- Day to day weather forecasting is a necessity for people’s lives as well as for industries such as agriculture, fisheries, and tourism. Seasonality in weather is a annual cyclical change repeated year after year. Even if the interest is on a particular community or region, weather forecasting has to be based on a global observation system.
- Climate variability refers to a “relatively short-term shift” in the patters of the natural climate system over years to decade. An example is the El Nino.
- Climate change is refers to long-term changes, from decades to centuries, associated with increasing concentrations of greenhouse gases (Eileen Shea, et al., Preparing for a Changing Climate).
- In recent years, concern over the consequences of climate change has led many to investigate the potential effects on human communities (ibid.)
- There are much longer-term changes in the climate and sea levels (see for example, Patrick Nunn, Environmental Change in the Pacific Basin).
Course Outline
2010-01-22
2. Climate Variability
The El Nino-Southern Oscillation(ENSO)
- Every few years, the circulation of the Walker Cell in the tropical Pacific reverses.
- At such times, winds along the Pacific Coasts of North and South America, which normally blows offshore allowing upwelling, blow onshore increasing precipitation, preventing upwelling and thereby depleting fishstocks.
- Known as El Nino, this effect has been linked to the Walker Circulation reversal (the Southern Oscillation); the combined phenomenon is referred to as ENSO.
- ENSO is measured by the Southern Oscillation Index (SOI). When the SOI is positive, the situation is normal; the east Pacific is cool and the low equatorial Pacific islands experience mostly easterly winds and are dry. When the SOI is negative, then and El Nino condition prevails. The east Pacific is hot … while islands close to the outer limits of the tropics commonly experience prolonged droughts.
Abnormal Conditions associated with the El Nino in the South Pacific Ocean
| West Pacific: | Above-normal pressure Below-normal precipitation Weakened South Asian summer (July) monsoon Longer dry season |
| Central Pacific: | Above-average precipitation South Pacific Convergence Zone shifts east Tropical cyclones occur further east Tradewinds weaken/reverse |
| East Pacific: | Below-normal pressure (Easter Island high weakens) Above-average precipitation Sea-surface temperature rise Upwelling is suppressed Reduced nutrients at ocean surface Sea-level rise |
El Nino and Extreme Weather Conditions
- El Nino has been linked to extreme weather conditions in most parts of the Pacific Basin:
- Heavy rain and flooding in South America
- Storms and associated mass movements in California
- Drought and famine in Indonesia and the Philippines
- Droughts and destructive bush fires in Australia
- One of the challenges of reconstructing the history of environmental change, during the Holocene (3 ka – present) in particular, is to successfully marry the effects of such short-lived yet extreme changes with the effects of long-term changes of lesser magnitude.
Source: Nunn, Environmental Change in the Pacific Basin
3. Climate Change
- Global phenomena, such as the increase in atmospheric temperature associated with greenhouse warming, have powerful local implications.
- Throughout the earth’s history, ice ages have repeatedly accompanied changes in earth orbit and solar activities.
- On a shorter time scales, seasonal patterns and year-to-year variability, such as those associated with natural cycles like ENSO, are sustained within the climate system and punctuated by extreme events.
References
- Patrick D. Nunn, Environmental Change in the Pacific Basin, Wiley, 1999.
- Eileen L. Shea, et al., Preparing for a Changing Climate, The Potential Consequences of Climate Variability and Change, A Report of the Pacific Islands Regional Assessment Team for the U.S. Global Change Research Program, East West Center, 2001.
- Intergovernmental Panel on Climate Change, Emissions Scenarios, Cambridge University Press, 2000.
- William D. Nordhaus, Managing the Global Commons, The Economics of Climate Change, Massachusetts Institute of Technology, 1994.
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John E. Hay, et al. Climate Variability and Change and Sea-Level Rise in the Pacific Islands Region: A Resource Book for Policy and Decision Makers, Educators and other Stakeholders, Ministry of the Environment, Japan, and South Pacific Regional Environmental Programme (SPREP), 2003.
- International Energy Agency (IEA), Dealing with Climate Change, Policies and Measures in IEA Member Countries, 2002.