Climate Trivia: Central American Seaway and the Global Climate
If Earth had a newspaper to chronicle its 4.5 billion year existence, one of the biggest headlines of the last 10 million years would be the joining of North and South America through the closure of the Central American Seaway (CAS). The Central American nations of Panama and Costa Rica are “young” landscapes, formed by volcanism over just the past few million years – a very recent development in the context of geologic time. The period when the CAS closed corresponds to a period of major changes in ocean circulation, ocean temperature distributions and climatic conditions in remote locations throughout the world.
Trivia Question: As the Central American Seaway closed around four million years ago, the Earth’s climate:
c) Became more sensitive to the influence of orbital cycles.
d) a and c.
e) b and c.
The correct answer is e. The closure of the CAS around four million years ago was followed by a period of brief warming, then steady cooling until the modern 100,000 year glacial-interglacial cycles began around two million years ago. Prior to the closure of the CAS, Earth was between five and 6.5 degrees Fahrenheit warmer than it has been over the past 10,000 years. What would today be considered tropical sea surface temperatures extended all the way into midlatitude waters, with less of a temperature gradient between the tropics and high latitudes. The east-west gradients between warm and cool water patches, such as the gradient that exists in the tropical Pacific particularly during La Niña events, were also reduced. This more diffuse distribution of warm ocean waters meant enhanced evaporation in the tropics and subtropics, which led to more high tropical clouds that work to warm the planet. The closure of the CAS impacted the ocean circulation system that determines sea surface temperature distributions by increasing the salinity contrast between the Pacific and Atlantic Oceans. The closure is the most likely explanation for the retreat of warm tropical waters out of the midlatitudes, the increased strength of La Niña events in the tropical Pacific and gradual cooling of the Earth. This overall cooling and shift in the ocean circulation system made Earth more susceptible to the influence of periodic orbital variations, allowing for growth in ice masses and ice age conditions.
Seasons: Winter, Spring, Summer, Fall
Source: LaRiviere, JP et al. “Late Miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing.” Nature 486 (2012): 97-100.