Changes in climate |

Changes in climate

Nature abhors a vacuum – dig a hole and things fall in to fill it up.

Nature also abhors a pile – make one and it soon begins to crumble. The abhorrence applies to piles of all sorts – sand, water, energy.

Sunlight hits Earth face-on in the tropics. Heat energy “piles up,” then flows outward, toward the poles, carried in currents of air and water. The currents bring warmth and water to the lands they pass. These currents, along with cold currents returning to the tropics, help create the climate.

Tropical and sub-tropical plants are often inundated with rain and warmth. It’s to their benefit if they can shed water easily, lest they become easy prey for fungi. Many such plants have evolved pointy “drip tips” (think of houseplants like philodendron).

If you collect fossil leaves, and many have drip tips or other warm/wet adaptations, the chances are good they grew in a tropical or sub-tropical environment. Such fossils show up in the gold-bearing gravels hydraulicked out of the local diggins. Our climate, 40 million years ago, was sub-tropical.

At Grouse Ridge and higher, grooves in the bedrock, and “erratic” rocks dropped here and there imply that, 20,000 years ago, the climate was cold enough to inundate the region with year-round ice.

Climate changes when the warmth- and moisture-bearing currents of air and water shift course. One of the challenges of climatology is to figure out what drives these course changes.

At tomorrow’s Sky Watch, we’ll see Polaris, the north star; Thuban, the north star of the Egyptian pyramid-builders, five thousand years ago; and Vega, the north star of stone age hunter-gatherers, 12,000 years ago.

Pulled this way and that by the sun, moon and planets, Earth wobbles, pointing its north pole first toward this star, then toward that. These gravitational tugs also alter our orbit, changing our relation to the sun over the seasons. These changes in turn change how much energy piles up in the tropics – how energy flows around the globe – how landmasses are warmed and wetted. They change our climate.

There are other extraterrestrial climate-drivers. Cosmic rays – pieces of atoms from exploding stars – trigger cloud formation when they hit the atmosphere; interstellar dust clouds, like fog on the freeway, dim sunlight when our solar system drifts through them; the sun itself dims and brightens over time.

And there are terrestrial drivers of climate.

Roses are red and violets are blue because pigments in their petals absorb the other colors. Air absorbs no colors, so it’s transparent – in the visible. Some gases – carbon dioxide, methane and water vapor, especially – absorb infrared (IR), and then re-radiate it. We can’t see IR, but we can feel it as heat.

Volcanoes spew huge amounts of carbon dioxide (along with a lot of dust); green plants absorb it for use in photosynthesis; fungi and bacteria emit carbon dioxide as they break down biomass.

Anything that warms or cools the atmosphere (and thus the oceans) can change the flows of energy and moisture, and thus change the climate.

With so many drivers, how can scientists figure out whether the global warming they’re measuring is natural, or anthropogenic (human-caused)?

At the risk of simplifying a very complex question: totting up the calculated effects of all the known natural climate “forcings” simply can’t explain the amount of warming (and how fast it’s happened) in the past half century.

The Unitarian Universalist Church (274.1675) will host a discussion on climate change, at which I’ll be speaking, next Thursday at 7 p.m. Tomorrow’s Sky Watch begins at 8:30 p.m. at the old airport.


Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesday’s on KVMR-FM (89.5).

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