One of the characteristics of modern thermohaline circulation is that deepwater produced in the North Atlantic but not in the North Pacific, and this asymmetry has a deep impact on the climate. Theoretically, there are multi-equilibria states of the thermohaline circulation corresponding to different climates. However, whether the deep water was produced in the ancient North Pacific is a debate topic. Reasons of no deepwater formation in the modern North Pacific are introduced. Among others, vapor transport by Asian monsoon and lower evaporation are two major factors.