In the 1990s, researchers developed models indicating that global warming could result in increases in fresh water in the oceans as a result of progressive melting of polar icecaps. The models suggested that, combined with the change in temperature, these could, for example, trigger a rapid collapse of the Atlantic Gulf Stream. As a consequence this conveyor of warm temperatures to northern Europe would no longer operate, resulting in severe temperature reductions, making the weather comparable to that of North America at the same latitudes. Controversy surrounded the exact thresholds and triggers for this phenomenon.