Army Spc. Caitlyn Lacomb, 404th Civil Affairs Battalion, collects a water sample in a creek near the arid Lake Abbe in Djibouti, May 20, 2015. Village elders said it has not rained in two years, causing a drought and increasing malnourishment amongst the population. A study released this week calls for countries to consider worst-case scenarios when examining the effects of climate change, to include failures of entire nations, terrorism, and resource competition.

While some politicians still refuse to accept the science, a new report says climate change already is influencing national and international security and warns that world leaders need to prepare for the worst.

“Climate Change: A Risk Assessment” — released this week by the Centre for Science and Policy at Cambridge University in the United Kingdom — indicates all that may not be enough. It expresses concerns about failures of entire nations, terrorism, mass migration or displacement, humanitarian crises and resource competition.

Many of those living in vulnerable areas — such as Latin America and Africa — consider climate change the top security threat facing their nations, according to a 40-country survey conducted earlier this year by the Pew Research Center.

The U.S. Department of Defense is already integrating climate change-related threats into its strategic planning. The Pentagon’s 2014 Quadrennial Defense Review describes the direct effects of climate change, such as water scarcity and disruptions in food supply, as multipliers of threats such as terrorism.

In 2009, the Navy established Task Force Climate Change, which focuses particularly on naval strategy in the Arctic as international competition intensifies because of the receding ice cap. The task force is also looking at how changing sea levels will affect vulnerable nations.

And joint training exercises around the Pacific include working on survival strategies for low-lying island countries that could be inundated by rising sea levels.

According to the Cambridge report, majorities polled in 19 of 40 nations cited climate change as their biggest security concern, making it the most widespread worry of any issue included in the survey, which included cyberattacks, a nuclear-armed Iran and the jihadist Islamic State.

The report looks at direct risks from climate change, such as drought and river flooding, and systemic risks, as in the global food system. It sought to determine thresholds where “the inconvenient may become the intolerable,” such as limits of humans or crops to heat stress.

“A growing body of credible, empirical evidence has emerged over the past decade to show that the climate change that has occurred thus far — involving an increase of 0.8°C in global average temperatures — is already influencing dynamics associated with human, sub-national, national and international security,” the report said.

“This evidence does not generally attempt to pinpoint precise causal relationships, but instead considers how climate change may have altered probabilities and interacted with other factors to increase the risks.”

For example, climate change has played a significant role in a decades-long drying trend in the Middle East, North Africa and Mediterranean region, according to the report. Extreme drought between 2007 and 2011 in Syria led to severe crop and livestock losses, and by 2009 more than 800,000 Syrians had lost their livelihoods.

By 2011, an estimated 2 million to 3 million Syrians were driven to “extreme poverty,” the report said.

The so-called Arab Spring protests began in Syria in early 2011, which eventually led to the current civil war.

“While many other factors were important in driving the political unrest and conflict that followed [in Syria], it is difficult to imagine that this widespread impoverishment and large-scale displacement did not play a role,” the report said.

Scientists already have mooted most of the scenarios in the report. But it takes a new approach by arguing that climate change issues need not be addressed solely as environmental issues or separate from other foreign policy and security priorities, said Francesco Femia, director of the Center for Climate and Security, a nonprofit policy institute in Washington, D.C.

While many point out that the U.S. needs to focus on “real threats” such as Islamic State expansion in the Middle East and island disputes in the South China Sea, those are not separate issues from climate change, said Femia, who was one of 11 authors of the report’s section on international security.

“We need to look at how climate change affects, for example, the South China Sea and what that might do with interactions with China as fish stocks move northward,” he said. “It’s not helpful to be thinking about climate change as a distraction.”

The Centre for Science and Policy commissioned CNA, a nonprofit research and analysis organization located in Arlington, to design and conduct a wargame exercise to assess future security-risk scenarios related to climate change.

Twenty-four senior scientists, security experts, diplomats and retired military personnel from various countries, including India, China and the U.S., assumed the roles of leaders of major countries and regions “aiming to further national economic and security interests in the context of a changing climate over the next half-century or more,” the study said.

In the near-term future, climate change would most likely increase risk of state failure in nations already stressed by water shortages and food insecurity, the report said. Countries in the Middle East and North Africa are particularly at risk because they are already water-stressed, and populations in some countries in the region are expected to rise 50 percent to 130 percent by 2050.

While terrorism has complex causes, the study said, the direct results of climate change can hasten the two essential conditions that nurture it: an “appealing, unifying or disruptive idea” and the “social disenfranchisement of a section of society.” The power vacuum left by a failing state allows terrorist groups to exploit that marginalization with an appealing message, the report said.

Climate change can create or quicken migration because of sea level rise, river flooding, desertification and increased weather-related disasters. Large-scale migration becomes a security risk when it destabilizes borders, heats up conflicts over resources, aggravates cultural or ethnic disputes and creates conditions that spread diseases.

The exercise found it “extremely likely” climate change would exacerbate humanitarian crises, with great uncertainty whether the international community would — or could — respond to all these crises in the future.

The exercise participants suggested that “multiple pressures could contribute to a shift towards nationalism, and away from values associated with human rights, democracy and cooperative global governance.”

One notable action not provoked in the scenarios was the decision to invade a region to gain control of its resources.

“This may have been related to the fact that climate change tended to have the most severe impact on the resources of countries that were already relatively weak in terms of both military and economic power, reinforcing inequality between countries,” the report said.

It claims there’s little support for the hypothesis that scarcity leads to warfare — pointing to the Indus Water Treaty between India and Pakistan, the Mekong River Commission and treaties and consultations on the use of the Nile River. But the report also says political tensions can heat up between countries sharing a common water resource, especially if their relations are poor due to other reasons, and can lead to diplomatic, trade and other forms of non-military conflict.

olson.wyatt@stripes.com

Twitter: @WyattWOlson