Generalised Additive Models (GAMs) are used to predict the simulated plankton biogeography in space and time. Predictive skill varies across test cases, and between functional groups, and errors are more attributable to spatiotemporal sampling bias than to sample size.

Overall, the GAMs yield poor end-of-century predictions. Given that statistical methods are unable to capture changes in relationships between variables over time, we advise caution in their application and interpretation, particularly when modelling complex, dynamic systems.

Future phytoplankton diversity in a changing climate

Abstract: The future response of marine ecosystem diversity to continued anthropogenic forcing is poorly constrained.  An extremely diverse set of organisms form the base of the marine ecosystem: phytoplankton. Currently, ocean biogeochemistry and ecosystem models used for climate change projections typically include only 2-3 phytoplankton types, and are thus too simple to adequately assess the potential for changes in plankton community structure.

Here we analyze a complex ecosystem model with 35 phytoplankton types to evaluate the changes in phytoplankton community composition, turnover and size structure over the 21st century. We find that the rate of turnover in the phytoplankton community becomes faster during this century, i.e. the community structure becomes increasingly unstable in response to climate change. 

Combined with alterations to phytoplankton diversity, our results imply a loss of ecological resilience, with likely knock-on effects on the productivity and functioning of the marine environment. 

Global cancer risk from unregulated polycyclic aromatic hydrocarbons

Key Points:

  • Benzo[a]pyrene is a small contributor to human cancer risk of PAHs worldwide (11 %)

  • Using benzo[a]pyrene as a surrogate compound leads to erroneous conclusions about high-risk populations and the importance of uncertain chemical processes
  • Science and policy could be improved by considering a wider group of both emitted PAHs as well as their degradation products

Summary: Nearly 90% of global human lung cancer risk from polycyclic aromatic hydrocarbons (PAHs) comes from compounds omitted by prior analyses and not regulated directly. PAHs in the atmosphere are a complex mixture, but regulators and researchers often represent them using a single compound, namely benzo(a)pyrene. We show that benzo(a)pyrene is a poor indicator of global PAH cancer risk; its use as a proxy leads to erroneous conclusions about high-risk populations and atmospheric chemical processes. We find that approximately 17% of risk comes from PAHs that are produced in atmospheric reactions and are not regulated or routinely monitored. Regulators and researchers should focus on the entire mixture of PAHs in the atmosphere, and we recommend that benzo(a)pyrene not be used as a sole reference compound.

From the abstract:

Changes in temperature, precipitation, sea level and coastal storms will likely increase the vulnerability of infrastructure across the USA. Using models that analyze vulnerability, impacts and adaptation, this paper estimates impacts to railroad, roads, and coastal properties under three infrastructure management response scenarios: No Adaptation; Reactive Adaptation, and Proactive Adaptation. Comparing damages under each of these potential responses provides strong support for facilitating effective adaptation in these three sectors.

Climate effects on US infrastructure
Climate effects on US infrastructure: the economics of adaptation for rail, roads, and coastal development

Abstract: Changes in temperature, precipitation, sea level and coastal storms will likely increase the vulnerability of infrastructure across the USA. Using models that analyze vulnerability, impacts and adaptation, this paper estimates impacts to railroad, roads, and coastal properties under three infrastructure management response scenarios: No Adaptation; Reactive Adaptation, and Proactive Adaptation. Comparing damages under each of these potential responses provides strong support for facilitating effective adaptation in these three sectors.

Under a high greenhouse gas emissions scenario and without adaptation, overall costs are projected to range in the $100s of billions annually by the end of this century. The first (reactive) tier of adaptation action, however, reduces costs by a factor of 10, and the second (proactive) tier reduces total costs across all three sectors to the low $10s of billions annually. For the rail and road sectors, estimated costs for Reactive and Proactive Adaptation scenarios capture a broader share of potential impacts, including selected indirect costs to rail and road users, and so are consistently about a factor of 2 higher than prior estimates. 

The results highlight the importance of considering climate risks in infrastructure planning and management.

 

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