Friday :: Feb 29, 2008


by Christina Hulbe

I had a nice conversation earlier this week with the hosts of our local Air America affiliate's morning show (Portland's KPOJ), about the hoax perpetuated by climate orthodoxy. (Really.) Our conversation was prompted by an opinion column in our local paper, The Oregonian. Later on, in the first hour of his national show, Thom Hartmann talked about the costs of addressing global warming with Marc Morano, aid to Oklahoma's Senator James Inhofe. Morano took the opportunity to toss out some of the same red herrings regarding climate science and I've seen similar statements in a scattering of recent editorials from conservative outlets. Maybe there was a memo. I'm not that excited about "debunking," I'd rather write about the science and let it stand on its own, but I thought it might be a good idea to spend some time with two claims that have been making the rounds lately. For each, I begin with a quote from the column in the Oregonian.

ice core CO2 and temperature
By 1999, improving ice-core techniques produced a stunning reversal, showing that the global temperature changed many centuries before carbon dioxide changed. This proved that natural climate cycles were causing changes in atmospheric carbon dioxide, probably by affecting how much remained dissolved in the oceans.

Using new ice-core evidence, Caillon, et al. (Science, March 2003), concluded that "CO2 is not the forcing that initially drives the climatic system."

The reference here is to the long ice core records of atmospheric CO2 and temperature from Antarctica. The CO2 is trapped in air bubbles in the ice and the temperature records are reconstructed using ratios of stable isotopes of oxygen and hydrogen (the ratios vary over time, in part due to temperature at the site where the water evaporated and at the site where it later precipitated).

Careful statistical analyses do indeed find temperature leading CO2 over intervals where it is possible to do the calculation--times when the rate of change is large, like warming up out of a glacial maximum. A few research groups have made this calculation, with results in the few hundreds of years range. The most recent estimate is something less than 200 years for the CO2 lag during warming (the paper is here in an open-access journal of the European Geosciences Union) and the longest estimate is about 800 years. There is a lag associated with cooling toward a glacial maximum as well. In order to understand these lags, we need to place them into the context of the complete glaciation and deglaciation cycle and to consider the physical processes that underlie climate change on these time scales.

(I'm nost sure what stunning reversal means, these calculations clarified the understanding from "we can't tell" to something better.)

Over the last about 900,000 years (740,000 of which are recorded in the oldest Antarctic ice core yet recovered; pdf), the full glaciation and deglaciation cycle has a very distinctive, asymmetric pattern. Each cycle lasts about 100,000 years, with the bulk of that time devoted to gradual cooling and the gradual growth of ice sheets toward a "glacial maximum" condition. The great changes in ice volume transpire mainly in the northern hemisphere, though the Antarctic ice sheets grow too. In contrast, deglaciation is rapid, requiring 10,000 or fewer of those 100,000 years. Deglaciation is followed by relatively short (10 to 20 thousand years, as recorded in a variety of climate proxies) warm interglacial intervals. The one external climate forcing that we have on these kinds of time scales, changes in Earth's orbit around the sun (I've written about this here) can't produce this very asymmetric cycle. This fact alone tells us that feedbacks in the climate system must be important.

The large amplitude glaciation and deglaciation cycles are an internal modulation of the global response to the external orbital forcing. A short list of the components involved includes ice sheets, sea ice, atmospheric circulation, atmospheric chemistry, the terrestrial and marine carbon cycles, and ocean circulation. Our understanding of how these components interact and produce the asymmetric, 100,000 year cycle comes many lines of evidence, not just ice cores. I've written about a variety of these here at The Left Coaster over the last year.

A thumbnail version of the warming part of the cycle: at the termination of a glacial maximum, atmosphere and ocean warming begins around Antarctica; this warming causes CO2 to begin to return to the atmosphere from the deep ocean; the additional CO2 produces additional warming, now of the whole planet because CO2 mixes quickly through the troposphere; the additional warming leads to even more CO2 release to the atmosphere; and so on. CO2 works to amplify the warming once it begins. Viewed over the full time interval, temperature and CO2 vary together, through feedbacks in the coupled climate system.

The rapid transfer of carbon from the lithosphere to the atmosphere that we accomplish in burning fossil fuels is in addition to whatever other changes would transpire in our absence. When we burn fossil carbon, we become a new forcing in the climate system, driving change all on our own and altering the trajectory of the coupled system.

temperature trends
[...]we are being victimized by a vast array of opportunists. They point out anecdotal evidence of warming and ignore counter evidence -- such as the fact that the global temperature last year "was actually lower than any year since 2001. "

The quote is from John Tierney, a columnist at the New York Times and it is just plain weird. The high-quality instrumental record goes back to 1880 so I don't know why anyone would feel constrained to examine only the last handful of years. The shorter the time interval the less reliably we can attribute significance to any temporal change. Indeed, 2007 was one of the warmest years in the entire record.

A related assertion is that global temperature has reached a "plateau." This assertion is typically made by looking back to 1998 and no farther. If you do this, you will indeed find that 1998 is the hottest (global mean) year over that interval, with 2007 following closely behind. Connect those two dots and voila, you have yourself a plateau*. Again, the assertion relies on the careful selection of the time window.

A second problem with the plateau assertion is that it ignores the effects of inter-annual variability. 1997 and 1998 featured the strongest El Nino of the 20th century, an extreme state of the tropical mode of variability known as the El Nino Southern Oscillation (ENSO). During the El Nino phase of the oscillation, the eastern side of the tropical Pacific becomes anomalously warm as the upwelling of cool deep water is suppressed and the strength of the tropical easterlies decreases. While ENSO is a coupled oscillation of the tropical atmosphere and ocean, its reach is global. 1997 and 1998 were exceptionally hot as a result of the strong El Nino, superimposed on the background global warming trend (NOAA's Annual Review for 1998). By contrast, the very warm 2007 was not an El Nino year. Indeed, it started off in a weak El Nino condition, began immediately to shift toward a neutral state, and eventually toward the other end of the oscillation, La Nina (NOAA's Annual Review for 2007).

The point of all this is twofold: 1) time windows of only a few years are almost guaranteed to mislead due to internal oscillations in the climate system and 2) we need to embrace the effects of those fundamental modes of variability in our analyses of temperature records. The editorial comment writer tricks himself (and perhaps the casual reader) on both counts.

* It is worth noting that this plateau argument doesn't work if you compute a best fit through all of the global monthly means between 1998 and 2007. In that case, you would compute a warming trend that is about the same as the trend for the prior few decades.

the hoax
On a personal note, I find it quite disappointing that many people who express skepticism about global warming (which is fair enough) also accuse the scientists involved in this work of intentionally misleading the public or adhering to an orthodoxy in order to keep their jobs.

First, this reveals a lack of insight into how the scientific community operates. We're a critical, skeptical, argumentative bunch by nature. Sure, our community is sometimes swept by fads but they don't last long and are not often adopted very widely. One important way in which we make progress is by finding flaws in existing ideas and making improvements. Indeed, the whole scientific review process is set up to root out flaws. We laud the people who do this.

Second, I could have a less stressful existence and a larger income in some other line of work. I am a research scientist and university professor because I love the theoretical and observational pursuit of knowledge, not because it's the only job I can get. The day I am forced to toe a particular line would be the day lose my intellectual freedom and the day I leave this job. This planet Earth is a wonderful, complicated, cathedral of interconnected geophysical and biogeochemical processes. What I care about is understanding it (and doing what I can to protect its vulnerable parts, including its human population).

Christina Hulbe :: 3:50 PM :: Comments (21) :: Digg It!