Rising sea levels are perhaps the greatest long-term threat posed by climate change. Scientists predict that gradual yet inevitable rises, estimated at about 4mm per year, “” Consider the millions of people living in coastal cities and you begin to comprehend the devastation ahead. Add waves, storm surges, and other extreme weather events into the mix—which are exacerbated by warming oceans—and those remote estimates quickly resolve into a global humanitarian crisis.
A recent study conducted by researchers at The University of Oxford reexamines the impact greenhouse gas emissions have had on the earth’s oceans since the late 19th century. Using computer models of ocean currents, Professor Laure Zanna and her colleagues traced 150 years of surface temperatures along their circulation routes, revealing a much deeper picture of submarine heat absorption over time.
Their findings, in the journal Proceedings of the National Academy of Sciences, show that upward of 90 percent of the heat trapped by greenhouse gas emissions has been absorbed by the oceans, while only a few percent have impacted the air, land, and ice caps. By tracking currents, the team was able to isolate the source of warming in specific oceans. In the Atlantic, for example, approximately half the rise in the past 50 years could be attributed to heat flowing in from deep ocean storage zones.
According that references the Oxford study, the total heat stored by oceans since the 1870s amounts to “1,000 times the annual energy use of the entire global population.” In case that doesn’t alarm you sufficiently, that same article went nuclear, calculating that the average warming over this time period is equivalent to one-and-a-half atomic bombs per second. That’s an average, mind you. Depending on your dataset, today’s estimate is a whopping three to six Hiroshima blasts per second.
Why are scientists only beginning to understand this now? Because the practice of recording deep ocean temperatures only began in the past few decades. Likewise, recent estimates of total heat absorption were based on data gathered since 1950. This new analysis projects temperatures dating back to 1871. And as any good climate scientist knows, understanding historical warming trends is necessary for predicting future ones. More accurate, region-specific predictions will help us design our communities more wisely and be better prepared in emergencies.
We’ve already felt the impacts of warming waters around the world. As oceans warm, they expand, increasing in volume. This thermal expansion not only rises sea levels, but also intensifies natural disasters. Reconstructing ocean temperature changes “,” as Zanna’s team puts it, could mean the difference between life and certain death for coastal populations worldwide.