The Uncertainty of Global Warming

### Welcome to the Anthropocene The graphs we see these days, John Baez began, all look vertical-- carbon burning shooting up, CO2 in the air shooting up, global temperature shooting up, and population still shooting up. How can we understand what really going on? "It's like trying to understand geology while you're hanging by your fingernails on a cliff, scared to death. You think all geology is vertical." So, zoom out for some perspective. An Earth temperature graph for the last 18,000 years shows that we've built a false sense of security from 10,000 years of unusually stable climate. Even so, a "little dent" in the graph of a drop of only 1 degree Celsius put Europe in a what's called "the little ice age" from 1555 to 1850. It ended just when industrial activity took off, which raises the question whether it was us that ended it. Nobel laureate atmospheric scientist Paul Crutzen suggests that the current geological era should be called the "Anthropocene," because it is increasingly dominated by human-caused effects. Baez noted that oil companies now can send their tankers through a Northwest Passage that they may have created, since it is fossil fuel burning that raised the CO2 that raised the summer temperatures in the Arctic that melts the polar ice away from the land. Zoom out further still to the last 65 million years. The temperature graph shows several major features. One is the rapid (every 100,000 years) wide swings of major ice ages. When they began, 1.35 million years ago, is when humans mastered fire. But almost all of the period was much warmer than now, with ferns growing in Antarctica. "Now it's cold. What's wrong with a little warming?" Baez asked. The problem is that the current warming is happening too fast. Studies of 1,500 species in Europe show that their ranges are moving north at 6 kilometers a decade, but the climate zones are moving north at 40 kilometers a decade, faster than they can keep up. The global temperature is now the hottest it's been in 120,000 years. One degree Celsius more and it will be the hottest since 1.35 million years ago, before the ice ages. Baez suggested that the Anthropocene may be characterized mainly by species such as cockroaches and raccoons that accommodate well to humans. Coyotes are now turning up in Manhattan and Los Angeles. There are expectations that we could lose one-third of all species by mid-century, from climate change and other human causes. Okay, to think about major extinctions, zoom out again. Over the last 550 million years there have been over a dozen mass extinctions, the worst being the Permian-Triassic extinction 250 million years ago, when over half of all life disappeared. The cause is still uncertain, but one candidate is the methane clathrates ("methane ice") on the ocean floor. Since methane is a far worse greenhouse gas than carbon dioxide, massive "burps" of the gas could have led to sudden drastic global heating and thus the huge die-off of species. Naturally the methane clathrates are being studied as an industrial fuel for when the oil runs out in this century, "which could make our effect on global warming 10,000 times worse," Baez noted. "Zooming out in time is how I calm myself down after reading the newspapers," Baez concluded. "A mass extinction is a sad thing, but life does bounce back, and it gets more interesting each time. We probably won't kill off all life on Earth. But even if we do, there are a hundred billion stars in our galaxy, and ten billion galaxies in the observable universe."