There are calls to better define what constitutes "climate migration" amid concern that policies are not keeping up with the growing issue and countries are failing to properly help those fleeing disasters.

Anywhere from tens of millions to one billion people could become climate migrants by 2050, according to a recent report from the RAND Corporation. The number varies so widely depending on the definition used.

"They may be reacting to rapid-onset shocks, such as extreme storms, or slow-onset and gradual stressors, such as drought or heat," the report reads.

Jay Balagna is a disaster risk management expert at the RAND Corporation and one of the co-authors of the report. He said while climate migration existed on a spectrum — anything from rising sea levels to people leaving domestic conflicts exacerbated by drought — having a definition was still important.

"This is already happening. We know it's already happening ... We've seen it start to happen at either end of the spectrum," Balagna said.

Distinguishing who is a climate migrant and who isn't can make a difference when it comes to the privileges, rights and respect that they're granted, Balagna said, in the same way that different types of refugees are covered under international laws and treaties.

For the report, the RAND Corporation focused on Bangladesh, Kiribati, Kenya, Norway, Vanuatu and the United States to examine current climate migration and related policies.

"Movement isn't inherently bad," Balagna said. "It can be good or it can be bad. But what makes it good is the policy that facilitates it, that ensures that it happens in a safe and just way, and in a way that doesn't impact host communities too much, either."

He said the best kinds of policies didn't just focus on the immediate impact after a catastrophic event, but also accounted for the long-term needs essential to people fleeing them.

"One kind of policy that might help would be something that enables people, when they move, to maintain the sorts of social structures that exist in their original home," Balagna said. "[That] facilitates movement, perhaps, to places where they have family. Facilitates movements to places that they're employable."

Kayly Ober is the senior advocate and program manager of the climate displacement program at Refugees International. In issues of climate displacement, Ober said governments needed to work on development planning for medium and long-term impacts.

She said this included helping those who can't or don't need to move yet, with measures like better irrigation systems in areas that are experiencing shifting rainy seasons, or help in sourcing alternative crops resistant to extreme weather like droughts or floods.

Ober said good policy also recognized that some people would need to leave the livelihoods they've known and find a completely new job in a new place.

"When folks in the rural parts of the world are having these sorts of environmental or climatic challenges, they often go to urban centers because that's where opportunity lies," Ober said. "So it's also about urban development and urban planning. Ensuring that people have access to safe infrastructure, safe shelter, that they're able to have access to social services in the city, that they're able to have jobs that are not so precarious."

Making sure the receiving areas can support incoming migrants in terms of housing, schools and physical infrastructures like sewer systems and electrical grids was also important, Balagna said.

Bangladesh is one of the few countries taking a good approach, he said.

"They call it their National Strategy on the Management of Disaster and Climate Induced Internal Displacement," Balagna said. "It does things like enshrining certain rights for people who are displaced by climate-related factors to ensure that their movement is handled in a just way that doesn't burden host communities, but also that allows them to thrive wherever they end up."