The smoke that billowed from the burning oil fields was so thick it blocked out the sun. By the time I reached Qayyarah, where Islamic State fighters had set fire to 19 oil wells, a film of black soot had settled over the Iraqi town like toxic snow. Even the sheep had turned black.

Pools of thick oil ran in the streets. In the sky above the town, the black smog mixed with white fumes from a nearby sulphur plant that the jihadists had also set on fire as they retreated. The plant burned for months, spewing as much sulphur dioxide into the atmosphere as a small volcanic eruption. Hundreds of people were hospitalised.



The fires may have been extinguished, and Isis ousted from the city, but the environmental devastation caused by the battle for Mosul will linger for decades. The destruction of hospitals, weapons factories, industrial plants and power stations has left behind a toxic cocktail of chemicals, heavy metals and other harmful waste. Many of these pollutants are mixed up with unexploded bombs and mines in the vast amount of rubble generated by the fighting.

Our team has already found high levels of lead and mercury in Mosul’s water and soil. This is the toxic legacy of one of the fiercest urban battles of the modern age.



'We have no home to go back to': citizens of Mosul return to ruin – in pictures Read more

When we measure the brutality of war, we often count the dead bodies, the destroyed homes and the lives upended by violence. Rarely do we pause to consider the environmental devastation that wars cause. In the din of battle and the rush to treat and shelter its survivors, the toxic legacy of war is often ignored – as is the long-term damage to the health of millions of people forced to live amid the pollution.



There is nothing new in the waste generated by war. Parts of Belgium and France are still suffering from the contamination of heavy metals used in the weapons of the first world war. In Vietnam, the herbicide Agent Orange, sprayed to strip trees of foliage that gave the enemy cover, has caused birth defects, cancers, skin disorders and mental disability.



Facebook Twitter Pinterest Oil wells smoulder in the background as children play football in Qayyarah, south of Mosul. Photograph: Odd Andersen/AFP/Getty Images

When bombs fall, the environment suffers. In Colombia, which hosts 10% of the planet’s biodiversity, half a century of war has destroyed some of the world’s most vibrant ecosystems. The mining of gold, which funded rebel forces during the conflict, has polluted the country’s rivers and land with mercury. In Ukraine, three and a half years of fighting in the heavily industrialised country has contaminated the groundwater. Decades of conflict in Afghanistan has destroyed more than half the country’s forests.



Often, the environmental destruction is deliberate. Environmental infrastructure is increasingly targeted to drain the enemy of popular support. When power plants, water facilities and sewage systems are destroyed, disease and pollution spread and civilian health plummets, prolonging the suffering of people whose lives have already been devastated by violence.



Failing to respond appropriately when the bullets stop only generates more environmental calamity. Plans to rebuild Mosul with sand and gravel dredged from the Tigris would be disastrous for a river that irrigates about two-thirds of Iraq’s agricultural land and supplies water and electricity to millions of people. Instead, recycling the debris so that it can be used to reconstruct the shattered city would save millions of dollars, limit quarrying and generate 750,000 days of work for some of Mosul’s long-suffering residents.



The environment isn’t just a silent victim of war. When poorly managed, the environment can also trigger and fuel armed conflict. In Syria, severe drought drove millions into cities that were ill-equipped to cope with the burden. Popular anger grew inside some of the country’s poorest urban areas, fuelling protests that erupted into a civil war that has killed more than 400,000 people and sparked one of the largest humanitarian crises of our time. Around the world, natural resources are funding militias, prolonging violence and making it even harder for peace deals to stick.



The wars of tomorrow will increasingly be fought over natural resources, as populations boom and supplies of food and water dwindle in regions most vulnerable to the impact of climate change. Never has it been more important for the world to place the environment at the very heart of how we prevent, solve and respond to conflict.



Facebook Twitter Pinterest An Iraqi shepherd watches over his smoke-blackened sheep as they graze near Qayyarah. Photograph: Thomas Coex/AFP/Getty Images

There are encouraging signs that the world is beginning to wake up to this need. Social media, smartphones and satellite imagery are making it easier to identify pollution hotspots, allowing governments and aid agencies to respond faster and more effectively to reduce the harm to human health. The UN is drafting new laws to protect the environment during conflict, laws which have barely evolved since the 1970s. And the international criminal court may soon try cases that involve the destruction of the environment and the illegal exploitation of natural resources during conflict.



In December, the third UN Environment assembly will take place in Nairobi. Curbing pollution – in all its insidious, life-threatening forms – will dominate the agenda. Worrying about the environment during war may seem like a luxury. But this is not about birds and butterflies. This is about protecting the soil, air and water that all of us depend on to survive. When we destroy the ecosystems that sustain us, when we pollute the rivers and land with heavy metals and toxic chemicals, we cripple our health and our ability to rebuild amid the ruins. If we continue to ignore the environmental toll of conflict, then we will continue to perpetuate the misery of war and prolong the suffering of those caught in the crossfire.