Perhaps the most common talking point against climate science these days, "the climate always changes," is but a slogan designed to keep people from thinking about why climate changes.

Greenhouse gases have always been involved.

This graph shows that global temperatures have marched in lock step with the two most important, noncondensing greenhouse gases the entire 800,000-year length of the ice core record.

About half the time, the above response will evoke a follow-up talking point, that if you look very closely, the peaks and valleys in the graph are ever-so-slightly offset.  Temperatures start to move, and then greenhouse gases follow.

That much is true, but let's dig deeper so we don't miss the underlying physics.  

Here's what causes us to come out of those ice ages.  Earth's orbit changes, warming the poles at the expense of the equator.  As the poles warm, they lose ice and become darker, absorbing more sunlight.  The reflectivity of the equator doesn't change, so on balance, the earth warms.  Warming oceans hold less dissolved gas, so they give off carbon dioxide and methane, which being greenhouse gases, warm the earth more, resulting in warmer oceans giving off more greenhouse gas, warming the earth still more, and the cycle continues.

That's why, when ice ages end, the vast majority of the warming follows the uptick in carbon dioxide.  Greenhouse gases have always trapped heat.

• Note: natural warming occurs when oceans GIVE OFF carbon dioxide. 
• In modern warming, oceans are GAINING carbon dioxide. 

This is further evidence that what we're seeing is not natural.