Frequently asked questions

Slow, regular changes in the shape of Earth’s orbit, the tilt of its axis and the direction the axis points. Over tens of thousands of years they change how much sunlight reaches each latitude in each season.

Big ice sheets grew at high northern latitudes. If summer there is cool enough, winter snow survives and piles up year after year. Midsummer sunlight at 65°N is the usual yardstick for that.

No. Eccentricity hardly changes the sunlight Earth gets over a year. Mainly it sets how much the wobble matters. The 100,000-year rhythm in the ice record comes from the whole climate system, with its ice sheets, oceans and carbon dioxide, responding to all three cycles. Exactly how is still debated.

The axis alone takes about 25,800 years to turn once. The orbit’s ellipse turns too, so the seasons return to the same place on the orbit about every 21,000 years. The climate record shows peaks near 19,000 and 23,000 years.

No. The orbit’s shape is drawn five times too stretched by default, because the real orbit looks like a circle at screen size. Choose “True shape” to see it as it is. Earth, the Sun and their distances are not to scale either. Calculations always use the real values.

The orbit comes from the La2004 solution by Jacques Laskar and colleagues, sampled every 1,000 years. The ice line is the LR04 stack of 57 seabed sediment records (Lisiecki and Raymo, 2005), which tracks ice volume through the oxygen isotopes in tiny fossils.

It is an illustration. The amount of ice follows the measured record, but the outline is drawn by hand to resemble the last ice age. Use it for scale, not for geography.

No, but it gives a rough estimate. At a past date it shows the measured ice record and the temperature that goes with it. For an orbit you set by hand it asks what would happen if that orbit lasted about 15,000 years, using the link between sunlight and ice over the last 800,000 years. It leaves out carbon dioxide, oceans and the ice already there, and it is not a forecast.

From ice. In the sea-floor record, ice and global temperature move together, and the last ice age was about 6.1 °C colder than before industry. The lab scales the ice share to that figure. It is the orbit’s share only, and it does not include today’s warming, which is about 1.2 °C above that baseline.

No. The orbit changes over tens of thousands of years and cannot explain the speed or pattern of today’s warming. That comes mainly from greenhouse gases released by human activity.