Final answer:
An increase in greenhouse gases in the atmosphere leads to global warming through the greenhouse effect, affecting ecosystems by causing climate-related changes like more intense storms, changes in agriculture, and loss of biodiversity.
Step-by-step explanation:
An increase in the concentrations of greenhouse gases would most likely affect ecosystems worldwide by warming the global climate (A). The greenhouse effect contributes to global warming due to the emission of carbon dioxide, methane, and other greenhouse gases. These gases trap heat in Earth's atmosphere, leading to a rise in global average air and ocean temperatures. This warming can cause a multitude of ecological changes such as more intense storms, altered precipitation patterns affecting agriculture, a decrease in biodiversity especially in rainforests, and rising sea levels that impact coastal and marine ecosystems.