The air quality degradation occurs concurrently with climate change, affecting natural habitats, plants, ecosystems, and biodiversity stability in the long term (Agathokleous et al., 2022). For the first time, the conference will be held in Southeast Asia, in Thailand, which is particularly vulnerable to climate change and air pollution given its large population, relatively high biodiversity, and large number of forest-dependent communities.

Climate change and Air pollution in Asia

The Working Group II contribution to the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report assesses the impacts of climate change, looking at ecosystems, biodiversity, and human communities at global and regional levels. The IPCC indicates that past and present climate trends in Asia point to an increase in surface air temperature of between 1-4 °C over a century (IPPC, 2022). The number of rainy days and the annual amount of precipitation have decreased over time. In general, the frequency of intense rainfall events in many parts of Asia has increased, causing an increase in the number and severity of floods, landslides, debris and mud flows. In coastal areas of Asia, the current rate of sea-level rise is reported to be between 1-3 millimeters per year, which is slightly greater than the global average. An increase in the occurrence of extreme weather events, including heat waves and intense rainstorms, is thus projected for South Asia, East Asia, and Southeast Asia.

Air pollution and climate change are tightly linked (De Marco et al., 2022). Air quality policies around the world have been unsuccessful in equally mitigating all air pollutants. For instance, while fine particles (PM2.5) pollution was offset by 30-40% in China in 2013-2017, surface ozone pollution worsened (Li et al., 2019), and currently ozone is the most damaging air pollutant for vegetation (Agathokleous et al., 2022).

Air Pollution in cities

In South Asia, the annual PM2.5 and nitrogen dioxide (NO2) mean concentrations increased by on average 2.0% and 1.7% per year, respectively, in urban areas with more than 50,000 inhabitants between 2000 and 2019, in line with socioeconomic development (Sicard et al., 2023). In East Asia, the annual PM2.5 decreased by on average 0.4% per year, while the NO2 mean concentrations increased by 0.8% per year. The summertime average daily maximum 8-hour ozone concentrations increased by 1-2% per year in South Asia and East Asia with the highest increase in India (over 3% per year) over the period 2000-2009. In Thailand, the annual PM2.5 and NO2 mean concentrations increased in urban areas with more than 50,000 inhabitants, by on average 0.57% and 1.04% per year, respectively. The summertime average daily maximum 8-hour ozone concentrations rose in all cities in Thailand (on average, 1.79% per year).

Threatened hotspot for biodiversity and forest ecosystems

The biodiversity of Southeast Asia has been threatened over the past decades and is expected to decline by 13-85% by 2100 (Sodhi et al., 2010). Natural forests have been degraded in both lowland, with a 50% loss over the past 20 years (Namkhan et al., 2020), and mountainous areas, facing increased agricultural expansion (Feng et al., 2021). Between 1990 and 2010, the forests of Southeast Asia contracted in size by 3.32 million hectares, an area greater than that of Viet Nam (FAO, 2011). The rates of deforestation are highest in Southeast Asia, where forest cover decreased by 0.41% per year between 2000 and 2010, compared to a 0.28% annual decrease in South Asia and an annual increase of 1.16% in East Asia (FAO, 2011). A key driver of deforestation throughout the region is agricultural expansion for industrial and food crops, which in turn is being driven by population growth and a growing global demand for timber production, biodiesel, food grain, and cash crops.
Continuing forest loss will impede a number of ecosystem services such as mitigation of floods and droughts, soil preservation, nutrient cycling, agricultural pest control, biodiversity maintenance, protection from coastal erosion, partial stabilization of climate and moderation of extreme weather, water purification and recreational, cultural and spiritual benefits (Millennium Ecosystem Assessment 2003).

Vulnerability of forests and forest communities to climate change

Climate change, in combination with air pollution and other natural and anthropogenic stresses, are likely to increase the risk of extinction for many flora and fauna species in Asia (IPCC, 2022), and will result in substantial changes in the structure and function of forest ecosystems (Bytnerowicz et al., 2007). Forest ecosystems are particularly sensitive to changes in air temperature and precipitation, which can alter future composition of forests in Southeast Asia and create an uncertainty in the nature and extent of the services they provide. Rapid sea level rise will deteriorate coastal ecosystems, cause coastal erosion, and increase the flood risk in populous coastal cities including Bangkok.

Subtropical forests - The subtropical domain contains many key biodiversity hotspots, whose endemic species are predicted to decline, leading to cascading changes in ecosystem structure and function.

Tropical forests - These are particularly climate-sensitive. For instance, small changes in climate could affect the timing and intensity of flowering and seeding events, with negative impacts on forest biodiversity and ecosystem services. Forest fragmentation and deforestation mean that species mobility is reduced, and therefore the risk of climate-induced extinction is increased. A substantial decline in tropical forest (and hence global) biodiversity is anticipated.

Mangrove ecosystems - The vulnerability of mangrove ecosystems is particularly relevant to Southeast Asia, which is home to a larger area of this unique forest type than either Africa or Latin America (Ward et al., 2016). Due to temperature stresses, mangroves will suffer reduced photosynthetic and growth rates, and shifts in species composition, but the greatest threat to ecosystem integrity is from projected sea-level rise (IPCC, 2022). Mangroves could potentially move inland to cope with sea-level rise.

Further research is required to address the knowledge gaps especially in South Asia, to allow researchers to tease apart the processes that influence both vulnerability and resilience to climate change. Tropospheric ozone is a threat to vegetation across the world, particularly in Asia. The impact of surface ozone on vegetation is largely under-investigated at the global scale despite large areas worldwide are exposed to high surface ozone levels. In the Northern Hemisphere, changes in surface ozone by 2100 worldwide range from + 4-5 ppb in the RCP8.5 scenario to reductions of 2-10 ppb in the most optimistic scenario, RCP2.6 (Sicard et al., 2017). Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness that faces high ozone risk by 2100 (Agathokleous et al., 2020).

Knowledge on ozone impacts on tropical ecosystems is still very limited. The rising trend in ozone concentration-based metrics in many parts of Thailand highlight the threat of ozone to human health and food security in tropical and subtropical areas (Kittipornkul et al., 2023).

Forest ecosystems: a major opportunity for climate change adaptation and mitigation

Globally, the forestry sector has a significant mitigation potential, but is estimated to account for 17.4% of the global greenhouse gas emissions. Research has shown that the Asia-Pacific region is the major source of global forest-related emissions, more than sub-Saharan Africa or Latin America.

Forests also present a major opportunity for climate change adaptation and mitigation, as they have the potential to act either as a carbon source and accelerate climate change (through deforestation and forest degradation), or as a carbon sink and an adaptation strategy (through afforestation and sustainable management). Recognizing the important role of forests as they relate to climate change and wisely managing their potential capacity is crucial for future climate change mitigation and adaptation.

Many forest-related initiatives and strategies have been developed to utilize the potential of forests for climate change mitigation and adaptation. The Kyoto Protocol indicated that forests could contribute to meeting carbon emission reduction targets, and REDD ++ (Reducing emissions from deforestation and forest degradation, and the role of conservation, sustainable management of forests and enhancement of forest carbon stocks in developing countries) has become an important means of achieving these targets (Mollicone et al., 2007).

Despite many available initiatives and strategies, the extent to which forests contribute to climate change mitigation and adaptation remains limited.

Combating air pollution is a great challenge, which can hardly be addressed by local efforts and policies alone, especially because of the major involvement of secondary pollutants and transport of air pollutants across countries, regions, and continents (Jbaily et al., 2022). Climate change and long-range transport might reduce the benefits gained from local-to-regional ozone control strategies, by increasing background ozone levels in the future (Sicard, 2021). Hence, climate change mitigation would require the concurrent mitigation of air quality pollutants, and air quality impairment and climate change should be addressed together. Moreover, not all policies for climate have positive feedback on air quality and vice versa.


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