What conclusion can you make about how the carbon dioxide level has changed over time?

It can be concluded that the carbon dioxide level has drastically increased over time.

This is seen through global warming throughout the world and the rising temperatures in some areas with bipolar weathers in others.

This is caused by many things; gas emissions, human activity, pollution, etc. The biggest cause just might've been the industrial revolution when people began producing in factories, emitting smoke and dumping pollutants at an extreme rate. 

That eventually began to build up, carbon emissions and greenhouse gases floating above and into the ozone layer, causing it to become more dangerous and causing carbon levels to drastically increase over time.

Therefore, the conclusion you can make about the changing of carbon dioxide levels over time is that it has drastically increased due to many forces.

Hope this helps!