What is the significance of reaching this new milestone? And now that El Niño is waning, what might the future bring?
Pattern of temperature anomalies across the globe in February 2016. The month was the warmest on record. (Source: NASA GISS) | Please see important correction at end | Earlier this month, a spate of headlines proclaimed that February 2016 was the warmest such month on record for the globe. At that time, I wrote that we should wait until official, reliable analyses were in before drawing any final conclusions. SEE ALSO:February may have been the warmest on record, but we don't know for sure — despite reports to the contrary The first of those reliable analyses has just been released, and it shows that this past month did indeed set a new record for warmest February in a record extending back to 1880. According to the analysis by NASA's Goddard Institute for Space Studies, this past month was 1.35 degrees C (2.43 F) warmer than the month's long-term average (measured between 1951 and 1980). February's spike was not just a one-off. January also set a record. In fact, we've now experienced a string of five record-setting months in a row. But the increase temperature anomaly spike seen last month was particularly steep. As Gavin Schmidt, head of NASA GISS, put it on Twitter today: "Normally I don't comment on individual months (too much weather, not enough climate), but last month was special." According to Gerald Meehl, a research scientist at the National Center for Atmospheric Research, the odds of monthly records being set are raised right now, thanks to "the juxtaposition of a large El Niño and ongoing human-caused warming." A spike of El Niño warmth has, in fact, occurred atop the long-term global warming trend-line. But as the string of recent monthly records suggests, that trend line also seems to be angling sharply upward now, after what many climate scientists regard as a multi-year period of slower warming. But Meehl also cautions that we should not expect each successive month necessarily to be warmer than the preceding one. That's in part because El Niño's fade — as this one appears to be doing. And they often transition into La Niña, the opposite of an El Niño, resulting in cooling. Moreover, climate can be quite labile, with natural variation causing lots of ups and downs.
What's going on and what should we make of it?
In anticipation of the release of NASA's climate analysis for February (a second one from NOAA will follow soon), I've been in touch with six scientists to get their perspectives on a number of issues, including these:
What take-home messages should we draw from these monthly and annual analyses of global climate?
Since climate is a phenomena measured in decades, should we be focusing so much on monthly records?
Given just how warm things have been, what are the relative influences of El Niño, other natural variations, and human-caused climate change?
With El Niño now on the wane, and it's opposite — La Niña — possibly on the way, what might the next couple of years bring?
Deke Arndt, Chief of the Monitoring Branch of the National Centers for Environmental Information at NOAA, emailed me today to make a philosophical point about these issues:
There's nothing magical about a calendar year. It's entirely a human construct, and an accident of history, that a year begins on January 1. We (myself included) really, really overdo the cook-off comparisons of one year versus another. It's an easy, convenient, and not particularly harmful way to organize our thinking about climate change.
But the fact is, we've been setting a new "warmest 12 month stretch in recorded history" record almost every month for the past year. That's the story, scientifically. We choose a January 1 starting line because that's when we reset the annual accounting of our lives. But it's not that important, scientifically.
This graphic helps us see the pattern of change through an ironically beautiful pattern of colors:
Global temperatures visualized month-by-month since 1901. Each square is colored to indicate how it varied from the long-term average for that month. The extraordinary warmth of February 2016 required the addition of a new color to the palette. (Source: Makiko Sato, Columbia University) We're clearly in the midst of a particularly warm stretch of months, thanks in large measure to human-caused climate change. But there are other important influences to consider as well, since they will also help determine what we'll experience in the months, years and decades ahead. To get a better handle on these issues, I posed some questions in an email to NCAR's Jerry Meehl
. He studies El Niño and La Niña, human and natural influences on climate, and possible future changes in weather and climate extremes in a warmer world. Here's what Meehl said in an email message:
. . . 'global warming' is not a relentless march towards warmer temperature with every month and season and year and decade being warmer than the preceding month and season and decade. That is because there is a lot of internally generated, naturally occurring variability in the climate system. This natural variability is superimposed on the response to human-caused warming.
Keep that in mind if you find yourself reading stories saying things like "global warming has gone into overdrive" (as this story did). Yes, the average temperature of the globe is climbing more steeply now than it has in recent years. And a spike of El Niño warmth has been superimposed on that.
But sooner or later, we'll come off the extreme highs we're seeing, and we could even experience a temporary period of slower warming lasting years. This won't repeal the long-term upward rise in global temperature — not by a long shot. But when temperatures do cool off for a bit, people might be left wondering whatever happened to global warming going into overdrive and crossing terrifying thresholds.
Data: NASA GISS. Interactive Plotting Tool: Wood For Trees
The graph above shows how temperatures have varied from the long-term average from 1970 to the present. I've marked the two strongest El Niños during the period: in 1997/1998, and our current episode.
I've also indicated the period when warming of the Earth appears to have slowed despite all the greenhouse gases we humans emitted into the atmosphere.
In addition to these variations, you'll also note lots of smaller ups and downs. But the long-term upward trend is clear.
Wiggles and squiggles
To understand these wiggles and squiggles better, along with the underlying trend, I spoke with John C. Fyfe, Senior Research Scientist with Environment and Climate Change Canada. Fyfe uses model simulations and observations to study climate variability and climate change.
The variation takes place across several scales, he said. “First, there is the multi-decadal scale,” which stretches across two or more decades. That’s the scale on which humans are causing long-term warming of the planet. There is also a timescale between multi-decadal and annual. Jerry Meehl, who co-authored a paper
on the global warming slow-down with Fyfe and other researchers, described it this way:
. . . it's possible to have 15-year periods when the rate of global surface temperature increase slows compared to a previous 15-year period. Conversely, there can be a 15-year period when there is a more rapid rate of global surface temperature increase compared to a previous 15 year period.
El Niño and La Niña are phenomena that take place over the third timescale — the annual one. They typically last two years, give or take.
In the graph above, note how the size of the warming spike in the 1997/1998 El Niño is roughly the same size as the spike right now. This isn't surprising, since both El Niño episodes are probably in a tie for the strongest on record.
"El Niño events do cause an increase in the global mean temperature, usually within about a three- to seven- month lag," says Anthony Barnston, a climate and ENSO forecaster with the International Research Institute for Climate and Society at Columbia University.
Follow the heat
The current El Niño peaked in November — three months ago. So we are just now experiencing the strongest effects on global average temperature.
The warming occurs because a huge amount of heat energy pours out of the tropical Pacific ocean and into the atmosphere during an El Niño. Most of it is not the result of human activities, according to Barnston.
But why the lag? As NOAA's Deke Arndt puts it, "The reason the 'back end' of El Niños are often warmer is that the cumulative effect piles up during the course of the event."
So right now, we're experiencing the pile-up of El Niño heat energy.
But have a look at the graph again. Even though the El Niño spike in 1997/1998 is about as big in magnitude as what we're experiencing now, global temperatures today are way higher. That's because in all the years since 1998, long-term, human-induced warming has raised the baseline on which this year's El Niño spike is built.
Bending the curve
There are also more than just El Niño spikes represented in that graph. There are also downward La Niña spikes as well. (Not all of the downward fluctuations are La Niña's though.) Put enough of them together, and you'll bend the long-term trend down a bit, causing a slowing in global warming. Fyfe believes that may have been a major contributor to the slower rate of warming noted in the graph above. (But keep in mind that there is a good deal of scientific debate over the slowdown.) He also says it's quite possible that we're now coming out of it. In fact, we could be at the outset of a new trend. The future, Fyfe said, may bring “fewer La Niñas and more El Niños. "That may be where we’re heading with this recent super El Niño." But it's too soon to tell. Amidst all these variations on different timescales, Fyfe emphasizes that "one thing is almost fixed: the long term, human-caused warming. It is unequivocal, and it will carry on into the future. All these wiggles are simply superimposed on it."
Whither El Niño?
El Niño is expected to transition to neutral conditions by late spring in the Northern Hemisphere. Moreover, there's a 50/50 chance that a La Niña could take hold in the fall.
At NOAA's ENSO blog, Emily Becker noted this recently:
La Niña conditions have followed six of the ten moderate and strong El Niños since 1950, including two of the three previous strongest El Niños. However, this small number of cases means that it’s hard to make a very confident forecast based only on the previous events.
If a strong La Niña does ensue, "It would make it likely that 2017 will average cooler than 2015," said Columbia University's Anthony Barnston.
But what about the rest of this year? Have El Niño plus strong human-caused warming combined to make it a "shoo-in" for warmest year on record, as o
ne blogger put it recently?
That claim "is an unwarranted extreme statement," says Kevin Trenberth, a colleague of Meehl's at NCAR. That's because there are major uncertainties this far out. Moreover, with El Niño on the wane, heat is starting to be taken up by the oceans. This suggests 2016 could well turn out to be cooler than last year, Trenberth argues.
Deke Arndt of NOAA has a different perspective:
If my wife asked me if I thought 2016 was going to be the warmest year, I'd say 'yes' pretty confidently. However, as a public servant and as a scientist, we're a pretty conservative lot, and I don't think we'd say that until we were 100 percent sure. For reference, we started expressing confidence in 2015's first place status in late summer.
Two things are for sure. The first is that we will soon find out!
The second is this, from Jerry Meehl:
Human-caused warming due to increasing greenhouse gases can best be seen over the long term so that the internal variations average out, leaving the more steady increase of global temperatures over those longer time scales.
Keep that in mind when a cool spell inevitably kicks in, and you then hear people questioning long-term global warming.
| Correction: An earlier version of this story said February was the warmest month of all months on record. That was incorrect. It was the warmest February in records that go back to 1880. |