The rise in the mean surface temperature of the Earth is attributed to the trapping of the sun’s energy in the atmosphere by "greenhouse gases" (e.g., carbon dioxide and methane) produced by the burning of fossil fuel by industries, and also by agriculture and even by forest fires.

The heating up of the Earth’s surface results in the melting of the polar glaciers and rise in sea level. Ocean currents which transfer heat from the Equator to the North Atlantic and are critical for the regulation of climate in our planet will also be disrupted by global warming, according to marine scientists.

The United Nations Intergovernmental Panel on Climate Change has projected that the increase in the Earth’s mean surface temperature can be three to five degrees Celsius in the next l00 years and consequently, sea level rise can be as much as l0 to 89 centimeters.

With the oceans absorbing as much as one-third of the human-generated carbon dioxide, the acidification of sea water which can limit the production of limestone by corals (the "rain-forests of the sea") is feared. Coral "bleaching" (whitening due to the death of algae living in symbiosis with polyps) also occurs when seawater temperature reaches 34 degrees Celsius.

What can the impact of climate change be on Philippine fisheries?

Fisheries (including aquaculture) are an important sector of the Philippine economy contributing four percent to GDP and directly employing over one million Filipinos. In 2006, aquaculture (farming of aquatic plants and animals) accounted for 47.5 percent of the country’s total fisheries production of 4,409,526 metric tons while municipal fisheries (inland and coastal fishing) contributed 28 percent and commercial fisheries (deep-sea fishing) contributed 24.5 percent.

The frequent occurrences and longer episodes of the El Niño (associated with dry spells in the country) caused by the warming of the surface water in the Central and Eastern Pacific Area are believed to be related to climate change. The El Niño of l997-98 seriously affected Philippine agriculture and fisheries due to drought and high surface temperatures. The economic losses of fisheries were estimated to be over R6 billion for aquaculture and R1 billion for marine fisheries.

The major commodities produced from aquaculture in the country are seaweeds which are grown in coastal waters, milkfish which is mainly produced in brackish-water fishponds and tilapia which is farmed in freshwater ponds and cages in lakes/reservoirs.

With climate change, two extreme climatic conditions, namely, droughts and intense typhoons, are expected to impact Philippine fisheries with more direct and greater damage to aquaculture than to inland and marine fisheries in the short to medium terms.

In times of drought, freshwater fishponds dependent on irrigation and underground water supply are the most vulnerable. High temperatures will cause heat stress on cultured fish, slow down their growth and even cause mortality due to disease. Low water levels and high surface water temperature of lakes and reservoirs will also similarly affect fish in cages.

The growth of cultured species in brackish-water ponds is also adversely affected by the high saline and temperature conditions during dry spells brought about by the low water levels and lack of freshwater in tidal rivers. On the other hand, the high temperatures of shallow coastal waters reduce the growth of seaweeds and make them susceptible to disease.

With intense typhoons, flooding commonly occurs. Fishponds can get inundated if peripheral dikes are not adequate and if provisions are not made to prevent the loss of the cultured stocks with overtopping of the ponds. Massive soil erosion from the uplands brought about by flashfloods exacerbates the sedimentation of rivers and coastal waters.

In the long term, the impact of global warming on our marine ecosystems (i.e. mangroves, sea grass beds and coral reefs) needs to be ascertained. Specifically, the effects of the variations in sea level, temperature, pH and salinity need to be monitored and studied. Moreover, the possible modification in ocean currents which can affect our marine fisheries requires thorough investigation.