Chapter 16. Global Climate Change and the Oceans

Transcription

1 Chapter 16 Global Climate Change and the Oceans

2 Oceans and the Planet Oceans are critical to the dynamic processes and the state of Earth s climate over short and extremely long time scales. Ocean water stores and redistributes immense quantities of heat. Climatic warming may occur because of the increased buildup of CO2 in the atmosphere. Molecules of CO2 permit sunlight to pass through the air and heat the Earth s surface, but absorb and trap heat that is radiated from the ground and ocean.

3 Oceans and the Planet (Continued) The amount of CO2 in the atmosphere has increased 44% over the last 150 years. The oceans absorb 30% to 50% of CO2 emissions created by burning fossil fuels. Figure 16.01: The 40-year record of CO2 concentrations in the atmosphere measured at Mauna Loa Observatory in Hawaii. Adapted from Rhode, R. A. Atmospheric Carbon Dioxide, Global Warming Art, October 1, 2008,

4 Global Warming Can Cause Polar Ice Caps to Melt, Resulting in Sea Level Rise Figure 16.02a: The recent global rise of sea level. Data from V. Gornits, S. Lebede, and J. Hausen, Science 215 (1982):

5 Climate Change Global and regional wind and precipitation patterns can (and do) change. Effects of climate change will vary geographically: Some regions will experience longer growing seasons and more rainfall. Others will become hotter and drier.

6 Climate Change (Continued) Climate warming will affect oceans and ocean life in diverse and complex ways. Every aspect of ocean chemistry, circulation, heat content. Every facet of ecological, environmental, and biological activity. All will be impacted by changes in temperature and ph. Increased CO2 changes both temperature and ph of the oceans. Figure 16.04: This diagram shows some direct (solid arrows), indirect (dashed arrows), and possible (dotted arrows) consequences of increasing atmospheric CO2. Adapted from Kennedy, V.S., et al. Coastal and marine ecosystems and global climate change: Potential effects on U.S. resources, report of the Pew Center on Global Climate Change, Arlington, VA 2003.

7 Ecosystems Coastal ecosystems are affected by a variety of environmental variables: Sea level Temperature Wave action CO2 concentration, etc. These ecosystems have difficulty adapting to rapid environmental changes. Figure 16.06: Coastal systems are affected directly by climate change and indirectly by external marine and terrestrial influences. Adapted from Nicholls, R. J., et al. Coastal systems and low-lying areas, Climate Change 2007: Impacts, Adaptation, and Vulnerability, Parry, M.L., et al., eds. Cambridge University Press, 2007,

8 Coastal Ecosystems Current estimates predict that sea level will rise 10 to 90 cm by the year Some inhabited islands and coastal areas will be submerged by the end of this century. Figure 16.07: Estimates of the contribution of the melting of ice sheets and mountain glaciers to the expected rise of sea level in the twenty-first century. Adapted from Haslett, S. K. Coastal Systems. Routledge, 2003.

9 Coastal Ecosystems (Continued) Coastal delta plains are particularly vulnerable to seawater incursion. They are subsiding under a heavy sediment load, which accelerates the relative rise of sea level. Figure 16.08: A scheme that estimates the relative vulnerability of the world s major river deltas. Adapted from Nicholls, R. J., et al. Coastal systems and low-lying areas, Climate Change 2007: Impacts, Adaptation, and Vulnerability, Parry, M. L., et al., eds. Cambridge University Press, 2007,

10 Coastal Ecosystems (Continued) Storm surges are expected to be higher than usual. They will result in more flooding, erosion, and damage to coastal property. Intrusion of seawater into groundwater aquifers will contaminate the freshwater supplies of coastal communities.

11 Coastal Ecosystems (Continued) Anthropogenic structures interfere with ecosystems ability to adapt to environmental change. They prevent coastal ecosystems from shifting landward as sea level rises. Many salt marsh plants rot after prolonged exposure to seawater.

12 Salt Marsh Retreat: Natural Progression Interrupted by Human Construction Figure 16.09: Salt marshes respond to sea-level rise by migrating landward, provided there is room.

13 Salt Marshes and Mangrove Swamps Provide natural protection from storm surges and coastal flooding. Serve as critical nurseries and refuges for many species of shellfish and finfish. Their demise: Opens the shoreline to greater erosion and damage Will have major negative impact on commercial fisheries

14 Possible Ways to Alleviate the Effects of Sea-level Rise Include Elevating buildings and infrastructure Engineering of coastal areas to offset/prevent erosion Planned relocation of coastal buildings and other infrastructure Prohibiting future coastal development.

15 Water Temperature Influences behavior and mortality of marine organisms. Changes in water temperature can affect: Predator/prey relations Ecological niches Resource allocations Species distribution Timing of reproduction/rate of development These alterations can be detrimental to the survival of populations and species.

16 Coastal Water Aquaculture in coastal areas is a rapidly increasing source of human food. Rising temperatures could mean that microbial infections of aquacultured organisms increase. Warmer coastal water may foster more frequent and larger algal blooms, such as red tides. This can devastate shellfish fisheries and cause human illness and even death.

17 Seawater The temperature and salinity of seawater cause dense water masses to sink. This helps drive a global conveyor belt of water movement. Climate change will influence deep-water flow. Atmospheric effects control seawater density. It is hard to predict how climate change will affect thermohaline circulation.

18 Global Warming and Thermohaline Circulation Major change in the redistribution of flow patterns, oxygen, and nutrients could result from increasing ocean temperatures Figure 16.12: The circulation conveyor belt.

19 Salinity Melting of ice sheets decreases ocean salinity. Decreased salinity is expected to slow down the rate of downwelling in the North Atlantic. If prolonged, may shut it down entirely. Shutdown of circulation would cut off the supply of oxygen-rich water to the deep sea. This would cause hypoxia and anoxia in the deep ocean, inducing mass extinctions.

20 Arctic Sea Ice Is Melting at an Alarming Rate In terms of total cover In terms of seasonal cover Figure 16.13a: Inside of a decade ( ), the area of the ice sheet that is melting rapidly has expanded markedly. Figure 16.13b: The floating terminus of a Greenland glacier called Jakobshavn Isbrae has retreated almost 50 kilometers since Adapted from King, M. D., et al. Our Changing Planet: The View from Space. Cambridge University Press, Figure 16.14a: This satellite photo shows the extent of melting of the sea-ice cover of the Arctic Ocean during the summer season. Courtesy of Josefino Comiso and NAA/Goddard Space Flight Center Scientific Visualization Studio. Figure 16.14b: The sea-ice cover of the Arctic Ocean has been shrinking alarmingly during the past decades. Data from Post, E. and others Science. 34 (2013):

21 Sea Ice Melting sea ice affects mammals adapted to icecovered water. Arctic seals require extensive areas of ice for breeding and resting. These seals are essential prey for walruses and polar bears. Sea ice also affects plankton productivity, which is the basis of the food web.

22 Sea Ice (Continued) The absence of sea ice during summer will allow open water to absorb more heat. This will accelerate seawater temperature increase. Increased water temperature: Delays onset of winter freezing Promotes an earlier spring breakup of sea-ice cover Figure 16.15a: Open water absorbs much more sunlight than ice-covered water. Figure 16.15b: Examples of positive feedback loops involving incident solar radiation and sea-ice expansion and contraction. Adapted from King, M. D., et al. Our Changing Planet: The View from Space. Cambridge University Press, 2007.

23 As Waters Warm: Warm-water species displace cold-water species. Phytoplankton populations decrease. Food webs must readjust to these changes, sometimes causing collapse of populations.

24 CO2 As CO2 builds up in the lower atmosphere, more of it diffuses into the ocean. CO2 complexes with water molecules to form carbonic acid. This increases the acidity of the seawater. Figure 16.17: The relative levels of various carbonate ion species such as carbonate (CO23 ) and bicarbonate (HCO3 ) vary with the ph of the water. Adapted from Buddemeier, R. W., Kleypas, J. A., and Aronson, R. B. Coral Reefs and Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems. Report of the Pew Center on Global Climate Change, 2004.

25 Changes in Reefs Ocean acidification also decreases the amount of carbonate ions in the water. This has an impact on organisms that secrete calcium carbonate shells and form reefs. Coral reef-building could decrease 20% to 30% this century. Warmer waters also increase the bleaching events that devastate coral.

26 Coral Bleaching, 2002 and 2005 Figure 16.18a: This satellite image obtained from NOAA reveals the distribution of significant coral bleaching events and SST data for the year Figure 16.18b: This satellite image obtained from NOAA reveals the distribution of significant coral bleaching evens and SST data for the year Maps provided by ReefBase: and courtesy of NOAA and The WorldFish Center.

27 We Know that Human Activities Are Degrading the Environment We can: Adopt sustainable lifestyles Form forward-looking political affiliations Think up novel solutions to environmental problems Strive to mitigate human impact on marine ecosystems If we work to mitigate the causes now, we can slow perhaps even stop some ecological cascades. Many ecosystems are resilient and biota can adapt to some environmental changes.

28 What We Can Do? Scientists can provide insight into ecosystems across many scales of time and space. Understanding an ecosystem helps us identify how we can address its degradation and develop mitigation and restoration strategies. We must all work together to enact policy changes directed to achieving a sustainable relationship with nature.