evidence: Earth's orbit cannot explain modern climate change Slowly changing orbital cycles did, indeed, control the timing of ice ages over the last several million years, but they cannot explain the much more rapid climate change seen in the last century. Human-caused greenhouse gas emissions have strengthened Earth's greenhouse effect, and this is clearly the cause of global warming. [...] The cycles include the shape of Earth’s orbit around the Sun, the angle of tilt of Earth’s axis, and the precession of that axis—like the wobbling of a spinning top. The shortest of these cycles is roughly 20,000 years long, while the shape of the orbit changes over about 100,000 years. The cycles line up with the 40,000 and 100,000-year-long ice ages that occurred over the last 3 million years.