Every morning when we go to work, the energy that gets us going comes from our breakfast. If we ate eggs, the eggs came from a hen, and the hen ate corn or some other food. The corn came from Nature's wonderful mixing (by photosynthesis) of the sun's energy, carbon dioxide from the atmosphere, water from the hydrosphere, and nutrients from the lithosphere. All these materials are new and are constantly being produced and recycled; otherwise, we would simply run out of eggs.
Every time that we go to work, we use a car or some means of public transportation: bus, train, or airplane. Typically, the vehicles are propelled by gasoline or other fossil fuel. These fuels were produced over a long period of time, starting about 300,000,000 years ago. By comparison, our species, Homo sapiens, is only about 200,000 years old, and civilization, as we know it, is only 10,000 years old. The fossil fuels contain organic matter, which, when burned, releases carbon dioxide and water, returning these materials to where they came from originally.
There is only one problem: the carbon in the fossil fuels is old carbon, and when released into the air it competes for space with the new carbon, i.e., the carbon being generated by burning vegetative matter. So we are mixing two carbons, old and new, in the same place. (To make a point: Imagine what would happen if the people who died in the past 100 years all of a sudden decided to resurrect and set foot on Earth. Wouldn't we feel crowded?).
Given these facts, the question is: Will the atmosphere become polluted with more carbon if we continue to burn fossil fuels? It stands to reason that it will. Can the ecosphere absorb the extra carbon? All indications are that this is what has been happening. But there is a limit. We now appear to have reached that limit.
What happens if the atmosphere fills up with extra quantities of carbon dioxide? Let's not hide our heads under the rug. The increased surface air and ocean temperatures of the past three decades correlate strongly with human pollution of the atmosphere with carbon dioxide. There are too many people using too many machines burning too much fossil fuel on the Earth today. This excess is causing perceptible changes in weather patterns, and more frequent or intense "natural" disasters such as floods, droughts, forest fires, and hurricanes. Ethics and reason demand that we stop.
The long-range strategy must be a worldwide move away from fossil fuels, toward renewable energy. We note that that is the way our ancestors lived more than 150 years ago, merely a blip in geologic time. This is the only truly sustainable strategy.
Such is the predicament of modern civilization. We are all in this together, and we all have to agree to fix it. This is the real challenge.