Climate change is expected to exacerbate armed conflict, even as military efforts themselves serve as a driving source of global warming. This is the conclusion of multiple reports published this week probing the relationship between climate change and global conflict.

The dynamic between climate change and global stability has been a source of contention for years, with experts largely agreeing that a link between the two does exist, even if on a minute level. But a series of reports released this week indicate that the connection between rising temperatures and conflict is becoming increasingly clear.

According to one of the studies, global warming that rises beyond the dangerous 2 degrees Celsius threshold is likely to substantially escalate clashes and conflicts within countries. These findings echo another report this week that warns climate change will harm global peace and stability within the next decade.

Both of these studies come as some 2020 Democratic presidential candidates are increasingly discussing the connection between climate change and national security. That relationship goes both ways in the United States, where research has repeatedly emphasized the military’s long-running status as a major polluter.

Experts have long argued over the extent to which climate change impacts national and international conflicts. Other stressors, they agree, also play a significant role, like socioeconomic and political factors.

But a Stanford-led study published in Nature on Wednesday moves beyond that ongoing debate. The study takes an unorthodox approach: 11 experts in fields related to climate and conflict participated in individual interviews and group discussions about the relationship between those things. They concluded that climate has already influenced between 3% and 20% of armed conflicts over the past century.

That wide range includes the possibility that only a very small percentage of past conflicts can be linked to climate change. Despite this, the experts agreed that as temperatures rise, the impact on conflicts within nations would grow. Conflicts between nations were not included in the study as they are less common — but notably many international conflicts have initiated as domestic disputes.

According to the study, with 2 degrees Celsius of global warming above pre-industrial temperatures — which the Paris climate agreement seeks to prevent — the influence of climate change on armed conflict could rise to at least 13%. In a far more dire scenario of 4 degrees Celsius of warming, there would be a 26% chance of “a substantial increase in conflict risk.”

The rationale is that as climate change gets worse, it impacts weather and disasters — making hurricanes and wildfires more intense, droughts drier, and rainfall wetter. This in turn can greatly influence economies — impacting crops, livestock, and fisheries — subsequently hindering livelihoods and reinforcing social divides.

That has played out in countries like Syria, where reports have shown that climate change exacerbated already poor conditions, with a drought and water scarcity adding to political tensions and ultimately leading to civil war. Experts have similarly argued that climate change is worsening conditions in many parts of Central America, prompting many residents to migrate elsewhere.

“Knowing whether environmental or climatic changes are important for explaining conflict has implications for what we can do to reduce the likelihood of future conflict, as well as for how to make well-informed decisions about how aggressively we should mitigate future climate change,” Marshall Burke, an assistant professor of Earth system science and a co-author on the study, said in a statement.

The study heavily stipulates that direct connections between climate change and armed conflict are hard to establish, largely because so many other social and political factors are in play. But the researchers’ findings align with other emerging conclusions about the relationship between global warming and violence.

According to an annual peace index released Wednesday by the Australia-based Institute for Economics and Peace (IEP), climate change poses a severe threat to global harmony over the next 10 years. Competition over resources and migration, along with economic impacts, are seen as the key drivers behind the climate-driven instability.

That index found that almost a billion people are already at high risk from climate change based on where they live; of those, 40% are in countries struggling with conflict.

Steve Killelea, executive chairman of the IEP, told Reuters that the trends are alarming. “Going forward, climate change is going to be a substantial problem,” he said, calling climate impacts a “tipping point” that can exacerbate conflicts and escalate them.

That connection hasn’t been overlooked by national security experts in the United States. The Pentagon has warned that climate impacts are imperiling around half of all U.S. military sites. In a hearing before the House Intelligence Committee last week, top government intelligence experts, including Rod Schoonover, a State Department intelligence official, testified that climate change is a top global threat.

But military and intelligence experts have faced pushback from the White House and officials appointed by President Donald Trump when trying to call attention to the security threat posed by climate change.

William Happer, appointed by Trump to the National Security Council (NSC), has sought in particular to undermine the connection between climate change and national security. When Schoonover testified last week, Trump advisors withheld his testimony from the Congressional Record. The New York Times later published the NSC’s responses to Schoonover’s prepared comments, in which someone believed to be Happer accused the State Department official of “climate-alarm propaganda” and largely panned the expert’s testimony.

That division between experts and the Trump administration has spilled onto the campaign trail, where climate action has already proven to be a hot-button issue for Democrats. Several candidates have already released sweeping climate plans and a number have also highlighted the link between global warming and national security.

Gov. Jay Inslee (D-WA), who has devoted his campaign entirely to climate action, has argued repeatedly that addressing climate change is critical to ensuring national safety. He has even gone so far as to warn global warming is “a clear and present danger to the United States.” Both Inslee and former Rep. Beto O’Rourke (D-TX) have also cited climate change as a factor in destabilizing countries in Central America, prompting an influx of migrants at the U.S.-Mexico border.

Another growing conversation for 2020 contenders is the extent to which national security itself contributes to global warming. A study released this week by Brown University found that from 2011 to 2017, the Pentagon’s emissions totaled some 766 million metric tons — a distinction the report says makes the Department of Defense “the world’s largest institutional user of petroleum,” and “the single largest producer of greenhouse gases” in the world.

At least one candidate has a plan addressing that issue. Sen. Elizabeth Warren (D-MA) has called for decarbonizing U.S. non-combat bases and infrastructure by 2030, an approach that would greatly reduce global greenhouse gas emissions. While some have labeled Warren’s “green military” approach hawkish, the Brown study’s findings show that war itself makes up only around half of the military’s emissions, with “military industry” contributing significantly more.

The complicated dynamic posed by a military concerned about climate change that nonetheless serves as a major source of emissions is likely to gain further scrutiny as Democratic candidates vie for votes. Polls increasingly show that U.S. voters consider climate change a leading issue and national security has historically been a major talking point for candidates on both sides of the aisle.

And teasing out the circular relationship between security and instability will likely mean addressing long-established military norms. Another climate change factor highlighted by the Brown report is U.S. dependence on fossil fuels, particularly foreign oil. While the Pentagon is worried about climate change, the authors note, the U.S. military is meanwhile driving up emissions to safeguard oil in areas like the Persian Gulf.

“The Pentagon focuses their efforts on adapting to climate change and preparing for climate caused insecurity, even as they continue to ensure that Americans continue to have relatively inexpensive access to imported oil,” the report notes.

That enduring cycle and other drivers of global warming mean escalating climate impacts. And per this week’s reports, that in turn means an increasingly unstable world.