Since late September, North Korea has launched a flurry of ballistic missile tests as part of what experts believe is a program to develop so-called tactical nuclear weapons. If the reclusive state were to move beyond testing missiles to testing actual nuclear warheads, as some analysts are predicting, it would not only ramp up political tensions, but also pose a significant environmental threat. 

In the past, countries such as the United States, the former Soviet Union and the United Kingdom tested their nuclear weapons in the open atmosphere and in the sea — and around Pacific Islands, the Australian desert, mainland US, remote parts of the USSR and other places. These tests left contaminated landscapes and spread their radioactive clouds far afield. 

Thanks to global treaties, nuclear tests were largely moved underground after 1963, a slightly preferable scenario environmentally speaking. And since a 1996 test ban, only India, Pakistan and North Korea have tested weapons at all. 

North Korea is the only country known to have conducted tests in the 21st century. 

The impact of nuclear testing on mammals

"The legacy of nuclear weapons testing has been absolutely catastrophic for humans and for the environment," said Alicia Sanders, the policy research coordinator at the International Campaign to Abolish Nuclear Weapons. 

One of the unique consequences for the environment, she added, "is that it lasts essentially forever."

Putting aside the development required to set up test sites, the first major effects are felt in the microseconds after the explosion. 

A 2015 paper on the environmental impact of military actions found that nuclear blasts represent an extreme threat to local biodiversity. 

The massive energy released in the thermal emission from the blast — comprising light and heat — kills any organisms unfortunate enough to be near the epicenter. Depending on the yield of the bomb, even organisms several kilometers away face lethal temperatures. What remains is a charred mess.  

The effect from the thermal shock on animals is not well researched, but humans face serious, life-threatening burns even several kilometers away, depending on the power of the bomb. A similar effect is assumed for other mammals. They also suffer from the pressure of the blast, which causes lung damage and hemorrhaging.

And animals that aren't killed immediately are more likely to die from infections in the days and weeks following the explosion, leading to a localized die-off event, the 2015 review found.

The impact on plants, birds and marine life

Plants are also not spared the effects of a nuclear blast. The sheer force strips trees of their foliage, tears down branches and uproots vegetation.  

For fish, meanwhile, the impact is similar to that of a non-nuclear explosion, but on a much larger scale. The US tests in Alaska, and those of France in French Polynesia in the late 1960s and early 70s were associated with large-scale die-offs of fish, as their gas-filled swim bladders ruptured.

Marine mammals and diving birds suffered similarly, post-mortem analysis showed. However, marine non-vertebrates appeared to be more resistant to pressure waves as they do not have gas-containing organs, according to defense studies at the time. 

Long-term environmental impacts

During the Cold War, the United States detonated scores of nuclear weapons in atmospheric tests in the Pacific. Entire islands were incinerated and many are still uninhabitable. Local residents were forced to leave. A 2019 study found that some of the affected areas had radiation levels 1,000-times that of those found in Chernobyl and Fukushima. 

Significant long-term environmental consequences of nuclear testing are the contamination of surface soil and groundwater, land disturbances in the form of craters or partially collapsed mountains — as in the case of the North Korean testing site — and the addition of radionuclides to sediments in seabeds.

Atmospheric nuclear tests spread radionuclides — unstable particles that releases radiation as they break down — far and wide, contaminating topsoil.

But even in underground testing, high pressure conditions can propel radionuclides into the atmosphere — a phenomenom known as venting — where they can be carried by winds and deposited far away from the test sites and enter food-chains.

Ankit Panda, a senior fellow at the Carnegie Endowment for International Peace's nuclear policy program, says Pyongyang has thus far avoided the pitfall of venting.

"The North Koreans have actually, with their last five nuclear tests at least, been very effective at preventing the venting of radionuclides," he said. "Because some of these radionuclides can even offer hints about the specific materials that are being used in the nuclear device."

At the very least, underground tests deposit huge quantities of radioactive material which will remain there for millions of years. The long-term ecological damage from such contamination is unknown.  

The impact on drinking water

Underground testing also poses a threat of radionuclides leeching into drinking water.

Studies at the US nuclear testing site near Las Vegas, found that some contaminants released by underground nuclear tests can get into the surrounding water. Plants and animals are particularly liable to pick up radioactive strontium and caesium, which are easily spread in water.

With a half-life of 30 years, these two radionuclides can cause health issues in the food chain for decades. A common shrub in New Mexico, chamisa, has roots that extend deep into the ground, bringing strontium back up to the surface near the Los Alamos testing site in New Mexico, from where it can be widely distributed as the leaves fall, decay, and contaminate the soil understory.

"Animals will eat from contaminated land and that becomes very dangerous. These can be key sources of food for people," ICAN's Sanders said.

Organizations such as ICAN continue to push for complete denuclearization. 

Until that happens, one factor that might help clean up the legacy of nuclear testing is a provision in the 2017 Treaty on the Prohibition of Nuclear Weapons, which requires signatories to provide assistance to victims of nuclear weapons and begin to remediate contaminated environments. States should next year begin initial assessments of environmental damage and use that as a basis for future remediation efforts. 

Edited by: Tamsin Walker