Oceans’ role in regulating climate
Oceans make up 95 percent of the space that is habitable on our planet and encompass 71 percent of its surface. They offer us free goods and services, such as the food we eat and the oxygen we breathe, and they are the Earth’s life support system. The oceans control climate on a variety of timescales, from geological and millennial to decadal, interannual, and shorter, through a variety of natural processes and feedback mechanisms. The oceans also control the climate on a global scale. They moderate temperature, control precipitation, and prevent droughts and floods. One way that the oceans of the world influence weather and climate is by helping to keep our planet warm. The ocean absorbs the majority of solar energy, especially in tropical areas around the equator where it functions as a giant, heat-retaining solar panel. Land areas also absorb a small amount of sunlight, while the atmosphere keeps heat from escaping into space after sunset.
The ocean not only stores solar radiation but also aids in the distribution of heat around the world. When water molecules are heated, they freely exchange with the surrounding air, a process known as evaporation. Ocean water constantly evaporates, raising the temperature and humidity of the surrounding air, resulting in rain and storms carried by trade winds. In fact, nearly all rain that falls on land originates in the ocean. The tropics are especially rainy because heat absorption and thus ocean evaporation are greatest in this region.
Another function of oceans is to mitigate climate change; due to the ocean’s capacity to absorb heat and greenhouse gases like carbon dioxide (CO2), they have largely buffered (neutralized) the impacts of rising levels of greenhouse gases from human activity in the atmosphere. It is estimated that they contribute to 83 percent of the carbon cycle. However, there is strong evidence that many of the systems that contribute to this buffering function have been evolving, possibly in reaction to climate change in certain situations.
Figure 1. Through the storage of solar radiation, global distribution of heat and moisture, and control of weather systems, the ocean has an impact on weather and climate. Credits: https://www.seatemperature.org/
Changes in ocean climate
Even though human activities are frequently blamed for influencing the stability of marine ecosystems, particularly fisheries, the ocean biosphere is currently undergoing rapid global climate change. According to theoretical data from the Intergovernmental Panel on Climate Change (IPCC), depending on the greenhouse gas emission scenario, the air temperature will likely rise by about 0.4 to 2.6 °C in the short term (2016–2035). It is also anticipated that as global temperatures rise, glaciers will retreat, rainfall patterns will shift globally in terms of frequency and intensity, and extreme temperatures will rise including ocean temperatures.
According to recent studies, the oceans have absorbed 83 percent of the warming experienced by the planet over the past 200 years. As a result, rising seawater temperatures are expected to have a significant impact on marine species and community structures, as well as changes in ocean primary productivity, in turn affecting the entire food web and ecosystem services. Climate change has an impact on the plants and animals that live in the water column (pelagic ecosystems), ranging from phytoplankton to zooplankton to higher trophic levels. Phytoplankton is the tiny plants that absorb solar energy and convert it into food; they are the producers of the subpolar and polar food web. Because they are so small, they can divide and grow very quickly in response to the more intense and longer-lasting light of summer. On other hand, zooplankton is the tiny animals that feed directly on phytoplankton. In Antarctica, they are frequently krill (tiny crustaceans), which provide food for the majority of the larger animals. Global climatic modifications have already been documented as causing “rapid and unprecedented changes in the marine ecosystem,” particularly in commercially important fisheries that relied on krill.
Phenology changes
Another negative effect of climate change on ecosystems is the disruption of biological interactions caused by changes in species phenology. The field of research known as phenology investigates how climatic conditions affect the life cycles of organisms. Climate change’s main effect, an increase in global average temperature, has the potential to alter the phenological synchrony of biological relationships between species, as seen in whale feeding webs.
Whales are the largest animals to have ever lived, even larger than the largest dinosaurs. There are two reasons for their enormous size, which is well over a hundred tonnes for the largest blue whales and approaching this amount for some other whale species. First, because they live in the oceans, their large volume can be supported by the buoyancy of the water rather than having to be supported on land by legs and muscles. Second, whales feed on the first levels of the food chain (zooplankton), which means there is more energy available for the whales to grow to enormous sizes. Because there are more steps and thus more energy is lost as you move up the food chain, the biomass of the animals (that is, the number of animals multiplied by their weight) decreases.
Calanus finmarchicus is a species of copepod that plays an important structural role in the North Atlantic polar biome. As a phytoplankton grazer and prey for higher trophic levels such as the larval stages of many fish species and mammals, the species plays an important trophic role in subpolar and polar ecosystems. Right whales almost entirely feed on dense aggregations of calanoid copepods, primarily Calanus finmarchicus. However, decadal changes in the spatial distribution of Calanus finmarchicus in the North Sea between 1960 and 2005 revealed a progressive reduction in the species’ spatial habitat at the southern edge of its range, putting copepod-dependent populations in danger. Climate change causes the shrinking of the highly productive marginal sea ice biome by 42 percent in the Northern Hemisphere and 17 percent in the Southern Hemisphere. Therefore, this decrease in copepod populations is most likely the result of climatic fluctuations in ocean temperatures.
Whale populations trends
Trends in species abundance can help identify factors limiting population size and best protection practices. According to the World Wildlife Fund’s (WWF) Living Planet Report 2020, monitored population sizes of mammals, fish, birds, reptiles, and amphibians declined by an average of 68 percent between 1970 and 2016.
Since 2011, the population of North Atlantic right whales has been declining. With only 400-450 individuals left, the right whale (Eubalaena glacialis) is one of the world’s most endangered baleen whales. Right whales can currently be found in coastal areas stretching from the southeast of the United States to the Gulf of St. Lawrence and the Scotian Shelf. Right whale sightings are occasionally reported in isolated locations to the north and east of this range, in regions that once belonged to the species’ historical range. Even though they have been protected from commercial whaling since 1935, right whale populations have been slow to recover from near extinction due to more than three centuries of sustained hunting across their habitat.
Right whale phenology shifts are probably a result of widespread changes in habitat use throughout the species’ range. This drop is caused by both lower calving rates and higher anthropogenic mortality. However, entanglement in fishing gear and ship impacts are currently the main causes of right whale mortality. Because of these immediate effects of human activity as well as longer-term concerns from shifting distributions of food supplies as a result of climate change, the long-term survival of the species is now thought to be doubtful.
The Gulf of Maine is one of the ocean’s fastest-warming regions, making it an ideal system for studying phenological and biological responses to climate change. Over the past three decades, aerial and shipboard investigations have identified seven sites where right whales generally congregate periodically. One of seven locations in the Gulf of Maine where right whales seasonally concentrate is made up by Massachusetts Bay (MB) and Cape Cod Bay (CCB).
A group of researchers led by the New England Aquarium and including researchers from the University of Massachusetts Amherst, the USGS Northeast Climate Adaptation Science Center, the Center for Coastal Studies, UCLA, the National Marine Fisheries Service, and the Canadian Wildlife Service investigated the hypothesis that the phenology of the habitat use of large whales (right whales, humpback whales, and fin whales) in Cape Cod Bay (USA) has changed and is related to changes at a regional scale in the thermal beginning of spring.
The researchers found that until 2011, right whales in these feeding areas followed consistent phenology. However, to date for right whales, the peak habitat usage date shifted by +18.1 days (0.90 days/year), whereas for humpback whales, it shifted by +19.1 days (0.96 days/year). According to these findings, right whales, which are more specialized planktivorous eaters than fin and humpback whales, which are more general piscivorous eaters, would respond more strongly to thermal phenology and are more susceptible to climate change.
As a result, recent demographic models predict that the North Atlantic right whale will become extinct within the next 200 years if current mortality, phenological disruptions, and reproduction trends continue. Although overfishing is frequently cited as the cause of the decline of the marine ecosystem, temperature obviously has a similar impact.
The only item on the shortlist: reducing climate change
Many times, public perceptions of climate change’s causes, effects, and wider implications determine how individuals, societies, and polities respond to it. In the context of climate change, significant emissions reductions, the development and deployment of low-carbon energy technologies, and the implementation of adaptation measures all call for varying degrees of citizen involvement, from the issuance of policy mandates to active behavioral change. However, the evidence suggests that, while many people are motivated, they lack the necessary knowledge to act.
The shortlist is a collection of solutions or approaches proposed by the scientific community to address climate change. These approaches include acceptance of the reality of climate change, acceptance of a human role in its causes, level of concern for its effects, and beliefs about one’s own and broader responsibilities for addressing it. Unfortunately, the public perception of climate change at the global level suggests that even roughly 40 percent of the population does not know anything about it or suggests that this is not a severe problem.
What are the most effective energy-saving actions that the public can take, and how can policymakers at all levels assist the public in achieving these savings? Talking about climate change is one of the most meaningful and effective things we can do. Get informed, share information, and discuss it with your friends, family, and community members. Awaken your consciences, because the climatic emergency has arrived and will be our legacy to future generations.
Figure 2. According to experts, there are only 400-450 critically endangered North Atlantic right whales left, and phenological disruptions between food sources and reproductive refuges are important treats for this iconic species.
Credits: Adam Ernster on pexels
References
- Sarmiento, J. L. et al. Response of ocean ecosystems to climate warming. Glob. Biogeochem. Cycles 18, (2004).
- Gardner, G. T. & Stern, P. C. The Short List: The Most Effective Actions U.S. Households Can Take to Curb Climate Change. Environ. Sci. Policy Sustain. Dev. 50, 12–25 (2008).
- Kirby, R. R. & Beaugrand, G. Trophic amplification of climate warming. Proc. R. Soc. B Biol. Sci. 276, 4095–4103 (2009).
- Reygondeau, G. & Beaugrand, G. Future climate-driven shifts in distribution of Calanus finmarchicus. Glob. Change Biol. 17, 756–766 (2011).
- Rogelj, J., Meinshausen, M. & Knutti, R. Global warming under old and new scenarios using IPCC climate sensitivity range estimates. Nat. Clim. Change 2, 248–253 (2012).
- Pendleton, D. E. et al. Decadal-scale phenology and seasonal climate drivers of migratory baleen whales in a rapidly warming marine ecosystem. Glob. Change Biol. 28, 4989–5005 (2022).
- Charif, R. A. et al. Phenological changes in North Atlantic right whale habitat use in Massachusetts Bay. Glob. Change Biol. 26, 734–745 (2020).
