The thermohaline circulation is a global ocean circulation. It is driven by differences in the density of the sea water which is controlled by temperature and salinity (Broecker, 1995). The thermohaline circulation is sometimes called the “ocean conveyor belt” and plays an important role in supplying heat to the polar regions. There are projections that global warming could shut down or slow down this thermohaline circulation and trigger cooling in the North Atlantic, or lessen warming in regions such as Europe which are dependent on the Gulf Stream to keep them warm.

ocean_conveyorSource: www.ipcc.ch

The oceans have a tremendous capacity to absorb carbon dioxide from the atmosphere, making the water more acidic. “Ocean acidification” is the name given to the ongoing decrease in the pH of the oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere. Between 1751 and 2004 surface ocean pH is estimated to have dropped from approximately 8.25 to 8.14 (Jacobson, 2005). This changing ocean chemistry may lead to sharp decline in marine biodiversity. Many species of marine organisms that form calcite shells may become extinct as a direct result of ocean acidification. Observed species composition changes may be driven by the changes in ocean acidification and beginning with changes to species at the bottom of the food web and affecting species throughout the food web all the way to top predators in a cascade of effects. We are already seeing dramatic changes of indicators species in all of the world’s oceans.

Glaciers have been retreating worldwide since the end of the Little Ice Age (around 1850), but in recent decades glaciers have begun melting at rates that cannot be explained by historical trends. Projected climate change over the next century will further affect the rate at which glaciers melt. Average global temperatures are expected to raise another 1.4-5.8ºC by the end of the 21st century (IPCC, 2001). Glaciers from the Andes to the Himalayas are melting bringing long-term threats of higher sea levels that could swamp island states and low-lying coastal areas. Like a canary in a coal mine, the dwindling of the glaciers is visible evidence, an indicator that the earth really is getting hotter. Read about how melting glaciers are predicted to cause significant rises in sea level over the course of the twenty-first century increasing the risk of coastal flooding for countries like Maldives and India.

The geographic ranges of most plant and animal species are limited by climatic factors, including temperature, precipitation, soil moisture, humidity, and wind. Any shift in the magnitude or variability of these factors in a given location will impact the organisms living there. Species sensitive to temperature may respond to a warmer climate by moving to cooler locations at higher latitudes or elevations (McMichael et al, 1996) Species that already live at higher elevation are likely to lose their habitat altogether and go extinct.

The Arctic’s sea ice is home to a wide variety of wildlife including polar bears, arctic foxes, seals and walruses. The sea ice is also used as a transportation route by caribou and is a traditional hunting ground for the Inuit. Long term temperature records from the surrounding land masses in the Arctic, including ice cores, tree rings, and lake bed pollen samples, suggest that the Arctic land area is now warmer than it has been in at least 400 years. This warming trend is creating significant impact on the Inuit community and depriving them of their daily livelihood.

Coral reefs, atolls, mangroves, boreal and tropical forests, can be especially vulnerable to climate change. Climate change may increase existing risks of extinction of already threatened or vulnerable species. Biodiversity loss is the likely outcome of climate change and may exceed that seen on earth over the last 50 million years. In 1998 coral reefs around the world experienced the most extensive and severe bleaching in recorded history. If the overall warming is accompanied by more frequent periods of sustained high temperatures, mass bleaching events will become more frequent and widespread (Wilkinson et al., 1999)

Warmer temperatures increase the probability of drought. Greater evaporation, particularly during summer and fall, could exacerbate drought conditions and increase the risk of wildfires. Extremes events like heat waves, river and coastal flooding, droughts, landslides, storms, hurricanes and tornadoes may become more intense and occur more frequently. These severe weather and geological events will have negative effects on society by damaging homes and villages and resulting in loss of life.

 

Written By: Meghna Tare
Meghna Tare was born in India and graduated in 1997 with a BS in environmental science from the University of Nagpur, India. Summer internship in an environmental consultancy exposed her to the application of chemical analysis and instrumentation in the detection of toxic metals in waste water. This led her to study towards a MS degree in Analytical and Environmental chemistry from the Department of Chemistry, University of Nagpur, India. In 2002 Meghna graduated from the University of San Francisco with a MS degree in Analytical and Bio-Inorganic Chemistry, during which she studied the synthesis and characterization of artificial enzymes called metalloenzymes. These enzymes have application in the area of bio-chemistry and environmental biotechnology.

 

References

Broecker, W. 1995. Chaotic Climate, Scientific American, November, 62-68

Brook, E., 2005. Tiny bubbles tell all. Science 310, 1285-12

Jacobson, M. Z. 2005. Studying ocean acidification with conservative, stable numerical schemes for nonequilibrium air-ocean exchange and ocean equilibrium chemistry. J. Geophys. Res. Atm. 110, D07302

Houghton, J. 2005. Global warming. Rep. Prog. Phys. 68:1343–140

Houghton, J. T., Y. Ding, D. J. Griggs, M. Noguer, P. J. van der Linden and D. Xiaosu, eds. 2001. Climate Change 2001: The Scientific Basis (Cambridge Univ. Press, Cambridge, U.K.)

McMichael, A.J., A. Haines, and R. Slooff. 1996. Climate Change and Human Health. World Health Organization, World Meteorological Organization, United Nations Environmental Program, Geneva: 305.

Pittock, B., D. Wratt, R. Basher, B. Bates, M. Finlayson, H. Gitay, A. Woodward, A. Arthington, P. Beets, B. Biggs. 2001. in Climate Change 2001: Impacts, Adaptation, and Vulnerability (Cambridge Univ. Press, Cambridge, U.K.).

Raven, J. A. 2005. Ocean acidification due to increasing atmospheric carbon dioxide. The Royal Society, London, UK. This report can be found at www.royalsociety.org

Wilkinson, C.O., H. C. Linden, G. Hodgson, J. Rubens, and A. E. Strong. 1999. Ecological and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: An ENSO impact and a warning of future change? Ambio 28: 188-196