Abrupt climate change: Are we there yet?

The most unsettling information about the potential for harmful impacts of a changing climate comes not from some runaway simulation of a computer model but rather from actual data -- the large and rapid changes that are recorded in clearly measurable physical remnants found in the last 15 years in polar ice cores and sediments in the sea floor.

People who argue that climate models are not up to the task of foretelling our future are correct in the sense that the computers do not very accurately capture the system's natural behavior, but they are very wrong about the direction and shape of things to come.  Yes, the computer models are "wrong" -- they are too optimistic.

Long before humankind came along and began tinkering with the composition of the atmosphere and other elements of the system, climate change was running roughshod over Earth -- jerking the biosphere between radically different states of warm and wet and cold and dry. Contrary to just about everything we grew up thinking, it turns out that as far back as we can see, abrupt change is climate's natural behavior. 

Take a look at this temperature profile (right to left) of the past 100,000 years that emerges from oxygen isotope analyzes of ice cores from Greenland, and keep this thought in mind: this herky-jerky pattern, these sudden swings between warm and cold regimes, is the climate system doing its own thing, behaving naturally. The actual values are not as important as the pattern, but suffice to say that the lower temperatures represent a Northern Hemisphere that is colder and drier and windier and seriously less hospitable to human civilization. Only the period of the last 10,000 years (far left) qualifies as a stable, equable climate, congenial to an urban world populated by billions of humans.

This rumination was inspired by an article in the current issue of the journal Nature that reviews progress in the technical field that studies the dynamics of complex systems such as fish and wildlife populations and other ecological circumstances, such as financial systems and global markets, such as Earth's climate.  Theory has advanced to the point where certain common patterns are seen to emerge as complex systems reach the verge of a "critical transition" between radically different stable states.

The idea that this insight could lead to the identification of useful "early-warning signals" that could tell us how close or far away we are to the next abrupt climate change is pretty darn wonderful, but is it something you can take to the bank?  Well, they aren't there yet. Climate models are good at doing a lot of valuable things in the science, but replicating abrupt change still is not one of them.  Which is too bad, because we know that abrupt change is out there somewhere, looming out of our vision like the edge of a cliff in a dark field, and it would be great to have some more light on the subject.

IMAGE: National Academy Press