In the last decade, an overwhelming consensus has emerged among the world’s most reputable climate scientists that the world has entered a period of rapid global climate change, much of which is accountable to anthropogenic greenhouse gas (GHG) emissions (NSAC 2009). The agreement is demonstrated in the 1996 report of the Intergovernmental Panel on Climate Change (IPCC), an international body of leading natural and social scientists sponsored by the United Nations Environment Programme and the World Meteorological Organization. According to the panel’s report, an equivalent doubling of atmospheric carbon dioxide (CO2) concentration will force a rise in global average surface temperature of 1.0 to 3.5 degrees Celsius by 2100. It will result in an increase of sea level by 19 to 59 cm. Because a warmer atmosphere holds more water vapor, average precipitation also will go up as much 10 to 15 percent (IPCC 2007).

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Agriculture is highly sensitive to climate variability and weather extremes, such as droughts, floods and severe storms. Even warmer climate may give positive effects on food production, the increased potential for droughts, floods and heat waves will pose challenges for farmers. Global climate change is also expected to impact agriculture by causing shifts in precipitation, soil quality, pest regimes, and seasonal growth patterns (NSAC 2009). The exact nature and degree of these changes for any given region will be difficult to predict.
CASE OF VIETNAM
Situated in South East Asia in the Indochinese Peninsula, Vietnam territory is lasting from 8°15′ to 23°22′ latitude and between 102°8′ to 109°30′ longitude (ADPC 2003). It has 329,314 sq. km of natural area, in which 7,348.5 thousand hectares (22.2 percent) is arable land, with population about 83 millions (WHO). Viet Nam lies in the region of tropical monsoon climate with a high temperature. The average temperature varies between 21°C and 27°C, rainfall volume of 1800-2000 mm/year and is not evenly distributed among the months of the year (Tran 2009). Versatile and various climates of the regions create a variety of vegetation and domestic animals which originated in the temperate, sub-tropical and tropical regions.
Being an agricultural country, 75 percent of Vietnamese labor-force is engaged in agriculture, forestry, and fisheries. This sector contributes roughly 20 percent to the GDP. The output value structure of agriculture, forestry and fisheries was 77 percent, 4 percent and 19 percent, respectively (Tran 2009).
Vietnam is likely one of the most vulnerable countries in the world to climate change, because of its geographical location (Oxfam 2008). During the last 50 years, Viet Nam’s annual average surface temperature has increased by approximately 0.50 – 0.70 C, while the sea level along its coastline has risen by approximately 20 cm (ISPONRE 2009). The El-Nino and La-Nina phenomena have caused increasingly adverse impacts to Viet Nam. Changes in climate can have serious implications for economic development, especially in the agricultural sector, due to its direct exposure to and dependence on weather and other natural conditions. Studies for the Southeast Asian region show that climate change could lower agricultural productivity 2-15 percent in Vietnam (Bingxin et al. 2009).
It is very likely that global warming is leading to an increase in weather extremes like heat waves and heavy rainfall. Droughts will occur more often, and that tropical cyclones (typhoons and hurricanes) will become more intense. Vietnam has always been suffering from extreme weather events and is struck by typhoons annually. Strong winds and sea surges cause death and destruction along the narrow and low-lying coastal area, while heavy rains hit the mountainous hinterland and river deltas with floods and landslides (Vietnam Red Cross 2007). For example, the river flood in Mekong Delta in 2000 killed 548 people; it flooded and damaged 401,342 ha of rice fields. An estimated loss of this flood is about 250 million USD (Chaudhry & Ruysschaert 2007). The peak occurrence for typhoon landfalls has been during the month of October in the Central region and November in the South. A partial explanation of this lies in the sea surface temperatures (SSTs), which decrease later in the season. Typhoons are generated where SSTs are 26 °C or above, and by September, this is only found in those ocean areas further south where the SST remains around 25-28 °C throughout the year (ADPC 2003). Climate change may lead to an increase in sea surface temperatures in higher latitudes and a resulting increase of typhoon activity in North Vietnam. An increase of extreme events, both in intensity and duration, will be the most catastrophic preventing the agriculture development. Flood damage is expected to be aggravated because of a predicted increase in daily rainfall of 12 – 19% by 2070. In other times of the year, an increase in evaporation and the variation in rainfall will intensify drought problems about 3 percent in coastal zones and 8 percent in inland areas by 2070 (Chaudhry & Ruysschaert 2007).
Climate change impacts on agriculture are also channeled through changes in temperature. According to the third assessment report of IPCC, the temperature in this century will increase by 4-50 C. The International Rice Research Institute (IRRI) modeler determined that, as a general rule, yield of rice will decrease by 0.5 ton per hectare for every 10C increase in growing seasonal minimum temperature (Javellana 2007). According to the medium emissions scenario, the average temperature is expected to increase by nearly 2°C in the southern regions of Viet Nam and up to 2.8°C in the northern regions by 2100. However, in the high emissions scenario this could be as much as 3.6°C in the North Central Coast region (United Nation 2009). So, it is predicted that yields of summer rice will decrease by 3 – 6% by 2070 when compared to the 1960-1998 period. The impact on spring rice may be more serious, especially in the north where yields are expected to decrease by 17% (Chaudhry & Ruysschaert 2007). The evapotranspiration rate will also increase due to increasing temperature, depicted in figure 1 & 2. Rainfall in the dry season will decrease by 2070 in Central parts of Viet Nam and droughts would occur more frequently, because rainfall would be concentrated in the rainy season (WHO).
Figure 1: The projected change of mean daily maximum temperature since 1980s to 2070s (Le 2010)
Figure 2: The projected change of mean daily minimum temperature since 1980s to 2070s (Le 2010)
Climate also creates a shift in amount and pattern of precipitation. It will affect hydrology and runoff, which will alter the availability of water for irrigation and other uses. The projected runoff changes for the two major rivers from three organizations show different trends. In the Red River, the IPSL scenarios show decreased wet-season flow. GISS and MONRE projections show increased dry season flow. In Mekong River, major flow reduces under IPSL projection, depicted in figure 3 (Ringler 2010). Significant rice yield decline is observed in all scenarios, ranging from 4.2 percent in MONRE-2030 to 12.5 percent in IPSL-2030. The impact is especially large in the Central Highlands and the northern zones, highlighting the enlarged gaps in food supply in these regions. Although the impact of climate change is relatively moderate in the major rice-producing region of the Mekong River Delta, the average rice yield is projected to drop by 1.4-8.3 percent by 2030 (Bingxin et al. 2010).
Figure 3: Percentage of Basin Runoff Changes (Ringler 2010)
Besides increasing average temperature, global warming also raises the sea water level which has resulted in salt-water-invasion and land loss. A recent study on the potential impacts of sea level rise in 84 developing countries suggested that Vietnam would rank among the top 5 affected countries. About 43 million Vietnamese or about 55% of the country’s population are living in vulnerable low elevation coastal zones (LECZ) (38 % of Vietnam’s urban population) (Waibel 2008). In Vietnam, the sea level has risen between 2.5 to 3.0 cm per decade in the last 50 years, but with regional variations (Oxfam 2008). According to ADPC report, sea levels may increase by 9 cm in 2010, 33 cm in 2050, 45 cm in 2070, and 1 meter in 2100 (ADPC 2003). If sea level rises 1 meter, a national potential land loss is predicted of 12% which will expose about 17.1 million people or 23.1 % of the population (Schaefer 2002). The Mekong River Delta will be the most affected region with 1.77 million ha of saline land, accounting for 45 percent of the land (Chaudhry & Ruysschaert 2007). Land loss and sea water invasion in the Mekong River Delta and parts of the Red River Delta, which are the most important agricultural areas in Vietnam, will cause serious risks to farmers as well as agricultural exports, and possibly to national food security.
In summary, climate change is a very real threat to Vietnamese socio-economical development. Higher temperatures, the rising of sea water level and extreme weather events will all have significant impacts across the nation. However, the concept of climate change and its effects are just well known by experts and management agencies. Dealing with the serious implications of climate change will be a major challenge for Vietnam in the next decades.