Friday, March 20, 2009

A Noisy Climate

This story has been in the blogosphere/low rent end of the MSM for a week or two now, going under titles like "Global Warming: On Hold?" (and worse). Finally, science writer Carl Zimmer was able to reach the two authors for clarification. Its all an interesting read (skip the George Will Stuff), but this is the general summa:

Swanson and Tsonis observe that over the past century, the average global temperature has risen, but there have been periods when it has dropped temporarily. Swanson and Tsonis have been investigating how the natural climate variability may explain the shifts between these phases. This variability includes oscillations in the circulation of the ocean and the air. El Nino is the most famous of these oscillations, but there are others as well in the North Pacific and the North Atlantic. Only three times in the twentieth century did all these oscillations synchronize, after which the climate moved to a new state. This figure, from the paper, shows the periods of synchronization as cross-hatched bars.

Based on the study of chaotic systems, Swanson and Tsonis propose that the synchronization and climate shift are connected through cause and effect. Once a lot of oscillations are working in sync, even a small change to one of them can radiate out through the whole system and trigger a change. And along with the three shifts in the real climate, climate models also show a similar response when oscillations line up.

In their paper, Swanson and Tsonis then look at the past few years. They see a peak in synchronization in 2001 and 2002, and they also observe that in the years since, the temperature change has been on average flat (although much warmer than at the beginning of the century). They estimate that all the warming due to carbon dioxide should have driven the temperature up .25 degrees C since then. The fact that it hasn’t leads them to propose the the oceans and atmosphere have changed the way they handle heat. The oceans may have absorbed more heat due to a change in circulation, or the atmosphere may radiate more heat away by clouds. If this hypothesis is true, then it’s possible that the climate will remain in this new stage for some years to come before it shifts again.

My favorite bit is where the two scientists speak of their work's reception in the popular press:

I was worried that this will happen, that is why we caution in the paper that while climate shifts may be part of the natural variability of the climate system they may be superimposed on a anthropogenic warming trend. We mentioned that also in the MSNBC story, and this will be my answer to anybody who asks me.

I like to report on the science only. If political organizations want to pick up what they like in order to pass their point and ignore the real science, there is nothing we can do.

Also, some interesting comments from (now infamous) climate scientist and blogger Michael Tobis on why the Swanson/Tsonis paper did not cause a big scientific (separate from blogospheric) splash:

Despite all the attention, the fact is that this is under the category of "yet another Tsonis paper". Now, it's not just that I want to be polite to Tsonis. He actually comes up with some interesting stuff. But frankly it doesn't take the climatology world by storm. The reasons for this are hard to explain in brief. The fact is that for practical purposes what he is doing is at best a crude qualitative model of the climate system, and that's being generous. It hasn't got any physics behind it. He is essentially a mathematician and not a climatologist, and comes up with interesting excursions into nonlinear dynamics, inspired by climate time series, but he could use just about any time series in the same way. It is, for the purposes of anything the press might have a legitimate interest in, completely and totally irrelevant.

Here is a copy (maybe a pre-print) of the origonal paper.

PS. I bet Swanson and Tsonis would prefer not to be in the company of these folks.


Mark Francis said...

Earth's climate is being affected by global warming, but is not completely dominated by it. Normal climate variabilities are still in place. This is why the average global temperature over time is a wriggly line tending upwards, rather than an even line always slopping up.

No news here.

bigcitylib said...

Exactly, except if you look one post up the CATO institute is citing this very paper to show that Global Warming has stopped.

Dante said...

It has stopped.
Anybody who looks at the data can see that.

Get your head out of Michael Mann's ass and you would realize it