Is It Warm in Here?

May 18, 2013

The May 11 issue of The Economist has an interesting, though disturbing, short article on one measure of global climate change: the percentage of carbon dioxide [CO2] in the atmosphere.  This has recently reached a new high in recent history.

AT NOON on May 4th the carbon-dioxide concentration in the atmosphere around the Mauna Loa Observatory in Hawaii hit 400 parts per million (ppm).

Now, 400 ppm does not sound very high; after all, it is only 0.04%.  However, as the article goes on to point out, this concentration of CO2 has not been routinely present since the Pliocene epoch, about 4 million years ago.

The data series  is from the observatory at Mauna Loa in Hawaii, run by the Scripps Institution of Oceanography, part of the University of California at San Diego.  This series (sometimes called the Keeling Curve in honor of the scientists who initiated the project) is of particular interest for two reasons:

  • The observation site is remote from large centers of human population, minimizing fluctuations due to temporary pollution spikes.
  • The observations have been made consistently, at the same place, since 1958.

There is a regular seasonal fluctuation in CO2 levels, tied to plants’ growth cycles.  In the northern hemisphere, levels tend to peak in May, and then fall until about October, as plants’ growth removes carbon dioxide from the atmosphere.

Carbon Dixoide Levels at Mauna Loa

Source: Scripps Institution of Oceanography

The seasonal pattern is clearly visible in the graph.  The more striking thing, of course, is the steady rise in the carbon dioxide levels, an increase of more than 25% over the observation period.  And there is no evidence that the rate of increase is getting smaller.

A Cool Development

July 22, 2012

Summer here in the Washington DC metro area is often hot and humid; and this summer, at least so far, is no exception.  Of the 22 days in July so far, 11 have had daytime temperatures of 95 F (35 C) or higher, as measured at Dulles airport (IAD).   Local legend has it that, at one time, British diplomats assigned to Washington were given extra pay for living and working in tropical conditions.  So it’s probably good that a recent post on the “Babbage” technology blog at The Economist reminds us that things could be a lot worse.

It was just a bit more than 110 years ago, on July 17, 1902, that Willis Carrier, an employee of the Buffalo Forge Company,  finalized his design of the first modern air conditioner, to be installed at Sackett & Wilhelms,  a printing firm in Brooklyn NY.   The printers wanted it mainly for humidity control, not cooling; varying humidity levels can make a mess of paper, as anyone who has fetched in his or her daily newspaper on a rainy day will know.  The humidity-induced changes in the paper stock wrought havoc with color printing especially, since the same sheet needed to pass through the presses multiple times. The new device was a success, and other customers soon appeared.

A drug firm and a silk mill swiftly followed Sackett & Wilhelms in adopting Carrier’s device. A host of other companies in different industries, including Gillette’s safety-razor factory where humidity caused corrosion, converted soon after. In 1915 the Carrier Corporation was founded. It exists to this day as a division of United Technologies, an industrial conglomerate.

Carrier’s design incorporated the basic elements (evaporator, compressor, condenser) that are used today in air conditioners, refrigerators, and heat pumps.   (The Wikipedia article on “Heat Pump and Refrigeration Cycle” provides a good overview.)   One significant design choice is what to use as a refrigerant.

In early system, carbon dioxide (CO2) was often used, but fell out of favor because high pressure is required to liquefy it from a gas, requiring strong (and therefore expensive) plumbing.   New compounds were developed as substitutes, particularly chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which have better thermodynamic properties.   (Freon is a DuPont trademark for a range of related refrigerants of this type.)  These refrigerants came under fire beginning in the 1970s, when it was discovered that they could act to deplete the ozone layer in the Earth’s atmosphere.  A new class of refrigerants, hydrofluorocarbons (HFCs), was developed and gradually adopted; however, although the HFCs do not attack the ozone layer, they are very potent greenhouse gases (~10,000 times as potent as carbon dioxide).

One of the effects of all this has been to re-examine an old choice: carbon dioxide as a refrigerant.  Modern manufacturing and construction techniques have made the construction of suitable high-pressure systems less problematic.  CO2 is non-toxic, and there is certainly plenty of it available.   Some commercial units are already using it.

John Mandyck, a vice-president of modern-day Carrier, says the company has already begun rolling out its first CO2-based products. They extract the gas from the air, making them carbon-neutral and easy to replenish in the event of a leak.

There are other methods being tried to improve the efficiency and environmental friendliness of air conditioning, of course.  Two look back to ideas that predate Carrier’s: using ice (made at night when power is cheap) to cool air, and using evaporative cooling.   With more steamy weather in the current forecast, I’m glad we have it, however it works.

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