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 1.0ºC, 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.