Climate change is proving a bigger factor in people's decisions to migrate more than income and political freedom combined, Kiwi researchers say.
An analysis by Otago University economics researcher Dr Dennis Wesselbaum and Victoria University Master's student Amelia Aburn crunched figures around migration flows between 16 OECD destination and 198 origin countries, including New Zealand, across 35 years.
Research into the drivers of migration has traditionally focused on economic factors like wage differences and moving costs, and only recently have climactic factors been added to the mix.
In what's thought to be the first time researchers have studied the full picture over a wide timeframe, capturing long-term effects and year-to-year variations, Wesselbaum and Aburn were able to isolate climate change as a major influence.
Their results suggested it to be a more important driver than even income and political freedom put together.
"In combination, the effect of climate change through higher temperatures and an increase in the incidence of disasters is more important than the effects of income and policy at origin [country] together," they reported.
"In conclusion, our results suggest that climate change is a key driver of migration."
The UN Intergovernmental Panel on Climate Change's most recent report projected global surface temperature was likely to rise a further 0.3C to 1.7C in the lowest emissions scenario, and 2.6C to 4.8C in the highest emissions scenario.
Studies have shown climate change is likely to lead to water scarcity and threaten food production - an issue compounded by the projected increase in world population - while also creating major health problems, stoking conflict over resources and displacing millions from low-lying regions.
"Given the overwhelming evidence about the expected adverse effects of climate change in the future, we can expect that it will become an even more important driver of migration in the future," the authors stated.
Wesselbaum has been particularly interested in the effects of temperature and weather-related disasters, and how migration responds over time to changes in its driving forces.
Including temperatures and disasters was important, as research had shown people understood the effects of climate change through changes in local weather patterns rather than from changes in temperature.
"This gives a valuable insight into whether climate change does influence immigration, and by how much; looking at these figures over a long time period is the key to understanding the effects of climate change," Wesselbaum said.
Wesselbaum amassed data from each country on significant weather events and temperatures and data on immigration from 1980 to 2014, then modelled immigration flows over that time to determine patterns and identify significant factors.
That work showed events like storms, floods, heatwaves and droughts had different effects on migration.
In particular, temperature rise was having a major influence in immigration decisions - intuitively, people were moving away from the negative effects of climate change.
He has also suggested how single or unforeseen events, such as storms, could have a long-lasting impact on a country's immigration figure.
Migration figures were much higher for countries that mostly relied upon agriculture.
Most interestingly, after an increase in temperatures, migration decreased for roughly four years before it increased for about 10 years.
This offered an important but tight window of opportunity for policy makers, as the speed of the policy response was crucial in limiting the effects of shocks from such events in origin countries - and therefore the effects on migration.
Wesselbaum said the research made clear that global migration patterns were increasingly being driven by climate change, and this raised crucial issues for policy makers.
"It is clear climate migration is a global issue that needs cross-country discussion," he said.
"Both developed and at-risk countries need more planning and policy to prepare for what is likely to be a growing trend of people wanting to move from countries experiencing climate change.
"Climate refugees have yet to be recognised officially by international law and included in the UN refugee convention, but the predicted 2-3C rise in global temperature will see climate refugees rather sooner than later.
"This raises the question for New Zealand of how we, as an individual country, can prepare for the impact on our population as well as our land."