Africa is the most vulnerable continent to the adverse effects of climate change, and urgently needs to deal with them. But doing so will be costly.

That was the message heard at a session at the international climate change conference, COP 17, currently underway in Durban.

The cost of adapting to the harm being done to the African continent such as severe weather changes, drought, desertification and so on could be as much as USD 20 to 30 billion a year, according to an economist.

John Ward, from Vivid Economics, delivered the results of a study commissioned by the African Development Bank (AfDB), one of the organizing partners of COP 17, at the forum. Ward reviewed the impact of climate change, the sensitivity to impact, and the ability to adapt. "We need to decide what consensus can be drawn out from the evidence", said Ward.

Adaptation is the practical action that can be taken to reduce vulnerability to climate change effects. Ward outlined the impact as being derived from exposure and sensitivity, and noted that a country's vulnerability determines its adaptive capacity.

Africa faces more physical exposure than other regions, with 50 percent of its population living in countries that are most exposed to the physical impacts of climate change.

Regarding sensitivity, the structure of Africa's economy is heavily skewed toward climate sensitive factors, especially agriculture, on which the daily life of the continent heavily depends.

The adaptive capacity of a country relates to its ability to respond to changes in climatic conditions.

However, Al-Hamndou Dorsouma, a senior climate change expert at the AfDB, admitted the efficiency of the methodologies used to classify countries into vulnerable groups is a matter for concern.

"It impinges on the very nature of the African climate, which is subject to continual change, even within countries. So, using a global model doesn't accurately capture African climate change, be it at local or regional level. The climate data at our disposal is also problematic", he said.

However, he went on to say, "This is a recent exercise, still at the initial stage. But it enables us to fill the gaps, and is something to work with. Based on these studies, decision makers can make decisions on an informed basis."

Different economic structures will be differently exposed to vulnerability. Countries with large gross domestic products are better able to withstand the impact of climate change. "The gross domestic product impact of climate disaster is twice as high in low income countries than high income countries", said Ward.

To illustrate that vulnerability grows as temperatures rise, Ward used a graph to show that over time, on an absolute basis, temperatures can rise more in Africa than in the rest of the world.

"Yet despite the vulnerability, our understanding of it is growing", said Ward. But adaptation efforts, globally and in Africa, are underway, and are continually improving. "It's difficult to draw a line between adaptation and development", he added. He says it should be seen as a continuum.

Ward highlighted adaptation to climate change includes addressing the drivers of vulnerability-activities which seek to reduce poverty and other non-climatic stressors. He said: "Of immediate importance is the building of responsive capacity through robust systems for problem solving." Climate risk must be managed through incorporating climate information and confronting climate change.

Cost adaptation studies have varied in their calculations, partly the whole business of looking at climate change is a work in progress. Three major studies have been conducted in Africa.

The first, carried out by the UN Framework Convention on Climate Change, another COP 17 co-organizer, and the World Bank, estimated between adaptation costs at between two and ten million US dollars.

The second, by the World Bank, said USD18 billion would be needed between 2010 and 2050. The London School of Economics was responsible for the third study, which is regarded as the most reliable and predicted a cost of between USD 20 to 30 billion a year until 2030.

"Adaptation investments are cost-effective", said Ward. "These are investments that do their job, and provide exposure in an empathic way."

Saleemul Huq from the International Institute for Environment and Development mentioned adaptation investment needs to become part of a country's National Development Commission. He gave the example of his own country, Bangladesh, which he said "carried out an adaptation plan, realized it's expensive but is needed", he explained. "It's now part of the National Development Commission, and the government funds it with USD 100 million every year."

It is necessary to move from reactive to proactive policies, strategies and plans, Haq maintained, but funding is required to move from planning to implementation.

He also further urged organisations to pursue adaptation finance, saying global funds could take a long time to trickle down.

Ward concluded by reiterating the need to build adaptive capacity. "Decision makers must factor climate change into all long-term strategic decisions starting immediately, especially infrastructure."

The African Union and the South African government are also co-organizers of COP 17