Final answer:
Global warming, primarily caused by human activities such as the burning of fossil fuels, has led to a rise in Earth's temperatures. The greenhouse gases like carbon dioxide that result from these activities create an enhanced greenhouse effect, intensifying global warming beyond natural climate variability. Option a is the correct answer.
Step-by-step explanation:
Earth's average temperature has been rising, largely due to human activity and the burning of fossil fuels. This burning releases greenhouse gases, such as carbon dioxide (CO2), into the atmosphere. These gases trap heat by absorbing infrared radiation, leading to what is known as the greenhouse effect, thereby increasing temperatures on Earth's surface—an effect further intensified by feedbacks like loss of reflective snow and ice, increased atmospheric water vapor, and altered land and ocean carbon sinks.
While Earth has natural mechanisms for temperature fluctuation, such as changes in solar radiation, Earth's orbit, and volcanic activity, the rapid climatic changes observed after the Industrial Revolution are attributed to anthropogenic factors. With a significant rise in CO2 since the mid-20th century, climate change accelerated. Ironically, what historically made Earth hospitable through a natural greenhouse effect is now pushing the planet toward a hazardous warming trend due to excessive CO2 levels.
Therefore, in response to the original question, the statement that increased heat can result from natural causes is true, yet the current trend of global warming being a direct result of human actions, mainly through the emission of greenhouse gases from fossil fuel consumption, is also true. With overwhelming scientific consensus, human contributions to climate change cannot be denied. Ongoing societal reliance on fossil fuels is altering the climate and posing a threat to global ecosystems.