Final answer:
Atmospheric carbon dioxide levels have increased significantly due to human activities such as deforestation and the burning of fossil fuels, with current levels exceeding 400 ppm, the highest in at least 800,000 years. This increase contributes to global warming through the greenhouse effect and has altered plant growth patterns.
Step-by-step explanation:
The question 'Why did atmospheric carbon increase 550 million years ago?' relates to changes in atmospheric carbon dioxide levels. Several factors are responsible for the increase of atmospheric CO2, but the most significant recent changes have been driven by human activities. Starting a few centuries ago and especially in the last 200 years, CO2 levels have risen dramatically. This rise is attributed mainly to two human activities: deforestation and the burning of fossil fuels as an energy source for machines and heating.
Reliable data from ice cores shows that CO2 concentrations in the atmosphere are currently at the highest level in at least 800,000 years. This recent dramatic increase in CO2 has occurred much more rapidly than historical cycles of CO2 levels, which used to fluctuate between 180 ppm and 300 ppm over the course of around 50,000 years. Today's levels are above 400 ppm, well over the historical maximum.
The additional carbon dioxide acts as a sort of 'fertilizer' for plants, leading to increased leaf cover, and also contributes to the greenhouse effect, which in turn causes global temperature rises. Swedish physicist Svante Arrhenius first posited the concept of the greenhouse effect, establishing the relationship between atmospheric gases and the earth's temperature. Today, with the current rate of increase and the overall levels of atmospheric carbon, the impact on the earth's climate and ecosystems is considered significant.