The world has increasingly been concerned with the changes in our climate due largely to adverse impacts being seen not just globally, but also in regional, national and even, local scales. In 1988, the United Nations established the IPCC to evaluate the risks of climate change and provide objective information to governments and various communities such as the academe, research organizations, private sector, etc. The IPCC has successively done and published its scientific assessment reports on climate change, the first of which was released in 1990. These reports constitute consensus documents produced by numerous lead authors, contributing authors and review experts representing Country Parties of the UNFCCC, including invited eminent scientists in the field from all over the globe.

In 2007, the IPCC made its strongest statement yet on climate change in its Fourth Assessment Report (AR4), when it concluded that the warming of the climate system is unequivocal, and that most of the warming during the last 50 years or so (e.g., since the mid-20th century) is due to the observed increase in greenhouse gas concentrations from human activities. It is also very likely that changes in the global climate system will continue into the future, and that these will be larger than those seen in our recent past (IPCC, 2007a).

Fig.4 shows the 0.74 C increase in global mean temperature during the last 150 years compared with the 1961-1990 global average. It is the steep increase in temperature since the mid-20th century that is causing worldwide concern, particularly in terms of increasing vulnerability of poor developing countries, like the Philippines, to adverse impacts of even incremental changes in temperatures.

The IPCC AR4 further states that the substantial body of evidence that support this most recent warming includes rising surface temperature, sea level rise and decrease in snow cover in the Northern Hemisphere (shown in Fig.5).

Additionally, there have been changes in extreme events globally and these include;

• widespread changes in extreme temperatures observed;
• cold days, cold nights and frost becoming less frequent;
• hot days, hot nights and heat waves becoming more frequent; and
• observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures (SSTs).

However, there are differences between and within regions. For instance, in the Southeast Asia region which includes Indonesia, Malaysia, the Philippines, Thailand, and Vietnam, among others, temperature increases have been observed; although magnitude varies from one country to another. Changes in rainfall patterns, characteristically defined by changes in monsoon performance, have also been noted. Analysis of trends of extreme daily events (temperatures and rainfall) in the Asia Pacific region (including Australia and New Zealand, and parts of China and Japan) also indicate spatial coherence in the increase of hot days, warm nights and heat waves, and the decrease of cold days, cold nights and frost; although, there is no definite direction of rainfall change across the entire region (Manton et. al., 2001).

The Philippines, like most parts of the globe, has also exhibited increasing temperatures as shown in Fig.6 below. The graph of observed mean temperature anomalies (or departures from the 1971-2000 normal values) during the period 1951 to 2010 indicate an increase of 0.648 C or an average of 0.0108 C per year-increase.

The increase in maximum (or daytime) temperatures and minimum (or night time) temperatures are shown in Fig.7 and Fig.8. During the last 60 years, maximum and minimum temperatures are seen to have increased by 0.36 ºC and 1.0°C, respectively.

Analysis of trends of tropical cyclone occurrence or passage within the so-called Philippine Area of Responsibility (PAR) show that an average of 20 tropical cyclones form and/or cross the PAR per year. The trend shows a high variability over the decades but there is no indication of increase in the frequency. However, there is a very slight increase in the number of tropical cyclones with maximum sustained winds of greater than 150kph and above (typhoon category) being exhibited during El NiÑo event (See Fig.10).

Moreover, the analysis on tropical cyclone passage over the three main islands (Luzon, Visayas and Mindanao), the 30-year running means show that there has been a slight increase in the Visayas during the 1971 to 2000 as compared with the 1951 to 1980 and 1960-1990 periods (See Fig.11).

To detect trends in extreme daily events, indices had been developed and used. Analysis of extreme daily maximum and minimum temperatures (hot-days index and cold-nights index, respectively) show there are statistically significant increasing number of hot days but decreasing number of cool nights (as shown in Fig.12 and Fig.13). 

However, the trends of increases or decreases in extreme daily rainfall are not statistically significant; although, there have been changes in extreme rain events in certain areas in the Philippines. For instance, intensity of extreme daily rainfall is already being experienced in most parts of the country, but not statistically significant (see in Fig.14). Likewise, the frequency has exhibited an increasing trend, also, not statistically significant (as shown in Fig.15).

The rates of increases or decreases in the trends are point values (i.e., specific values in the synoptic weather stations only) and are available at PAGASA, if needed.

Responses of the local climate to the mid-range compared to the high- and low-range scenarios are as shown in Fig. 22 below. Although there are vast differences in the projections, the so-called temperature anomalies or difference in surface temperature increase begin to diverge only in the middle of the 21st century. As has already been stated, the climate in the next 30 to 40 years is greatly influenced by past greenhouse gas emissions. The long lifetimes of the greenhouse gases already in the atmosphere, with the exception of methane (with a lifetime of only 13 years), will mean that it will take at least 30 to 40 years for the atmosphere to stabilize even if mitigation measures are put in place, not withstanding that in the near future, there could be some off-setting between sulfate aerosols (cooling effect) and the greenhouse gas concentrations (warming effect).

A warmer world is certain to impact on systems and sectors; although, magnitude of impacts will depend on factors such as sensitivity, exposure and adaptive capacity to climate risks. In most cases, likely impacts will be adverse. However, there could be instances when likely impacts present opportunities for potential benefits as in the case of the so-called carbon fertilization effect in which increased carbon dioxide could lead to increased yield provided temperatures do not exceed threshold values for a given crop/cultivar.

In areas/regions where rainfall is projected to decrease, there will be water stress (both in quantity and quality), which in turn, will most likely cascade into more adverse impacts, particularly on forestry, agriculture and livelihood, health, and human settlement. Large decreases in rainfall and longer drier periods will affect the amount of water in watersheds and dams which provide irrigation services to farmers, especially those in rain fed areas, thereby, limiting agricultural production. Likewise, energy production from dams could also be rendered insufficient in those areas where rainfall is projected to decrease, and thus, could largely affect the energy sufficiency program of the country. Design of infrastructure, particularly of dams, will need to be re-visited to ensure that these will not be severely affected by the projected longer drier periods.

In areas where rainfall could be intense during wet periods, flooding events would follow and may pose danger to human settlements and infrastructure, in terms of landslides and mudslides, most especially, in geologically weak areas. Additionally, these flooding events could impact severely on public infrastructure, such as roads and bridges, including classrooms, evacuation centers, and hospitals.

Adaptive capacity is enhanced when impact and vulnerability assessments are used as the basis of strategic and long-term planning for adaptation. Assessments would indicate areas where critical water shortages can be expected leading to possible reduction of water available for domestic consumption, less irrigation service delivery, and possibly, decreased energy generation in dams. Note that the adverse impacts would cascade, so that long-term pro-active planning for these possible impacts is imperative in order to be able to respond effectively, and avoid maladaptations. A number of adaptation strategies should be considered. Among the wide array of cost effective options are rational water management, planning to avoid mismatch between water supply and demand through policies, upgrading/rehabilitation of dams where these are cost-effective, changes in cropping patterns in agricultural areas, establishing rain water collection facilities, where possible, and early warning systems.

Changes in rainfall regimes and patterns resulting to increase/decrease in water use and temperature increases could lead to a change in the forests ecosystem, particularly in areas where the rains are severely limited, and can no longer provide favorable conditions for certain highly sensitive species. Some of our forests could face die-backs. Additionally, drier periods and warmer temperatures, especially during the warm phase of El Nino events, could cause forest fires. A very likely threat to communities that largely depend on the ecological services provided by forests is that they may face the need to alter their traditions and livelihoods. This change in practices and behavior can lead to further degradation of the environment as they resort to more extensive agricultural production in already degraded areas.

Adverse impacts on forestry areas and resources could be expected to multiply in a future warmer world. The value of impact and vulnerability assessments could not be underscored. These assessments would help decision makers and stakeholders identify the best option to address the different impacts on forest areas, watersheds and agroforestry. Indigenous communities have to plan for climate-resilient alternative livelihoods. Thus, it is highly important to plan for rational forest management, particularly, in protected areas and in ancestral domains. One of the more important issues to consider is how to safeguard livelihoods in affected communities so as not to further exacerbate land degradation. Early warning systems in this sector will play a very important role in forest protection through avoidance and control/containment of forest fires.

Agriculture in the country could be severely affected by temperature changes coupled with changes in rain regimes and patterns. Crops have been shown to suffer decreases in yields whenever temperatures have exceeded threshold values and possibly result to spikelet sterility, as in the case of rice. The reduction in crop yield would remain unmitigated or even aggravated if management technologies are not put in place. Additionally, in areas where rain patterns change or when extreme events such as floods or droughts happen more often, grain and other agricultural produce could suffer shortfalls in the absence of effective and timely interventions. Tropical cyclones, particularly if there will be an increase in numbers and/or strength will continue to exert pressure on agricultural production.

Moreover, temperature increases coupled with rainfall changes could affect the incidence/outbreaks of pests and diseases, both in plants and animals. The pathways through which diseases and pests could be triggered and rendered most favorable to spread are still largely unknown. It is therefore important that research focus on these issues.

In the fisheries sub-sector, migration of fish to cooler and deeper waters would force the fisher folks to travel further from the coasts in order to increase their catch. Seaweed production, already being practiced as an adaptation to climate change in a number of poor and depressed coastal communities could also be impacted adversely.

Decreased yields and inadequate job opportunities in the agricultural sector could lead to migration and shifts in population, resulting to more pressure in already depressed urban areas, particularly in mega cities. Food security will largely be affected, especially if timely, effective and efficient interventions are not put in place. Insufficient food supply could further lead to more malnutrition, higher poverty levels, and possibly, heightened social unrest and conflict in certain areas in the country, and even among the indigenous tribes.

A careful assessment of primary and secondary impacts in this sector, particularly, in production systems and livelihoods will go a long way in avoiding food security and livelihood issues. Proactive planning (short- and long-term adaptation measures) will help in attaining poverty eradication, sufficient nutrition and secure livelihoods goals. There is a wide cross-section of adaptation strategies that could be put in place, such as horizontal and vertical diversification of crops, farmer field schools which incorporate use of weather/climate information in agricultural operations, including policy environment for subsidies and climate-friendly agricultural technologies, weather-based insurance, and others. To date, there has not been much R&D that has been done on inland and marine fisheries technologies, a research agenda on resilient marine sector could form part of long-term planning for this subsector.

The countrys coastal resources are highly vulnerable due to its extensive coastlines. Sea level rise is highly likely in a changing climate, and low-lying islands will face permanent inundation in the future. The combined effects of continued temperature increases, changes in rainfall and accelerated sea level rise, and tropical cyclone occurrences including the associated storm surges would expose coastal communities to higher levels of threat to life and property. The livelihood of these communities would also be threatened in terms of further stress to their fishing opportunities, loss of productive agricultural lands and saltwater intrusion, among others.

Impact and vulnerability assessment as well as adaptation planning for these coastal areas are of high priority. Adaptation measures range from physical structures such as sea walls where they still are cost-effective, to development/revision of land use plans using risk maps as the basis, to early warning systems for severe weather, including advisories on storm surge probabilities, as well as planning for and developing resilient livelihoods where traditional fishing/ agriculture are no longer viable.

Human health is one of the most vital sectors which will be severely affected by climate change. Incremental increases in temperatures and rain regimes could trigger a number of adverse impacts; in particular, the outbreak and spread of water-based and vector-borne diseases leading to higher morbidity and mortality; increased incidence of pulmonary illnesses among young children and cardiovascular diseases among the elderly. In addition, there could also be increased health risk from poor air quality especially in urbanized areas.

Surveillance systems and infrastructure for monitoring and prevention of epidemics could also be under severe stress when there is a confluence of circumstances. Hospitals and clinics, and evacuation centers and resettlement areas could also be severely affected under increased frequency and intensity of severe weather events.

Moreover, malnutrition is expected to become more severe with more frequent occurrences of extreme events that disrupt food supply and provision of health services. The services of the Department of Health will be severely tested unless early and periodic assessments of plausible impacts of climate change are undertaken.