Compiled by Lewis Loflin
Today, CO2 is recognized as a key driver of global warming, raising temperatures and altering weather. Yet, a 1975 National Academy of Sciences study, "Understanding Climatic Change: A Program for Action," flagged a different concern: cooling tied to industrial pollution—soot, sulfur dioxide (SO2), and particulates—before the EPA’s 1970 launch curbed such emissions. Found in August 2019 (climate_1975.pdf), it showcases a mid-20th-century cooling trend amid Earth’s vast variability. Extracts below highlight this duality—past pollution’s chill, today’s CO2 heat, and a climate always in flux.
The study prioritizes practical risks—not ice sheets burying cities, a slow shift—but changes in temperature, rainfall, and frost hitting farms. It states, “World grain reserves are but a few percent of annual consumption,” noting the 1972 Ukraine drought’s global reach. Our climate, it calls “highly abnormal,” with industrial pollution like soot and SO2 possibly amplifying natural shifts pre-EPA. Mitchell (1970) data shows northern hemisphere temperatures climbing from the 1880s to 1940, then dropping—Starr and Oort (1973) record a 0.6°C decline from 1958-63, sharpest in polar and arid zones.
The cooling’s cause wasn’t pinned down, but it flags variability as a constant—human activity then meant pollution, not just CO2.
We’re in a rare icy epoch—polar caps define now, but Earth’s history leans warm. Glaciations struck 600 million and 300 million years ago, then eased. By 65 million years ago, climates were balmy, with continents blocking southern currents. Australia’s drift 50 million years ago opened the Antarctic circumpolar flow, launching a 55-million-year cooling—the Cenozoic decline.
Antarctic waters cooled 35 million years ago; glaciers edged in by 25 million, despite CO2 levels exceeding 800 PPM around 34 million years ago—showing cooling can defy high CO2. The Miocene (20 million years ago) had warmer mid-latitudes, but 10 million years ago, cooling deepened—northern glaciers grew, Antarctic ice thickened. Northern ice sheets formed 3 million years ago, setting our glacial age.
Over the last million years, ice pulsed every 100,000 years. Peaks hit 135,000 and 14,000-22,000 years ago—cold maxima followed by warm spells. The Holocene, our current phase, peaked 6,000 years ago. Deglaciation from 14,000 to 7,000 years ago melted vast ice—Cordilleran sheets vanished by 10,000 years—marked by 2,000-3,000-year swings.
From 7,000 to 5,000 years ago, it was warmer than now, with colder snaps every 2,500 years. The Little Ice Age (1430-1850) chilled Europe and North America, peaking in the 1400s and late 1600s, per tree rings and glaciers.
In 1975, industrial pollution—think soot and SO2 pre-EPA—fed cooling fears; a 0.6°C drop had experts eyeing an ice age. Today, CO2 drives warming, a shift from that era’s focus. Yet, the study underscores variability—cooling then, warming now, natural swings always. It asks, “Will we spot significant change early?” With food and population stakes rising, grasping these patterns—pollution’s past chill, CO2’s current heat—guides us forward.
This mix of variability and human roles complicates prediction. CO2 boosts warming and plant growth, while land use—like urban sprawl or forest management—alters local climates. Past pollution cooled; today’s cuts shift the balance. The study’s 34-million-year cooling with 800+ PPM CO2 shows natural forces can override gas levels. Computer models struggle to pin down these overlaps—Earth’s 100,000-year cycles, plus human inputs, defy simple forecasts. History informs; science refines the tools.
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