The much-advertised, long-lasting Arctic outbreak with ties to the polar vortex will be accompanied by a significant winter storm over the weekend.

Threat level: The storm is set to deliver upwards of a foot of snow in parts of the Plains, Midwest and Appalachians, with somewhat lower amounts for Washington, D.C., Baltimore and potentially Philadelphia as well.

• Multiple states are forecast to see a thick layer of ice build up that could lead to widespread, enduring power outages. The ice zone will stretch from parts of Nebraska eastward to Kentucky and West Virginia.
• "Treacherous travel conditions are expected with power outages likely in areas that receive over a quarter-inch of ice accumulation," the National Weather Service said via X on Thursday evening.

By the numbers: As the storm exits late this weekend into early next week, Arctic air will be drawn southward out of Canada, sending temperatures plunging below 0°F, across the northern Plains and Upper Midwest.

• Temperatures may drop below freezing as far south as the Gulf Coast next week.
• During the next seven days — week one of an enduring cold snap that could stretch through Inauguration Day — 234 million people in at least 40 states could see temperatures at or below 32°F, according to WeatherBell Analytics.
• Some cities, including Washington, may not see high temperatures rise much above the mid-30s for several days in a row.
• For most, the cold will be noteworthy for its duration rather than its severity, as computer models have backed off from earlier projections of historically low temperatures.

For many U.S. residents, this event will bring the coldest air in several years, following a few unusually mild winters.

Context: This Arctic outbreak is tied in part to a stretching of the polar vortex, which is an area of low pressure in the upper atmosphere, and the air circulation around it, that forms each winter in the Northern Hemisphere.

• Other weather features, such as a strong high pressure area off the West Coast and Alaska, and another so-called "Blocking High" over Greenland, have opened the Arctic's refrigerator door.
• Some scientists have published studies linking rapid, human-caused Arctic climate change with shifts in the polar vortex, though this is part of an active debate.

Zoom out: The colder than average start to January across much of the U.S. is causing natural gas prices to spike.

• At the same time, Ukraine is limiting the transport of gas to Europe via Russia, which is raising prices in Europe.

An Arctic outbreak featuring punishing cold weather is beginning across much of the U.S. at the same time that Europe prepares for plunging temperatures.

Why it matters: About three weeks of cold east of the Rocky Mountains — potentially accompanied by major winter storms — will boost natural gas prices, pose a risk of power outages and disrupt travel.

Threat level: The cold will hit the U.S. in waves, with the first moving in this week, a second early next week on the heels of a significant Plains to Mid-Atlantic winter storm, and additional ones after that.

• Each push is likely to be colder than the one preceding it.
• By early next week, daily high temperatures may be stuck in the single digits across parts of the Midwest, with the possibility of temperatures dropping to 32°F all the way to the Gulf Coast.
• In the East, highs in Washington, D.C., may not get much above freezing for several days in a row during the Jan. 4-10 period, with the possibility of even colder weather arriving after that.
• Before this event ends, residents of at least 30 states will have been affected. Millions will see increased heating bills as natural gas prices spike, and some could be affected by rolling blackouts during the coldest periods.

Zoom in: The polar vortex is an area of low pressure that exists over the Arctic at the upper levels of the atmosphere, in the stratosphere, during winter.

• Strong winds circulate counterclockwise around this low pressure area, and build up and trap some of the coldest air in the Northern Hemisphere across the Arctic.
• When these strong winds slacken, parts of the polar vortex can detach and meander southward, bringing ultra-cold air to southern Canada, the U.S. and Europe.
• This occurred back in the winter of 2013-14, but this new event is distinct.
• Instead, the stratospheric polar vortex is becoming "stretched" from north to south across the North Pole.

Between the lines: The stretched vortex may be setting in motion a complicated board of atmospheric chess pieces that include a strong area of high pressure over Greenland.

• That stops storms from heading out to sea and directs cold weather in the eastern United States.
• This setup, known as a Greenland Block, along with other, broader patterns of air pressure over the Arctic and North Atlantic, also tends to favor unusually cold conditions in northern Europe.
• The Greenland Block is combining with a high pressure area stretching from California to Alaska to promote air to flow from Siberia, across the pole, and southward toward the continental U.S.

This cross-polar air flow can translate to temperatures of about 20°F to 30°F below average for this time of year.

What they're saying: "It is the stretching of the polar vortex that allows colder temperatures normally confined to the Arctic to spread much further south of normal," said Judah Cohen, a meteorologist at AER who researches Arctic climate change and the polar vortex, via email.

Zoom out: Uncertainty remains about how cold the U.S. will get, along with the timing and occurrence of any major storms beyond the first one this weekend.

• Some computer models have backed off initial predictions of truly historic cold that would rival outbreaks dating back several years, if not longer.
• The possibility still exists of a lobe, or piece, of the tropospheric polar vortex diving south from Canada and into the South and Southeast, sending temperatures plunging well below the levels currently forecast.
• This would lead to extremely cold conditions, most likely during the Jan. 9-Jan. 14 time frame.
• In such a scenario, some state power grids could struggle to keep up with demand as power plants deal with cold weather-induced reductions in generation, as occurred in Texas in 2021.

Context: Studies suggest polar vortex shifts may be more likely due to human-caused climate change, but this is an area of active research.

• Cohen, for example, has published research tying rapid, human-induced Arctic warming to a chain of events including disappearing fall sea ice concentrations in the Barents and Kara seas.

Friction point: But scientists are somewhat at odds over the extent to which shifts in the orientation of the polar vortex are driving this particular cold snap.

• Cohen points to the stretching polar vortex and long-term climate change as significant players.
• But Amy Butler, an atmospheric scientist at NOAA's Chemical Sciences Laboratory, told Axios she sees other factors as more significant drivers right now.
• "In this case, I'm not convinced that the polar vortex stretching is driving the cold," Butler told Axios via email.
• "To me, it seems more likely that the persistent blocking high over Greenland over the next few weeks, along with a building ridge off the coast of California, are working in concert to drive cold into the eastern US for an extended period of time," she said.

The bottom line: Regardless of the causal chain, extreme cold is on the way for more than 150 million Americans.

Areas of the U.S., including the South and Southeast, are likely to see frigid air that could break records by mid-month, along with potentially blockbuster winter storms.

Threat level: Pieces of the polar vortex are projected to swirl southward out of northern Canada and into parts of the U.S. during early and mid-January.

• Accompanying the cold will be the threat of multiple significant winter storms.
• The weather pattern features a strong high pressure area over Greenland and a deep dip, or trough, in the jet stream across the East.
• This setup uniquely favorable for producing potentially significant snowstorms for the Southeast, Mid-Atlantic or Northeast.

Between the lines: The cold itself could present infrastructure challenges, depending on where the most frigid air sets up.

• The most extreme scenarios may pose risks of power outages in some states, but there is still considerable uncertainty about the magnitude of the cold and hardest hit areas.
• There are some broad outlines that are known this far out, however. Computer models have been signaling for days that the South, including areas from Texas to Alabama, as well as Southeast and Appalachians may see the brunt of the coldest air.

Overnight low temperatures below 0°F are possible in these areas during the coldest periods.

When the coldest weather may hit

The big picture: At least two rounds of extreme cold and storm threats are slated for the Midwest and Eastern U.S.

• The first should take place soon after New Year's, though this storm may produce a wintry mix rather than mainly snow across New England.
• Next up is the time period that meteorologists are eyeing closely for potentially significant East Coast winter storms, between about Jan. 6 through the 14th.
• Even without a storm or two, extreme cold will be on the move, crossing the U.S.-Canadian border and diving all the way to the Gulf Coast.
• The coldest air of the season so far and dangerous wind chills are expected across much of the Southeast from Jan. 7-13.

"Below freezing temperatures are possible as far south as the Gulf Coast and much of the Florida Peninsula," the National Weather Service's Climate Prediction Center warns. "Impacts to highly sensitive citrus crops are possible."

• Modeling and NOAA projections show that if the cold were to reach its full potential, temperatures may plunge to 25°F to 35°F degrees below average for this time of year during mid-January.

pic.twitter.com/TmeiACrRC0

— NWS Climate Prediction Center (@NWSCPC) December 30, 2024

Zoom in: The polar vortex is an area of low pressure that exists over the Arctic at the upper levels of the atmosphere, in the stratosphere, during wintertime.

• Strong winds circulate counterclockwise around this low pressure area, and build up and trap some of the coldest air in the Northern Hemisphere across the Arctic.

Yes, but: When these strong winds slacken, parts of the polar vortex can detach and meander southward, bringing ultra-cold air to southern Canada, the U.S. and Europe.

• This most famously occurred during the winter of 2013-2014, and some computer models show this is likely to happen again in mid-January, with a piece of the polar vortex sliding from Minnesota to the Southeast.
• During this event, the stratospheric polar vortex is forecast to be "stretched" from north-to-south across the North Pole, rather than oriented as a tight circle.
• This could favor unusually cold weather and winter storms in the East, but it is not a classic setup for the coldest-possible event, according to meteorologist Judah Cohen of AER, a Verisk company.

Context: Numerous studies suggest polar vortex excursions may become more likely in a warming world, but this is still an area of active research.

• One such study, published in the journal Environmental Research: Climate, on Dec. 11, found that as global average temperatures continue to increase, due mainly to human emissions of greenhouse gases, cold air outbreaks in the midlatitudes could become more frequent.
• This study is unique since it puts forward a hypothesis of how such extreme cold events are becoming more likely, rather than just finding statistical correlations.

The bottom line: Extreme cold and snowstorms, capable of producing billions in economic impacts, are on the way for much of the U.S..

Editor's note: This article was corrected to show that, in the northern hemisphere, winds circulate counterclockwise (not clockwise) around low pressure areas.

A severe weather outbreak, including long-lasting and intense tornadoes, is affecting a swath of the South on Saturday into Saturday night.

Threat level: The Storm Prediction Center has issued a rare "moderate risk" outlook, or level 4 out of 5 on the threat scale, for portions of Mississippi and Louisiana, indicating confidence in a potentially significant outbreak.

• Already, long-lasting, damaging tornadoes have struck southeastern Texas, including coastal sections of Harris County and near Port Arthur.
• Some of these circulations have persisted for more than 60 miles, with tornadoes on the ground for a significant portion of that distance.
• The text of the tornado warnings has included enhanced language, indicative of the threat level involved: "This is a particularly dangerous situation! Take Cover Now!" the NWS forecast office in Lake Charles, La. warned as one tornado sped towards southeastern sections of Port Arthur.
• Other tornadoes have been reported, along with damaging straight-line winds, hail and flash flooding in parts of Mississippi, Louisiana and Alabama.

The big picture: The NWS issued a high-end "Particularly Dangerous Situation" tornado watch for southeastern Arkansas, central and southwestern Louisiana, southwestern Mississippi and southeastern Texas until 9pm local time. The watch states the expectation for "numerous tornadoes" along with a few intense tornadoes of EF-2 strength or greater.

• This outbreak follows severe weather earlier this week in Texas, and is the result of a deep dip, or trough, in the jet stream that is pulling moisture from the Gulf of Mexico northward.
• The storm forming in eastern Texas and northern Louisiana is forecast to move northeast while intensifying, eventually making its way into the Ohio Valley, Northeast and Quebec by early next week.

At lower levels of the atmosphere, there is ample wind shear (winds that blow at different speeds and/or directions at different altitudes) present to support long-lasting, rotating thunderstorms that can produce an array of extreme weather hazards, including tornadoes.

Zoom in: About 2 million people live in the moderate risk zone, which includes the cities of Jackson and Hattiesburg, Mississippi, along with Alexandria, Louisiana.

• About 4.6 million people reside in an area designated as being under "enhanced risk" of severe weather, including the cities of Baton Rouge, Shreveport, Louisiana and Mobile, Lafayette and Tuscaloosa, Alabama.
• This region is in a level 3 out of 5 on the risk scale.
• New Orleans is in the "slight risk" zone, indicating a lower threat there, though a heavy rains and thunderstorms are still expected in the Big Easy Saturday afternoon into Saturday night.

Context: Although spring and summer are typically thought of as tornado season, the South and Southeast tends to see severe weather during the winter as well, since that is when strong storm systems form near the Gulf Coast.

• This yields collisions between warm, humid air to the south and cold, dry air to the north.
• Climate change affects the conditions in which thunderstorms form and may be leading to larger outbreaks, though fewer of them, by adding to the instability of the atmosphere while simultaneously cutting back on wind shear.
• However, when both ingredients are present in enough abundance, major outbreaks can occur, studies show.

Editor's note: This story has been updated with the latest conditions.

2024 will be the second straight "hottest year" on record. But it wasn't supposed to be as hot as it was, coming in far ahead of 2023's alarming global temperature spike.

Threat level: For reasons climate scientists don't yet fully understand, 2024 is likely to temporarily eclipse the Paris Agreement's 1.5°C temperature target, when compared to preindustrial levels.

Between the lines: Earth's extreme heat can be partially explained by human-caused warming, the lingering effects of a strong El Niño event, and other factors. But the truth is, researchers aren't completely sure why the planet's fever has increased faster than anticipated.

• The unsettling possibility in play is that climate change is accelerating, which implies that tipping points, such as the shutdown of major ocean currents, are closer than once thought.

The latest: People worldwide suffered an average of 41 extra days of dangerous heat this year because of climate change, according to a report out Friday from scientists at World Weather Attribution and Climate Central.

The big picture: Millions of people endured stifling heat this year.

• Northern California and Death Valley baked. Sizzling daytime temperatures scorched Mexico and Central America. Heat endangered already vulnerable children in West Africa.
• Skyrocketing southern European temperatures forced Greece to close the Acropolis. In South and Southeast Asian countries, heat forced school closures. Earth experienced some of the hottest days ever measured and its hottest-yet summer, with a 13-month heat streak that just barely broke.

Court cases involving climate change are taking on increased importance with global efforts proceeding far slower than the climate is warming and national policy subject to whiplash.

Why it matters: Cases under deliberation at the Hague, newly decided in Montana and in process elsewhere show that courts are increasingly receptive to the duty of governments and corporations to limit emissions.

What they're saying: The surge in cases is a symptom of those entities' failures to act on climate, says Patrick Parenteau of the Vermont Law School.

• "The courts aren't going to save us, but when the political process is failing, that's where you turn to," he told Axios in an interview.
• Questions remain about the practical implications of court rulings, and whether they can truly cut planet-warming greenhouse gas emissions, are more symbolic measures — or lie somewhere in between.

The big picture: In the U.S., cities, states and citizens have pursued legal action to force the government and fossil fuel industry to take responsibility for causing global warming and enact new emissions curbs or provide compensation for climate change-related damage.

• Many of these lawsuits have been quashed on jurisdictional grounds or for other reasons.
• This month, though, has brought two major developments that may mark a turning point in climate change-related legal battles.
• At the International Court of Justice at the Hague, the tiny island nation of Vanuatu brought a case seeking an advisory opinion on the obligations that countries have to combat global warming.
• A rare two weeks of public testimony has concluded, but not before fractures between industrialized and developing nations were laid bare.

The intrigue: The U.S. and Russia, among other nations, argued that human rights law shouldn't apply.

• They want any advisory opinion to stick to obligations under climate pacts like the Paris Agreement, while developing nations argued that major polluters are violating more vulnerable nations' basic human rights.

Then, on Wednesday, a 6-1 majority on the Montana Supreme Court backed a lower court's decision that the state's fossil fuel policies and lack of action to curb global warming violated young people's constitutional right to a clean environment.

• The decision in Held v. Montana also directs state agencies to consider greenhouse gas emissions from proposed development projects.
• Montana is a significant producer of coal, the most carbon-intensive fossil fuel. It's also an increasingly important state for mining minerals used in renewable energy sources.

State of play: The Montana decision is especially significant since several other states have similar constitutional provisions, potentially leading to a domino effect of state legal actions to force certain steps to be taken.

• Illinois, Pennsylvania, New York, Massachusetts and Rhode Island have similar constitutional provisions, and efforts are underway to enact language in other states, said Michael Gerrard, a climate change law scholar at Columbia University.
• In Hawaii, a case with similarities to Montana's was settled on favorable terms to the plaintiffs, he noted. The state committed to decarbonizing its transportation system, among other steps.

Zoom out: Gerrard said legal action on climate change can be effective in settings in which courts are independent and influential.

• "We're certainly seeing a tremendous growth of climate litigation," he told Axios in an interview.
• He noted cases in the Netherlands that spurred governmental action and a Supreme Court ruling in Nepal that resulted in Parliament passing a climate law.
• "The courts are having an influence in some cases," Gerrard said.

Yes, but: Some court victories for climate activists have turned into setbacks on appeal, however.

• A 2021 ruling by a Dutch district court directing the oil and gas giant Shell to cut its emissions by 45% by 2030 relative to 2019 levels was overturned in November.
• Between the 2021 decision and the appeals court's actions this year, Shell made more investments in its oil and gas production while deemphasizing its renewables business, in an effort to benefit investors.
• The company also moved its headquarters out of the Netherlands, though that was for multiple reasons including tax considerations.

Between the lines: This raises the question of whether such cases make a meaningful difference for what really matters: greenhouse gas emissions.

• In the Shell case, that answer is clearly no.
• And even in the Montana case — which many activists hailed as a breakthrough decision — the only relief the state Supreme Court granted was to ensure that planet-warming emissions would be incorporated into project planning.

The bottom line: Neither the political process, nor the courts, are successfully limiting climate change and its many damaging effects.

Just a month before President-elect Trump's inauguration, the Biden administration on Thursday put out new and more far-reaching national greenhouse gas reduction goals.

Why it matters: Even if, as expected, Trump withdraws the U.S. from the Paris Agreement for the second time and rolls back emissions regulations, the new targets were devised with some of his likely policies incorporated.

Zoom in: The U.S. Nationally Determined Contribution (NDC) — the official name for the non-binding climate goals under Paris — sends a signal to other countries ahead of Trump's arrival.

• In particular, it puts pressure on China — the world's top emitter — to issue more aggressive targets that include methane and other warming contributors by the UN deadline.

The big picture: "American industry will keep inventing and keep investing. State, local, and tribal governments will keep stepping up," President Biden said in a video message released Thursday morning.

• Senior administration officials said the numbers they are aiming for — to slash greenhouse gas emissions economy-wide by 61% to 66% below 2005 levels by 2035 — can be achieved with aggressive state, local and regional actions.
• The proposal includes a methane emissions reduction target of 35% below 2005 levels by 2035.
• During Trump's first term, governors and mayors helped put downward pressure on emissions while the executive branch favored more fossil fuel development and fewer regulations.
• "Sub-national leaders in the United States can continue to show the world that American climate leadership is determined by so much more than whoever sits in the Oval Office," top U.S. climate diplomat John Podesta told reporters in a Wednesday press call.

But the new targets could be imperiled if congressional Republicans and the Trump White House succeed in reversing most of the emissions-cutting laws and regulations enacted during the past four years.

• That includes a broad repeal of the Biden climate law, also known as the Inflation Reduction Act.
• The Paris Agreement requires that countries submit new NDCs by mid-February.

Yes, but: The targets come even though the U.S. isn't yet on track to meet its current guideposts — laid out in 2021 — of cutting emissions by 50% to 52% below 2005 levels by 2030.

• According to calculations by the Rhodium Group, the U.S. is currently on course to cut emissions by 32% to 43% relative to 2005 levels by 2030.
• This could drop considerably, though, to 23% to 34% below 2005 levels if EPA emissions regulations are repealed along with other measures, potentially including a whole-scale repeal of the sweeping Biden climate law.
• According to Podesta, the new goals would put the country on a linear, or slightly steeper, path to achieving its longer-term objective of net zero emissions by 2050.

By the numbers: Independent research shows the administration's target ranges are within reach but would be more difficult to achieve in the face of comprehensive rollbacks at the federal level.

• In fact, additional actions would be needed to achieve the previous goals for 2030.
• According to Rhodium's analysis, for example, the U.S. is headed for a 38% to 56% reduction in greenhouse gas emissions below 2005 levels by 2035. But this could be reduced to between 24% to 40%, depending on federal policies.
• The group's calculations of the impacts of rollbacks and repeals show that federal action alone could add 1 billion tons of CO2 emissions. For comparison, last year the U.S. emitted 4.9 billion tons of CO2 from burning fossil fuels, such as gas, coal and oil.

Separate research from the University of Maryland found that "strong leadership" from non-federal actors could get the U.S. to between a 54% to 62% emissions reduction target relative to 2005 levels by 2035.

• This built on previous work comparing emissions scenarios that incorporated various non-federal and national actions.

Zoom out: The details on the new U.S. goals come at a time when fundamental questions are being asked about whether the UN negotiations process is still able to address mounting environmental challenges.

• Recent summits ranging from COP29 in Azerbaijan to negotiations on a plastics treaty in Korea and biodiversity in Colombia have ended in divisive agreements or deadlocked.
• Meanwhile, governments that took up the mantle of climate leadership during Trump's first term, such as Germany, France and Canada, are enmeshed in political instability.

What they're saying: "The value of submitting the NDC is to send a clear signal internationally about this administration's commitment to the Paris Agreement and especially to set a strong benchmark for U.S. states, cities and other stakeholders to pursue," David Waskow of the World Resources Institute told Axios.

The bottom line: The new U.S. targets lie somewhere between symbolic and serious, given the potential for Trump to affect emissions more radically than anticipated.

Winters are rapidly warming across the Northern Hemisphere because of human emissions of greenhouse gases from burning fossil fuels, a new report shows.

• This is now being seen in many more days with temperatures above freezing.

Why it matters: More warm winter days means fewer opportunities for winter recreation and can have knock-on effects on water supplies during the following warm season.

The big picture: Climate change has added at least an additional week of winter days with temperatures above freezing each year during the past decade in more than one-third of 123 countries analyzed, researchers found.

• The analysis compares recent trends with what would be expected to occur in a world without increasing amounts of heat-trapping greenhouse gases.

Zoom in: While previous analyses have looked at winter warming rates in the U.S., the new work — from the climate science and communications group Climate Central — covers the entire Northern Hemisphere.

• It specifically zeroes in on the increase in the number of days during which temperatures remain above freezing during meteorological winter, which spans from December through February.

What's especially unique about this report is the attribution aspect.

• Rather than only describing trends, the authors used published research and an in-house tool known as the Climate Shift Index to pin the increase in warm winter days directly to climate change.
• About 44% of cities analyzed saw at least an additional week's worth of days above freezing each year due to human-caused climate change, the report found.
• The cities with the greatest increase in warm winter days are located in Europe, which is the world's fastest-warming continent, and Asia.
• Fuji, Japan, Khujand, Tajikistan and Turin, Italy each have gained 30 or more days during winter with above freezing temperatures annually during the past decade, owing to human-caused climate change, the analysis found.

The intrigue: In the U.S., 28 states and 63% of cities analyzed experienced at least a week of what the group terms "lost winter days" each year during the past decade due to climate change.

• Boston has gained 14 winter days with above freezing temperatures each year during the past decade from climate change, the report found.
• New York City has gained 13 lost winter days each year during the past decade, while Chicago and Milwaukee have picked up 12 such days thanks to climate change, and Washington, D.C., has gained 11, the report found.

The Climate Shift Index (CSI) is based on peer-reviewed methods, though the new analysis itself has not been peer reviewed.

• The CSI tool allows climate scientists and the public to see how long-term, human-caused climate change is manifesting itself in present-day weather conditions, on land and at sea.
• The trends the new analysis depicts match other data on winter temperature trends, which show that in many places, the cold season is warming faster than other times of the year.

By the numbers: Europe stands out as the global winter hot spot, with Denmark, Estonia, Latvia and Lithuania each seeing an average of at least three additional weeks of lost winter days due to human-caused climate change.

• Nineteen countries — including Germany, Poland, the Czech Republic and Belgium — have seen at least two additional weeks' worth of above freezing days during the past decade, compared to what would have happened in the absence of global warming.
• Climate change added between one to two weeks' worth of above freezing winter days each year during the past decade in France, Italy, Japan, the Netherlands, Spain and the U.K., the research found.

Yes, but: Typically, attribution studies show how climate change altered the likelihood of a particular extreme weather event.

• But researchers claim that Climate Central's CSI tool can be used to estimate what temperatures would be in the absence of climate change with considerable precision.

The bottom line: Winters are warming, and winter days that dip below freezing are becoming more rare.

The year is closing out with more global temperature records that, in aggregate, largely defy what many climate scientists expected for 2024.

Why it matters: Among the potential factors driving this year's — as well as 2023's — record warmth is the unsettling possibility that global warming is accelerating and the planet's climate behaving differently than expected.

• If so, the climate scenarios that form the basis for countries' decarbonization goals could be faulty, with higher warming levels and greater societal consequences likely to arrive sooner than expected.

Driving the news: New data from NOAA, NASA and the EU's Copernicus Climate Change Service shows that the planet just had its second-warmest November on record.

• These centers use different methods to track global average surface temperatures. They agree that 2024 is on track to be the planet's hottest year in well over a century of instrument record-keeping — and likely at least 125,000 years when including tree rings and ice core data.
• Copernicus, in fact, is out front in saying that 2024 may end up close to 1.6°C (2.88°F) above the pre-industrial average, exceeding the Paris Agreement's most ambitious target for a single year.
• The 1850-1900 average is used as a baseline to approximate the period before the addition of greenhouse gases from burning fossil fuels such as coal, oil and gas.

By the numbers: According to the new Copernicus data, November was the 16th out of the past 17 months during which global average surface temperatures exceeded the 1.5°C target relative to pre-industrial temperatures.

• Separately, NOAA found that so far this year, six continents have had their warmest temperatures on record for the year so far, while Asia has ranked second-warmest.
• During November, a record 10.6% of the world's surface had a record high monthly average temperature, beating the previous milestone set in 2023, NOAA found.
• In addition, the ratio of warm temperature records to cold temperature records set globally during the month was about 50-to-1. That was roughly equal to November 2023 and an increasingly common occurrence in recent years, but largely unheard of prior to about 2010.

The intrigue: At the American Geophysical Union conference in Washington last week, top climate researchers discussed how to account for the steep, as yet incompletely explained warming spike seen during 2023 and 2024.

• They dissected studies that investigated suspects such as changes in low-level cloudiness, a pollution reduction measure that altered the amount of sulfur in marine shipping fuels and a strong El Niño event to try to explain temperature trends.

Between the lines: At the end of a Dec. 10 session on the causes of the 2023 and 2024 warming spike, NASA climate scientist Gavin Schmidt asked for a show of hands from those attending the year's largest climate science conference.

• Only a smattering went up when Schmidt asked them to agree with the statement: "We have understood the anomalies in '23 and '24 with all of the information that has been presented here and that exists elsewhere."
• Instead, the overwhelming majority backed the position that a sufficient explanation hasn't been offered and more research is needed.
• "There is something to explain and there is still work to do," Schmidt said.

The bottom line: While there's virtually zero uncertainty that 2024 will be the hottest on record, plenty of unnerving debate exists regarding how and why this happened — and what it means for the near future.

Officials in the French Indian Ocean territory of Mayotte estimate Tropical Cyclone Chido killed hundreds of people after the worst storm in 90 years struck the Indian Ocean archipelago.

The big picture: Mayotte hospital officials confirmed Tropical Cyclone Chido killed at least 11 people and wounded some 250 others on Saturday, but a top Mayotte official told local news outlet Mayotte La 1ere Sunday he expects the death toll to rise exponentially.

• "I think there will certainly be several hundreds, maybe we will reach a thousand, even several thousands," prefect Francois-Xavier Bieuville said.

Driving the news: Tropical Cyclone Chido was at least the equivalent of a Category 3 hurricane in the Atlantic when it made landfall in Mayotte, per the U.S. military's Joint Typhoon Warning Center.

• It was possibly stronger since it was so compact.
• Surface wind readings of higher intensity suggest it was stronger from the storm, which also brought powerful winds and heavy rains to Mozambique when it made landfall on Sunday.
• During the passage of the cyclone in Mayotte, 140 mph winds were recorded in the eye wall at Pamandzi on Mayotte's island of Petite-Terre, per a post to X by the weather agency Météo-France.

State of play: French President Emmanuel Macron said on X that he's closely monitoring the situation on Mayotte — which is the poorest territory in the European Union, with some 77% of people living below the national poverty line.

• "Our island is at this moment deeply affected by the most violent and destructive cyclone that we have seen since 1934," Bieuville said on Facebook Saturday. "Many of us have lost everything."
• European Commission president Ursula von der Leyen said on Bluesky that "Europe stands alongside the people of Mayotte in this terrible ordeal" and the EU was "ready to provide support in the days to come."
• Phone and internet networks were still disrupted on Sunday, as French Interior Minister Bruno Retailleau prepared to visit Mayotte on Monday.

Between the lines: Studies show that climate change is increasing maximum wind speeds of hurricanes and causing them to intensify more rapidly.

• They are also producing greater amounts of precipitation than they did just a few decades ago.

These storms are the same type of weather system, but with different terminology depending where they occur.

• Hurricanes and typhoons form in the Atlantic and western Pacific, respectively. Cyclones occur off the southeastern coast of Africa, among other locations.

In photos: Cyclone Chido causes widespread destruction in Mayotte

Go deeper: Why climate change hits poorest countries hardest

Editor's note: This is a breaking news story. Please check back for updates.

A wildfire threatening Malibu homes has forced thousands to evacuate, and forecasters warn "very dry air and elevated fire weather conditions would persist" into Wednesday night, even after red flag warnings ended earlier in the day.

The big picture: Santa Ana winds and very low humidity have driven the dire conditions, as hundreds of firefighters tackle the fast-moving Franklin Fire, which was burning out of control across an estimated 4,000-plus acres in Malibu Wednesday.

Go deeper: How wildfire smoke impacts your health

Editor's note: This article has been updated with new details throughout.

Parts of Southern California are still facing "elevated to brief "critical conditions" into Thursday night as a fast-moving wildfire that forced thousands in Malibu to evacuate continues to grow.

Threat level: Red Flag warnings ended as powerful Santa Ana winds eased on Wednesday afternoon, but the National Weather Service's Los Angeles office said on X that breezy areas of southwest Santa Barbara County and the San Gabriel Mountains were still under threat amid "very dry" conditions.

• Meanwhile, Malibu's Franklin fire had swollen to more than 4,000 acres as of Wednesday afternoon after rapidly expanding overnight. It was 7% contained. The cause of the blaze remains under investigation.

State of play: Flames had reached the Pacific Coast Highway on Tuesday, shutting down parts of the road, according to the City of Malibu.

• Due to the anticipated long duration of dry and windy conditions, there is a heightened risk that new ignitions could have "very rapid fire spread and extreme fire behavior," according to the NWS LA.
• Malibu Schools will remain closed on Wednesday and Thursday.
• At least seven structures have been destroyed, and eight have been damaged, according to a Tuesday evening update from Malibu.
• California Gov. Gavin Newsom announced Tuesday that the state had secured federal assistance from FEMA to help bolster its response to the fire.

Zoom in: This past Santa Ana wind event has been unusually intense, exceeding 90 mph in spots, particularly in and around hilly terrain.

• The NWS forecast office in Los Angeles warned of "extreme & life-threatening wildfire behavior."
• "This event has the potential to be as strong as the November 5th-6th Santa Ana event that led to the Mountain Fire," the NWS stated, referencing the fire that burned nearly 20,000 acres and damaged or destroyed more than 400 structures near Camarillo, Calif.

What they're saying: The Franklin Fire is manufacturing its own weather, drawing air in from nearby areas, the NWS stated in an online forecast discussion.

• "The combination of winds, very low humidities and dry fuels make for an explosive fire environment."
• The fire at one point went from 1 acre to 100 acres in under an hour.

Zoom in: Southern California typically sees Santa Ana events during the fall, and they are characterized by strong winds, extremely dry air flowing from land to sea, and cooler-than-average temperatures.

• Some of the region's worst wildfires have occurred during these periods, since the winds can quickly spread flames into heavily populated areas.
• While red flag warnings are often issued for fire weather threats, the "PDS" designation indicates heightened risk. Such designations are issued only for "the most extreme events," the NWS stated.
• The most dire conditions are expected to occur across western portions of LA County along with eastern Ventura County, including the communities of Malibu, Santa Clarita, Thousand Oaks and Oxnard.
• A larger area of "critical" wildfire danger is also forecast to cover much of Southern California as the winds increase overnight Monday and extend potentially into Wednesday.

Context: Similar weather patterns have historically been associated with fast-spreading and deadly fires in the "wildland urban interface," where homes border areas with dry vegetation and hilly terrain.

• Climate change is a key factor leading to an increase in days with extreme fire weather conditions in the Southwest.
• This fall, heat waves following wet conditions helped lead to a buildup of fire-prone, dry vegetation in the Southwest.

Go deeper: How wildfire smoke impacts your health

Editor's note: This story was updated with the latest containment data.

The first day of International Court of Justice hearings on countries' obligations to combat climate change revealed deep dissatisfaction with the climate finance agreement struck at COP29 last month.

Why it matters: The court's advisory opinion will be nonbinding. But vulnerable nations — led by Vanuatu — see it as a potential boost to efforts to hold big greenhouse gas emitters accountable, compared to the COP process.

• Given the court's significance in international law, this case could have more of an impact than COP on countries' behavior and corporate policies — and on future legal action, compared to past more parochial climate cases.

The big picture: Representatives from Barbados expressed the prevailing, dim view of the UN climate summit process among many developing countries appearing Monday before the 15-judge panel.

• "To say that we Barbadians are disappointed is to measure the distance between what has over the years been promised against what has in fact been delivered," said Robert Volterra, a co-representative of the country, before the ICJ.
• The outcome of COP29 was an agreement that calls for "at least" $300 billion a year for climate finance flowing from industrialized countries by 2035.
• That amount was agreed to even though studies have shown developing countries need at least $1 trillion per year to adapt to climate change impacts and decarbonize their energy systems.

Our thought bubble: Had the annual climate summits proven effective at cutting emissions and addressing developing countries' climate justice concerns, the ICJ case might not be necessary.

Zoom in: The case at the world court concerns countries' obligations under international law to take action on climate change, and what they have done to date.

• Arguments on Monday centered around the scope of a potential decision, as well as the plight of the world's most vulnerable nations.
• Vanuatu's representatives, for example, emphasized the inequities between the countries that have emitted the most greenhouse gases and the ones suffering from their effects.
• "The conduct on trial is that of states, which have failed for over a century, despite increasingly dire warnings, to rein in the emissions from their territories," said Vanuatu climate envoy Ralph Regenvanu.

Meanwhile, the Bahamas called for countries to be held accountable for their planet-warming emissions from burning fossil fuels for energy.

• "We insist on liability, and we demand reparations," said Bahamas Attorney General Leo Pinder, emphasizing the country's extreme vulnerability to climate change-related sea level rise and more severe hurricanes.

Yes, but: Some countries are seeking to limit the scope of any advisory opinion from the 15-judge panel.

• According to Earth Negotiations Bulletin, representatives of Saudi Arabia told justices that they should limit their decision to considering country obligations under three specific climate agreements, rather than incorporating other areas of international law, such as human rights.
• The Saudis also argued against the notion that future generations — which will be more severely affected by climate change impacts than some current generations — have rights to a hospitable climate.
• Other countries, like Germany, also advocated for climate agreements to date to form the basis of the advisory opinion, not broader human rights law.

The intrigue: In its remarks on Monday, Barbados pushed back against the idea that only three international climate agreements are applicable to the ICJ case.

• The country's representatives noted that other nations share their view that the climate agreements struck over the years, such as the 1992 U.N. Framework Convention on Climate Change, 1995 Kyoto Protocol and 2015 Paris Agreement, are not an "exclusive self-contained legal regime," Volterra said.
• In other words, human rights law and rulings on air pollution that crosses national boundaries — among other legal instruments — may apply to this case, Barbados and others asserted.

What we're watching: How the next two weeks of testimony unfold, including U.S. contributions scheduled for Wednesday.

• The hearings may offer hints as to what the nonbinding ruling will say, along with any potential ramifications for countries rich and poor.

Emerging research points out how much scientists have yet to learn about human-caused climate change — and raises the possibility that they, along with policymakers, are underestimating some risks lurking ahead.

Why it matters: The studies and media comments from scientists illustrate that the Earth's climate system — made up of the oceans, land and atmosphere — may no longer be behaving as it used to.

Driving the news: One recent study found emerging "hot spots" where heat waves are far outpacing global temperature trends.

• These places are defying predictions and can be found on each continent except Antarctica.
• Because of quirks of the jet stream and other reasons, the regional hot spots are seeing extreme heat events that have killed tens of thousands of people in recent years.
• Those events also have primed the environment for devastating wildfires and harmed crops.

The study, published in the journal Proceedings of the National Academy of Sciences, focuses on a newly identified known-unknown in climate science.

What they're saying: "This is about extreme trends that are the outcome of physical interactions we might not completely understand," said lead author Kai Kornhuber, an adjunct scientist at the Columbia Climate School and a researcher in Austria.

• "These regions become temporary hothouses," he said in a statement.

Zoom in: Kornhuber and his colleagues produced the first global map of these hothouse regions, showing how they emerged from records of heat waves stretching back to 1958.

• The areas on which they focused have seen maximum temperatures during heat waves far exceed previous records. One example occurred in Lytton, British Columbia, during the Pacific Northwest heat wave of 2021.
• The town set the record for the highest temperature on record in Canada that June, at 121.3°F. Most of the town then burned to the ground in a wildfire the next day.

Threat level: The study found extreme heat waves have become more common in about the past five years, particularly in parts of Asia, the Arabian peninsula, eastern Australia, Canada's far northern regions, northern Greenland and parts of Siberia.

• The strongest signal, though, comes from northwestern Europe, where the hottest days are warming twice as fast as the summer mean temperatures, the study found.

Between the lines: One hypothesis, which comes from Kornhuber's past work, is that the shifting temperature balance between the equator and the poles (the poles are warming at about three times the global rate) is altering the shape and persistence of jet stream patterns.

• This may be transporting hotter air further north and keeping it there for unusually long periods, trapped under slow-moving ridges of high pressure.
• But alterations in the jet stream are only one of several factors that may be at work. The study points out that such "extreme-extremes" aren't seen in research using the mean results from multiple climate models.
• The coauthors' clearest conclusion was to call for cuts to burning fossil fuels to reduce overall global warming and lower the likelihood of more severe hot spots emerging.

Other researchers are trying to account for the record global heat seen this year, which will eclipse 2023 as the hottest year on record.

• Writing on the Substack "The Climate Brink," climate scientist Zeke Hausfather shows that global average surface temperatures during the run-up to, during and post-period of the 2023-2024 El Niño event have departed from previous El Niño events.
• Such climate events, which feature unusually hot ocean temperatures in the eastern tropical Pacific Ocean, tend to elevate global average temperatures.
• However, the past few years — with two consecutive years of record-breaking global temperatures — have been exceptional.
• "Even looking at the longer record, the evolution of global surface temperatures both before and after the El Niño is unprecedented," Hausfather wrote last week.

"Temperatures rose earlier than we've seen before, and temperatures have remained at elevated levels for a longer period of time."

Yes, but: He did find that one El Niño event in 1958 showed a spike in global temperatures well after the El Niño conditions had dissipated, lending at least a bit of credibility to the possibility that natural climate variability is at play now.

Zoom out: Global efforts to limit warming to the Paris Agreement's temperature targets are faltering.

• There are increasing concerns that countries or wealthy individuals will turn to geoengineering, which would involve deliberately altering the planet's climate to hold warming at bay temporarily, as a risky stopgap.
• According to recent reporting in the New York Times, NOAA and the Energy Department are working on a detection system to be able to discern if any country or nongovernmental actor is pursuing such a plan.

The bottom line: All of these developments add up to a portrait of humanity entering a new, more turbulent stage of the era of climate consequences, where it may be getting more difficult to anticipate what may happen next.

The West Coast is in the midst of a long-lasting heavy rain event tied to a bomb cyclone in the northeastern Pacific Ocean, with the National Weather Service warning of "life-threatening flooding" in Northern California.

Threat level: The rapidly intensifying storm that is directing a strong atmospheric river at southwestern Oregon and Northern California brought hurricane-force winds to parts of Oregon, Washington and Canada late Tuesday into early Wednesday, causing widespread power outages.

• At least one person has died.
• The National Weather Service issued a rare "high" likelihood of excessive rainfall on Thursday, which highlights the danger of more heavy rain on already saturated soils, particularly in Northern California.
• The agency is forecasting precipitation totals of 12 to 16 inches or more, and warns of rock and landslides in this region.
• "High risk" days are associated with a majority of all flood-related property losses in the Lower 48 states, and about two out of five flood-related fatalities, according to the NWS' Weather Prediction Center.

The forecast office in Eureka, California, noted that an atmospheric river producing very heavy rainfall would end up "parking itself" over northwestern California starting Tuesday night and continue potentially into the weekend.

• That's raising flooding concerns for urban areas as well as rivers and streams over time.

State of play: The latest computer model projections show rainfall amounts that could reach 15 to 20 inches, or even higher, along coastal areas, once the rainfall during multiple days is added up.

• The highest totals will be in elevated areas.
• Weather Service data shows the Washington cities of Sunrise (Rainier) and Enumclaw saw wind gusts of 77 mph, 74 mph, respectively Tuesday evening as the bomb cyclone rapidly intensified and made its closest approach to the region.
• A woman in her 50s died Tuesday evening after a "large tree fell on a homeless encampment" in Lynnwood, Washington, during heavy winds connected to the bomb cyclone, per a South County Fire Facebook post.

Forecasters warned of the arrival Thursday into Friday of a second intensifying low pressure area, which will pinwheel around the first bomb cyclone in an atmospheric interaction known as the Fujiwara Effect.

• The result of these storms will be periods of heavy rain and more high winds through Friday.

An estimated 330,000 customers remained without power in Washington Thursday morning due to downed trees and power lines from the first phase of the storm Tuesday and Wednesday.

• Thousands also lost electricity in parts of California and Oregon, and could do so again.

Zoom in: The original bomb cyclone is drifting well northwest of Washington State while slowly weakening.

• Additional low pressure systems, including a second rapidly intensifying storm, are forecast to pinwheel around it through the early part of this weekend
• The main low pressure area qualified as a bomb cyclone due to its rapid rate of intensification. In fact, it greatly exceeded the meteorological definition of the phenomenon known as "bombogenesis," when a low pressure area intensifies by at least 24 millibars in 24 hours.
• The storm intensified by more than 50 millibars in that same timespan. As a general rule, stronger storms have lower minimum central air pressures associated with them.

What we're watching: The impacts of the strong atmospheric river, which has been stuck in place since Wednesday night.

The big picture: The atmospheric river is located to the south of the bomb cyclone, and is carrying copious amounts of moisture from the subtropics into Northern California and parts of Oregon.

• As their name suggests, atmospheric rivers are corridors of concentrated water vapor located in the middle atmosphere, about 10,000 to 20,000 feet above the surface.
• This particular atmospheric river event is forecast to rate as a 4 out of 5 on the Scripps Institution of Oceanography's severity scale, which takes into account the potential for heavy rainfall.

Context: Human-caused climate change is causing atmospheric rivers to carry more moisture and making them capable of producing more rain and snow.

• One 2022 study found that atmospheric rivers that hit California in 2017 were up to 15% wetter due to human-caused climate change.
• Other recent studies show future atmospheric river events may heighten this trend.
• Warmer air and ocean temperatures add more water vapor to the atmosphere, which storms can ingest and wring out over land.

In California, atmospheric rivers have been responsible for some of the biggest flooding events on record, though this storm's heavy rain and mountain snow aren't expected to lead to a historic event.

Editor's note: This a breaking news story. Please check back for updates.