"Shifting weather patterns threaten food production through increased unpredictability of precipitation (and) rising sea levels contaminate coastal freshwater reserves and increase the risk of catastrophic flooding," Yapa told a forum on trade, climate change and food security in South Asia.
Most sectors of the global economy are affected by climate change and these impacts will often have implications for trade.
Many of the sectors affected such as agriculture, forestry, fisheries and tourism are critical for south Asian countries, Yapa said.
"Climate change is likely to alter the comparative advantage of these countries in such sectors and thereby alter the pattern of international trade," he said.
"Moreover, climate change is expected to have an impact on trade infrastructure and transportation routes."By the same token, trade could help counter the effects of climate change, Yapa told the forum organised by South Asia Watch on Trade, Economics and Environment, Kathmandu, Sri Lanka's Institute of Policy Studies and Oxfam Novib of The Netherlands.
"Trade may provide a means to bridge differences in demand and supply so that countries where climate change creates scarcity are able to meet their needs by importing from countries where these goods and services continue to be available," Yapa said.
Yapa also said there was a direct link between trade and the amount of greenhouse gas emissions.
"International trade involves emissions of greenhouse gasses through transportation of such goods," he said.
"On the other hand, trade opening could facilitate both the adoption of technologies that reduce the emission intensity of goods and their production process and the change in the mix of a country's production from energy-intensive sectors towards less energy-intensive sectors.
"By increasing the diffusion of mitigation technologies, trade liberalisation can help mitigate climate change."
Yapa noted that current international talks under the World Trade Organisation include ways to reduce or eliminate tariff and non-tariff barriers to environmental goods and services.
"The aim is to improve access to more efficient, diverse and less expensive environmental goods and services on the global market, including goods and services that contribute to climate change mitigation and adaptation."