Bolstered by a record-challenging El Niño event, which redistributed excess heat from the tropical Pacific Ocean around the planet, temperatures during each of the first eight months of the year hit record highs.

As El Niño waned and was replaced by La Niña this fall, and tropical Pacific Ocean temperatures cooled, temperatures stopped setting record highs, but remained well above normal.

The record-setting global temperatures for 2016 fit into a long-term warming trend fueled by rising greenhouse gas concentrations resulting from human activities. It was the 40th straight year in which global temperatures have been above the 20th century average.

Including 2016, 16 of the 17 warmest years in NOAA’s 137-year climate record have occurred since 2000.

AD

AD

The past year brought some astonishing warm-weather extremes. In July, Mitribah, Kuwait, soared to a blistering 129.2 degrees, the hottest temperature ever reliably measured in the Eastern Hemisphere. In November and December, Arctic temperatures spiked 30 to 35 degrees above normal on two separate occasions, stunning climate scientists.

I queried 15 climate scientists about what they feel 2016’s warmth signifies.

The great majority said 2016 offers further evidence that climate warming is real, driven by human activities, and is leading to consequential changes in extreme weather. Several urged action on the part of decision-makers.

A minority of respondents replied the global average surface temperature is limited as a metric and pointed to satellite temperatures which, while warming, show a less dramatic rise.

AD

AD

None questioned that 2016 was the warmest year in modern records.

Their answers follow, some edited for length . ..

Reaction: ‘We are driving into a new unknown’

The warming is consistent with observations of greenhouse gasses, climate model projections, and 150 years of known physics.

Politicians and policymakers can’t say they weren’t warned.

We are heading into a new unknown. It’s like driving on a new road, at night, at speed, without headlights, and looking only through the rearview mirror. Hope we don’t meet Thelma and Louise along the way.

The question remains: What will it take to convert a vague sense of awareness of the warming climate into sustained, deliberate, and bipartisan action to decarbonize the global energy system?

AD

— David Titley, director, Center for Solutions to Weather and Climate Risk, Penn State University

Reaction: Record is a ‘big red flag’

I fear this news will become like the car alarm at the mall. It just keeps happening but no one pays attention. The fact that we are consistently seeing some of the warmest years on record is a big red flag.

AD

Yes, the climate changes naturally. … Yes, climate scientists know about urban heat islands, El Niño, and other things that modify temperature. …

But no, these oft-cited retorts don’t change the fact that our climate is changing, in part, due to some human steroid on top of that natural variability, and it is affecting “kitchen table” issues: agricultural yields, national security, public health, water supply, insurance claims from disasters, and so forth.

AD

As startling as the 2016 record is (and it happened in a non-El Niño year), the narrative has to shift to the ways that Earth has started to respond. Some past projections have been conservative compared to what is actually happening.

As scientists, we are obligated to communicate the science so that people understand that the concern is about shared values, impacts to society and solutions rather than some particular interest or ideology. I have nothing at stake for being right on this. In fact, I am happy to be wrong for my kids’ sake.

AD

— Marshall Shepherd, director of Atmospheric Sciences Program, University of Georgia

Like frogs in boiling water, record-breaking years seem normal to many of us, now. And just like a frog, the time for us to heed these warnings is now.

AD

It’s true that some amount of future change is inevitable, the result of all carbon we’ve spewed into the atmosphere over the past hundred years and more. But today, our future is in our hands and we have a serious choice to make.

Are we going to do our best to roll back the clock, prop up and support dirty energy, keep it going until its last gasp?

Or will we join the rest of the world — led by China and India — in the new clean energy “moon race,” to a world where we’re powered by wind, sun and tides that don’t pollute our air and will never run out on us? I know which one I’d choose.

AD

— Katharine Hayhoe, professor of atmospheric science, Texas Tech

AD

It’s easy to become immune to the news that we have a new winner in the race for the warmest year ever recorded. But this was no photo finish — 2016 shattered the record from 2015, which shattered the record from 2014. It’s a dizzying string of records even for the most seasoned climate scientist.

This is a not-so-friendly reminder from Planet Earth that we are wasting precious time in the battle against man-made climate change. The solutions are at our fingertips, and can be implemented while spurring economic growth and jobs creation, as demonstrated at many levels across the nation.

— Kim Cobb, professor of atmospheric science, Georgia Institute of Technology

AD

Reaction: 2016 ‘should tip the balance’ for those unconvinced about human-caused warming

If there are still any people out there who remain unpersuaded by past science and data of climate change, the record high temperatures of 2016 should tip the balance.

AD

With the high temperatures of 2016, the evidence for human-induced global warming is now so strong that no sensible person can deny a human role in these temperature increases.

We can argue about what we should or should not do with this knowledge, but the argument is over: Greenhouse gas emissions cause our climate to get hotter.

— Ken Caldeira, climate scientist, Carnegie Institution for Science

AD

For the first time in recorded history, we have now had three consecutive record-warm years for both the globe and the Northern Hemisphere. The likelihood of this having happened in the absence of human-caused global warming is minimal.

As we have shown in previously published work, the spate of record-warm years that we have seen in the 21st century can only be explained by human-caused climate change. The effect of human activity on our climate is no longer subtle. It’s plain as day, as are the impacts — in the form of record floods, droughts, superstorms and wildfires — that it is having on us and our planet.

AD

— Michael Mann, director of Earth System Science Center, Penn State University

The box of ammunition used by those who try to spread misinformation about the influences of humans on the climate system is rapidly dwindling. 2016 not only reached a new high for global temperature, it also shattered records for Arctic high temperatures, low sea ice in seven of 12 months, and Arctic amplification, to name only a few.

All of these events have long been predicted in response to increasing greenhouse gases, but they’re happening faster than anticipated.

What does it mean for society? Ongoing sea-level rise. More extreme weather events. Increasingly acidic oceans.

Can it be stopped? No.

Can it be slowed down? Certainly, but it will take a concerted effort by all of us on many fronts, and we cannot wait any longer.

AD

— Jennifer Francis, research professor, Rutgers University

Reaction: ‘Focus on the long-term trends’

The frequent breaking of previous high temperature records is consistent with the general warming trend, but it would be a mistake to focus on one particular metric. There will no doubt be stretches of many years ahead of us where such records are not broken.

Rather, one must focus on the long-term trends. Here, the clear signals of long-term planetary warming, rising sea levels, retreating alpine glaciers, and thinning and shrinking arctic sea ice are all in line with physics-based predictions of the response of our planet to increasing greenhouse gases. They are the canaries-in-the-mine that warn us that we are putting our descendants at risk.

— Kerry Emanuel, professor of atmospheric sciences, Massachusetts Institute of Technology

Some years will be warmer and some years will be cooler than others, but as long as human-produced greenhouse gases continue to increase in the atmosphere from the burning of fossil fuels, the long-term global temperature trend averaged over multiple decades will be upward.

— Gerald Meehl, senior scientist, National Center for Atmospheric Research

Reaction: 2016 record heat supercharged extreme weather

The weather experienced around the world is a combination of natural variability plus global warming from human influences. When the natural variability, in this case from El Niño, is going in the same direction as global warming, as in the past two years, we break records.

The conditions experienced in the past year has had some unusual and unique aspects to it because of the super-El Niño event, but it shows us the sort of thing that will become routine in a decade or so. This includes record numbers and record intensity of hurricanes and typhoons, record wide spread heavy rains and flooding (think Houston, Louisiana, the Carolinas (Hurricane Matthew), and now California), record drought, heat waves and wild fires, and increasing inundations in coastal regions from rising sea level. The costs from the added boost from global warming are in the tens of billions of dollars each year.

— Kevin Trenberth, climate scientist, National Center for Atmospheric Research

For me, it is the contribution (not necessarily cause) of this increase in temperature to extreme weather events that are more relatable to society and also most important for socioeconomic impacts.

For years, scientists have sought and studied the increased variability and shift in the probabilities of extreme weather that models indicate would happen as a result of a warmer world.

2016 gave us evidence that this may indeed be true. Some examples include: (1) extreme rainfall and flooding in the U.S. (e.g., Houston, Ellicott City, Louisiana), (2) destructive wildfires in Canada (caused by excessive heat and drought); (3) extremely early tropical activity (Pali in the central Pacific and Alex in the Atlantic); and (4) unbelievable warmth in the Arctic regions, including Alaska.

The record warmth’s effects are to load the dice for increased chances and magnitude of future extreme weather events. We (society in general) have contributed to this record warmth and are committed to further warmth over the next few decades. Thus, the wager is on the table, and we now await the dice rolls.

— Jason Furtado, assistant professor of meteorology, University of Oklahoma

Reaction: ‘This is no surprise’, but we have a lot to learn

As human-activities continue to put a pressure on the climate to warm, we will continue to see record global temperatures being periodically set under the current climate regime — especially when natural variability is acting to contribute a warming influence as well (as was the case in 2016). This is no surprise.

The question is not whether greenhouse gas emissions act to warm the climate, but rather, how large is their impact and in what manner is it manifest. It’s these latter questions, hand in hand with a better understanding of the complexities and intricacies of natural variability, that demand our scientific focus.

Observations from the last several decades indicate that we still have a lot to learn both in terms of our understanding of the observed history, as well as what changes can best be anticipated to lie ahead.

— Chip Knappenberger, assistant director, Center for the Study of Science, Cato Institute

Reaction: Global surface temperature is a flawed metric and not ideal for monitoring global warming

Unfortunately, the surface temperature analysis contains several uncertainties and systematic biases when used to diagnose global warming. One of them is with respect to land minimum temperatures over land. Rather than measuring changes in heat content through depth in the atmosphere, even slight changes in vertical mixing of heat (even with no net heating) can produce warmer minimum temperatures.

Ocean heat content changes is, by far, the much better way to assess global warming. Ocean heat changes can be much more directly related to the radiative imbalance at the top of our atmosphere.

— Roger Pielke Sr., senior research scientist, University of Colorado-Boulder

Reaction: Satellite-measured atmospheric temperatures show less-pronounced warming

The NOAA report refers to surface temperatures. However, the bulk atmospheric temperature is another important climate variable for people to know about. It too shows that 2016 was the warmest, edging out 1998 for first place. As in 1998, a strong El Niño was the main cause.

As the world cools now, the global atmospheric temperature change from February to December has been over one degree. 2017 will be cooler than 2016.

Overall, the atmospheric warming since 1979 has been about 0.25 degrees per decade, bolstered somewhat by two cold episodes caused by volcanic events in 1982 and 1991. Had these volcanoes not occurred, the upward trend would still be there, but smaller.

The atmospheric warming, while clearly present, is quite a bit less than anticipated from climate model projections which attempt to tell us how extra greenhouse gases affected the climate during the past 38 years.

— John Christy, professor of atmospheric science, University of Alabama in Huntsville

2015 and 2016 were years with a very strong El Niño. Similar to the previous very strong El Niño in 1997-98, a spike in surface and atmospheric temperatures was observed.

According to surface temperature data sets, 2016 is the warmest year in the record (approximately the last 150 years). However, examination of the satellite data record of atmospheric temperatures, 2016 was only 0.02 degrees Celsius warmer than 1998 — a difference that is not statistically significant.

Understanding the difference in trends between the surface temperature data sets and the satellite data sets of atmospheric temperature remains an outstanding challenge for scientists.

What is the significance of the ‘warmest year’? Following the 1998 peak in warming, temperatures dropped substantially for the next several years. In 2016, we are seeing substantial drop in temperature anomalies following the warm peak in February. It will be another five years before we have perspective on this recent spike in temperatures.