Final answer:
Climate change would persist for centuries even if CO₂ emissions dropped to zero today, due to long-lived greenhouse gases in the atmosphere and the slow response of the ocean as a heat sink. Surface temperatures would continue to warm, and climate change impacts would remain severe for a long time.
Step-by-step explanation:
If CO₂ emissions went to zero today, the correct answer to how long climate change would persist is c) Centuries. This is due to the fact many greenhouse gases, including CO₂, remain in the atmosphere for long periods. Even if emissions stopped entirely, atmospheric greenhouse gas concentrations would stay elevated for hundreds of years. This is because the climate system, particularly the oceans, has a delayed response to changes in the concentration of greenhouse gases.
The oceans act as a heat sink and take decades to fully respond to the increased levels of greenhouse gases. Thus, even with zero emissions from now on, surface air temperatures would continue to warm due to the delayed response of the ocean. Additionally, the Earth's climate system would continue adapting to past greenhouse gas emissions for many years, maintaining the risk of severe climate change impacts.
Climate models project significant temperature increases and changing conditions even with drastic emission reductions. Unless energy policies change substantially, the emitted greenhouse gases already present in the atmosphere will influence Earth's climate for a lengthy future duration. Furthermore, it is predicted that the Earth's CO2 levels will reach twice the pre-industrial level before the end of the century, with potentially catastrophic effects.