The physiological response of picophytoplankton to temperature and its model representation

Picophytoplankton account for most of the marine (sub-)tropical phytoplankton biomass and primary productivity. The contribution to biomass among plankton functional types (PFTs) could shift with climate warming, in part as a result of different physiological responses to temperature. To model these responses, Eppley's empirical relationships have been well established. However, they have not yet been statistically validated for individual PFTs. Here, we examine the physiological response of nine strains of picophytoplankton to temperature; three strains of picoprokaryotes and six strains of picoeukaryotes. We conduct laboratory experiments at 13 temperatures between –0.5 and 33°C and measure the maximum growth rates and the chlorophyll a to carbon ratios. We then statistically validate two hypotheses formulated by Eppley in 1972: The response of maximum growth rates to temperature (1) of individual strains can be represented by an optimum function, and (2) of the whole phytoplankton group can be represented by an exponential function Eppley (1972). We also quantify the temperature-related parameters. We find that the temperature span at which growth is positive is more constrained for picoprokaryotes (13.7–27°C), than for picoeukaryotes (2.8–32.4°C). However, the modeled temperature tolerance range (ΔT) follows an unimodal function of cell size for the strains examined here. Thus, the temperature tolerance range may act in conjunction with the maximum growth rate to explain the picophytoplankton community size structure in correlation with ocean temperature. The maximum growth rates obtained by a 99th quantile regression for the group of picophytoplankton or picoprokaryotes are generally lower than the rates estimated by Eppley. However, we find temperature-dependencies (Q10) of 2.3 and of 4.9 for the two groups, respectively. Both of these values are higher than the Q10 of 1.88 estimated by Eppley and could have substantial influence on the biomass distribution in models, in particular if picoprokaryotes were considered an independent PFT. We also quantify the increase of the chlorophyll a to carbon ratios with increasing temperature due to acclimation. These parameters provide essential and validated physiological information to explore the response of marine ecosystems to a warming climate using ocean biogeochemistry models

First report on research needs for verification

Biases and spread in the estimates of each term of the global carbon budget challenge the robust detection of a trend in their central estimates, and moreover inhibit the attribution of a trend in atmospheric CO2 to anthropogenic emissions. We outline the key sources of bias and spread in each term of the global carbon budget, highlight examples of progress made in recent years and opportunities for further progress in the coming decades. Overall, we suggest that the capacity to verify changes in atmospheric CO2 on sub-decadal timescales will require concerted effort to incrementally address biases and uncertainties across all components of the budget

Implications for workability and survivability in populations exposed to extreme heat under climate change: A modelling study

Background: Changes in temperature and humidity due to climate change affect living and working conditions. An understanding of the effects of different global temperature changes on population health is needed to inform the continued implementation of the Paris Climate Agreement and to increase global ambitions for greater cuts in emissions. By use of historical and projected climate conditions, we aimed to investigate the effects of climate change on workability (ie, the ability to work) and survivability (the ability to survive). Methods: In this modelling study, we estimated the changes in populations exposed to excessive heat stress between the recent past (ie, 1986–2005) and 2100. We used climate data from four models to calculate the wet-bulb globe temperature, an established heat exposure index that can be used to assess the effects of temperature, humidity, and other environmental factors on humans. We defined and applied thresholds for risks to workability (where the monthly mean of daily maximum wet-bulb globe temperature exceeds 34°C) and survivability (where the maximum daily wet-bulb globe temperature exceeds 40°C for 3 consecutive days), and we used population projections to quantify changes in risk associated with different changes to the global temperature. Findings: The risks to workability increase substantially with global mean surface temperature in all four climate models, with approximately 1 billion people affected globally after an increase in the global temperature of about 2·5°C above pre-industrial levels. There is greater variability between climate models for exposures above the threshold for risks to survivability than for risks to workability. The number of people who are likely to be exposed to heat stress exceeding the survivability threshold increases with global temperature change, to reach around 20 million people globally after an increase of about 2·5°C, estimated from the median of the models, but with a large model uncertainty. More people are likely to be exposed to heat stress in urban than in rural areas. Population exposure can fluctuate over time and change substantially within one decade. Interpretation: Exposure to excessive heat stress is projected to be widespread in tropical or subtropical low-income and middle-income countries, highlighting the need to build on the Paris Agreement regarding global temperature targets, to protect populations who have contributed little to greenhouse gas emissions. The non-linear dependency of heat exposure risk on temperature highlights the importance of understanding thresholds in coupled human-climate systems

The Challenge of Urban Heat Exposure under Climate Change: An Analysis of Cities in the Sustainable Healthy Urban Environments (SHUE) Database

The so far largely unabated emissions of greenhouse gases (GHGs) are expected to increase global temperatures substantially over this century. We quantify the patterns of increases for 246 globally-representative cities in the Sustainable Healthy Urban Environments (SHUE) database. We used an ensemble of 18 global climate models (GCMs) run under a low (RCP2.6) and high (RCP8.5) emissions scenario to estimate the increase in monthly mean temperatures by 2050 and 2100 based on 30-year averages. Model simulations were from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). Annual mean temperature increases were 0.93 degrees Celsius by 2050 and 1.10 degrees Celsius by 2100 under RCP2.6, and 1.27 and 4.15 degrees Celsius under RCP8.5, but with substantial city-to-city variation. By 2100, under RCP2.6 no city exceeds an increase in Tmean > 2 degrees Celsius (relative to a 2017 baseline), while all do under RCP8.5, some with increases in Tmean close to, or even greater than, 7 degrees Celsius. The increases were greatest in cities of mid to high latitude, in humid temperate and dry climate regions, and with large seasonal variation in temperature. Cities are likely to experience large increases in hottest month mean temperatures under high GHG emissions trajectories, which will often present substantial challenges to adaptation and health protection

The myriad challenges of the Paris Agreement

The much awaited and intensely negotiated Paris Agreement was adopted on 12 December 2015 by the Parties to the United Nations Framework Convention on Climate Change. The agreement set out a more ambitious long-term temperature goal than many had anticipated, implying more stringent emissions reductions that have been under-explored by the research community. By its very nature a multidisciplinary challenge, filling the knowledge gap requires not only climate scientists, but the whole Earth system science community, as well as economists, engineers, lawyers, philosophers, politicians, emergency planners and others to step up. To kick start cross-disciplinary discussions, the University of Oxford's Environmental Change Institute focused its 25th anniversary conference upon meeting the challenges of the Paris Agreement for science and society. This theme issue consists of review papers, opinion pieces and original research from some of the presentations within that meeting, covering a wide range of issues underpinning the Paris Agreement

Sensitivity of global ocean biogeochemical dynamics to ecosystem structure in a future climate

Terrestrial and oceanic ecosystem components of the Earth System models (ESMs) are key to predict the future behavior of the global carbon cycle. Ocean ecosystem models represent low complexity compared to terrestrial ecosystem models. In this study we use two ocean biogeochemical models based on the explicit representation of multiple planktonic functional types. We impose to the models the same future physical perturbation and compare the response of ecosystem dynamics, export production (EP) and ocean carbon uptake (OCU) to the same physical changes. Models comparison shows that: (1) EP changes directly translate into changes of OCU on decadal time scale, (2) the representation of ecosystem structure plays a pivotal role at linking OCU and EP, (3) OCU is highly sensitive to representation of ecosystem in the Equatorial Pacific and Southern Oceans

Going beyond two degrees? The risks and opportunities of alternative options

Since the mid-1990s, the aim of keeping climate change within 2 °C has become firmly entrenched in policy discourses. In the past few years, the likelihood of achieving it has been increasingly called into question. The debate around what to do with a target that seems less and less achievable is, however, only just beginning. As the UN commences a two-year review of the 2 °C target, this article moves beyond the somewhat binary debates about whether or not it should or will be met, in order to analyse more fully some of the alternative options that have been identified but not fully explored in the existing literature. For the first time, uncertainties, risks, and opportunities associated with four such options are identified and synthesized from the literature. The analysis finds that the significant risks and uncertainties associated with some options may encourage decision makers to recommit to the 2 °C target as the least unattractive course of action

Use of aviation by climate change researchers: Structural influences, personal attitudes, and information provision

Aviation is a fast-growing sector, releasing more carbon dioxide per passenger kilometre than other transport modes. For climate change researchers, work-related travel – including for conferences and fieldwork – is a major carbon-emitting activity. At the same time, many argue that climate scientists have an important role in curbing their own aviation emissions to align their practices with their assertions in relation to emissions reduction. We examine the tensions between competing professional demands in relation to flying; measure levels of flying by climate and non-climate researchers; assess influences on choices and attitudes; and consider how information provision and structural changes might enable changes in practice. Study 1 entails a large, international survey of flying undertaken by climate change (including sustainability and environmental science) researchers and those from other disciplines (N = 1408). Study 2 tests effects of varying information provision on researchers’ behavioural intentions and policy support to reduce flying (N = 362). Unexpectedly, we find climate change researchers – particularly professors – fly more than other researchers, but are also more likely to have taken steps to reduce or offset their flying. Providing information about the impacts of aviation increases behavioural intentions and support for institutional policies to reduce flying, particularly amongst more pro-environmental respondents. However, while attitudinal factors (e.g., personal norm) predict willingness to reduce flying, structural/social factors (e.g., family commitments, location) are more important in predicting actual flying behaviour. Recent initiatives to develop a low-carbon and more inclusive research culture within climate science and the broader research community thus need to be supported by broader policies and technologies to encourage and enable low-carbon and avoided travel

Certificates for CCS at reduced public cost: securing the UK's energy and climate future, Energy Bill 2015

This Paper concerns the Energy Bill, which starts its Committee stages in the Lords on Monday 7th September and Wednesday 9th September 2015. The Bill is mainly tasked to create the OGA (Oil and Gas Authority). In addition the Bill creates responsibilities for the OGA regarding Carbon Capture and Storage (CCS) licensing. Most importantly, the Bill raises the opportunity for a discussion of how the envisaged development of CCS will be paid for. At present, the funding model involves significant taxpayer support through the CCS competition and levy control framework on electricity. We make a simple proposal that would remove this burden of Government support, and spread the cost of CCS development and deployment across the entire fossil fuel sector through a Certificate scheme that would rely only on data already reported to Government and the OGA, thus minimising the costs of compliance.This Paper concerns the Energy Bill, which starts its Committee stages in the Lords on Monday 7th September and Wednesday 9th September 2015. The Bill is mainly tasked to create the OGA (Oil and Gas Authority). In addition the Bill creates responsibilities for the OGA regarding Carbon Capture and Storage (CCS) licensing. Most importantly, the Bill raises the opportunity for a discussion of how the envisaged development of CCS will be paid for. At present, the funding model involves significant taxpayer support through the CCS competition and levy control framework on electricity. We make a simple proposal that would remove this burden of Government support, and spread the cost of CCS development and deployment across the entire fossil fuel sector through a Certificate scheme that would rely only on data already reported to Government and the OGA, thus minimising the costs of compliance