Climate Fact: SST Changes with Latitude
In today’s modern Holocene climate, warm surface waters in the tropical oceans gradually transition into the near-freezing surface waters near the poles. During warmer periods of Earth’s distant past, this temperature gradient was far less pronounced. In the early Eocene epoch (56-53 million years ago), average annual temperatures in Siberia and Canada were about 65 degrees Fahrenheit (compared to 32 degrees today) and Earth had no permanent polar ice caps. During this time, there was little temperature difference between waters in the tropics and waters in the mid-latitudes and sub-polar regions. Waters in the sub-polar regions of the southern hemisphere were even warmer than the tropical waters of today – as high as 93 degrees Fahrenheit. Cooler waters could only be found at the poles, with the average annual surface temperature at the North Pole being around 73 degrees Fahrenheit. These high temperatures did not last and over the course of the next 20 million years the mid- and high latitudes cooled. By around 35 million years ago, permanent ice sheets had grown on Antarctica. Temperatures in the tropics, however, remained largely the same, giving us the latitudinal temperature contrasts that characterize today’s climate.
Seasons: Winter, Spring, Summer, Fall
Sources: Bijl, PK et al. “Early Palaeogene temperature evolution of the southwest Pacific Ocean.” Nature 461 (2009): 776-779 and Baez, J. “Temperature.” Department of Mathematics: University of California Riverside. 1 October 2006. Accessed Online 6 November 2009 <http://math.ucr.edu/home/baez/temperature/>