Orbital cycles and today’s climate
Do orbital cycles explain modern warming?
No. Orbital cycles change sunlight over tens of thousands of years. They cannot explain the speed or the pattern of today’s warming, which comes mainly from greenhouse gases released by human activity.
Orbital cycles: tens of thousands of years
Far too slow
The orbit changes noticeably only over thousands of years.
Greenhouse gases
Burning fossil fuels raises carbon dioxide and other gases that trap heat.
Context
The cycles explain the timing of ancient ice ages, not the present trend.
The timescales don’t match
Eccentricity, tilt and precession change over tens to hundreds of thousands of years. Warming since the 1800s is far too fast to come from them.
Two different mechanisms
Orbital cycles move sunlight between seasons and latitudes. They do not make a quick, lasting rise in heat-trapping gases. Burning fossil fuels does, and it slows how fast Earth sheds heat to space.
Scientists tell the two apart by timing, by where and when the warming happens, and by direct measurements of Earth’s energy balance.
Why the old climate still matters
Ice-age records show how ice, oceans and carbon dioxide can amplify a small change in sunlight. That helps scientists work out how sensitive the climate is.
The orbit helped set the timing of the ice ages. The main driver of today’s warming is human-made greenhouse gas.
Try it yourself
Change the orbit
Move all three motions and watch midsummer sunlight at 65°N change.
Questions
Quick answers
Are the cycles still running?
Yes. The orbit keeps changing, but its slow changes today do not explain the rapid warming.
Can natural and human causes both exist?
Yes. Climate has natural drivers on many timescales. Several independent lines of evidence attribute today’s warming mainly to human greenhouse-gas emissions.