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Record-Warm Oceans: How Worried Should We Be?

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Record-Warm Oceans: How Worried Should We Be?
A sea turtle swims above a fragile coral reef in Wailea, Maui, Hawaii. M Swiet Productions / Moment / Getty Images

By Ilissa Ocko

The world's oceans are heating up. Scientists have found that 2018 was the hottest year ever recorded for our oceans, and that they are warming even faster than previously thought.

When documenting global warming trends, we often focus on air temperature. But the oceans actually absorb more than 90 percent of the excess heat trapped by human emissions of greenhouse gases. So if we really want to know how much our planet is warming up, we look to the oceans.


And what the oceans are telling us is alarming.

Using multiple measurement devices, scientists from across the globe found that the amount of heat in the upper part of the world's oceans in 2018 was the highest ever recorded since observations began in the 1950s. In fact, the past five years are the warmest years on record and the increase in ocean heat has been accelerating since the 1990s.

Scientists also found that the oceans are warming faster than data previously published in a 2013 landmark report by the United Nations' Intergovernmental Panel on Climate Change.

Studies now show that in recent decades, the rate of warming in the upper ocean—the top 2,000 meter or 6,500 feet layer of the ocean—was about 40 percent higher than the earlier IPCC estimates showed. The new data, made possible by vast improvements to ocean heat records in recent years, is also consistent with model projections of ocean warming.

So how worried should we be?

Why Warmer Oceans Matter

Rising ocean temperatures are a major concern for societies and ecosystems across the globe. Hotter oceans lead to:

  • rising sea levels when water molecules expand from increasing temperatures, and then erode coasts, threaten infrastructure and contaminate freshwater with intruding saltwater.
  • heavier downpours and widespread flooding because more ocean water evaporates as temperatures increase, supplying the atmosphere with more moisture.
  • more destructive hurricanes because of the increased moisture in the air and higher sea levels that worsen storm surges.
  • dying coral reefs as the corals' colorful algae, their main food source, leave the corals due to heat stress. This bleaches corals of their vivid colors, causing them to starve, while affecting the survival of thousands of species that live in the reefs.
  • fish moving poleward because their current habitats are becoming too warm, disrupting fisheries.

There Is Still Time

Recent scientific reports have concluded that our greenhouse gas emissions so far have not yet committed us to future warming levels that can cause catastrophic climate impacts. That is great news.

There are, in fact, countless reasons to feel hopeful. Numerous countries are reducing greenhouse gas emissions while growing their economies. Renewable energy sources are increasingly more affordable. And new technologies, such as carbon dioxide removal, are emerging.

Oceans are warning us, and we need to act now. As disconcerting as this oceans news has been, there's still time.

Ilissa Ocko is a climate scientist at Environmental Defense Fund.

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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