Tag Archives: physics

Uncertainty in the Physics and Philosophy of Climate Change

Posted on July 25, 2011 by | 2 comments

I wrote this post last year for the National Journal, but it also relates to the way I think about Petermann Glacier’s ice islands. There are now at least 4 larger ice islands that formed from last year’s single calving: one is the tourist attraction off Labrador and Newfoundland, a second has left Petermann Fjord last week, a third was grounded off Ellesmere Island for much of the year and is now where #1 was Nov.-2010, while the fourth … I do not know. Last I heart, it was grounded off central Baffin Island. With this much variation of where pieces of the ice island went, how can we possibly claim any skill in predicting anything?


Neither climate nor weather is linear, but this neither makes them unpredictable nor chaotic. The simple harmonic pendulum is the essence of a linear system with clear cause and effect relations. Oscillations are predictable as long as the initial forcing is small. Furthermore, a linear trend will show the pendulum to slow down due to friction. Corrections are straightforward.

Unfortunately, climate is not a simple, harmonic, or linear system. While this does not make it unpredictable or chaotic, it means that our “common sense” and loose talk of “totality of events” can easily fool us. We know that CO2 emissions for the last 150 years changed global temperatures. We also know that our current climate system has been very stable over the last 10,000 years. What we do not yet know is how small or how large a perturbations the last 150 years have been. If the pendulum is forced too much, if the spring is stretched too far, the system will find another stable state by breaking. Climate dynamics can find an adjustment less tuned to the areas where people presently live. This is what “tipping points” are about. Only numerical experimentation with the best physics and models will suggest how close to a different stable climate state we are. The IPCC process is one way to do so.

Ice cores from Greenland contain air bubbles 100,000 years old, which clearly demonstrate that our present climate state is the “anomaly of quiet” in terms of temperature fluctuations. The absence of large fluctuations for about 10,000 years made agriculture and advanced civilizations possible. The ice cores show that abrupt climate change has happened and may happen again, not this election cycle, but it is one possibility perhaps as likely as the possibility that climate change is mundane, linear, and follows trends that we can easily correct or mitigate later. Both are excellent hypotheses.

For scientists, these are exciting times as we conduct a massive, global experiment to see how much CO2 we can add to the atmosphere to perhaps find a different climate state. Dr. Terry Joyce, Senior Scientist at Woods Hole Oceanographic Institution once said: “I’m in the dark as to how close to an edge or transition to a new ocean and climate regime we might be. But I know which way we are walking. We are walking toward the cliff.” I agree with this sentiment, but add that we do not know if this cliff is a 1000 feet fall or a 2 feet step. Can we affort to wait until we know for sure? As a scientist I do not care. As a citizen, however, I think the time to act responsibly is now.

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Is Climate Change Causing Wild Weather?

Posted on July 23, 2011 by | 4 comments

Almost a year ago, Amy Calder of the National Journal asked:

Are extreme weather events, when considered collectively, evidence that climate change is occurring? If not, what are the missing links scientists still need to study in order to make a more conclusive find? Could these weather events revive congressional efforts to pass comprehensive climate legislation?

My answer is still the same, even though I grapple with what my resonsibilities and moral obligations are as a scientist learning, a tenured professor teaching, and a citizen voting. Here it is:

No, climate does not cause weather, the balances of forces, masses, and energies in the atmosphere do. Furthermore, the atmosphere interacts with oceans, ice sheets, lands, and livings things. Ask an equally ill-posed question “Is climate change contributing to wild weather?” and my answer becomes yes, but with the caveat that butterflies flapping their wings in Tokyo contribute as well. There is more to the question than meets the eye.

Globally averaged air temperatures have increased by about 0.6 degrees Celsius per decade over the last 50 years. This warming is not uniform as it varies in both space and time. Some places cool, some places warm, some places cool or warm more than expected. Floods, droughts, mudslides, and calving glaciers always have and always will occur. Some weather events separated in space and time are physically linked via large-scale tele-connections such as Rossby waves in the atmospheric jet stream or the El Nino-Southern Oscillations.

So, how much of the currently observed extreme weather events are due to globally increasing air temperatures that also coincide with globally increasing ocean temperatures? Does global warming increase, say, the intensity of hurricane by 1% or 10% or 50%? These much tougher questions are at the forefront of both observational and computational work on environmental physics. The IPCC numerical models and new understanding of key physical processes, I feel, are the only way to attribute global warming effects on extreme weather events. Ice-ocean interactions around Greenland are one such physical process poorly incorporated in IPCC models. Another such process is the way that hurricanes may dominate the ocean heat flux towards Greenland.

Three weeks before Katrina hit New Orleans in 2005 MIT professor Dr. Kerry Emanuel published that the power dissipation by hurricanes has increased by about 60% over the last 30 years and that this increase correlates with increasing sea surface temperatures in the tropical North Atlantic. Nevertheless, Dr. Emanuel himself stressed that nothing could be more absurd than stating that Katrina was caused by global warming. Furthermore, refining his methodology in 2008, he finds that “… global warming should reduce the global frequency of hurricanes, though their intensity may increase in some locations.” [Emanuel et al., 2008: Hurricanes and global warming, Bull. Amer. Meteor. Soc. 89, 347-367.]

Just because a pattern of extreme weather events feels like evidence of global warming, it does not make it so. This scientific uncertainty, however, should not distract from the potential costs that a potentially man-made climate change will cause. Climate zones may shift, sea level may rise, volatile weather events may become more volatile, etc. All of this may cause additional political instabilities in marginally stable nation states ill-equipped to deal with either natural or man-made disasters.

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