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Science Corner: Climate change crosses disturbing threshold

ARCTIC SEA ice levels have been declining more than 10 percent a decade and are at their lowest levels on record. Land ice is similarly retreating.

ARCTIC SEA ice levels have been declining more than 10 percent a decade and are at their lowest levels on record. Land ice is similarly retreating.

— It’s been nearly six months since my last rant about climate change, arguably one of the biggest science stories of our time. In early May we reached the milestone level of 400 parts per million carbon dioxide (CO2) in the atmosphere, a good excuse to revisit the latest signs of global warming.

During the preindustrial 1800s, before coal and other fossil fuels were so widely used, the atmospheric CO2 level was roughly 280 parts per million (ppm). When the Keeling family began tracking CO2 levels on Mauna Loa in 1958, the level had already risen to 315 ppm. This year marks the first time the level has reached 400 ppm in probably 2.5 million years.

Efforts to curb global warming shift

Efforts to curb global warming have quietly shifted as greenhouse gases inexorably rise. See related story.

Ice core samples dating back 800,000 years show no CO2 levels above about 300 ppm. The most recent geologic evidence of a level over 400 ppm was in the Pliocene era, between 3 and 5 million years ago. Temperatures were up to 15 degrees Fahrenheit warmer at the poles, and green forests stretched to the shores of the Arctic ocean.

Carbon dioxide is one of the best known greenhouse gases, along with water vapor and methane. It is invisible, odorless and accounts (now) for only 400 of every million molecules in the atmosphere. CO2 allows visible sunlight to pass through unobstructed, reaching the Earth’s surface and warming us during the day. At night though, it blocks the resulting infrared heat from escaping back out through the atmosphere.

When in balance, this process helps keep the planet a comfortable temperature. But with human activities adding 35 billion metric tons of CO2 to the atmosphere last year, the predictable and now increasingly obvious effect is global warming. The present rate of increase in CO2 levels is estimated to be as much as 75 times faster than ever found in the geologic record.

Plenty of other evidence supports the reality of climate change. Because the pace is accelerating and meeting or exceeding experts’ predictions, it’s becoming nearly impossible to ignore or deny. That doesn’t stop climate deniers from trying. Their claims and political spin can sound convincing, so for visual proof visit http://climate.nasa.gov and click on “Key indicators.” The pattern of major climate measurements is clear and unmistakeable.

Key indicators NASA tracks are carbon dioxide, global temperature, arctic sea ice, land ice and sea level. The site includes lots of additional information, but it’s worth the visit just to see convincing evidence of global warming in under 60 seconds.

The increase in CO2 levels I’ve already outlined above. There’s nothing magical about the 400 ppm level, except that it reflects the steady climb closer to a tipping point of unavoidable extreme weather, higher sea levels and worldwide problems. Once in the atmosphere, it can take decades or centuries for these high levels to drop.

Global temperature is up about 2 degrees F since 1910, most of the increase occurring since 1970. That may not sound like much, but as few as 10 degrees F can be the difference between an ice age and our balmy climate today.

Arctic sea ice levels have been declining more than 10 percent a decade, and are at the lowest levels ever recorded. Land ice (glaciers and snow pack) is similarly retreating. A recent study showed one-fifth of the ice and snow in the Rocky Mountains disappearing over the last 30 years due to warmer and earlier spring temperatures.

Sea levels are presently rising over an inch every 10 years. Given the accelerating rate of ice melt off and ocean warming, the projected rise could approach 4 feet by the year 2100, enough to flood many coastal plains.

Seeing is believing. You can read climate deniers’ editorials and their cherry-picked facts, but recognize that broad-based evidence like that offered by NASA easily discredits their arguments. Scientific knowledge is why 97 percent of climate experts agree on the causes and fact of climate change.

Lifelong Oregonian Fred Schubert, a The Dalles biologist, has a lifelong interest in general science and science writing.Submit any comments on this article or suggestions for new topics to fcscience @qnect.net.

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