According to the best available science, this is very unlikely. Here’s why:
Around the globe, a natural ocean “conveyor belt” slowly winds its way through the oceans, helping to regulate our planet’s climate. For example, it brings warm waters from the tropics to the North Atlantic, making places like Iceland and Western Europe warm enough to be comfortable.
As Earth’s average temperature increases due to global warming, melting glaciers and increased rainfall and runoff will inject additional freshwater into the North Atlantic. The saltiness of the conveyor current is critical for maintaining the flow, and an influx of freshwater, which significantly reduces the salinity of the North Atlantic branch of the current, can slow the movement of the conveyor belt. In theory, a major reduction or halting of this flow—especially if it happened suddenly enough—could destabilize the global climate, causing some regions of the globe to become much cooler, even as average global temperatures continue to increase.
However, the general climate conditions during the two most recent episodes of abrupt cooling were vastly different than they are today. For instance, those episodes were probably triggered by sudden, massive injections of freshwater into the North Atlantic, released when melting ice dams collapsed and vast quantities of freshwater from pent-up glacial lakes were rapidly dumped into the ocean. That can’t happen today, because those lakes are all long gone.
There is some evidence that the water in the North Atlantic seems to be growing less salty due to global warming and that the conveyor belt may be slowing. But scientists currently believe that even if part of the ocean conveyor were to fail, it wouldn’t be for several decades, and any cooling effects would be overpowered by the continued general warming over the same period.
There is little disagreement that the real concern is climate warming, which is real and will have serious consequences. That’s what we need to worry about—and work to fix—right now.