4 - Existing Evidence of Climate Change and Variability

Summary

Climate change and variability have profound and wide-ranging effects on the agricultural sector, the environment, and society. Global, regional, and local evidences of climate change and variability have grown in recent years, and historical records from the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA), combined with past and recent studies, provide evidence that climate change is no longer an anticipated scenario but a reality. Climate change is defined as shifts in mean climate variables or variance in the distribution of climate variables based on historical records over a significant period of time (IPCC 2007, 2014, p. 6). Changes may be evident in temperature and precipitation levels, as well as in other indicators, such as the number of wet and dry days, the number of warm days and cold nights, extremes of climate, and so on.

This chapter presents historical evidences of changes in climate variables at local and national levels. The implications of climate variability and climate change on the agricultural sector are also discussed, along with some beneficial agricultural practices, climate adaptation strategies, and location-specific measures for coping with changing climate at different levels.

LOCAL EVIDENCES OF CLIMATE CHANGE AND VARIABILITY

Observed Trends in Temperature and Precipitation

One of the earliest studies analyzing observed trends climate variables in the Asia and Pacific region, as well as in specific countries, is the work of Manton et al. (2001, pp. 269–84), which made use also of historical data from selected weather gauging stations in the Philippines. Their analyses confirmed that the observed trends are statistically significant. Recently, these results were further updated by Cinco, de Guzman, Hilario, and Wilson (2014, pp. 12–26) using the historical climate data for thirty-four synoptic stations in the archipelago.

Analysis of time-series data on historical yearly mean temperatures (based on available PAGASA data) shows an increasing trend relative to normal values (that is, a thirty-year average for the period 1971–2000). The plot shows that the mean temperature increased by 0.65°C between 1951 and 2010 (Figure 4.1). Averaged across the country, yearly mean temperatures increased at a rate of 0.0164°C per year during 1981–2010, and by 0.0108°C per year during 1951–2010.