Celestial wobbles

Small deviations in Earth's orbit cause climate change, but not today's version.

- Andrea Graves

Dear Maureen, 

Pull up a pew so we can talk climate change. Last month, you said, "We have cooled and warmed, cooled and warmed over millions of years." But you were waiting for proof that humans have caused the current warming.

I'm glad you raised this, because many people don't understand how modern climate weirdness is different from the age-old shifts. We know Earth was 6°C cooler during the last ice age. At that stage, the sea level was 120m lower and a land bridge connected Asia and North America.

Interglacial periods had similar temperatures to pre-industrial times, but the last one was a degree or two warmer (much like now), causing ice melt at the poles and raising sea levels by several metres.

If today's climate chaos was the result of the forces that prompted that freezing and defrosting, trying to stop it would be futile. That's because those forces were celestial.

When Earth makes its yearly orbit around the sun, it's buffeted slightly by gravitational pull from other planets, moons and the sun itself. That skews its tilt and degree of wobble, and distorts its orbital path from circular to slightly elliptical and back again. These deviations repeat over tens to hundreds of thousands of years and strongly affected climate over the last three million years or so. For evidence, look up "Milankovitch cycles".