The Combining of Carbon Dioxide and Hydrogen How does this work exactly? Does it need some sort of kick in order to come together, or does it come together when put in a pressurized chamber?
I believe you are referring to the Sabatier process. $$\ce{CO2 + 4H2 -&gt; CH4 + 2H2O}$$

The reaction uses a $\ce{Ni}$ catalyst and is done at $300-400\,^{\circ}{\rm C}$ and high pressures. The reaction is exothermic, $\Delta H = −165.0~\mathrm{kJ\,mol}^{-1}$, but requires initial heating in order to start the reaction off due to the activation energy.

Read more on Wikipedia.