Yes, it is possible for the average global temperature to rise and result in the melting of polar ice caps during the summer, causing the slowing or stopping of the thermohaline circulation in the Atlantic Ocean. The thermohaline circulation, also known as the ocean conveyor belt, is driven by differences in temperature and salt concentration, and it plays a crucial role in regulating the Earth's climate. The melting of Arctic ice, which is often caused by global warming, could alter the water temperature and salinity in the Atlantic Ocean, leading to a slowdown or complete stop of the thermohaline circulation.
However, the process is complex and depends on several factors such as the amount of melting, the distribution of meltwater, and other oceanographic processes. A complete stop of the thermohaline circulation is unlikely, but a significant slowdown could have significant impacts on the Earth's climate, such as changes in precipitation patterns and ocean currents. The melting of polar ice caps is a major concern and a challenge for our planet, and it is important to take action to reduce the emission of greenhouse gases and limit the warming of the Earth's surface.