Thursday, January 4, 2007

Temperature Temperance


Sunny, mild. Under some scattered high clouds and a southerly breeze, temperatures have reached the 60s this afternoon in the Washington metro area; the official high was 62°. Clouds will increase tonight, and showers will arrive tomorrow, as a low pressure area developing along the Gulf Coast moves toward the Ohio Valley.

Tonight and Tomorrow

Increasing clouds, mild; showers developing. Clouds will increase tonight with lows in the upper 40s to 50°. Showers will develop after dawn tomorrow morning, continuing through the afternoon. The heaviest rain, however, should remain west of the mountains and through the Ohio Valley. Highs will be in the low 60s.

For the outlook through the weekend and beyond with Larson's Long-Range, scroll on down to Josh's post below.

Warmth in Perspective

While today's temperatures certainly felt out of place for January, they were well short of the record 73° for the date. In fact, only 4 dates in January have failed to ever reach 70° in Washington. (Interestingly, this is 2 fewer than the 6 in December.) Two of them have already passed, including the lowest, 68° on the 3rd. What is noteworthy about the current warmth, however, is its persistence. The current string of 25 consecutive above-average days is longer than last January's run. Although there were only 3 average or below days in January 2006, they were scattered through the month.

The warmth is also pervasive through the whole country. The plot above of temperatures at midnight last night (from Unisys) shows only a very small extent of sub-30° temperatures (blue and blue-green), nearly all in the southern Rockies. The daily high temperature map shows above-freezing temperatures in all 48 states. I could find only 4 locations with temperatures below 32°. If you can find more, please let us know in the comments where they are located.

Modeling Myths

A common myth, especially, it seems, among operational meteorologists, is that climate models must be inaccurate simply because daily forecast models become inaccurate beyond about a week with current technology. Therefore, the argument goes, how can you possibly forecast years, decades, centuries into the future? A "Quick Study" in the latest (January 2007) issue of Physics Today called "The physics of climate modeling" helps to explain this apparent paradox. The article is open to non-subscribers and is quite accessible, no equations necessary. The key distinction between the two types of models is the following:
Weather concerns an initial value problem: Given today's situation, what will tomorrow bring? Weather is chaotic; imperceptible differences in the initial state of the atmosphere lead to radically different conditions in a week or so. Climate is instead a boundary value problem-a statistical description of the mean state and variability of a system, not an individual path through phase space. Current climate models yield stable and nonchaotic climates, which implies that questions regarding the sensitivity of climate to, say, an increase in greenhouse gases are well posed and can be justifiably asked of the models.
Unfortunately, the online version omits a figure from the carbon-based version which shows how well climate models are able to reproduce the effects from the eruption of Mt. Pinatubo in 1991, although the results are described in the text. Hopefully this will appear in the pdf version, which is not yet online.

Also pertinent to this question is the article "Belief and knowledge-a plea about language" in the same issue. It discusses how different meanings for the same words can produce misunderstandings about scientific concepts. Saying "I don't believe the results of climate models" without verifiable contrary data is simply an ideological assertion. On the other hand, the statement, "[Scientists believe that] climate is changing in many ways, and there is strong observational and scientific evidence that, at least over the last 50 years, human activities are the major contributor to climate change," reflects the current state of scientific knowledge.

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