Estimated impacts of climate warming on California’s high-elevation hydropower

California’s hydropower system is composed of high and low elevation power plants. There are more than 150 high-elevation power plants, at elevations above 1,000 feet (300 m). Most have modest reservoir storage capacities, but supply roughly 74% of California’s in-state hydropower. The expected shift of runoff peak from spring to winter due to climate warming, resulting in snowpack reduction and increased snowmelt, might have important effects on power generation and revenues in California. The large storage capacities at low-elevation power plants provide flexibility to operations of these units under climate warming. However, with climate warming, the adaptability of the high-elevation hydropower system is in question as this system was designed to take advantage of snowpack, a natural reservoir. With so many high-elevation hydropower plants in California, estimation of climate warming effects by conventional simulation or optimization methods would be tedious and expensive. An Energy-Based Hydropower Optimization Model (EBHOM) was developed to facilitate practical climate change and other low-resolution system-wide hydropower studies, based on the historical generation data of 137 high-elevation hydropower plants for which the data were complete for 14 years. Employing recent historical hourly energy prices, the model was used to explore energy generation in California for three climate warming scenarios (dry warming, wet warming, and warming-only) over 14 years, representing a range of hydrologic conditions. The system is sensitive to the quantity and timing of inflows. While dry warming and warming-only climate changes reduce average hydropower revenues, wet warming could increase revenue. Re-operation of available storage and generation capacities help compensate for snowpack losses to some extent. Storage capacity expansion and to a lesser extent generation capacity expansion both increase revenues, although such expansions might not be cost-effective.     

Adapting California’s water management to climate change

California faces significant water management challenges from climate change, affecting water supply, aquatic ecosystems, and flood risks. Fortunately, the state also possesses adaptation tools and institutional capabilities that can limit vulnerability to changing conditions. Water supply managers have begun using underground storage, water transfers, conservation, recycling, and desalination to meet changing demands. These same tools are promising options for responding to a wide range of climate changes. Likewise, many staples of flood management—including reservoir operations, levees, bypasses, insurance, and land-use regulation—are available for the challenges of increased floods. Yet actions are also needed to improve response capacity. For water supply, a central issue is the management of the Sacramento-San Joaquin Delta, where new conveyance, habitat investments, and regulations are needed to sustain water supplies and protect endangered fish species. For flood management, among the least-examined aspects of water management with climate change, needed reforms include forward-looking reservoir operation planning and floodplain mapping, less restrictive rules for raising local funds, and improved public information on flood risks. For water quality, an urgent priority is better science. Although local agencies are central players, adaptation will require strong-willed state leadership to shape institutions, incentives, and regulations capable of responding to change. Federal cooperation often will be essential.     

Air quality planning in California’s changing climate

California is home to some of the worst air quality in the nation and ninety percent of the state’s population lives in areas that are out of attainment with at least one of the National Ambient Air Quality Standards. Increasing temperatures associated with climate change will make meeting air quality standards more difficult. Under a changing climate, additional emission reductions will be needed to achieve clean air standards. These additional emission reductions and associated costs are called the “climate penalty.” Air quality planning is the process of assessing the emission reductions needed to meet air quality standards and outlining the programs and policies that will be implemented to achieve these emission reductions. This paper reviews the challenges that a changing climate will pose for air quality planning in California and identifies opportunities for adaptation. While state air quality regulators in California are taking enormous strides to address global warming, less work is happening at the regional, air district level. Air districts are the agencies responsible for developing air quality improvement plans. An important first step for regional air quality regulators will be to quantify the climate penalty and understand their region’s vulnerability to climate change. Limitations in regulatory authority could impede measures to improve preparedness. Regional agencies will likely need to look to state and federal agencies for additional emission reductions.     

Uncertainty in the 2°C warming threshold related to climate sensitivity and climate feedback

Climate sensitivity is an important index that measures the relationship between the increase in greenhouse gases and the magnitude of global warming. Uncertainties in climate change projection and climate modeling are mostly related to the climate sensitivity. The climate sensitivities of coupled climate models determine the magnitudes of the projected global warming. In this paper, the authors thoroughly review the literature on climate sensitivity, and discuss issues related to climate feedback processes and the methods used in estimating the equilibrium climate sensitivity and transient climate response (TCR), including the TCR to cumulative CO₂ emissions. After presenting a summary of the sources that affect the uncertainty of climate sensitivity, the impact of climate sensitivity on climate change projection is discussed by addressing the uncertainties in 2°C warming. Challenges that call for further investigation in the research community, in particular the Chinese community, are discussed.     

Adaptation of California’s electricity sector to climate change

Climate change is likely to pose considerable new challenges to California’s electricity sector. This paper primarily focuses on the adaptation challenges of an important component of the energy arena: electricity demand in the residential and commercial sectors and electricity supply. The primary challenge to California’s electricity sector will likely be the increase in demand for air conditioning as a result of rising temperatures. In addition, renewable energy sources, which are an increasing share of the electricity portfolio, are particularly vulnerable to climate change. Many of the key players have been actively considering the implications of climate change. Because electricity generation accounts for nearly 30% of greenhouse gas emissions, this sector has been a target of the state’s efforts to reduce emissions. Fortunately, many of the same tools can simultaneously improve the sector’s resilience to a changing climate. Demand management strategies and supply diversification are both important strategies. Local governments can play a central role in encouraging the adoption of more energy efficient building codes and the use of more renewable sources, such as solar energy. The positive steps taken by many local governments are encouraging. Steps to increase public awareness are an important, often missing component, however. Increases in research, development, and demonstration to improve system resiliency and develop new energy conservation tools are also needed.     

Erratum to: Simulating the impacts of climate change, prices and population on California’s residential electricity consumption

We discovered an error in the computer code generating the simulation results in section 5 of Auffhammer and Aroonruengsawat (Clim Chang 109(Supplement 1):191–210, 2011). While four out of five main findings are unaffected, the simulated impacts of climate change on annual residential electricity consumption are an order of magnitude smaller, which is consistent with findings in the previous literature.     

California’s local health agencies and the state’s climate adaptation strategy

A changing climate will exacerbate many of the problems currently faced by California’s public health institutions. The public health impacts of climate change include: an increase in extreme heat events and associated increases in heat-related morbidity and mortality, increases in the frequency and severity of air pollution episodes, shifts in the range and incidence of vector-borne diseases, increases in the severity of wildfire, increased risks of drought and flooding, and other extreme events. This article assesses the readiness of California’s public health institutions to cope with the changes that will accompany a changing climate and how they relate to strategies laid out in the state’s Climate Adaptation Strategy. County-level health offices are the front line actors to preserve public health in the face of numerous threats, including climate change. Survey results show that local health officers in California believe that climate change is a serious threat to public health, but feel that they lack the funding and resources to reduce this risk. Local health agencies also have a number of tools in place that will be helpful for preparing for a changing climate.     

Climate warming, water storage, and Chinook salmon in California’s Sacramento Valley

The Chinook salmon (Oncorhynchus tshawytscha) spawns and rears in the cold, freshwater rivers and tributaries of California’s Central Valley, with four separate seasonal runs including fall and late-fall runs, a winter run, and a spring run. Dams and reservoirs have blocked access to most of the Chinook’s ancestral spawning areas in the upper reaches and tributaries. Consequently, the fish rely on the mainstem of the Sacramento River for spawning habitat. Future climatic warming could lead to alterations of the river’s temperature regime, which could further reduce the already fragmented Chinook habitat. Specifically, increased water temperatures could result in spawning and rearing temperature exceedences, thereby jeopardizing productivity, particularly in drought years. Paradoxically, water management plays a key role in potential adaptation options by maintaining spawning and rearing habitat now and in the future, as reservoirs such as Shasta provide a cold water supply that will be increasingly needed to counter the effects of climate change. Results suggest that the available cold pool behind Shasta could be maintained throughout the summer assuming median projections of mid-21st century warming of 2°C, but the maintenance of the cold pool with warming on the order of 4°C could be very challenging. The winter and spring runs are shown to be most at risk because of the timing of their reproduction.     

PM2.5 co-benefits of climate change legislation part 1: California’s AB 32

The Scoping Plan for compliance with California Assembly Bill 32 (Global Warming Solutions Act of 2006; AB 32) proposes a substantial reduction in 2020 greenhouse gas (GHG) emissions from all economic sectors through energy efficiency, renewable energy, and other technological measures. Most of the AB 32 Scoping Plan measures will simultaneously reduce emissions of traditional criteria pollutants along with GHGs leading to a co-benefit of improved air quality in California. The present study quantifies the airborne particulate matter (PM_2.5) co-benefits of AB 32 by comparing future air quality under a Business as Usual (BAU) scenario (without AB 32) to AB 32 implementation by sector. AB 32 measures were divided into five levels defined by sector as follows: 1) industrial sources, 2) electric utility and natural gas sources, 3) agricultural sources, 4) on-road mobile sources and 5) other mobile sources. Air quality throughout California was simulated using the UCD source-oriented air quality model during 12 days of severe air pollution and over 108 days of typical meteorology representing an annual average period in the year 2030 (10 years after the AB 32 adoption deadline). The net effect of all AB 32 measures reduced statewide primary PM and NO_x emissions by ~1 % and ~15 %, respectively. Air quality simulations predict that these emissions reductions lower population-weighted PM_2.5 concentrations by ~6 % for California. The South Coast Air Basin (SoCAB) experienced the greatest reductions in PM_2.5 concentrations due to the AB 32 transportation measures while the San Joaquin Valley (SJV) experiences the smallest reductions or even slight increases in PM_2.5 concentrations due to the AB 32 measures that called for increased use of dairy biogas for electricity generation. The ~6 % reduction in PM_2.5 exposure associated with AB 32 predicted in the current study reduced air pollution mortality in California by 6.2 %, avoiding 880 (560–1100) premature deaths per year for the conditions in 2030. The monetary benefit from this avoided mortality was estimated at $5.4B/yr with a weighted average benefit per tonne of $35 k/tonne ($23 k/tonne–$45 k/tonne) of PM, NO_x, SO_x, and NH₃ emissions reduction.     

Building resilience to climate change through development assistance: USAID’s climate adaptation program

The topics of climate change and of what to do about it have been the subject of discussion for over two decades. Much of the focus has been on mitigating greenhouse gas emissions to reduce the rate and magnitude of changes. Adapting to the impacts of those changes has received much less attention. In recent years, the development assistance community has recognized that climate change poses a stress on economic and social development in poor countries and has turned its attention to addressing climate stress. The US Agency for International Development developed a methodology of working with stakeholders to identify sources of climate related vulnerability and approaches to reducing that vulnerability. The methodology was developed iteratively with several pilot studies looking at vulnerability and adaptation in different sectors and settings.     

“Grand Paris”: regional landscape change to adapt city to climate warming

“Grand Paris” is a study carried out by ten teams of researchers and city planners in the aim of putting forward general guidelines for Paris urban area’s evolution by 2030. All the teams suggest making the area “greener” in some way, to combat climate warming by CO₂ sequestration. Our team also shows that extending the nearby forests by 30 %, favouring short farm-to-consumer circuits and using lighter coloured building materials will decrease the urban heat island, reducing the mortality during heat waves as well as the need for air-conditioning. These results lead us to reverse the way of thinking urban planning: the geographic and natural aspects should replace the urban infrastructure as a driver for planning urban development. This new strategy allows city changes on quite a large scale, that will have a favourable impact in terms of economics, leisure activities, greenhouse gas emissions and the local microclimate.     

Sea level rise and tigers: predicted impacts to Bangladesh’s Sundarbans mangroves

The Sundarbans mangrove ecosystem, shared by India and Bangladesh, is recognized as a global priority for biodiversity conservation. Sea level rise, due to climate change, threatens the long term persistence of the Sundarbans forests and its biodiversity. Among the forests’ biota is the only tiger (Panthera tigris) population in the world adapted for life in mangrove forests. Prior predictions on the impacts of sea level rise on the Sundarbans have been hampered by coarse elevation data in this low-lying region, where every centimeter counts. Using high resolution elevation data, we estimate that with a 28 cm rise above 2000 sea levels, remaining tiger habitat in Bangladesh’s Sundarbans would decline by 96% and the number of breeding individuals would be reduced to less than 20. Assuming current sea level rise predictions and local conditions do not change, a 28 cm sea level rise is likely to occur in the next 50–90 years. If actions to both limit green house gas emissions and increase resilience of the Sundarbans are not initiated soon, the tigers of the Sundarbans may join the Arctic’s polar bears (Ursus maritimus) as early victims of climate change-induced habitat loss.     

Challenges to addressing non-CO2 greenhouse gases in China’s long-term climate strategy

Under the Paris Agreement, countries are encouraged to submit long-term low greenhouse gas emissions development strategies. Such strategies will merge emissions goals with socio-economic objectives and enable countries to increase their ambition over time, thus offering an opportunity to close the gap between the current emissions trajectory and the Agreement’s ‘well below 2°C’ target. China is in the process of preparing its own long-term strategy. We argue in this article that non-CO₂ greenhouse gases (NCGGs) should be an essential component of China’s long-term low-emissions strategy. To incorporate NCGGs into China’s long-term low-emissions development strategy, key scientific and institutional challenges should be addressed, such as uncertainty about the accuracy of NCGG emissions inventories; uncertainty about future projections of NCGG emissions; and institutional coordination deficits and imbalanced policy approaches. Overcoming these barriers will have significant implications for climate change mitigation and can open a path for the development of concrete follow-up actions.

Key policy insights

• Non-CO₂ greenhouse gases (NCGGs) make up around 17% of China’s GHG emissions, but China has no quantified target to limit or reduce these gases.

• NCGG emissions mitigation should be an essential component of China's long-term low-emissions strategy, which is currently under development.

• Considerable uncertainty exists over both historical NCGG emissions data and forecasts. This poses challenges to developing a comprehensive multi-gas strategy.

• Institutional challenges must also be addressed, such as fragmentation of responsibility for NCGGs.

     

The western Mediterranean climate: how will it respond to global warming?

The paper discusses the newly produced temperature and precipitation series from instrumental observations in the Western Mediterranean (WM) area, dating back to 1654. The two series had a continuous swing and unstable coupling passing from correlation to anti-correlation. Only after 1950 are they permanently anti-correlated with increasing temperature and decreasing precipitation. It is not clear how long this coupling will persist. The analysis of the correlation between the Northern Hemisphere (NH) and the WM temperature anomalies and their trends shows a certain variability from 1850 to 1950; later a strong coupling between NH and WM. Results suggest that the WM climate is approaching a turning point that might locally oppose the adverse effects of Global Warming.     

The radiative forcing benefits of “cool roof” construction in California: quantifying the climate impacts of building albedo modification

Exploiting surface albedo change has been proposed as a form of geoengineering to reduce the heating effect of anthropogenic increases in greenhouse gases (GHGs). Recent modeling experiments have projected significant negative radiative forcing from large-scale implementation of albedo reduction technologies (“cool” roofs and pavements). This paper complements such model studies with measurement-based calculations of the direct radiation balance impacts of replacement of conventional roofing with “cool” roof materials in California. This analysis uses, as a case study, the required changes to commercial buildings embodied in California’s building energy efficiency regulations, representing a total of 4300 ha of roof area distributed over 16 climate zones. The estimated statewide mean radiative forcing per 0.01 increase in albedo (here labeled RF01) is ?1.38 W/m². The resulting unit-roof-area mean annual radiative forcing impact of this regulation is ?44.2 W/m². This forcing is computed to counteract the positive radiative forcing of ambient atmospheric CO₂ at a rate of about 41 kg for each square meter of roof. Aggregated over the 4300 ha of cool roof estimated built in the first decade after adoption of the State regulation, this is comparable to removing about 1.76 million metric tons (MMT) of CO₂ from the atmosphere. The point radiation data used in this study also provide perspective on the spatial variability of cool roof radiative forcing in California, with individual climate zone effectiveness ranging from ?37 to ?59 W/m² of roof. These “bottom-up” calculations validate the estimates reported for published “top down” modeling, highlight the large spatial diversity of the effects of albedo change within even a limited geographical area, and offer a potential methodology for regulatory agencies to account for the climate effects of “cool” roofing in addition to its well-known energy efficiency benefits.