Oceans are warming dramatically faster, new study warns

A new study finds the world's oceans are warming significantly faster than previously thought. The analysis, published Thursday in the journal Science, raises the stakes for curbing climate change.

Since 1970, the ocean has warmed 40 percent more than previous estimates, according to climate scientist Zeke Hausfather, one of the authors of the study.

The study examined four new or updated Ocean Heat Content records — a fancy term for measuring how warm the ocean is, taking into account deeper water, not just surface temperatures — and finds the ocean warming is significantly higher than estimated in the last comprehensive report by the U.N.'s Intergovernmental Panel on Climate Change (IPCC) in 2013.

Ninety-three percent of the excess heat trapped in the Earth's system by human-caused greenhouse gas emissions is stored in the oceans. If it weren't for this ocean buffer absorbing so much heat, our atmosphere would be roasting us by now. 

According to Kevin Trenberth, a senior scientist from the National Center for Atmospheric Research and co-author of the study, the increase in ocean heat content observed since 1992 is about 2,000 times the total electricity generation by U.S. utility companies in the past decade. 

That heat build-up has a debilitating impact on many aspects of ocean life. Coral reefs are a good example. 

Coral is very sensitive to increases in water temperature. When the water is too warm the corals bleach, turning white. A 2016 study estimates that 98 percent of coral reefs worldwide will experience bleaching-level stress each year by 2050. 

Bleaching can eventually lead to death of the reef community, turning them into Ghost Reefs. Since 25 percent of all life in the ocean depends on coral reefs, this loss has a ripple effect on the ecosystem.

Warmer water also holds less carbon dioxide, meaning more heat-trapping gas escapes back into the atmosphere, creating a self-reinforcing feedback loop of perpetuated warming.

And that's just the tip of the iceberg, literally. Warm water hastens the rate of glaciers melting, and expands the water column, and together the two phenomena raise sea levels. By 2100 the IPCC estimates sea levels may rise 2 to 3 feet, and some studies say more. The destabilizing effects of this on society are incalculable.

The most dramatic effect of warmer water is the impact we already feel most directly: extreme weather. A warmer ocean means stronger hurricanes and heavier flooding events. 

For example, it's estimated that rainfall from Hurricane Harvey was 15 percent to 38 percent greater because of climate change. As the ocean and air warms, extreme flooding events will increase. 

A well-cited study by highly respected NOAA climate modeler Tom Knutson shows that by late this century the number of Category 4 and Category 5 hurricanes may increase by 42 percent in the Atlantic Basin and over 300 percent in the Eastern Pacific. This is due to warmer water which acts as high-octane fuel to power storms. Stronger storms mean exponentially more damage.

Because the oceans are so large and less variable than the atmosphere, it makes ocean heat content a much better gauge for the pace of global warming.

Trenberth says, "The warmer ocean is the memory of the past climate change and the ocean heat content is breaking records every year."

Unlike the surface temperature record which can vary dramatically from year to year, the Ocean Heat Content record acts a bank and steadily accumulates heat. So, if the Earth is trapping excess heat, the Ocean Heat Content record will tick upward, with no ambiguity.

And that is where this study lays to rest a misconception about whether there was a global warming "hiatus" between 1998 and 2013. If you look at a short-term snippet of the surface temperature record, one could conclude that warming was negligible during that 15-year period. Those skeptical of climate change often refer to this to poke holes in the evidence.

But in this new analysis, the authors of the study say, "Although climate model results have been criticized during debates about a 'hiatus' or 'slowdown' of global mean surface temperature, it is increasingly clear that the pause in surface warming was at least in part due to the redistribution of heat within the climate system." 

In other words, the oceans were just hiding the heat and now new tools have enabled scientists to find it. 

The improvement in the four new datasets examined in this study is due partially to new analysis methods and partly due to the development of a vast network of ocean sensors called Argo. It's a global array of nearly 4,000 temperature and salinity profiling floats measuring temperatures as deep as 2,000 meters down.

The study also lays to rest a long-standing discrepancy in the climate science community, namely the question of why climate models over-project ocean heating. According to this new study, it turns out they don't. 

The new measure of actual ocean heat matches almost perfectly the average projection from the best coupled ocean-atmosphere models (CMIP5). By this metric, the climate models are performing very well. It gives climate scientists and the public greater reason for confidence in future projections.

This study is a reminder that the state of our oceans is the best bellwether of our changing climate. And the evidence shows our current climate is changing much faster than at any time in human history.