Few people still doubt that human emissions are causing long-term climate change, which is predicted to increase storm surges, drought and possibly hurricanes. So there's little doubt that humans influence natural disasters over the long term. But can we also trigger sudden "natural" catastrophes?
The answer is yes. From mud volcanoes to disappearing lakes, human actions can have all sorts of unforeseen environmental consequences.
Here we review five disasters with a human cause. We focus on sudden, short-term events rather than protracted environmental catastrophes.
On 28 May, steaming mud erupted from a gas well near Surabaya, East Java. Since then, each day between 7000 and 15,000 cubic metres of mud have poured out of what is now known as the Lusi Mud Volcano. Eleven villages have been displaced by the flow.
Lapindo Brantas, which operates a nearby mine, claims that the original eruption was caused by a large earthquake with an epicentre near the ancient city of Yogyakarta some 250 km from the gas drilling site 40 hours earlier.
But this has been discounted by several independent geological studies. "We suggest that a blowout in the Banjar Panji-1 well was the most likely mechanism for triggering the Lusi eruption," write Mark Tingay of the University of Adelaide, Australia, and colleagues in the latest such study, published this month in the journal Geology.
Lusi produced mud rather than molten lava, and geologists agree that humans cannot trigger real volcanoes. But we can certainly make the ground shake with great fury. Tremors in the crust beneath the North Sea have become more frequent since oil drilling operations began there, and mining operations are also known to increase the frequency of tremors.
Both drilling and mining redistribute the normal stresses present in rocks, but they are not the biggest cause of man-made earthquakes.
"Dams are the most dangerous man-made structure likely to cause quake," says David Booth of the British Geological Survey.
By artificially holding a large volume of water in one place, dams increase pressure on fractures beneath the surface of the earth. What's more, water has a lubricating effect, making it easier for the fractures – or faults – to slip.
Booth says the largest dam-induced earthquake occurred in Koyna, India on 11 December 1967. The region was previously considered nearly non-seismic but, shortly after a large dam was built and its reservoir filled, a magnitude 7.5 quake struck the area killing 200 people and injuring thousands more. Since then, the region has experienced frequent earthquakes.
"People often ask whether nuclear testing can generate earthquakes," says Booth. "The answer is no." This is because, unlike dams, nuclear explosions produce instantaneous and short-lived geological stresses. As the wave of pressure moves through the rocks, the particles inside them shake but quickly go back to their original position.
In addition to erupting and furiously shaking, the earth can be made to consume entire lakes.
On 20 November 1980, Lake Peigneur in Louisiana was sucked into the ground in an enormous whirlpool. Although the exact cause of the incident is difficult to ascertain as the evidence was washed away, it is generally believed that the lake's plug was pulled when a Texaco oil rig drilled into a salt mine directly beneath the lake.