Final answer:
The assertion that Earth would continue to warm even if human greenhouse gas emissions were reduced to zero is true due to the longevity of these gases in the atmosphere and the slow response time of the oceans to existing elevated levels.
Step-by-step explanation:
The statement that even if all greenhouse gas emissions by humans were reduced to zero, the Earth is still projected to keep warming for the foreseeable future is true. Many greenhouse gases, such as carbon dioxide (CO₂), can stay in the atmosphere for nearly a century, and as they trap heat, this leads to an ongoing increase in Earth's surface temperature.
Despite reductions in emissions, the existing concentration of greenhouse gases continues to exert a warming effect due to the lag time in climate response, particularly from the oceans that slowly adjust to higher levels of greenhouse gases. As a result, the climate models project that mean global surface temperature could rise between 0.3 to 4.8 degrees Celsius before levelling off, with variations depending on the region. The Arctic is expected to experience greater warming than other regions, and the land will warm more than the oceans due to different heat capacities.
The potential for continued warming exists because the elevated atmospheric greenhouse gas concentrations would take hundreds of years to dissipate, and the oceans, which have absorbed much of the extra heat, will also take a long time to respond to these changes and reach a new equilibrium. Hence, even with substantial reductions in greenhouse gas emissions, the planet will continue to warm, posing risks for more severe climate change impacts.