How much has the ocean temperature risen

I was fortunate to play a small part in a new study, just published in the journal Advances in Atmospheric Sciences, which shows that the Earth broke yet another heat record last year. Twenty-three scientists from around the world teamed up to analyze thousands of temperature measurements taken throughout the world’s oceans. The measurements, taken at least 2,000 meters (about 6,500ft) deep and spread across the globe, paint a clear picture: the Earth is warming, humans are the culprit, and the warming will continue indefinitely until we collectively take action to reduce greenhouse gas emissions.

We used measurements from the oceans because they are absorbing the vast majority of the heat associated with global warming. In fact, more than 90% of global warming heat ends up in the oceans. I like to say that “global warming is really ocean warming”. If you want to know how fast climate change is happening, the answer is in the oceans.

But this paper was not merely an academic exercise. It has tremendous consequences to society and biodiversity on the planet. As oceans warm, they threaten sea life and the many food chains that originate in the sea. Warmer ocean waters make storms more severe. Cyclones and hurricanes become more powerful; rains fall harder, which increases flooding; storms surges are more dangerous; and sea levels rise (one of the major causes of rising sea levels is the expansion of water as it heats).

How much did the world’s oceans warm in 2021 compared with the previous year? Well, our data shows that oceans heated by about 14 zettajoules (a zettajoule is 1,000,000,000,000,000,000,000 joules of energy). This is a mind-bending number, so it may help to use analogies. This is the equivalent of 440bn toasters running 24 hours a day, every day of the year. Another way to think about this is that the oceans have absorbed heat equivalent to seven Hiroshima atomic bombs detonating each second, 24 hours a day, 365 days a year. I have plotted the ocean heat, measured since the late 1950s, and the clear, persistent rise over the past three to four decades is unmistakable evidence of an Earth that is out of balance.

The oceans are vast, and you need many measurements spread out across the planet to get a good sense of what is happening to the oceans as a whole. This study used hi-tech temperature sensors on autonomous buoys that rise and fall in the ocean waters as they make measurements. These sensors then send the data to laboratories around the world for analysis. In addition, we deployed high-quality temperature sensors from ships, temperatures from stationary buoys, and even strapped sensors to animals so we could measure temperatures from the water they traveled through. Our research was enabled by thousands of in-field researchers who are obtaining and processing the raw data. Without their contribution, studies like this would not be possible.

We discovered that the temperatures are not rising uniformly across the planet. We found the fastest warming in the Atlantic, Indian and northern Pacific Oceans. In our work we also explore the question of why this pattern is emerging the way it is. Using climate model simulations, we directly tie various features of the ocean to human emissions of industrial pollution and greenhouse gases. These findings suggest that a similar pattern is likely to persist into the coming decades.

The information we used is absolutely crucial for understanding the planet. You could say that we took the Earth’s temperature – and the Earth’s fever is getting worse.

I asked my colleague Alexey Mishonov, a research scientist at the University of Maryland, about the implications of these findings. “Our results demonstrated that ocean warming is extensively penetrating deeper layers of the ocean,” Dr Mishonov said. “The resulting increase of the ocean heat content cannot be adequately assessed without real measurements. We need to continue our field missions and collect these data.”

My new year’s resolution is to help the planet cool down. It’s getting hot in here and there is no sign things are going to change anytime soon. Collectively, we certainly have the technology to reduce greenhouse gases, but we have never really shown the will.

• John Abraham is a professor of thermal sciences at the University of St Thomas in Minnesota

A controversial paper published two years ago that concluded there was no detectable slowdown in ocean warming over the previous 15 years - widely known as the "global warming hiatus" - has now been confirmed using independent data in research led by researchers from the University of California, Berkeley, and Berkeley Earth, a non-profit research institute focused on climate change.

The 2015 analysis showed that the modern buoys now used to measure ocean temperatures tend to report slightly cooler temperatures than older ship-based systems, even when measuring the same part of the ocean at the same time. As buoy measurements have replaced ship measurements, this had hidden some of the real-world warming.

After correcting for this "cold bias," researchers with the National Oceanic and Atmospheric Administration concluded in the journal Science that the oceans have actually warmed 0.12 degrees Celsius (0.22 degrees Fahrenheit) per decade since 2000, nearly twice as fast as earlier estimates of 0.07 degrees Celsius per decade. This brought the rate of ocean temperature rise in line with estimates for the previous 30 years, between 1970 and 1999.

This eliminated much of the global warming hiatus, an apparent slowdown in rising surface temperatures between 1998 and 2012. Many scientists, including the International Panel on Climate Change, acknowledged the puzzling hiatus, while those dubious about global warming pointed to it as evidence that climate change is a hoax.

Climate change skeptics attacked the NOAA researchers and a House of Representatives committee subpoenaed the scientists' emails. NOAA agreed to provide data and respond to any scientific questions but refused to comply with the subpoena, a decision supported by scientists who feared the "chilling effect" of political inquisitions.

The new study, which uses independent data from satellites and robotic floats as well as buoys, concludes that the NOAA results were correct. The paper will be published Jan. 4 in the online, open-access journal Science Advances.

"Our results mean that essentially NOAA got it right, that they were not cooking the books," said lead author Zeke Hausfather, a graduate student in UC Berkeley's Energy and Resources Group.

Long-term climate records

Hausfather said that years ago, mariners measured the ocean temperature by scooping up a bucket of water from the ocean and sticking a thermometer in it. In the 1950s, however, ships began to automatically measure water piped through the engine room, which typically is warm. Nowadays, buoys cover much of the ocean and that data is beginning to supplant ship data. But the buoys report slightly cooler temperatures because they measure water directly from the ocean instead of after a trip through a warm engine room.

NOAA is one of three organizations that keep historical records of ocean temperatures - some going back to the 1850s - widely used by climate modelers. The agency's paper was an attempt to accurately combine the old ship measurements and the newer buoy data.

Hausfather and colleague Kevin Cowtan of the University of York in the UK extended that study to include the newer satellite and Argo float data in addition to the buoy data.

"Only a small fraction of the ocean measurement data is being used by climate monitoring groups, and they are trying to smush together data from different instruments, which leads to a lot of judgment calls about how you weight one versus the other, and how you adjust for the transition from one to another," Hausfather said. "So we said, 'What if we create a temperature record just from the buoys, or just from the satellites, or just from the Argo floats, so there is no mixing and matching of instruments?'"

In each case, using data from only one instrument type - either satellites, buoys or Argo floats - the results matched those of the NOAA group, supporting the case that the oceans warmed 0.12 degrees Celsius per decade over the past two decades, nearly twice the previous estimate. In other words, the upward trend seen in the last half of the 20th century continued through the first 15 years of the 21st: there was no hiatus.

"In the grand scheme of things, the main implication of our study is on the hiatus, which many people have focused on, claiming that global warming has slowed greatly or even stopped," Hausfather said. "Based on our analysis, a good portion of that apparent slowdown in warming was due to biases in the ship records."

Correcting other biases in ship records

In the same publication last year, NOAA scientists also accounted for changing shipping routes and measurement techniques. Their correction - giving greater weight to buoy measurements than to ship measurements in warming calculations - is also valid, Hausfather said, and a good way to correct for this second bias, short of throwing out the ship data altogether and relying only on buoys.

Another repository of ocean temperature data, the Hadley Climatic Research Unit in the United Kingdom, corrected their data for the switch from ships to buoys, but not for this second factor, which means that the Hadley data produce a slightly lower rate of warming than do the NOAA data or the new UC Berkeley study.

"In the last seven years or so, you have buoys warming faster than ships are, independently of the ship offset, which produces a significant cool bias in the Hadley record," Hausfather said. The new study, he said, argues that the Hadley center should introduce another correction to its data.

"People don't get much credit for doing studies that replicate or independently validate other people's work. But, particularly when things become so political, we feel it is really important to show that, if you look at all these other records, it seems these researchers did a good job with their corrections," Hausfather said.

Co-author Mark Richardson of NASA's Jet Propulsion Laboratory and the California Institute of Technology in Pasadena added, "Satellites and automated floats are completely independent witnesses of recent ocean warming, and their testimony matches the NOAA results. It looks like the NOAA researchers were right all along."

More information: "Assessing recent warming using instrumentally homogeneous sea surface temperature records," Science Advances, advances.sciencemag.org/content/3/01/e1601207

Provided by University of California - Berkeley

Citation: Study confirms steady warming of oceans for past 75 years (2017, January 4) retrieved 21 October 2022 from https://phys.org/news/2017-01-steady-oceans-years.html

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