Abstract
The 2015 Paris Climate Agreement recognizes the need for effective and progressive responses to the urgent threat of climate change, through mitigation and adaptation measures, while taking into account the particular vulnerabilities of food production systems. The inclusion of adaptation measures in the fisheries and aquaculture sector is currently hampered by a widespread lack of targeted analyses of the sector’s vulnerabilities to climate change and associated risks, as well as the opportunities and responses available. The most up-to-date information on the disaggregated impacts of climate change for marine and inland fisheries, and aquaculture, in the context of poverty alleviation and the differential dependency of countries on fish and fishery resources.
The work is based on model projections, data analyses, as well as
national, regional and basin-scale expert assessments. The results indicate that climate
change will lead to significant changes in the availability and trade of fish products,
with potentially important geopolitical and economic consequences, especially for those
countries most dependent on the sector.
Foreword
By 2050 humans will face the challenge of having to provide food and livelihoods to a population likely to exceed nine billion people. This challenge is well reflected in the United Nations Agenda 2030 for Sustainable Development, a global commitment to end poverty and hunger and to ensure that economic, social and technological progress occurs in harmony with nature, through the sustainable management of natural resources.
An additional consideration to the above challenge is that it will have to be met at a time when the effects of climate change will be increasingly prominent. The two cannot be separated and, indeed, the 2015 Paris Climate Agreement of the United Nations Framework Convention on Climate Change (UNFCCC: United Nations Framework Convention on Climate Change) explicitly recognizes the fundamental priority of safeguarding food security and ending hunger when taking climate action.
One of the novelties of the Paris Climate Agreement is the inclusion of a long-term adaptation goal – to increase the ability to adapt to the adverse impacts of climate change and foster climate resilience …/… in a manner that does not threaten food production – alongside the goal for mitigation. It also notes that the level of adaptation needed will be determined by the success of mitigation activities. To implement the Agreement member states are required to prepare, communicate and maintain successive Nationally Determined Contributions (NDCs: Nationally Determined Contributions), submitted every five years to the UNFCCC secretariat. The next round of NDCs (new or updated) is to be submitted by 2020.
Climate change and aquatic systems
Since 1988 the Intergovernmental Panel on Climate Change1 (IPCC) has been providing regular, evidence-based updates on climate change and its political and economic impacts. These updates comprehensively synthesize the internationally accepted consensus on the science of climate change, its causes and consequences. Based largely on the 5th IPCC Assessment Report (AR5), and recent scientific literature, this chapter provides an overview of the major impacts of climate change on the dynamics of aquatic systems (oceans, seas, lakes and rivers), and particularly on the aspects that relate to aquatic food production, i.e. fisheries and aquaculture.
OBSERVED CHANGES IN THE CLIMATE SYSTEM
Information on the climate system is based on multiple lines of evidence, which include direct and indirect observations and historical reconstructions going back thousands of years as well as more recent instrumental observations, conceptual and numerical models, including radiative and heat budgets. Based on analysis of these data, and not with standing the uncertainties associated with knowledge and data gaps, the IPCC AR5 concluded that the warming of the climate system was unequivocal, and that many of the observed changes since 1950 are unprecedented compared with preceding decades to millennia. At the global level, the Earth’s average surface temperature has increased by more than 0.8 °C since the middle of the nineteenth century, and is now warming at a rate of more than 0.1 °C every decade. Heat waves are more frequent now, even though the reliability of data and level of certainty vary across continents.
The largest contribution to this warming is believed to be from the increase in atmospheric concentration of GHGs, such as CO2, methane CH4 and nitrogen dioxide NO2. GHGs act like a thermal blanket around the planet and are responsible for allowing life on Earth to exist. The exponential increase in the emission of GHGs since the industrial revolution has resulted in atmospheric concentrations of these gases that are unprecedented in the last 800 000 years. For example, atmospheric CO2 concentrations increased from 278 ppm in the middle of the eighteenth century to around the current level of 400 ppm. The IPCC AR5 has also concluded that it is extremely likely that humans have been the dominant cause of the observed warming since the mid-twentieth century, through the association of GHG emissions with gas and oil combustion, deforestation, and intensive agriculture.
Only one percent of the additional heat caused by anthropogenic climate change is retained in the atmosphere, whilst 93 percent has been absorbed by the global ocean. The remaining three to four percent is absorbed by the melting of ice and snow. The ocean’s heat buffer is thus enormous and any small change in the balance of heat between ocean and atmosphere would have huge impacts on global air temperature.
IMPLICATIONS FOR AQUATIC SYSTEMS
Hydrological cycle and rainfall patterns
The warming of the climate has significant implications for the hydrological cycle. Changing precipitation, temperature and climatic patterns and the melting of snow and ice affect the quantity, quality and seasonality of water resources, leading to inevitable changes in aquatic ecosystems. Climate change is already causing permafrost warming and thawing in high-latitude regions, and in high-elevation regions it is driving glacier shrinkage, with consequences for downstream water resources.
In the marine systems, the melting of the Arctic sea ice has the potential to disrupt or slow down the global ocean conveyor belt.
Water temperature
Anthropogenic forcing has made a substantial contribution to the upper ocean warming (above 700 m) that has been observed since the 1960s, with the surface waters warming by an average of 0.7 °C per century globally from 1900 to 2016.
Ocean temperature trends over this period vary in different regions but are positive over most of the globe, although the warming is more prominent in the Northern Hemisphere, especially the North Atlantic. The upper ocean (0 m to 700 m) accounts for about 64 percent of the additional anthropogenic energy accumulated in oceans and seas. Upper ocean warming is expected to continue in the twenty-first century, especially in the tropical and Northern Hemisphere subtropical regions, whereas in deep waters the warming is expected to be more pronounced in the Southern Ocean.
Oxygen content
Dissolved oxygen is an important component of aquatic systems. Changes in its concentrations have major impacts on the global carbon and nitrogen cycles. The average dissolved oxygen concentration in the ocean varies significantly, ranging from super-saturated Antarctic waters to zero in coastal sediments where oxygen consumption is in excess of supply over sufficient periods of time. A large variety of such systems exist, including the so-called oxygen minimum zones (OMZs) in the open ocean, coastal upwelling zones, deep basins of semi-enclosed seas, deep fjords, and other areas with restricted circulation, but the discovery of widespread decreases in oxygen concentrations in coastal waters since the 1960s, and the expansion of the tropical OMZs in recent decades has raised concerns.
Ice coverage
Over the period 1979 to 2012 the average annual extent of Arctic sea ice decreased at a rate of 3.5 percent to 4.1 percent per decade, and the extent of perennial sea ice (summer minimum) decreased by 11.5 percent ± 2.1 percent per decade. It is also very likely that the average annual extent of Antarctic sea ice increased by 1.2 percent to 1.8 percent per decade over the same period.
Sea level
In the recent past, sea level has increased by an average of 3.1 mm/year as a result of climatic and non-climatic factors. The rate of increase shows a high variability across regions, with values up to three times the global average in the Western Pacific or null or negative values in the Eastern Pacific. Sea level has already risen by a global mean of 0.19 m over the period 1901 to 2010. It is estimated that between 2000 and 2100, the projected global mean sea level rise will very likely (90 percent probability) reach between 0.5 m and 1.2 m.
Ocean circulation
Ocean circulation redistributes heat and freshwater across the globe, influencing local climates. A significant part of this redistribution is done by the meridional overturning circulation (MOC), responsible for much of the ocean’s capacity to carry excess heat from the tropics to middle and high latitudes, and for the ocean’s sequestration of carbon.
Ocean acidification
Ocean acidification refers to a reduction in the pH of the ocean over an extended period (typically decades or longer) caused primarily by the uptake of atmospheric CO2. It can also be caused by other chemical additions to or subtractions from the ocean. Anthropogenic ocean acidification refers to the component of pH reduction that is caused by human activity.
