The correct answer is - 4) The level of the carbon in the atmosphere will increase.
People have had huge effect on the climate changes in the past century, and one of the reasons for this is the is the much increased levels in the atmosphere because of the human activity. Big portion of the industry and vehicles contribute to much bigger release of carbon into the atmosphere, and also the destruction of the natural accumulators of the carbon, like the trees. Because of this we have witnessed increased temperatures on a global level, and if this trend continues we will have even higher temperatures because the carbon is the most important gas that is responsible for the Greenhouse effect in the atmosphere.
