Solving the Mysteries of Hiatus in Global Warming

LARGE_KC400_Hiatus 

Global mean temperatures have been flat for 15 years despite the increase in heat-trapping greenhouse gases, but a new Scripps study shows cooling in the equatorial Pacific Ocean explains the discrepancy New research by Scripps Institution of Oceanography, UC San Diego climate scientists attributes the attenuation of a worldwide temperature increase to a cooling of eastern Pacific Ocean waters, one that counteracts the warming effect of greenhouse gases.

When the climate cycle that governs that ocean cooling reverses and begins warming again, the researchers predict that the planet-wide march toward higher temperatures will resume with vigor. The study does not consider when the reversal might happen, but it brings scientists closer to understanding how to look for signs of it.

If researchers can estimate that climate cycle, they could also better estimate the end date of regional trends that are linked to ocean cooling, such as the drought in the southern United States that have caused an estimated tens of billions of dollars in agricultural damage since 2000.

Prior to 2000, global temperatures had risen at a rate of 0.13º C per decade since 1950. The hiatus has transpired while levels of carbon dioxide, the main greenhouse gas produced by human activities, continued a steady rise, reaching 400 parts per million for the first time in human history in May 2013.

The disconnect led some climate watchers to speculate that increases in the concentration of carbon dioxide are not as strongly coupled to global warming even though the heat-trapping properties of carbon dioxide have been identified for more than a century.

Scripps climate scientists Yu Kosaka and Shang-Ping Xie conclude, however, that natural variability in the form of eastern Pacific Ocean cooling is behind the hiatus. They arrived at the conclusion by using innovative computer modeling methods to simulate regional patterns of climate anomalies. This enabled them to see global warming in greater spatial detail, revealing where it has been most intense and where there has been no warming or even cooling.

“Climate models consider anthropogenic forcings like greenhouse gases and tiny atmospheric particles known as aerosols, but they cannot study a specific climate event like the current hiatus,” said Kosaka. “We devised a new method for climate models to take equatorial Pacific ocean temperatures as an additional input. Then amazingly our model can simulate the hiatus well.”

“Specifically the model reproduced the seasonal variation of the hiatus, including a slight cooling trend in global temperature during northern winter season,” added Xie, the first Roger Revelle Chair in Environmental Science at Scripps. “In summer, the equatorial Pacific’s grip on the Northern Hemisphere loosens, and the increased greenhouse gases continue to warm temperatures, causing record heat waves and unprecedented Arctic sea ice retreat.”

The study, “Recent global-warming hiatus tied to equatorial Pacific surface cooling,” appears online in the journal Nature on Aug. 28. The National Science Foundation, the National Basic Research Program of China, and the NOAA Climate Program Office supported the research.

“As carbon dioxide levels in Earth’s atmosphere increase, global temperatures have been rising,” said Anjuli Bamzai, program director in the National Science Foundation (NSF)’s Division of Atmospheric and Geospace Sciences.  “But there’s been a ‘hiatus’ in the warming trend over the past decade or so, which scientists haven’t been able to explain.  These researchers have found an answer:  prolonged cooling of tropical Pacific Ocean waters.”

“These compelling new results provide a powerful illustration of how the remote eastern tropical Pacific guides the behavior of the global ocean-atmosphere system, in this case exhibiting a discernible influence on the recent hiatus in global warming,” said Dan Barrie, program manager at the NOAA Climate Program Office.

The study considers the tropical Pacific Decadal Oscillation, a climate cycle that plays out over the course of several decades. Within this large pattern fall El Niño and La Niña, well-known faster cycles that cause shifts in the distribution of warm water in the equatorial Pacific Ocean. While El Niño and La Niña last only a few years, the Pacific Decadal Oscillation lasts several decades. The last time it was in a cooling phase – cooling waters in the eastern equatorial Pacific Ocean – it lasted from roughly 1940 to the early 1970s. During that cool phase, warmer, drier weather dominated in the midwestern United States.

The current cooling phase began just after a strong El Niño year in 1998. The Texas AgriLife Extension Service at Texas A&M University estimates that the drought it traces to that same year caused nearly $21 billion in agricultural losses through 2011. In 2011, Texas set a single-year record with losses of $7.62 billion.

The study authors said it is not known if the current cooling phase will last as long as the last one. Predicting equatorial Pacific conditions more than a year in advance is beyond the reach of current science.

“That speaks to the challenge in predicting climate for the next few years,” said Xie.  “We don’t know precisely when we’re going to come out of [the hiatus] but we know that over the timescale of several decades, climate will continue to warm as we pump more greenhouse gases into the atmosphere.”

16 comments on “Solving the Mysteries of Hiatus in Global Warming
  1. Chad says:

    To the researchers: Thank you.

    Thank you for all the hard work you’ve done on this site over the years. Thank you for working your asses off so that the rest of us may better understand the workings of our climate. Thank you for doing your best to explain your findings to the rest of us through informal posts such as this.

    Though it may be disheartening for you to hear some of the comments you receive on this site, please continue trying to explain this science whenever you get the chance. The Keeling Curve is a nicely intuitive tool with which to grasp the things we humans are doing to this planet, and these posts are a wonderful way to get a sense of the questions–and answers–this science holds.

    Keep up the good work.

  2. paresh patel says:

    well, first step is to reduce co2 level is first priorities, neither warming or cooling, and i have the project to reducing co2 from the air

    • Walter Horsting says:

      Paresh,

      To what level do you propose lowering CO2 in the Atmosphere? During the last ice age CO2 levels dropped to near plant starvation levels.

  3. Andrew says:

    We will all die sooner or later.

  4. If the cool phase of the PDO can cause several decades of cooling, then the warm phase of the PDO can cause several decades of warming.
    If the cooling phase can nix the effect of additional co2, the warming phase must have been responsible for a least half the warming of the late C20th.

    Which means the IPCC estimates, which took no account of this oceanic cycle, have the climate sensitivity too high, as shown by a recent crp of papers. Published just too late to make it into AR5 of course.

  5. Nichol Brummer (@Twundit) says:

    It looks like most of the world gets a bit of a respite in the *speed* of warming. But the US will get dryer weather, in combination with the already high temperatures: more droughts? Is that a correct summary, or is this not yet a prediction?

  6. Walter Horsting says:

    Our sun was its most active in the past 1,000 years up to 1998. The current cycle 24 is well below cycle 20 and cycle 25 portends to be very low in activity. Your graph should have gone back another 30-60 years to show the decline in early 70s. I expect we will see a near Dalton or Maunder event starting soon.

  7. John Tillman says:

    That speaks to the challenge in predicting climate for the next few years,” said Xie. “We don’t know precisely when we’re going to come out of [the hiatus] but we know that over the timescale of several decades, climate will continue to warm as we pump more greenhouse gases into the atmosphere.”

    No one can possible “know” any such thing. The naturally-changing climate might well cool over the next several decades, or both cool & warm.

    The GIGO models are worse than worthless, based upon feedback assumptions for which no evidence exists, indeed which have been shown false.

  8. JB Willikers says:

    “Predicting equatorial Pacific conditions more than a year in advance is beyond the reach of current science.”

    But you can predict temperature to within a couple degrees a 100 years from now or derive temperatures from 200 years ago (that can’t be refuted). This whole climate business is hog wash and a perversion of real science. Predictions that are not realized are adjusted with other presumptions. It’s an endless maze of nonsense by people sucked into the vortex and pretending to do something real.

    • lanevn says:

      Pff, I can’t predict if tomorrow in my town will be warmer or colder weather than today, but I can say for sure that in six months it will become much warmer

  9. Rufus says:

    Does the model consider the melting of the Arctic ice?

    • Rob Monroe says:

      Study co-author Shang-Ping Xie responds: “Yes, the model includes a module for Arctic sea ice that is interactive with ocean and atmosphere”

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