BCB311

Wednesday, March 08, 2006

EVIDENCE FOR PAST CLIMATER CHANGE, IS CURRENT CHANGE HUMAN INDUCED?

EVIDENCE FOR PAST CLIMATER CHANGE, IS CURRENT CHANGE HUMAN INDUCED?

Climate change is generally defined as a long term deviation or transformation from the mean and extreme climatic conditions. It has been firmly established that global climate has changed in the past, and more recently through human activities. Climate does vary naturally, with variation in the solar cycle, atmospheric composition and even changes in earth surface features. However change in climate over the last 100 years has shown significant increases in the rate of change, due to mainly burning of fossil fuel and increasing greenhouse gas emissions. A mere 10 000 years ago, marked the end of the 'little ice age' and since then global temperatures has been climbing. Current peaks in atmospheric temperature was last seen during the last interglacial period some 124000years ago. Modeling and signal analysis strongly suggest that or current climatic maximum is indeed anthropogenic.

There are various factors that serve as evidence for climate change. These include atmospheric and oceanic temperature increase, retreating glaciers and melting of sea ice as well as permafrost, rises in sea levels.

Oceanic temperature increase

In the last century there has been an increase in global air temperature of about 0.6 °C. This causes an increase in oceanic temperatures and reduces the solubility of oxygen and carbon dioxide in seawater. Thus global warming is increased because the oceans can't sequester carbon as effectively as in lower temperatures. Increased oceanic temperatures have caused destabilizing in major oceanic currents, for example the North Atlantic thermohaline circulation. The slowing down or total shutdown of this current would prevent heat transfers from the tropics to the poles and the transport of cool water from the poles to the tropics. Not only will the poles significantly decrease, and tropics increase in temperature, but cold nutrient rich bottom waters from the poles will also be unable to surface. Hence, leading to decreased phytoplankton primary productivity. In the last century, warmer temperature has resulted in more frequent and intense El Niño events with reduced La Niña events.

Atmospheric temperature increase

Atmospheric temperatures have shown remarkable increase, directly related to the increase in carbon dioxide emissions by various human activities (mainly fossil fuel burning). The increase in atmospheric temperature is due to the greenhouse effect by which long wavelength radiation (re-radiated from the earth's surface) is prevent from leaving the atmosphere directly. This heat is trapped by what is known as greenhouse gasses (CO2, methane, CFC's etc.).

Retreating glaciers

Almost all glaciers worldwide, except in New Zealand and Norway, are retreating because of increasing atmospheric temperatures. Glacial retreats at the poles, directly contribute to sea level rise. The ice in the Alps hasn't melted for centuries, but recent recession led to the discovery of the 5000 year old "ice man".

Melting of sea ice

Globally, there has been a reduction is sea ice of 13 500 km² to present, due to increasing temperatures. The reduction is clearly visible from satellite data. In 2002, the Larsen B shelf disintegrated, loosing a total of 5700 km² of ice. The melting of sea ice decreases oceanic salinity, and so doing influences oceanic salinity, and so doing influences oceanic deep water currents. Melting of sea ice decreases surface albedo, and so doing causes subsequent oceanic and atmospheric warming.

Sea level rise

Sea level rise is impart due to thermal expansion. When heated, water molecules expand and increase in volume. The main contributor to sea level rise is however glacial melting and subsequent inflows into the oceans.

Melting of permafrost

Large portions of permafrost in the Northern Hemisphere are currently undergoing thawing throughout the year as a result of increasing temperatures.

Changes in rainfall patterns

Globally, terrestrial precipitation has increased with 2% in the last 1000 years. However some isolated areas such as Sub Saharan Africa has actually experienced decreased rainfall. Globally, rainfall patterns are becoming more intense with a deviation from normal precipitation temporal cycles. More frequent, extreme weather events has alo been seen in recent years.

M.van der bank
2401402@uwc.ac.za

review: Wynn Haupt

1 Comments:

  • You might want to explore past climate change and the evidence for it in some depth. Otherwise a good review of current climate change evidence - do you fully explain the anthropogenic link?

    By Anonymous James, at Wednesday, March 15, 2006 5:07:00 pm  

Post a Comment

Links to this post:

Create a Link

<< Home