Climate change reducing ocean's carbon dioxide uptake

Jill Sakai in the University of Wisconsin -Madison News: How deep is the ocean’s capacity to buffer against climate change? As one of the planet’s largest single carbon absorbers, the ocean takes up roughly one-third of all human carbon emissions, reducing atmospheric carbon dioxide and its associated global changes. But whether the ocean can continue mopping up human-produced carbon at the same rate is still up in the air. Previous studies on the topic have yielded conflicting results, says University of Wisconsin-Madison assistant professor Galen McKinley.

In a new analysis published online July 10 in Nature Geoscience, McKinley and her colleagues identify a likely source of many of those inconsistencies and provide some of the first observational evidence that climate change is negatively impacting the ocean carbon sink.

“The ocean is taking up less carbon because of the warming caused by the carbon in the atmosphere,” says McKinley, an assistant professor of atmospheric and oceanic sciences and a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies.

“Because the ocean is so variable, we need at least 25 years’ worth of data to really see the effect of carbon accumulation in the atmosphere. This is a big issue in many branches of climate science – what is natural variability, and what is climate change?”

The analysis differs from previous studies in its scope across both time and space. One of the biggest challenges in asking how climate is affecting the ocean is simply a lack of data, McKinley says, with available information clustered along shipping lanes and other areas where scientists can take advantage of existing boat traffic. With a dearth of other sampling sites, many studies have simply extrapolated trends from limited areas to broader swaths of the ocean.

...the researchers found that rising temperatures are slowing the carbon absorption across a large portion of the subtropical North Atlantic. Warmer water cannot hold as much carbon dioxide, so the ocean’s carbon capacity is decreasing as it warms....

Image from the University of Wisconsin-Madison website