• President Joe Biden and his administration have faced pressure from across the political spectrum to stem the flow of migration at the U.S. southern border.
• The impact of Hurricanes Eta and Iota is one of many reasons migrants from Central America are making the dangerous journey to the U.S.-Mexico border to seek refuge
• Climate-related events like the twin hurricanes increasingly intensify drivers of migration, including violence, food insecurity and poverty.

Hurricanes Eta and Iota struck Central America last November, bringing torrential rain, flash floods, landslides and crop damage across Honduras, El Salvador, Guatemala and Nicaragua.

An estimated 7.3 million people in the region were affected by the twin hurricanes as of December, according to the United Nations.

The impact of the hurricanes is one of many reasons migrants from Central America are making the dangerous journey to the U.S. southern border to seek refuge — and just one example of climate-exacerbated drivers of displacement and migration.

"Climate change is reinforcing underlying vulnerabilities and grievances that may have existed for decades, but which are now leading to people having no other choice but to move," Andrew Harper, special advisor on climate action for the UNHCR, the United Nations Refugee Agency, said in an interview.

President Joe Biden and his administration have faced pressure from across the political spectrum to stem the flow of migration at the U.S. southern border.

U.S. Customs and Border Patrol reported encountering more than 172,000 people attempting to cross the southern border in March, a 71% increase compared with the previous month and a 34% increase from the same time frame in 2019. The vast majority of people arrive at the border are being expelled due to public health ordinance Title 42, although seeking asylum in the U.S. is a legal right.

CBP cited "violence, natural disasters, food insecurity, and poverty" in Mexico, Honduras, Guatemala and El Salvador for the rising numbers of encounters at the border.

"Climate change is never the sole driving factor behind migration decisions," said Kayly Ober, senior advocate and program manager for the Climate Displacement Program at Refugees International. "We see a confluence of events."

Ober said in addition to the sudden-onset disasters like Hurricanes Eta and Iota, longer-term climate challenges like drought contribute to instability, particularly in what's known as the Dry Corridor — a region running along the Pacific coast of Guatemala, El Salvador, Honduras and Nicaragua.

Krish O'Mara Vignarajah, president and CEO of Lutheran Immigration and Refugee Services, told CNBC at least a third of the migrants LIRS works with cite climate-related reasons as a primary factor for their displacement.

"You may see migrants who are initially internally displaced due to crop failures. But then because of that initial displacement, they become more vulnerable to gang violence and persecution, which then leads to international migration because the situation becomes worse," Vignarajah said.

Sarah Blodgett Bermeo, a professor of public policy and political science at Duke University, recently co-authored a study investigating root causes of migration from Honduras.

Using available data from 2012 to 2019, the study found that negative rainfall was associated with greater numbers of Honduran families apprehended at the U.S. southern border. Higher levels of violence, as measured by homicide rates, increased the magnitude of the association even further.

"As climate change continues to have impacts around the world, we're going to see more and more of these mixed migration flows, where people are coming for a variety of reasons from the same country," Bermeo said.

Meghan López, the International Rescue Committee's regional vice president for Latin America, also highlighted the intersecting factors driving migration.

"We cannot say it's violence, we can't say it's climate change, we can't say it's family reunification. It's everything. For any given family, it's a slightly different mix of any of these factors," López said.

"People want to get out of the situation they're in, and the next safe stop is the U.S.," López said. "The story is what people are fleeing from, not what they are running to."

Harper, the UNHCR's special advisor on climate action, stressed the importance of "forthright, ambitious" action from countries around the world to increase climate adaptability and disaster preparedness in particularly vulnerable regions like Central America.

"What we basically need is the mobilization which has occurred for Covid at the global level, but for climate," Harper said. "We cannot continue to push this down and say it's a threat in the future. It's a threat now."