Latest on the strongest evidence of climate change

On an article by Kevin Trenberth in Inside Climate News – must see graphics

Kevin Trenberth is the head of climate analysis at the National Center for Atmospheric Research and co-author of a new paper on ocean warming.  The rate at which the oceans are heating up has nearly doubled since 1992, and that heat is reaching ever deeper waters, according to a recent study. At the same time, concentrations of carbon dioxide in the atmosphere have been rising.  The excess energy amassed in the oceans since 1992 is roughly equivalent to 2,000 times U.S. electricity generation during the past decade, the researchers explained.

The charts that follow show how the oceans are changing and what they’re telling us as a thermometer of global warming.

Scientists say the accumulation of heat in the oceans is the strongest evidence of how fast Earth is warming due to heat-trapping gases released by the burning of fossil fuels.

Oceans have enormous capacity to hold heat. So ocean temperatures, unlike temperatures on land, are slow to fluctuate from natural forces, such as El Niño/La Niña patterns or volcanic eruptions. Think night and day, said Trenberth. As night falls on land, so do air temperatures. But in the oceans, temperatures vary little.

This makes it easier to tease out the influence of human-caused climate change from other possible causes of surging ocean heat.

How much extra heat are we talking about? And what are the impacts on the climate system? “On a day-to-day a basis, it’s really quite small,” Trenberth said, but the cumulative effects are not.

Though ocean temperature represents a clear signal of climate change, one challenge for researchers is that the record only goes back so far. Since the early 2000s, an international effort called Argo has launched nearly 4,000 ocean-going sensors that gather important data about the oceans, including temperature.

Meanwhile, as oceans heat up, thermal expansion causes sea levels that are already rising from the melting of land ice (triggered by higher air and sea temperatures) to rise even more. Nearly 50 percent of the sea level rise so far has come from ocean warming, according to new work by Cheng and Trenberth. Much of the rest comes from the melting of ice on Antarctica and Greenland.

Scientists say the West Antarctic Ice Sheet alone holds enough ice to raise global sea level by about 11 feet.