Geologist Dale Allen Pfeiffer claims that coming decades could see spiraling food prices without relief and massive starvation on a global level such as never experienced before. Since supplies of petroleum and natural gas are essential to modern agriculture techniques, a fall in global oil supplies (see peak oil for global concerns) could cause spiking food prices and unprecedented famine in the coming decades. Wheat is humanity's third-most-produced cereal. Extant fungal infections such as Ug99 (a kind of stem rust) can cause 100% crop losses in most modern varieties. Little or no treatment is possible and infection spreads on the wind. Should the world's large grain-producing areas become infected, the ensuing crisis in wheat availability would lead to price spikes and shortages in other food products. Several asteroids have collided with Earth in recent geological history. The Chicxulub asteroid, for example, was about six miles in diameter and is theorized to have caused the extinction of non-avian dinosaurs at the end of the Cretaceous. No sufficiently large asteroid currently exists in an Earth-crossing orbit; however, a comet of sufficient size to cause human extinction could impact the Earth, though the annual probability may be less than 10−8. Geoscientist Brian Toon estimates that while a few people, such as "some fishermen in Costa Rica", could plausibly survive a six-mile meteorite, a sixty-mile meteorite would be large enough to "incinerate everybody". Asteroids with around a 1 km diameter have impacted the Earth on average once every 500,000 years; these are probably too small to pose an extinction risk, but might kill billions of people. Larger asteroids are less common. Small near-Earth asteroids are regularly observed and can impact anywhere on the Earth injuring local populations. As of 2013, Spaceguard estimates it has identified 95% of all NEOs over 1 km in size. In April 2018, the B612 Foundation reported "It's a 100 per cent certain we'll be hit [by a devastating asteroid], but we're not 100 per cent sure when." Also in 2018, physicist Stephen Hawking, in his final book "Brief Answers to the Big Questions", considered an asteroid collision to be the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released the ""National Near-Earth Object Preparedness Strategy Action Plan"" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.