On the plus side, from 2025 onwards it looks like improved living standards could begin to outweigh rising climate exposure, although climate adaptation measures will still be needed.

"Right now, and for the next decade or two, both climate change and socio-economic development are pushing least-developed countries towards higher vulnerability," Anthony Patt of the International Institute for Applied Systems Analysis, Austria, told environmentalresearchweb, "since the highest risk levels are observed not in the very lowest developed countries, but rather in countries in the middle range of development. Towards mid-century, these countries may become developed enough such that further development will then lower risk levels, counteracting some or all of the effects of climate change."

At the moment, international funds available for climate adaptation are several orders of magnitude lower than the $9–100 bn each year that estimates indicate is required. Before this study there was little indication of the speed with which the money will be needed.

"Of course, as we look further and further out into the future, uncertainties rise and so we do not say anything about vulnerability past mid-century," said Patt. "Various findings reported in the most recent IPCC assessment suggest that there may be more serious climate impacts then, challenging the ability of any country to adapt."

Patt and colleagues believe that their study is the first to look at future climate-related deaths, which takes into account both socio-economic development and climate change. Other research that has looked at both factors has examined only the past, whereas projections into the future have considered each issue separately.

In this case, the team employed human losses to extreme weather events as an indicator of climate vulnerability.

"We used our empirical study of the past to generate a model to weight the various socio-economic and climate projections, deriving estimates for losses in the future," said Patt. "There has been one other study that has done similar work [by Richard Tol]), which looked at tropical disease deaths in the future, but which was less detailed in its analysis – Tol assumed that countries that passed a particular income threshhold would immediately eradicate all tropical diseases."

Once they had completed a detailed analysis for Mozambique, the researchers extended their investigation to 23 of the least-developed countries.

Patt says the study came about by a lucky accident. His team was brought on board to look at socio-economic drivers of vulnerability for an assessment of Mozambique's vulnerability to natural disasters over the next 50 years commissioned by the Mozambique National Disaster Agency (INGC). Working alongside was a team of climate and natural-disaster modellers.

"In the course of my literature review, I realized that there had been several empirical studies looking at how socio-economic factors influence disaster losses, but none of these had then looked forward," said Patt. "In our team, we would have the capacity to do so, because we had both socio-economic forecasters and climate and disaster-modellers on board. So I proposed to the other team members that we try to do so, and that is what happened."

Now Patt is working on a study for the World Bank of the economics of adaptation to climate change in six countries, including Mozambique; results are due in the next few months. "We are pulling together our results with results from other team members – micro- and macro-economic modelling-based projections of adaptation costs – to try to paint a more accurate picture of how climate-related losses may change in the future, and the economic costs of engaging in adaptation to avoid these losses," he said. "Note that in the [current] paper, we did not assess any adaptation costs at all."

The researchers, from the International Institute for Applied Systems Analysis, Austria; the University of Cape Town, South Africa; Autonomous University of Barcelona, Spain; Climatus, US; University of Edinburgh, UK; Wageningen University, The Netherlands; University of Eduardo Mondlane, Mozambique; and Austrian Academy of Sciences, reported their work in PNAS.