The 1st Threshold: We May Break 1.5C Barrier In 15 Years: GRL/WP

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Abstract

Global temperature is rapidly approaching the 1.5°C Paris target. In the absence of external cooling influences, such as volcanic eruptions, temperature projections are centered on a breaching of the 1.5°C target, relative to 1850–1900, before 2029. The phase of the Interdecadal Pacific Oscillation (IPO) will regulate the rate at which mean temperature approaches the 1.5°C level. A transition to the positive phase of the IPO would lead to a projected exceedance of the target centered around 2026. If the Pacific Ocean remains in its negative decadal phase, the target will be reached around 5 years later, in 2031. Given the temporary slowdown in global warming between 2000 and 2014, and recent initialized decadal predictions suggestive of a turnaround in the IPO, a sustained period of rapid temperature rise might be underway. In that case, the world will reach the 1.5°C level of warming several years sooner than if the negative IPO phase persists.

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http://onlinelibrary.wiley.com/doi/10.1002/2017GL073480/full

Global temperatures could exceed 1.5 degrees Celsius above their preindustrial levels within the next 15 years, according to a new scientific study, crossing the first threshold under the Paris climate agreement and placing the world at a potentially dangerous level of climate change.

The report comes as climate agreement participants are watching the United States — where the Trump administration is debating whether to withdraw from the Paris accord — and as scientists with the Intergovernmental Panel on Climate Change are working on a special report about the 1.5-degree goal (equivalent to 2.7 degrees Fahrenheit) and the consequences of overshooting it.

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“The paper emphasizes the way that natural climate variations, like the IPO, can interact with the progression of human-caused global warming,” Gerald Meehl, a senior scientist with the National Center for Atmospheric Research, told The Washington Post. “Therefore, the timing of when we cross certain thresholds depends on the interplay between these two factors.” Meehl was not involved with the new study but has previously published research on the IPO.

And the 2025 date for hitting the 1.5-degree temperature threshold is looking more and more likely. Multiple studies in the past few years suggest that the transition to a positive IPO phase has begun. Henley said there’s some uncertainty about whether that has happened, but other scientists are more confident. Scientists John Fasullo and Kevin Trenberth, also of the National Center for Atmospheric Research, have published research to this effect, and both told The Post that we have been in a positive phase for several years now.

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https://www.washingtonpost.com/news/energy-environment/wp/2017/05/09/earth-could-break-through-a-major-climate-threshold-in-the-next-15-years-scientists-warn/?utm_term=.1c4c6c8e00cb

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