Can't we reduce climate change by converting CO2 & CH4?
There are a few problems with what you're proposing:


The reaction requires energy.
Where do get the methane from?
What will you do with the carbon you're generating?


The energy problem can be solved by using surplus energy from renewable source like solar and wind, but, as airhuff also mentiond in a comment, there is much more CO2 in the atmosphere than methane. Also capturing CO2 from the air isn't simple,  and finally why would you use a valuable fuel like methane to create carbon or propane?

In any case I think a much more useful reaction is 
$$\ce{CO2 + 2H2O -&gt; CH4 + 2O2}$$

Water is split into oxygen and hydrogen using electrolysis. The hydrogen reacts with carbon-dioxide to form methane.
There are already small plants that do this, but AFAIK the idea hasn't really caught on yet. This may have something to do with the cost and/or the availability of carbon dioxide or surplus energy.

More recently scientists did something even cooler; they captured CO2 directly from the atmosphere and turned it into methanol (CH3OH) using Ruthenium as a catalyst. A drawback is that the reaction works at high temperatures (about 150 degrees C).