SeaWeb - Ocean Briefing Book

Climate Change and Ocean Wildlife

The Earth’s average surface temperature has increased by about 1°F (0.6°C) over the last century bringing the global temperature to its highest level for the past 1000 years. There is broad scientific consensus that this is, at least in part, a result of human activity. Projections laid out by the Intergovernmental Panel on Climate Change (IPCC) in their Third Assessment Report (2001) estimate a further rise in surface temperature of 2.5 - 10.4°F (1.4 - 5.8°C) between 1990 and 2100. For the same time period, the IPCC estimated a sea level rise of 3.5 in - 2.9 ft (0.09 - 0.88 m), primarily from thermal expansion of seawater and the melting of glaciers and icecaps. The IPCC projections, however, are based on the ‘worst-case’ scenario of no direct governmental intervention in reducing human forcing of the climate system. Projections are also based on the assumption that the global climate will change gradually. The wide range in the IPCC figures is largely due to significant uncertainties over future emissions (as related to potential technological, social and economic developments, and human population growth) and the response of the climate system to the buildup of greenhouse gases.

The Problem

The warming of the Earth’s climate is generating much scientific concern over the consequential biological and ecological changes, including: the range and distribution of species; their natural history traits (of which many are triggered by temperature-related cues); the cycles, composition, and interactions of communities; and the structure and functioning of ecosystems. Impacts on marine species as a result of rising temperatures have been recently documented and suggest that an array of changes is already underway. For example:
- The body condition and reproductive success of polar bears in western Hudson Bay (Canada) have, according to polar bear scientists, “declined significantly” over the past 25 years because of the advanced break-up of ice in the Arctic spring. Advanced ice break-up—which has been correlated with a long-term warming trend in the region—reduces the time the bears can feed on seals to build up fat reserves and extends the species’ time ashore during their summer fast. Continuation of such a trend suggests that more southerly populations of polar bears may face extinction.
- There have been increased rates of breeding failure and adult mortality in Brünnich’s guillemot in northern Hudson Bay—considered to be the combined result of increased mosquito parasitism and temperature stress. Warming temperatures in the Arctic have advanced the dates in peak abundance of mosquitos so that they now coincide with the nesting period of this seabird species.
- There has been a northward expansion of two important oyster diseases – Dermo and MSX – along the east coast of the U.S. in conjunction with warming winter temperatures. Dermo, caused by a protozoan parasite, was confined to Chesapeake Bay during the 1980s but by the mid-1990s had reached epidemic proportions in Delaware Bay and had extended its range to Maine.
- The intensity and frequency of coral ‘bleaching’ episodes has increased notably since the early 1980s and, in 1998, the warmest year on record, an estimated 16% of the world’s reef-building corals died. When exposed to elevated temperature—as little as 1.8°F (1°C) over the normal seasonal maximum—corals can bleach (i.e., the reduction or loss of their photosynthetic pigments); this curtails growth and reproduction and may ultimately lead to death of the coral. A variety of climate change-related factors have the potential to harm reefs including increases in sea surface temperature and the frequency and/or intensity of storm events, and a rising sea level, among others. Reductions in coral habitat are expected to have an impact on the viability of many reef-dwelling wildlife species.
Projecting impacts associated with a changing climate is extremely difficult given, for example, the chaotic nature of the climate system and complexity of the natural environment, the uncertainties and limitations associated with computer modelling, uncertainties associated with greenhouse gas emission scenarios, and the complexity of interactions involving climate with other components of human-mediated environmental change. Nonetheless, on the basis of current knowledge, a range of potential marine wildlife impacts has been suggested by scientists. Some of these include:
- Increase in algal poisoning events involving marine mammals, seabirds and fish if toxic phytoplankton species and their bloom dynamics are favored by oceanic changes—Over the last two decades a global increase in harmful algal blooms (HABs or ‘red tides’) has been documented—though no connection to the current trend in rising temperatures has been shown. Impacts of blooms and toxicity events on marine wildlife can be substantial as evidenced by recent mass mortalities involving such species as the California sea lion, bottlenose dolphin, monk seal and manatee.
- A bias in favor of the production of female sea turtles as a result of higher mean temperatures on nesting beaches— Sea turtles exhibit temperature-dependent sex determination in that incubation temperature during embryonic development will determine the sex of the hatchling. Therefore, mean nest temperatures above a pivotal point (~84°F or ~29°C) will result in females while temperatures below that point will result in males. Six of the world’s seven species of sea turtle are already classified as ‘endangered’ or ‘critically endangered.’
- Increase in disease-related mass mortalities in pinnipeds (i.e., seals, walruses, fur seals and sea lions) from lengthened ‘haul-out’ times associated with warmer temperatures—Relatively small increases in temperature can prompt some pinniped species to congregate on land to bask. The increased density of animals for longer periods can promote the rapid spread of an opportunistic pathogen as direct contact time among animals is extended and airborne transmission of disease agents is facilitated.
- Losses of intertidal habitat for shorebirds as a result of sea level rise—Low-lying coastal and intertidal areas are critical feeding areas for migrating and overwintering shorebirds. A recent study—using conservative estimates of sea level rise—projected losses of 20% to 70% over the next century in current habitat at four U.S. sites considered internationally important for shorebird conservation. It was concluded that the ability of these sites—Willapa Bay, Humboldt Bay, San Francisco Bay, and Delaware Bay—to support current shorebird numbers would be jeopardized.
- Losses of ocean habitat for Pacific salmon with increasing ocean temperature—Pacific salmon distribution is sharply limited by sea surface temperature. Projections employed by one study—assuming a doubled CO2climate—found that rising temperatures would likely force Pacific salmon out of the entire Pacific Ocean and into the Bering Sea.
The potential impacts of a changing climate are also suggested by anomalous weather events and natural climatic cycles and subsequent changes in oceanographic conditions. For example, an atypical increase in water temperature in the southeastern Bering Sea in 1997 altered euphausid (small crustacean) availability for the short-tailed shearwater and the resultant shortage of food killed an estimated 600 000 to 2 000 000 birds. Indeed, many seabird species appear to be particularly vulnerable to changes in climatic conditions, and persistent or extreme events can cause reproductive failure and starvation and, ultimately, massive declines in numbers. The warmer surface waters associated with the strong El Niño of 1982-83 reduced prey availability for Galapagos penguins and resulted in an 80% population decline in this now endangered species. El Niño events, notably, have been increasing over the past two decades and parallel the overall warming of the Pacific Ocean. The gradual warming in sea surface temperature due to another natural climate cycle, the Pacific Decadal Oscillation, is considered the reason behind the 90% drop in sooty shearwater numbers along the west coast of the U.S. during the late 1980s and early 1990s.

The Causes

Incoming energy from the Sun is absorbed by the Earth and then redistributed by atmospheric and oceanic circulation before being radiated back to space. Naturally occurring ‘greenhouse gases’ in the Earth’s atmosphere—water vapor (H2O), carbon dioxide (CO2), ozone (O3), methane (CH4) and nitrous oxide (N2O)—absorb some of this outgoing thermal radiation which is ultimately reflected back to warm the Earth’s surface and lower atmosphere. This phenomenon is typically known as the ‘greenhouse effect’.
An enhanced greenhouse effect, however, is now considered to be occurring, the result of substantially higher atmospheric concentrations of some of the natural greenhouse gases. Current atmospheric concentrations of CO2—the dominant human-influenced greenhouse gas—have not been exceeded during the past 420 000 years and likely have not been, according to the IPCC, for the past 20 million years. The primary human-related causes of CO2release are fossil fuel combustion (mainly oil, coal and gas) and deforestation. Atmospheric methane concentration has increased by approximately 150% since the mid-1700s, largely due to livestock production, the decomposition of refuse in landfills, and fossil fuel production and use. Nitrous oxide concentration has increased by 16% since the mid-1700s with the major human-related sources including nitrogen fertilizer use, industrial activities, and livestock production.
New, industrially-produced gases, such as the perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs), and sulphur hexafluoride (SF6), are also accumulating in the atmosphere. Though current atmospheric concentrations are small, some are very radiatively effective and extremely long-lived; SF6, for example, used in high voltage applications, is over 22 000 times more effective a greenhouse gas than CO2 and has an estimated lifetime of 3200 years.

The Context

The effect of climate change on marine wildlife needs to be viewed in the context of multiple human impacts—past, present, and future. These include, for example, nutrient and toxic chemical pollution, coastal development and habitat loss, overfishing and destructive fishing practices, and via the dispersal or introduction of non-native species and pathogens. For example, long-term monitoring in the Gulf of Maine has revealed profound changes since the early 1980s as a result of overfishing, the physical impacts on bottom communities from trawling, introduced species (seaweeds and invertebrates), and an increase in summer water temperatures. The scientists involved report that “[I]t is likely that climate change and the ecological release created by sustained overfishing are acting synergistically to create an environment that favors opportunists and introduced species, especially species from more temperate environments than have been historically prevalent in the Gulf of Maine.”
The U.S. National Research Council (NRC) affirmed in a 2002 report (Abrupt Climate Change: Inevitable Surprises) that recent research clearly shows that “major and widespread climatic changes” in the past occurred with “startling” speed. By example the NRC noted that approximately half of the north Atlantic warming since the last ice age took place within ten years and was accompanied by “significant” climatic changes across most of the globe. The NRC report further noted that: “[A]brupt climate changes were especially common when the climate system was being forced to change most rapidly. Thus, greenhouse warming and other human alterations of the earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events. The abrupt changes of the past are not fully explained yet, and climate models typically underestimate the size, speed, and extent of those changes. Hence, future abrupt changes cannot be predicted with confidence, and climate surprises are to be expected. The new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers.”
The U.S. is a signatory to the United Nations Framework Convention on Climate Change (UNFCCC). The Convention, which entered into force in 1994, calls for “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” The UNFCCC did not set out binding, quantitative emission reductions for the signatory countries and so, in 1997, the Kyoto Protocol was adopted to fulfill this need.
U.S. climate policy under the George W. Bush administration is geared towards voluntary reductions in greenhouse gas emissions, programs for societal adaptation, and continuing long-term research. Under the proposed voluntary reduction program, U.S. emission rates would continue to increase at about 14% per decade. The U.S. has also withdrawn from international engagement—such as the Kyoto Protocol— in reducing human interference of the climate system. Present U.S. measures, therefore, have been criticized as running counter to a ‘no-regrets’ or a ‘precautionary’ approach, particularly in light of the potential for rapid or unforeseen climatic changes and the lack of evidence suggesting that changes can be controlled once they have begun to occur.