Overall, the world’s oceans absorb over 90 percent of the heat associated with observed greenhouse gas emissions. As man-made emissions have increased, the ocean has absorbed greater quantities of carbon, simultaneously leading to higher ocean temperatures and a measurable rise in ocean acidification.
Yet scientists admit there is a north-south dichotomy in ocean data.
“There has been a general acknowledgement in the literature, that southern-hemisphere estimates of ocean warming are likely biased low,” says Paul Durack of California’s Lawrence Livermore National laboratory. “Our study is the first to attempt to quantify the magnitude of what this generally acknowledged underestimate is, using as much information as is available.”
Between 1970 and 2003, the temperature of the northern hemisphere’s oceans were frequently sampled by various groups and organizations. However, the southern hemisphere lacks the north’s volume of wealthy investors and countries, which over time has led to a considerable gap in direct temperature measurements. It was not until the turn of the millennium that a network of Argo floats were deployed and more accurate data could be gleaned from the southern oceans.
To help correct this disparity, a research team headed by Durack compared climate model data to direct and inferred sea temperature measurements from the ’70-’03 period. Their report, recently published in the journal Nature Climate Change, found that the long-term warming of the top 700 meters of the ocean are absorbing 24 to 58 percent more energy than previously estimated.
This new rate would mean that the entire Earth is actually warming faster. “The implication is that the energy imbalance – the net heating of the earth – would have to be bigger,” says Wenju Cai of Australia’s CSIRO.
This acceleration of southern warming rates could help to explain the tremendous loss of ice in Antarctica, which is shedding over 204 million tons of glacier mass every year.