In Is Global Warming Happening Faster Than Expected?, John Carey warns that feedback loops may be starting to kick in to spiral the climate system out of control.
The potential for faster feedbacks has turned some scientists into vocal Cassandras. Those experts are saying that even if nations do suddenly get serious about reducing greenhouse gas emissions enough to stay under the 450-ppm limit, which seems increasingly unlikely, that could be too little, too late. Unless the world slashes CO2 levels back to 350 ppm, “we will have started a process that is out of humanity's control,” warns James E. Hansen,...
Sea levels might climb as much as five meters this century,... Meanwhile increased heat and drought could bring massive famines. “The consequences are almost unthinkable,” Hansen continues. We could be on the verge of a rapid, irreversible leap to a much warmer world.
... the realization that specific feedback loops may be amplifying the change is causing a profound unease about the planet's future.
... about 125,000 years ago—sea levels rose and fell by up to two meters within 100 years.
... sea levels appear to have been more than six meters higher than they are today—in a climate much like our own.
Also surprising is how little extra energy, or “forcing,” was required to trigger past swings. For instance, 55 million years ago the Arctic was a subtropical paradise, with a balmy average temperature of 23 degrees C (73 degrees F) and crocodiles lurking off Greenland. The tropics may have been too hot for most life. This warm period, dubbed the Paleocene-Eocene Thermal Maximum (PETM), apparently was sparked by a preceding bump of about two degrees C in the planet's temperature, which was already warmer than today. That warming may have caused a rapid release of methane and carbon dioxide, which led to more warming and more emissions of greenhouse gases, amplifying further warming. The eventual result: millions of years of a hothouse earth.
We are also shoving the climate harder than the known causes of various ice ages did.
... the waxing and waning of ice ages can be linked to small variations ... These variations alter the solar energy hitting the planet's surface by an average of about 0.25 watt per square meter, Hansen says. That amount is pretty small. To cause the observed swings in climate, this forcing must have been amplified by feedbacks such as changes in sea ice and greenhouse gas emissions. In past warmings, “feedback just follows feedback, follows feedback,”...
The climate forcing from human emissions of greenhouse gases is much higher—three watts per square meter and climbing.
Plus, Siberia is dotted with giant hills of organic-rich permafrost called yedoma, formed by windblown material from China and Mongolia. Those carbon stores add up to ...“roughly double the amount in the atmosphere now,”... “That carbon is one of the ticking time bombs.”
Expanded wetlands could release as much, or more, additional methane as that from Arctic warming.
... even if these particular feedbacks do not bring near-term threats to humanity, they could drive other mechanisms that do.
Making this story even more complex is the potential for ecological feedbacks.
Climate models, which are good at explaining the past and present, stumble when it comes to predicting the future. “People can conceptualize these abrupt changes better than the models do,” Schuur says. Even if the planet is in a tipping point now, he adds, we may not recognize it.
“It would be immoral,” he [Hansen] says, “to leave these young people with a climate system spiraling out of control.” [emphasis mine]
Yep, the "tipping point" models seem to be winning. I first studied this back in about 1979 or so, when the term "global warming" hadn't even been coined yet, though we probably used it in our discussions. Gradual warming seemed to be more likely at the time, given our limited data. The Vostok deep cores weren't drilled until the early 1990's. Their data show conclusively that dramatic abrupt climate change has happened in the past, and is linked with atmospheric CO2 levels. I attended a presentation by Alder Stone Fuller last summer that echoed a lot of the things we had talked about over thirty years previously - it seems the Great Unwashed Horde is still as recalcitrant as ever, though perhaps some cracks are showing. Here's his website: http://alderstone3.com/
I've been more or less waiting for interesting things to start happening with the weather for a number of years now. The storms up here have started to get in line - we've had three "hundred-year event" storms in the last five years, if memory serves. And Sandy certainly qualified as unusually large. Stay tuned, things are just starting to get interesting.