Record warm years almost certainly due to human-made climate change, new study says

January 25, 2016

Record-setting temperatures over the past century and a half are extremely unlikely to have occurred without human-caused climate change, but the odds of that happening are not quite as low as previously reported, according to an international team of meteorologists.

"The press reports last year about the unlikely nature of recent global temperature records raised some very interesting questions, but the scientists quoted hadn't done a rigorous calculation," said Michael Mann, distinguished professor of meteorology and director, Earth System Science Center, Penn State. "As a result, the probabilities reported for observing the recent runs of record temperature by chance alone were far lower than what we suspected the true probabilities are. "

Although the new odds of chance producing recent runs of record temperatures are greater than the odds previously reported in the news—between 1 in 27 million and 1 in 650 million—they are still incredibly slim at between 1 in 5 thousand and 1 in 170 thousand. Including the data for 2015, which came in after the study was completed, makes the odds even slimmer.

The reason for the inaccuracy of the previous probability calculations is that the individual yearly temperatures analyzed are not independent of each other.

"Natural climate variability causes temperatures to wax and wane over a period of several years, rather than varying erratically from one year to the next," said Mann.

In calculating the odds, the previous reports did not take into account that the data did not end simply because December 31 occurred, but that trends overlap into previous and subsequent years. This needs to be taken into account to determine the real probabilities of chance causing the warming events.

"We provided a method for doing this based on combining information from state-of-the-art climate model simulations with the observational temperature record, and we used this method to estimate the probabilities correctly," said Mann.

Using a combination of observations and climate model simulations, the researchers examined temperatures from both the Northern Hemisphere and the entire globe for specific groups of years. They examined scenarios for record warm years of 1998, 2005, 2010 and 2014; for nine of the 10 warmest years occurring since 2000; and for 13 of the warmest 15 years occurring since 2000. They chose the last two scenarios because these are the ones previously reported in news accounts.

The reason that Mann's team found the probability of naturally occurring global warming more likely than previously reported in the news, is that the effective size of their statistical sample was considerably smaller than estimates based simply on the number of years available. This "serial correlation" means that the chance likelihood of runs of warm temperature—nine very warm years over the course of a decade—is much greater than if temperatures were uncorrelated from one year to the next.

The researchers tried a variety of different data sources and statistical approaches and found that in all cases, the odds of the patterns of warming occurring with no human intervention were similarly low.

The researchers note in today's (Jan. XX) issue of Nature Scientific Reports, that "while considerably greater than cited in some recent media reports, these odds are low enough to suggest that recent observed runs of record temperatures are extremely unlikely to have occurred in the absence of human-caused global warming.

"2015 is again the warmest year on record, which adds even more weight to our findings," said Stefan Rahmstorf, professor of physics of the oceans, Potsdam University, Germany. "What is more, the anomalous warmth has led to unprecedented local heat waves across the world—sadly resulting in loss of life and aggravating droughts and wildfires. The risk of heat extremes has been multiplied due to human greenhouse-gas emissions, as our data analysis shows."

By contrast, they found that the odds that human activity caused the warming are relatively high. Considering human-caused warming, they find the probabilities of nine of the 10 warmest years and 13 of the warmest 15 years occurring since the beginning of the 21st century, to be 88 percent and 83 percent, respectively, for the Northern Hemisphere.

"It just seemed like it was important to do this right, and address, in a defensible way, the interesting and worthwhile question of how unlikely it is that the recent run of record temperatures might have arisen by chance alone," said Mann.

The recent record temperature years are roughly 600 to 130,000 times more likely to have occurred under human-caused conditions than in their absence, according to the researchers. These findings underscore the impact that human forcing has already had on temperature extremes.

Explore further: 2015 to be hottest year ever, according to World Meteorological Organization

More information: Mann, M.E., Rahmstorf, S., Steinman, B.A., Tingley, M., Miller, S.K. (2016): The Likelihood of Recent Record Warmth. Scientific Reports, DOI: 10.1038/srep19831

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Shootist
1.6 / 5 (14) Jan 25, 2016
What record warm years?

For 400 years, centered around CE 1000, there were dairy cattle and wheat farms on the island of Greenland. There were commercial vineyards in Scotland (during both the Roman Climate Optimum, ca. 60 BC, and during the Viking Warm Period (CE 850 - CE 1250).

Nothing like that exists today. It is TOO Fricken' Cold.

For this and other reasons, "the polar bears will be fine" -- Freeman Dyson
jeffensley
1.6 / 5 (19) Jan 25, 2016
I wish they could use all this intellectual energy and computing power for something useful. Anyone who understands how short a time we've actually been "recording" temperature would know that breaking records just isn't all that exciting.
Evermars
3.4 / 5 (22) Jan 25, 2016
For 400 years, centered around CE 1000, ....

Temperatures in some regions matched or exceeded recent temperatures in these regions, but globally the Medieval Warm Period was cooler than recent global temperatures.

But when science doesn't tell you what you want to hear, by all means cherry pick your facts.
howhot2
4.8 / 5 (17) Jan 25, 2016
Then wanky old @shootlist says;
What record warm years?... bla bla bla and other nonsensical crap


Let me quote Richard Feynman and you meditate on it for a while.
The first principle is that you must not fool yourself and you are the easiest person to fool.

Feynman trumps Dyson anyday of the week!

Evermars
3.5 / 5 (22) Jan 25, 2016
I wish they could use all this intellectual energy and computing power for something useful.


People have the right to inquire about any mystery they choose. Your approval or lack of it is meaningless, except as an indicator of your biases.
jeffensley
2.2 / 5 (10) Jan 25, 2016
People have the right to inquire about any mystery they choose. Your approval or lack of it is meaningless, except as an indicator of your biases.


I'll accept that as long as your willing to admit that approval or attachment of meaning to things like the above studies come from ones personal biases as well.
TehDog
5 / 5 (14) Jan 25, 2016
"The first principle is that you must not fool yourself and you are the easiest person to fool."

I really hate to quibble, but I read that as two principles,
"The two main principles are that you must not fool yourself, and that you are the easiest person to fool."
:)
antigoracle
2.3 / 5 (12) Jan 25, 2016
Remember the now absolutely debunked Hockey Schtick that "cooked" the data. Yep, these warmest years are totally Mann made.
TehDog
5 / 5 (14) Jan 25, 2016
(If anyone goes anywhere near the Spanish Inquisition I will put them on ignore :P)
Vietvet
4.5 / 5 (15) Jan 25, 2016
What record warm years?

For 400 years, centered around CE 1000, there were dairy cattle and wheat farms on the island of Greenland. There were commercial vineyards in Scotland (during both the Roman Climate Optimum, ca. 60 BC, and during the Viking Warm Period (CE 850 - CE 1250).

Nothing like that exists today. It is TOO Fricken' Cold.

@Shooter is behind the times. Besides a commercial vineyard in Scotland climate change
is effecting vineyards all over Europe.
http://www.bloomb...-changes

HeloMenelo
2.5 / 5 (8) Jan 26, 2016
seems like shooti shot the potty miss yet again and shot a load right into his sockpuppets face aka himself/jeffey/antisciencegorillicle... i know there's not much to hold onto to aim, but try gently using a needle nose plier for better grip and aim it downwards.... ;) or ask your antisciencegorilla sock to give you a hand, his quote's aren't that entertaining anymore... yaaaawnnnn.... ;)
DouglasBarnes
2.7 / 5 (7) Jan 27, 2016
You guys need to learn from /r/science. Your comment sections are full of derp.
Mike_Massen
2.1 / 5 (11) Jan 27, 2016
jeffensley suggests
I wish they could use all this intellectual energy and computing power for something useful
Such as key Physics, specifically
1. https://en.wikipe...Enthalpy
ie. Amount of heat added to Earth energy balance ~1.6W/m^2 & rising !
https://en.wikipe..._forcing
2. Oceans have ~4000x heat capacity of atmosphere, therefore most important by far
https://en.wikipe...capacity
Especially re oceans
http://www.realcl...-warming

jeffensley says
Anyone who understands how short a time we've actually been "recording" temperature would know that breaking records just isn't all that exciting
Not about "exciting" see 1. in relation to 2.
jeffensley as someone claims to be Environment Scientist you miss basics, write facile notions & often bandy about vague doubts to obfuscate, not congruent with key uni study

Why is that, yah think ?
TehDog
5 / 5 (10) Jan 27, 2016
@DouglasBarnes
Damn, never even thought of reddit, looks like a good community, ta :)

physorg regulars beware, there will be mods...
https://www.reddi...science/
Mike_Massen
1.9 / 5 (9) Jan 27, 2016
DouglasBarnes observed
You guys need to learn from /r/science. Your comment sections are full of derp
Damn right & heap of odd ball voting sockpuppets with immense self-esteem failures not allowed on associated PhysicsForums.

A d.ck who copies my real name with obvious spelling error
https://sciencex...._Masson/

& in particular a nick who really failed at basic education
https://sciencex....thanyou/

& few others, please don't be dissuaded by their vengeful unintelligent obviously shallow behavior, can get a boost to ego as it means we are of great interest :-)

In any case votes don't mean anything here, interesting about psychology of those nicks is; more they follow a robotic pattern worse their feelings overall but, try to convince themselves they get a buzz putting people down. I'm fortunate to have a forum analysis script which "joins dots" re comment styles vs timing & other issues - amusing stuff :P
Bongstar420
1 / 5 (2) Jan 30, 2016
This article is saying warming events similar to the last 50 years occurs once out of every 5,000-170,000 years.

That sounds about right
JK.

But this isn't just CO2 in the calculations. Recognize

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