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About 89% of the public want their governments to do more to tackle the climate crisis, but don’t know they are in the majority.
As the Guardian article, A silent majority of the world’s people wants stronger climate action. It’s time to wake up points out, “At a time when many governments and companies are stalling or retreating from rapidly phasing out the fossil fuels that are driving deadly heat, fires and floods, the fact that more than eight out of 10 human beings on the planet want their political representatives to preserve a livable future offers a much-needed ray of hope. The question is whether and how that mass sentiment might be translated into effective action.”
The answer is the 89% of the heat of global warming that is going into the oceans that is 89% of the warming problem as well its solution.
The oceans play a crucial role in the global climate system by absorbing a significant portion of the excess heat generated from human activities that produce greenhouse gas emissions. This absorption has helped to moderate atmospheric warming; however, it has also caused substantial changes within the oceans, affecting marine ecosystems, contributing to sea-level rise, and influencing weather patterns. Ocean Thermal Energy Conversion (OTEC) offers a method for harnessing the thermal energy stored in the ocean by taking advantage of the temperature difference between warm surface waters and cold deep waters. While OTEC technology promises a sustainable and continuous energy source, its widespread adoption encounters challenges related to efficiency, cost-effectiveness, and potential environmental impacts. It is essential to explore these challenges and opportunities, along with other innovative uses of ocean heat, to fully understand the implications of ocean warming and to identify sustainable solutions.
The increasing concentration of greenhouse gases in the Earth’s atmosphere is trapping more thermal energy, leading to a significant imbalance in the planet’s energy budget. A major factor in this energy imbalance is the absorption of excess heat by the world’s oceans, which have absorbed about 89% of the additional heat added to the climate system as a result of human activities. This remarkable ability of the ocean to store heat has slowed the rate of atmospheric warming, yet it has profound effects on both the marine environment and the global climate.
The process by which the ocean absorbs heat from the atmosphere is complex. Sunlight, the primary source of energy for the Earth’s climate system, is easily absorbed by the ocean, especially in tropical regions. Covering over 70% of the planet’s surface, the ocean acts as a vast collector of solar energy. Additionally, increasing concentrations of greenhouse gases in the atmosphere, which are the result of the offgassing as the oceans warm, prevent heat radiated from the Earth’s surface from escaping into space. A significant portion of this trapped heat is transferred back to the ocean, raising its thermal content. This heat exchange primarily occurs at the ocean’s surface but gradually extends to deeper waters. The mixing of ocean waters, driven by waves, tides, and currents, plays a crucial role in distributing this heat both horizontally across different latitudes and vertically to greater depths. These processes ensure that the absorbed heat is circulated throughout the entire ocean basin rather than being confined to the surface. A key reason for the ocean’s ability to absorb large amounts of heat is the exceptionally high heat capacity of water compared to air. This property allows the ocean to absorb substantial heat energy with only a small increase in its overall temperature. For example, raising the temperature of water by one degree Celsius requires more than a thousand times the energy needed to do the same for air. This immense heat-storing capacity acts as a crucial buffer, preventing a much faster rise in atmospheric temperatures due to increasing greenhouse gas concentrations. Even seemingly minor changes in average ocean temperature signify the absorption of a tremendous amount of energy. Between 1993 and 2022, the total heat energy absorbed by the ocean was over 800 times the total electricity consumed by the United States in 2022, illustrating the sheer scale of energy involved.
The distribution of this additional heat within the ocean is not uniform. Initially, most of the excess energy is stored in the upper layers, particularly within the top 700 meters (approximately 2,300 feet). Scientific analyses indicate a clear long-term warming trend in these upper ocean layers since the mid-20th century. However, heat is gradually penetrating into deeper waters, reaching depths of up to 2,000 meters and even the ocean floor, although the rate of warming decreases with depth. Studies estimate that warming from 700 meters down to the ocean floor accounted for about 30% of the total increase in stored heat in the climate system between 1971 and 2010. Additionally, the rate of heat gain varies across different depth ranges. Geographically, ocean warming is also uneven; certain regions, such as parts of the North Atlantic and Indian Ocean, as well as the Arctic and Southern Oceans, are experiencing faster warming rates than others. This uneven distribution is influenced by factors such as ocean currents and local climate conditions.
Ocean currents play a vital role in the global climate by transporting heat around the planet. These currents function like a global conveyor belt, moving warm water from the equator towards the poles and cold water from the poles back to the tropics. This redistribution of heat helps regulate regional temperatures and influences weather patterns worldwide. Differences in water temperature and salinity create density gradients that drive these currents. The Southern Ocean, in particular, plays a significant role in absorbing anthropogenic heat due to a unique upwelling of deep waters that facilitates sustained heat absorption.
The Meridional Overturning Circulation is another crucial system that helps distribute heat throughout the ocean basins, including transporting heat to deeper layers. Changes in these ocean currents, potentially influenced by ongoing warming, could have significant implications for future climate patterns and heat distribution. The substantial increase in ocean heat content has numerous consequences, profoundly impacting marine ecosystems, contributing to rising sea levels, and altering global weather patterns. Marine ecosystems are especially vulnerable to the effects of ocean warming. One major impact is the increased frequency, duration, and intensity of marine heatwaves. These prolonged periods of unusually warm ocean temperatures can stress marine life, leading to mass die-offs of various species, including fish, marine mammals, and seabirds. For instance, a marine heatwave in the northeast Pacific Ocean from 2013 to 2016, known as “the Blob,” caused significant ecological changes and economic impacts along the coast.
Coral reefs, which are vital habitats for a vast array of marine life, are also severely threatened by warming waters, leading to coral bleaching. When water temperatures rise too high, corals expel the symbiotic algae that live in their tissues, causing them to turn white and potentially die. The loss of coral reefs can have devastating consequences for marine biodiversity and the overall health of ocean ecosystems.
Additionally, rising ocean temperatures are driving shifts in the distribution of marine species. Many fish species are migrating towards cooler waters, often towards the poles, which can affect fisheries and the livelihoods of communities that depend on them. These changes can also disrupt established breeding and feeding patterns. In some temperate regions, an increase in species diversity might be observed, while the changing conditions can favor the spread of invasive species, further destabilizing marine food webs. Furthermore, warmer ocean waters hold less dissolved oxygen. This, combined with increased ocean stratification that limits the mixing of oxygen-rich surface waters with deeper layers, contributes to the expansion of oxygen-depleted zones, often referred to as “dead zones,” rendering large areas uninhabitable for marine life. At the same time, the ocean’s absorption of atmospheric carbon dioxide is causing ocean acidification, which reduces the availability of carbonate ions that shell-forming organisms like corals, mollusks, and some plankton need to build and maintain their shells and skeletons. The combined effects of warming, acidification, and deoxygenation create a “deadly trio” of stressors that significantly threaten marine biodiversity and the functioning of ocean ecosystems.
Increased ocean heat content is a major contributor to global sea-level rise. When water warms, it expands in volume, a phenomenon known as thermal expansion. This thermal expansion of seawater is responsible for approximately one-third to one-half of the observed global sea-level rise. Since 1880, the global mean sea level has risen by about 8 to 9 inches, and the rate of increase has accelerated in recent decades. While thermal expansion is a significant factor, sea-level rise is also driven by the melting of glaciers and ice sheets, which adds water to the ocean. The combined effects of thermal expansion and ice melt pose serious threats to coastal infrastructure, ecosystems, and freshwater supplies, leading to increased flooding, erosion, and saltwater intrusion. In low-lying coastal areas and island nations, rising sea levels can result in permanent land loss and the displacement of populations. It is important to note that the rate of sea-level rise varies regionally due to factors such as land processes and changes in ocean currents.
The increase in ocean heat also significantly influences global weather patterns. Warmer sea surface temperatures provide more energy for the development and intensification of storms, including tropical cyclones and hurricanes. Higher temperatures lead to increased evaporation from the ocean surface, adding more moisture to the atmosphere, which can result in more intense rainfall and snowstorms. Changes in ocean temperatures and currents can also alter atmospheric circulation patterns, leading to shifts in precipitation. Some regions may experience more intense rainstorms and flooding, while others face exacerbated drought conditions. The warming ocean can also influence major climate phenomena, such as El Niño, potentially affecting their intensity and frequency. Overall, the increased heat in the ocean contributes to more extreme and unpredictable weather events worldwide.
All of these negative impacts can be mitigated by shifting the heat of global warming with a heat pipe and through a heat engine into deep water, from where the heat, unconverted to work by the heat engine, would remain for 250 years. After which it can be recycled 12 more times.
A heat pipe is one order smaller than the cold water pipe used in conventional OTEC, with the result systems using a heat pipe would be at least 30% cheaper.
OTEC stands as a promising renewable energy technology that harnesses the natural temperature difference existing between the warm surface waters of the ocean and the cold waters found at greater depths to generate electricity. The process fundamentally operates as a heat engine, leveraging the principles of thermodynamics, often employing the Rankine cycle to convert thermal energy into mechanical work, which in turn drives an electrical generator. Various configurations of OTEC systems have been developed, including closed-cycle systems that use a working fluid like ammonia, open-cycle systems that utilize seawater directly, and hybrid systems that combine aspects of both. A significant advantage of OTEC, particularly in tropical regions where the temperature gradient remains relatively constant throughout the year, is its potential to function as a base load power source, providing a steady and reliable supply of electricity. This consistency offers a notable benefit compared to other renewable energy sources such as solar and wind, which are inherently intermittent due to their dependence on weather conditions.
The efficiency of any heat engine, including an OTEC system, is defined as the ratio of the useful work output to the energy input. A theoretical upper limit for this efficiency is given by the Carnot efficiency, which depends solely on the absolute temperatures of the hot and cold reservoirs. The formula for Carnot efficiency is expressed as Efficiency = 1 – (Tc/Th), where Tc represents the absolute temperature of the cold reservoir and Th represents the absolute temperature of the hot reservoir, both measured in Kelvin. It is a fundamental principle of thermodynamics that the actual efficiency achieved by any real-world heat engine will always be lower than the theoretical Carnot efficiency due to various energy losses and system inefficiencies inherent in practical applications.
The typical thermal efficiency of early and many current OTEC systems falls within the range of 1 to 3%. This figure represents the net electrical energy output as a percentage of the thermal energy extracted from the ocean’s temperature gradient. Melvin Prueitt of Los Alamos National Laboratory, however, in his notable patent, US20070289303A1, focused on a novel method to enhance OTEC efficiency by employing small quantities of low-boiling-point fluids within a heat exchanger situated near the cold deep water. This design aimed at circumventing the energy-intensive process of pumping massive amounts of cold water to the ocean surface. By placing the condenser unit at a considerable depth, closer to the source of cold water, several potential advantages can be realized. One key benefit is the reduction in energy losses associated with pumping large volumes of cold water over long vertical distances to the surface. The consistently cold temperatures found at depth can also lead to more efficient heat transfer in the condenser. This improved heat transfer can allow for a lower condensing temperature of the working fluid, enhancing the overall efficiency of the thermodynamic cycle. Additionally, locating the condenser at depth can mitigate the environmental impact of discharging large quantities of cold, nutrient-rich water near the surface, which can disrupt local marine ecosystems. Some research even suggests that a deep-subsea OTEC concept could lead to a substantial increase in exergy efficiency. Additionally, a 1,000-meter-long column of the working fluid gas gains 5 degrees Celsius at the bottom of the column due to the influence of gravity, further enhancing the system’s efficiency.
The environmental impacts of Ocean Thermal Energy Conversion (OTEC) deployment are a critical consideration. Operating OTEC plants involves withdrawing and discharging large volumes of seawater, which can potentially affect the marine environment. The discharge of cooler, nutrient-rich deep water at the surface can alter local water quality by changing nutrient concentrations and potentially affecting dissolved gas levels. There is concern that this nutrient influx could increase the frequency and intensity of harmful algal blooms. Moreover, the large-scale operation of OTEC plants might influence local ocean circulation patterns.
A heat pipe, which allows for heated diffusion back to the surface at a rate of only 4 meters/year, would mitigate these problems, too.
The intake of large volumes of water poses risks to marine organisms through processes like entrainment, where small organisms are drawn into the plant, and impingement, where larger organisms become trapped against intake screens. These can cause stress, injury, or mortality to marine life.
To minimize these impacts, mitigation measures such as appropriately sized intake screens are necessary. Other potential environmental considerations include the use of biocides to prevent fouling in heat exchangers, which could affect water quality, and the electromagnetic fields emitted by underwater power cables that might influence the behavior of some marine species.
Beyond electricity generation, the thermal energy stored in the ocean and the byproducts of OTEC processes offer several other potential uses. One significant application is the desalination of seawater to produce freshwater. Open-cycle and hybrid OTEC systems are particularly well-suited for this purpose, as the steam produced in the open-cycle system is already desalinated. This capability is especially valuable for coastal and island communities facing water scarcity, providing a sustainable source of potable water powered by the ocean’s thermal energy.
One promising application of OTEC is in aquaculture, utilizing the cold, nutrient-rich deep seawater that results from OTEC operations. This deep seawater is often abundant in nutrients that can enhance growth rates and reduce stress on various aquatic species. A notable example is the successful farming of Maine lobsters in Hawaii, where cold deep water supplied by OTEC research facilities is used. This demonstrates the potential for creating sustainable seafood production systems that benefit from the unique properties of deep ocean water. Another application is seawater air conditioning (SWAC), which can leverage the cold deep seawater accessed by OTEC plants. By using this cold water to cool buildings, SWAC systems can significantly reduce energy consumption compared to traditional air conditioning, which is particularly high in tropical coastal regions where OTEC is most viable. For instance, a resort in Bora Bora employs deep-sea water for air conditioning, showcasing the practical advantages of this approach.
Beyond these established applications, there are innovative concepts for utilizing ocean heat. The electricity generated by OTEC can be used to produce hydrogen through the electrolysis of water. Hydrogen is a clean fuel with various applications, including transportation and industrial processes, which could help reduce reliance on fossil fuels. Additionally, the large volumes of deep seawater processed by OTEC plants may offer a potential source for mineral extraction, though this area requires further research and development.
The ocean’s absorption of a vast amount of heat due to global warming is a critical aspect of the changing climate. While this has temporarily buffered rapid atmospheric warming, it has also led to significant negative consequences for marine ecosystems, including marine heatwaves, coral bleaching, and shifts in species distribution, as well as contributing to sea-level rise and influencing weather patterns. OTEC presents a promising technology for harnessing the thermal energy stored in the ocean, offering a sustainable and continuous source of power, particularly for tropical regions with the necessary temperature gradient. However, challenges related to the efficiency and cost-effectiveness of OTEC systems, along with potential environmental impacts, must be carefully considered and addressed through ongoing research and development. Integrating OTEC with other applications, such as desalination, aquaculture, and seawater air conditioning, can enhance its economic viability and societal benefits. Furthermore, exploring innovative uses of ocean heat, such as hydrogen production and mineral extraction, could unlock additional value from this vast resource. Continued research, development, and pilot projects are essential to fully realize the potential of OTEC and other ocean-based technologies in mitigating climate change and providing sustainable energy solutions.
To enhance the utilization of ocean-stored heat and address the negative impacts of ocean warming, the following recommendations are proposed:
1. Investment in R&D: Significant investments should be directed toward research and development aimed at improving the thermodynamic efficiency and reducing the capital costs of Ocean Thermal Energy Conversion (OTEC) technology. This includes advancements in heat exchanger design, exploration of alternative working fluids and thermodynamic cycles, and the development of more cost-effective materials and construction techniques.
2. Pilot Projects: Support for pilot projects and demonstration plants at various scales is crucial for collecting comprehensive operational data on the performance, reliability, and economic viability of OTEC systems under real-world conditions. These projects should also focus on optimizing plant design for different applications and environments.
3. Environmental Impact Assessments: Thorough and comprehensive environmental impact assessments must be conducted for all proposed OTEC projects. Emphasis should be placed on developing and implementing effective mitigation strategies to minimize potential negative effects on marine ecosystems. This includes addressing concerns related to the entrainment and impingement of marine organisms, disruptions to water quality and nutrient distribution, and other ecological considerations.
4. Multi-Use Facilities: The development and promotion of multi-use OTEC facilities that integrate power generation with other valuable applications, such as desalination, aquaculture, and seawater air conditioning, should be prioritized. This integrated approach can enhance the economic attractiveness and overall sustainability of OTEC projects, especially in regions facing challenges related to energy, water, and food security.
5. Exploration of Byproducts: Further research should explore the potential for utilizing the thermal energy and byproducts of OTEC for other innovative industrial applications, such as hydrogen production and mineral extraction. These explorations could reveal additional value streams and support a more circular economy.
6. Supportive Policies: Governments and international organizations should develop supportive policies and regulatory frameworks that facilitate the responsible deployment of OTEC technology in suitable geographic regions. This includes providing incentives, streamlining permitting processes, and fostering international collaboration and knowledge sharing.
7. International Collaboration: Continued international collaboration and the open exchange of research findings, best practices, and lessons learned from existing and pilot OTEC projects are essential for accelerating the advancement and global adoption of this promising renewable energy technology that answers the call of 89% of the public for climate action.
