global warming

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Climate-wise, it was a full year of exceptional months

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Every month is above average —

Last June was the warmest June on record. Every month since has been similar.

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A red and orange background, with a thermometer representing extreme heat in the center.

June 2023 did not seem like an exceptional month at the time. It was the warmest June in the instrumental temperature record, but monthly records haven’t exactly been unusual in a period where the top 10 warmest years on record have all occurred within the last 15 years. And monthly records have often occurred in years that are otherwise unexceptional; at the time, the warmest July on record had occurred in 2019, a year that doesn’t stand out much from the rest of the past decade.

But July 2023 set another monthly record, easily eclipsing 2019’s high temperatures. Then August set yet another monthly record. And so has every single month since, a string of records that propelled 2023 to the warmest year since we started keeping track.

Yesterday, the European Union’s Copernicus Earth-monitoring service announced that we’ve now gone a full year where every single month has been the warmest version of that month since we’ve had enough instruments in place to track global temperatures.

History monthly temperatures show just how extreme the temperatures have been over the last year.

Enlarge / History monthly temperatures show just how extreme the temperatures have been over the last year.

As you can see from this graph, most years feature a mix of temperatures, some higher than average, some lower. Exceptionally high months tend to cluster, but those clusters also tend to be shorter than a full year.

In the Copernicus data, a similar year-long streak of records happened once before (recently, in 2015/2016). NASA, which uses slightly different data and methods, doesn’t show a similar streak in that earlier period. NASA hasn’t released its results for May’s temperatures yet—they’re expected in the next few days. But it’s very likely that NASA will also show a year-long streak of records.

Beyond records, the EU is highlighting the fact that the one-year period ending in May was 1.63° C above the average temperatures of the 1850–1900 period, which are used as a baseline for preindustrial temperatures. That’s notable because many countries have ostensibly pledged to try to keep temperatures from exceeding 1.5° above preindustrial conditions by the end of the century. While it’s likely that temperatures will drop below the target again at some point within the next few years, the new records suggest that we have a very limited amount of time before temperatures persistently exceed it.

For the first time on record, temperatures have held steadily in excess of 1.5º above the preindustrial average.

Enlarge / For the first time on record, temperatures have held steadily in excess of 1.5º above the preindustrial average.

Realistically, those plans involve overshooting the 1.5° C target by midcentury but using carbon capture technology to draw down greenhouse gas levels. Exceeding that target earlier will mean that we have more carbon dioxide to pull out of the atmosphere, using technology that hasn’t been demonstrated anywhere close to the scale that we’ll need. Plus, it’s unclear who will pay for the carbon removal.

The extremity of some of the monthly records—some months have come in a half-degree C above any earlier month—are also causing scientists to look for reasons. But so far, the field hasn’t come to a consensus regarding the sudden surge in temperature extremes.

Because it has been accompanied by significant warming of ocean temperatures, a lot of attention has focused on changes to pollution rules for international shipping, which are meant to reduce sulfur emissions. These went into effect recently and have cut down on the emission of aerosols by cargo vessels, reducing the amount of sunlight that’s reflected back to space.

That’s considered likely to be a partial contributor. A slight contribution may have also come from the Hunga Tonga eruption, which blasted significant amounts of water vapor into the upper atmosphere, though nowhere near enough to explain this warming. Beyond that, there are no obvious explanations for the recent warmth.

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Skyrocketing ocean temperatures have scientists scratching their heads

climate change, global warming, ocean temperatures, Science, syndication / /
beach scene with thermometer

jay_zynism via Getty

For nearly a year now, a bizarre heating event has been unfolding across the world’s oceans. In March 2023, global sea surface temperatures started shattering record daily highs and have stayed that way since.

You can see 2023 in the orange line below, the other gray lines being previous years. That solid black line is where we are so far in 2024—way, way above even 2023. While we’re nowhere near the Atlantic hurricane season yet—that runs from June 1 through the autumn—keep in mind that cyclones feed on warm ocean water, which could well stay anomalously hot in the coming months. Regardless, these surface temperature anomalies could be triggering major ecological problems already.

“In the tropical eastern Atlantic, it’s four months ahead of pace—it’s looking like it’s already June out there,” says Brian McNoldy, a hurricane researcher at the University of Miami. “It’s really getting to be strange that we’re just seeing the records break by this much, and for this long.”

You’ll notice from these graphs and maps that the temperature anomalies may be a degree or two Celsius warmer, which may not sound like much. But for the seas, it really is: Unlike land, which rapidly heats and cools as day turns to night and back again, it takes a lot to warm up an ocean that may be thousands of feet deep. So even an anomaly of mere fractions of a degree is significant. “To get into the two or three or four degrees, like it is in a few places, it’s pretty exceptional,” says McNoldy.

University of Maine

So what’s going on here? For one, the oceans have been steadily warming over the decades, absorbing something like 90 percent of the extra heat that humans have added to the atmosphere. “The oceans are our saviors, in a way,” says biological oceanographer Francisco Chavez of the Monterey Bay Aquarium Research Institute in California. “Things might be a lot worse in terms of climate impacts, because a lot of that heat is not only kept at the surface, it’s taken to depths.”

A major concern with such warm surface temperatures is the health of the ecosystems floating there: phytoplankton that bloom by soaking up the sun’s energy and the tiny zooplankton that feed on them. If temperatures get too high, certain species might suffer, shaking the foundations of the ocean food web.

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NASA scientist on 2023 temperatures: “We’re frankly astonished”

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Extremely unusual —

NASA, NOAA, and Berkeley Earth have released their takes on 2023’s record heat.

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A global projection map with warm areas shown in read, and color ones in blue. There is almost no blue.

Enlarge / Warming in 2023 was widespread.

Earlier this week, the European Union’s Earth science team came out with its analysis of 2023’s global temperatures, finding it was the warmest year on record to date. In an era of global warming, that’s not especially surprising. What was unusual was how 2023 set its record—every month from June on coming in far above any equivalent month in the past—and the size of the gap between 2023 and any previous year on record.

The Copernicus dataset used for that analysis isn’t the only one of the sort, and on Friday, Berkeley Earth, NASA, and the National Oceanic and Atmospheric Administration all released equivalent reports. And all of them largely agree with the EU’s: 2023 was a record, and an unusual one at that. So unusual that NASA’s chief climate scientist, Gavin Schmidt, introduced his look at 2023 by saying, “We’re frankly astonished.”

Despite the overlaps with the earlier analysis, each of the three new ones adds some details that flesh out what made last year so unusual.

Each of the three analyses uses slightly different methods to do things like fill in areas of the globe where records are sparse, and uses a different baseline. Berkeley Earth was the only team to do a comparison with pre-industrial temperatures, using a baseline of the 1850–1900 temperatures. Its analysis suggests that this is the first year to finish over 1.5° C above preindustrial temperatures.

Most countries have committed to an attempt to keep temperatures from consistently coming in above that point. So, at one year, we’re far from consistently failing our goals. But there’s every reason to expect that we’re going to see several more years exceeding this point before the decade is out. And that clearly means we have a very short timeframe before we get carbon emissions to drop, or we’ll commit to facing a difficult struggle to get temperatures back under this threshold by the end of the century.

Berkeley Earth also noted that the warming was extremely widespread. It estimates that nearly a third of the Earth’s population lived in a region that set a local heat record. And 77 nations saw 2023 set a national record.

Lots of factors converged on warming in 2023.

Enlarge / Lots of factors converged on warming in 2023.

The Berkeley team also had a nice graph laying out the influences of different factors on recent warming. Greenhouse gases are obviously the strongest and most consistent factor, but there are weaker short-term influences as well, such as the El Niño/La Niña oscillation and the solar cycle. Berkeley Earth and EU’s Copernicus also noted that an international agreement caused sulfur emissions from shipping to drop by about 85 percent in 2020, which would reduce the amount of sunlight scattered back out into space. Finally, like the EU team, they note the Hunga Tonga eruption.

An El Niño unlike any other

A shift from La Niño to El Niño conditions in the late spring is highlighted by everyone looking at this year, as El Niños tend to drive global temperatures upward. While it has the potential to develop into a strong El Niño in 2024, at the moment, it’s pretty mild. So why are we seeing record temperatures?

We’re not entirely sure. “The El Niño we’ve seen is not an exceptional one,” said NASA’s Schmidt. So, he reasoned, “Either this El Niño is different from all of them… or there are other factors going on.” But he was at a bit of a loss to identify the factors. He said that typically, there are a limited number of stories that you keep choosing from in order to explain a given year’s behavior. But, for 2023, none of them really fit.

Something very ominous happened to the North Atlantic last year.

Enlarge / Something very ominous happened to the North Atlantic last year.

Berkeley Earth had a great example of it in its graph of North Atlantic sea surface temperatures, which have been rising slowly for decades, until 2023 saw record temperatures with a freakishly large gap compared to anything previously on record. There’s nothing especially obvious to explain that.

Lurking in the background of all of this is climate scientist James Hansen’s argument that we’re about to enter a new regime of global warming, where temperatures increase at a much faster pace than they have until now. Most climate scientists don’t see compelling evidence for that yet. And, with El Niño conditions likely to prevail for much of 2024, we can expect a very hot year again, regardless of changing trends. So, it may take several more years to determine if 2023 was a one-off freak or a sign of new trends.

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First results are in: 2023 temperatures were stunningly warm

climate change, global warming, hot hot hot hot hot, Science, temperature records / /

Here we go again —

In the second half of the year, every month set a record.

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Image of a lot of squiggly lines moving from left to right across a graph, with one line in red standing far above the rest.

Enlarge / Month by month, 2023 stood far above the rest.

The confused wiggles on the graph above have a simple message: Most years, even years with record-high temperatures, have some months that aren’t especially unusual. Month to month, temperatures dip and rise, with the record years mostly being a matter of having fewer, shallower dips.

As the graph shows, last year was not at all like that. The first few months of the year were unusually warm. And then, starting in June, temperatures rose to record heights and simply stayed there. Every month after June set a new record for high temperatures for that month. So it’s not surprising that 2023 will enter the record books as far and away the warmest year on record.

The EU makes it official

Several different organizations maintain global temperature records; while they use slightly different methods, they tend to produce very similar numbers. So, over the next few weeks, you can expect each of these organizations to announce record temperatures (NASA and the National Oceanic and Atmospheric Administration will do so on Friday). On Tuesday, it was the European Union’s turn, via its Copernicus Earth-observation program.

Copernicus rates 2023 as being nearly 1.5° C above pre-industrial temperatures and about 0.17° C above 2016, the previous holder of the warmest year on record. The difference between 2023 and 2022 was the largest single-year change in the record as well, confirming that the amount of warming this past year was exceptional.

The 1.5° C landmark is significant because many countries have committed to trying to limit global warming to that mark. This doesn’t mean we’ve failed; the average temperature for the last decade is still below that. But it does highlight how little time we have left to act before we potentially experience more radical consequences of climate change.

The Copernicus analysis notes a couple of additional daily landmarks within the yearly record. It defines pre-industrial temperatures as those experienced between 1850–1900. The records from this period are sparse enough that, rather than daily temperature data, it’s been handled as a monthly average. So, the best Copernicus could do is compare 2023’s daily temperatures to the equivalent month in the pre-industrial record.

Even given that limitation, some of the results of this comparison were striking. For the first time ever, individual days in 2023 were 2.0° C above the preindustrial monthly average. Nearly half the days in 2023 were 1.5° C warmer than preindustrial records, and it was the first time every day was at least 1.0° C warmer.

Why so extreme?

The simplest answer is El Niño. The past few years have been spent in a reasonably strong La Niña, the cooler phase of the Southern Oscillation. But that started fading throughout the spring, and by mid-year, a weak El Niño had arrived. Normally, a relatively feeble El Niño like this would have a limited effect on global temperatures, and in any case, it would normally take some time for its effect to be felt in global temperatures.

Red means hot: last year saw a strong La Niña come to a close, with conditions shifting to a slight El Niño.

Red means hot: last year saw a strong La Niña come to a close, with conditions shifting to a slight El Niño.

But with temperatures poised near record levels to begin with, just a little push appeared to be all 2023 needed to soar to record heights.

Still, there are plenty of indications that the year wasn’t only the result of El Niño, which is a phenomenon that occurs in the tropical Pacific. For example, the North Atlantic, which is not directly connected to the Tropical Pacific, experienced exceptionally warm sea surface temperatures over the second half of the year.

Copernicus suggests that several additional, weak factors could have contributed to the year’s warmth. These include lower emissions of cooling aerosols from shipping, a peak in the solar cycle, and high levels of water vapor in the stratosphere due to the eruption of the Hunga Tonga volcano. On its own, the impact of any of these would likely be minimal. In combination with the weak El Niño and the continued emission of greenhouse gasses, however, they might have enhanced what was already an exceptionally warm year.

The announcement of 2023’s warmth comes only months after a set of UN climate negotiations that many have derided as lacking the sort of urgency the record might have provided. Instead, Copernicus notes that carbon dioxide and methane emissions increased last year.

Listing image by Marco Bottigelli

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