What do scientists believe has caused global temperatures over the past 100 years to rise faster than ever before

Global warming is what scientists conclude has caused the massive rise in temperature. Greenhouse gases are in the atmosphere, keeping heat trapped around Earth. The more these gases build up, the warmer or the more significant rise in temperature will take place. Greenhouse gases are released when we use fossil fuels, burn fires, etc. We are using more of these than ever, especially with the world's growing population. 

I hope this helps!
~kaikers

The correct answer is a)  a resource with a limited supply; it will run out.

Developed countries will see a decrease in natural resources, because their population will decrease.