New modeling will shed light on policy decisions' effect on migration from sea level rise

"I'm often asked 'How many people will migrate because of sea level rise?' The answer is the number depends entirely on decisions we make now," said David Wrathall, the paper's lead author and an assistant professor in Oregon State University's College of Earth, Ocean, and Atmospheric Sciences.

In the paper, a group of internationally known climate change researchers suggest that global policy decisions about greenhouse gas emissions and a range of policy decisions about where people live and work in coastal areas now will determine whether people need to migrate and where they may go.

"We've been looking at this problem the wrong way. We've been asking how many people will be vulnerable to sea level rise and assuming the same number of people will migrate," Wrathall said. "In reality, policies being made today and moving forward will exert a strong influence in shaping migration. People will move in very specific ways because of these policies."

Minimizing the negative impacts of sea level rise presents a significant societal challenge. About a billion people around the world live near the coastline and could be impacted directly or indirectly by rising sea levels as the planet warms due to climate change.

"Sea level rise is going to reorganize the human population around the globe," Wrathall said. "As the impacts of sea level rise occur, we will make decisions about how to best adapt, and those decisions will also shape migration."

The findings emerged from an interdisciplinary working group supported by the University of Maryland's National Socio-Environmental Synthesis Center.

In their paper, the researchers suggest that policymakers seeking to understand how their decisions may affect migration cannot afford to experiment on vulnerable populations in the real world with expensive and potentially dangerous policies. Instead, decision-makers can anticipate the effects of realistic policy alternatives using simulations thanks to advances in computation and modeling, Wrathall said.

A wide range of economic policies, planning decisions, infrastructure investments and adaptation measures have the potential to influence how, why and if people migrate to new places as a result of sea level changes, Wrathall said.

Armoring coastlines against surging tides and rising waters could impact whether people are able to stay in their homes or need to relocate. Tax incentives and zoning regulations that allow businesses to locate near ports, a global trend, potentially puts whole industries and labor markets at risk. Even interest rates can affect who can afford to borrow money, which could be a crucial part of people's decisions to migrate.

In addition, global decisions about the management of greenhouse gas emissions, which are responsible for the warming of the planet, could impact how quickly the planet warms and sea levels rise, Wrathall said.

"Right now, people are actually moving toward coastlines that will be more and more vulnerable as the planet warms," Wrathall said. "The only thing that will change this trend is policy. If we start changing the incentives to live, work and invest in safer places, we could make sea level rise-induced migration less expensive and disruptive down the line."

The researchers suggest that computational models should focus on global emissions policies under discussion to quantify migration impacts of sea level rise scenarios.

"All greenhouse gas emissions scenarios have a similar effect on sea level rise until about the year 2050," Wrathall said, "but then sea level rise outcomes really start to diverge. So a first step is modeling sea level rise, policy and migration in the near term."

Researchers should then simulate migration outcomes for expected adaptation policies going forward, which include defending coastlines and retreating from them.

Policy decisions also need to be modeled for their impact on the communities or regions where migrants are relocating, since those arriving will have a significant impact on their new community as well, Wrathall said.

"Future migrants will need jobs, houses and health care," he said. "Their kids will need schools. The availability of these things will affect where migrants go and their quality of life when they get there."

Modeling how those migrants make decisions will help researchers and policymakers better understand the range of realistic outcomes without having to experiment on vulnerable populations in the real world, Wrathall said. This modeling approach will provide insight on what to expect, including more realistic numbers of future migrants.

"Modeling allows us to look at all kinds of scenarios to identify the specific policies that might work to help people migrate and anticipate the policies that cause problems," Wrathall said.

The work was supported by the National Socio-Environmental Synthesis Center under funding received from the National Science Foundation, grant number DBI-1639145.