Global Warming: How Bad Could It Get?

Americans spent more than $1.2 trillion dollars on insurance premiums in 2008, or about $4,000 for every man, woman and child. Evidently, they understood that it pays to hedge your bets against small but real chances of catastrophic losses.

But when it comes to climate change, deniers cite scientific uncertainty as an excuse to do nothing. They say we can’t be certain that global warming will cause rising oceans to drown coastal communities, droughts to wither crops, new diseases to cause epidemics and fires to consume our forests—so why bother to act?

They have it exactly backwards.

Although climate scientists concede they can’t say for sure how bad things will get if humanity keeps emitting greenhouses gases into the atmosphere, that’s not cause for comfort. On the contrary, their uncertainty means life could easily become a lot worse for homo sapiens and other species than we’ve been led to believe.

As Harvard’s Martin Weitzman noted in a recent paper, “We seem headed for a unique planetary experiment of subjecting the Earth’s system to an unprecedented shock by geologically instantaneously jolting atmospheric stocks of (greenhouse gases) far above their highest level over the last several million years. We simply do not know what will happen under such extreme circumstances.”

No less an authority than Dr. Robert Watson, chair of the authoritative Intergovernmental Panel on Climate Change from 1997 to 2002, recently conceded that the IPCC’s last major report in 2007, which sounded a strong alarm over global warming, was in many cases too conservative, leading him to warn that the world could face “unthinkable impacts.”

For example, the IPCC’s projections of sea level rise did not take into account the melting of Greeland’s ice sheet, which is taking place much faster than previously believed. This December, scientists writing in the Proceedings of the National Academy of Sciences forecast an increase in global sea levels of five feet by 2100 if greenhouse emissions are not strongly curbed, a finding supported by many other recent studies.

“The ramifications of a major sea level rise are massive,” write ocean scientists Rob Young at Western Carolina University and Orrin Pilkey at Duke University:

Agriculture will be disrupted, water supplies will be salinized, storms and flood waters will reach ever further inland, and millions of environmental refugees will be created. . . . Miami tops the list of most endangered cities in the world, as measured by the value of property that would be threatened by a three-foot rise. This would flood all of Miami Beach and leave downtown Miami sitting as an island of water, disconnected from the rest of Florida. Other threatened U.S. cities include New York/Newark, New Orleans, Boston, Washington, Philadelphia, Tampa-St Petersburg, and San Francisco. Osaka/Kobe, Tokyo, Rotterdam, Amsterdam, and Nagoya are among the most threatened major cities outside of North America.

What terrifies these and other scientists is the possibility that ice caps on Greenland and Antarctica will melt much faster even than current models predict. Indeed, the last time CO2 levels were as high in the Earth’s atmosphere, about 15 million years ago, seas were 75 to 120 feet higher.

Ice cap melting is just one of nine potential “tipping elements” that scientists say could lead to abrupt and disastrous shifts in climate. Others include massive die-off of the Amazon rainforest, disruption of the monsoon system, and wholesale changes in Atlantic and Pacific ocean currents.

One of the biggest longterm “tipping” risks is that global warming will unlock vast amounts of carbon and methane currently frozen in Arctic permafrost. Methane, a greenhouse gas 20 times as potent as carbon dioxide, could accelerate the warming process with dire consequences. British and German researchers reported last August evidence that warming Arctic waters were melting methane hydrates stored in seabed sediments. High rates of Arctic methane seepage were reported this January by a researcher at the University of Alaska, and confirmed in a new paper published in the journal Science.

(If you want to get really masochistic, check out the 2003 paper in Geology, “Methane-Driven Oceanic Eruptions and Mass Extinctions,” which makes the case that the worst mass extinction of all time, some 251 million years ago, was caused by an explosive upwelling of methane from the ocean, which may have unleashed 10,000 times as much energy as the world’s entire stockpile of nuclear weapons.)

If the worst of these climate feedback loops prove real, average temperatures over the United States could jump an unimaginable 15°F to 18°F in 50 years, according to recent projections by the prestigious Met Office Hadley Centre in the UK. And a study led by the National Oceanic and Atmospheric Administration last year suggests that the catastrophic consequences would be “largely irreversible for 1,000 years.”

So the question isn’t whether we should buy insurance against climate change, or even whether we can afford to pay a little more for energy in order to phase out fossil fuels. The real question is, what are we waiting for?

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