Winter is still weeks away, but meteorologists are already talking about a snowy winter ahead in the southern Rockies and the Sierra Nevada. They anticipate more storms in the U.S. South and Northeast, and warmer, drier conditions across the already dry Pacific Northwest and the upper Midwest.

One phrase comes up repeatedly with these projections: a strong El Niño is coming.

It sounds ominous. But what does is that actually mean? We asked Aaron Levine, an atmospheric scientist at the University of Washington whose research focuses on El Niño.

What is a strong El Niño?

During a normal year, the warmest sea surface temperatures are in the western Pacific and the Indian Ocean, in what’s known as the Indo-Western Pacific warm pool.

But every few years, the trade winds that blow from east to west weaken, allowing that warm water to slosh eastward and pile up along the equator. The warm water causes the air above it to warm and rise, fueling precipitation in the central Pacific and shifting atmospheric circulation patterns across the basin.

This pattern is known as El Niño, and it can affect weather around the world.

A strong El Niño, in the most basic definition, occurs once the average sea surface temperature in the equatorial Pacific is at least 1.5 degrees Celsius (2.7 Fahrenheit) warmer than normal. It’s measured in an imaginary box along the equator, roughly south of Hawaii, known as the Nino 3.4 Index.

But El Niño is a coupled ocean-atmosphere phenomenon, and the atmosphere also plays a crucial role.

What has been surprising about this year’s El Niño – and still is – is that the atmosphere hasn’t responded as much as we would have expected based on the rising sea surface temperatures.

Is that why El Niño didn’t affect the 2023 hurricane season the way forecasts expected?

The 2023 Atlantic hurricane season is a good example. Forecasters often use El Niño as a predictor of wind shear, which can tear apart Atlantic hurricanes. But with the atmosphere not responding to the warmer water right away, the impact on Atlantic hurricanes was lessened and it turned out to be a busy season.

The atmosphere is what transmits El Niño’s impact. Heat from the warm ocean water causes the air above it to warm and rise, which fuels precipitation. That air sinks again over cooler water.

The rising and sinking creates giant loops in the atmosphere called the Walker Circulation. When the warm pool’s water shifts eastward, that also shifts where the rising and sinking motions happen. The atmosphere reacts to this change like ripples in a pond when you throw a stone in. These ripples affect the jet stream, which steers weather patterns in the U.S.

This year, in comparison with other large El Niño events – such as 1982-83, 1997-98 and 2015-16 – we’re not seeing the same change in where the precipitation is happening. It’s taking much longer to develop, and it’s not as strong.

Part of that, presumably, is related to the whole tropics being very, very warm. But this is still an emerging field of research.

How El Niño will change with global warming is a big and open question. El Niño only happens every few years, and there’s a fair amount of variability between events, so just getting a baseline is tough.

What does a strong El Niño typically mean for US weather?

During a typical El Niño winter, the U.S. South and Southwest are cooler and wetter, and the Northwest is warmer and drier. The upper Midwest tends to be drier, while the Northeast tends to be a little wetter.

The likelihood and the intensity generally scale with the strength of the El Niño event.

El Niño has traditionally been good for the mountain snowpack in California, which the state relies for a large percentage of its water. But it is often not so good for the Pacific Northwest snowpack.

The jet stream plays a role in that shift. When the polar jet stream is either displaced very far northward or southward, storms that would normally move through Washington or British Columbia are steered to California and Oregon instead.

What do the forecasts show for 2023?

Whether forecasters think a strong El Niño will develop depends on whose forecast model they trust.

This past spring, the dynamical forecast models were already very confident about the potential for a strong El Niño developing. These are big models that solve basic physics equations, starting with current oceanic and atmospheric conditions.

However, statistical models, which use statistical predictors of El Niño calculated from historical observations, were less certain.

Even in the most recent forecast model outlook, the dynamical forecast models were predicting a stronger El Niño than the statistical models were.

If you go by just a sea surface temperature-based El Niño index, the forecast is for a fairly strong El Niño.

But the indices that incorporate the atmosphere are not responding in the same way. We’ve seen atmospheric anomalies – as measured by cloud height monitored by satellites or sea-level pressure at monitoring stations – on and off in the Pacific since May and June, but not in a very robust fashion. Even in September, they were nowhere near as large as they were in 1982, in terms of overall magnitude.

We’ll see if the atmosphere catches up by wintertime, when El Niño peaks.

How long do El Niños last?

Often during El Niño events – particularly strong El Niño events – the sea surface temperature anomalies collapse really quickly during the Northern Hemisphere spring. Almost all end in April or May.

One reason is that El Niño sows the seeds of its own demise. When El Niño happens, it uses up that warm water and the warm water volume shrinks. Eventually, it has eroded its fuel.

The surface can stay warm for a while, but once the heat from the subsurface is gone and the trade winds return, the El Niño event collapses. At the end of past El Niño events, the sea surface anomaly dropped very fast and we saw conditions typically switch to La Niña – El Niño’s cooler opposite.

Aaron Levine receives funding from NOAA and has received funding in the past from the National Research Council. He is a member of the American Geophysical Union

Fifty years ago, a secret deal among Arab governments triggered one of the most traumatic economic crises to afflict the United States and other big oil importers.

Saudi King Faisal and other Arab leaders launched an oil embargo on Oct. 17, 1973, as payback for Washington siding with Israel in its war with neighboring Egypt and Syria.

The oil market hostilities arose from a pact between Faisal and the leaders of Egypt and Syria, whose armies planned surprise drives to retake their territory under Israeli occupation. If the United States intervened to assist Israel, Faisal and other Arab producers agreed to retaliate with the “oil weapon.”

When Washington airlifted in U.S. weapons that helped Israel thwart Arab gains, Faisal and OPEC’s Arab members retaliated. They increased oil prices, banned oil shipments to the United States and cut production by 5% per month.

The ensuing economic and political carnage is legendary. The embargo catalyzed a long period of upheaval in global oil markets and pain at the gasoline pump for Americans and consumers globally. Oil prices quadrupled nearly overnight and remained high for over a decade. Producing countries leveraged the opportunity to reclaim sovereignty over their oil reserves. By 1980, many had completed the process of kicking Western oil companies out of their territories.

Oil’s global regime change

The embargo’s disruptive power was due to two key factors: OPEC’s dominance of world oil supply, and oil’s supremacy in the global energy mix.

Prior to the embargo, oil fueled almost half of total energy consumption in the United States (47.5%) and worldwide (49%). While OPEC countries produced more than half (53%) of global oil, the concessions were operated by Western oil majors.

After the embargo, producer states took over. Control of global oil production passed from Western oil giants like Shell and Exxon to newly formed national oil companies.

As a result, a torrent of cash from oil sales poured into Middle Eastern countries where rudimentary services like electricity were still being built out. Oil revenues in Saudi Arabia jumped fortyfold between 1965 and 1975, from US$655 million to $26.7 billion. These countries also amassed new geopolitical power.

How the oil price spike played out in the West

In the West, price increases wreaked havoc on economies and transport systems that were far less efficient than today. Inflation soon boiled over into “stagflation,” a combination of economic stagnation and high inflation. Misguided policies, including gasoline price controls and rationing, exacerbated shortages, creating long lines at service stations and emboldening gasoline thieves.

America saw a pell-mell downsizing of gas-guzzling vehicles and a simultaneous ramping up of imports of fuel-efficient Japanese cars. Drivers obsessed over miles per gallon, and the U.S. government imposed corporate average fuel economy, or CAFE, standards, aimed at saving fuel by requiring automakers to sell more fuel-efficient cars.

Western oil companies, kicked out of the Middle East and other oil regions, pivoted to more difficult terrain: the offshore Gulf of Mexico and North Sea, and the Arctic regions of northern Alaska.

As scholars of energy policy, we have long studied the embargo’s spillover effects on the global economy and political systems. These outcomes are a central theme in Jim Krane’s 2019 book “Energy Kingdoms.” On the embargo’s 50th anniversary, Oct. 17, 2023, King Faisal’s son, the former Saudi Ambassador to Washington Prince Turki Al Faisal, is joining us for a conference at Rice University’s Baker Institute to discuss the still-valid lessons of the Arab oil embargo.

50 years later, new pressures

Fifty years on, markets have changed. But oil continues to be the world’s dominant energy source.

On one hand, crude oil use has grown dramatically. Global supply has risen from less than 60 million barrels per day in 1973 to nearly 94 million barrels per day in 2022. Motor fuel prices are still a critical input to inflation; we calculate that the increase in gasoline prices in 2022 cost the average American household roughly $1,000.

On the other hand, OPEC’s importance – and oil’s share of the global energy mix – has declined. OPEC’s 13 members account for just 36% of global oil production today. The high oil prices caused by the 1973 embargo created incentives for oil drillers to diversify toward new sources of oil and develop substitute fuels to replace oil.

Within 15 years of the embargo, production outside OPEC increased by a massive 14 million barrels per day. Oil from Alaska and the Gulf of Mexico helped stabilize U.S. production. Later, the shale revolution turned the United States into the world’s largest producer and a net exporter of oil, capping a 50-year quest.

The world has also become much more efficient, reducing the amount of oil needed to maintain the same activity. Global per-capita oil use per dollar of gross domestic product has fallen by a massive 60% since 1973, our calculations show.

But, as in 1973, energy security concerns are back at the top of national agendas.

Russia’s 2022 invasion of Ukraine reprised the risks of energy “weaponization.” Europe, in particular, has been hurt by overdependence on Russian natural gas and has raced to shift its energy sources. The Israel-Hamas war that began on Oct. 8, 2023, has not yet ignited retaliatory responses from Arab governments, and the initial impact on oil has been minimal, but geopolitical effects from such a large event could still roil markets.

Energy security itself is also being altered. The transition to renewable energy sources like wind and solar insulates consumers from most supply chain risks. Electric vehicles likewise protect owners from swinging oil prices. So, while crucial materials can still be manipulated by governments, shortages and price spikes mainly affect component manufacturers and their investors. If supplies are bottlenecked long enough, the energy transition could be delayed.

Like the embargo 50 years ago, today’s crises have rendered the future of energy massively uncertain. Changes in the global energy mix, especially the rapid growth of electric vehicles, could weaken the importance of oil and the cartel that oversees it.

As former Saudi oil minister Ahmed Zaki Yamani was reported to have said a quarter-century ago: “The Stone Age did not end for lack of stone, and the oil age will end long before the world runs out of oil.”

Jim Krane has received research funding from the government of Qatar and is affiliated with the Energy Policy Research Group at the University of Cambridge.

Mark Finley owns shares in bp. He has consulted for the King Abdullah Petroleum Studies and Research Center. He is also a member of the US Association for Energy Economics and the National Association for Business Economics.

Seawater intrusion is the movement of saline water from the ocean or estuaries into freshwater systems. The seawater that has crept up the Mississippi River in the summer and early fall of 2023 is a reminder that coastal communities teeter in a fragile land-sea balance.

Fresh water is essential for drinking, irrigation and healthy ecosystems. When seawater moves inland, the salt it contains can wreak havoc on farmlands, ecosystems, lives and livelihoods.

I am a coastal hydrogeologist and have studied water across the land-sea interface for 25 years. I think of seawater intrusion as being like a seesaw: The place where fresh water and salt water meet is the balance point between forces from land and forces from the sea.

A push from the land side, such as heavy rainfall or high river flows, moves the balance point seaward. A push from the sea side – whether it’s sea-level rise, storm surge or high tides – moves the balance point landward. Droughts or heavy use of fresh water can also cause seawater to move inland. As climate change and population growth stress freshwater supplies, one result will be more seawater intrusion.

When the ocean moves upriver

The current seawater intrusion in the lower Mississippi River is due primarily to drought in the Midwest, which has reduced the river’s volume. Both the magnitude of reduction in river flow and the length of time that the river is low influence how far upriver the salt water moves. As of Oct. 2, 2023, the saltwater “wedge” in the Mississippi had moved nearly 70 miles upstream from the river’s mouth.

This isn’t the first time that low water on the river has allowed seawater to move inland. But as climate change raises sea levels and causes more severe weather anomalies, intrusion will become more common and will inch farther upstream.

And the problem isn’t unique to the Mississippi. In Delaware, seawater is traveling farther up small tidal streams during storms and the highest tides, flooding farmland and killing crops.

In the Sundarbans of India and Bangladesh – one of the largest coastal mangrove forests in the world – seawater is intruding into the mouth of the Ganges River. The main causes there are upstream dams and water diversions from the river for irrigation and navigability, plus encroachment due to sea-level rise. Seawater intrusion could threaten many types of plants and animals in this UNESCO World Heritage Site, which is home to countless rare and endangered species.

Invading underground

Another interface between fresh water and salt water at the coast is less obvious because it’s underground. Many coastal communities draw their freshwater supply from groundwater – clean water that moves through pore spaces between grains of sand and soil.

Groundwater doesn’t just stop at the coastline: Under the ocean floor, the groundwater is salty, and somewhere between land and the ocean, there is an underground meeting point. It typically is landward of the coastline because salt water is denser than fresh water, so it has a greater force and naturally pushes in. But just as with a river, that interface moves when groundwater levels drop on land or water levels rise offshore.

In groundwater basins of central and southern California, widespread pumping has caused groundwater levels to drop hundreds of feet in some areas. This is tipping the seesaw and causing groundwater from the sea to move far inland. Accessible groundwater has supported irrigated agriculture in these areas, but now the double hazard of reduced groundwater availability and seawater intrusion threatens crops like strawberries and lettuce.

Seawater intrusion into groundwater is happening all over the world, but perhaps the most threatened places are communities on low-lying islands. Fresh groundwater is often the sole source of water for drinking and irrigation on small islands, and it exists in a thin lens that floats on top of saline groundwater.

The lens can shrink in response to droughts, pumping and sea-level rise. It can also become salty from floodwater infiltration during storms or high tides.

In the Marshall Islands, for example, a combination of sea-level rise and wave-driven flooding is predicted to make many islands uninhabitable by the end of the century.

Shifting the balance

As salt water continues to encroach on freshwater systems, there will be consequences. Drinking water that contains even 2% seawater can increase blood pressure and stress kidneys. If salt water gets into supply lines, it can corrode pipes and produce toxic disinfection by-products in water treatment plants.

Seawater intrusion reduces the life span of roads, bridges and other infrastructure. It has been implicated as a contributor to the Champlain Towers South condominium collapse in Surfside, Florida, in 2021. Seawater intrusion changes ecosystems, creating ghost forests as trees die and marshes move inland.

Smart management can tip the seesaw back toward the sea. Limiting surface water extraction and groundwater pumping, or injecting treated wastewater into vulnerable aquifers, can increase the force pushing against intruding salt water.

Constructing seawalls or maintaining healthy dune systems also can help hold seawater at bay, though these approaches protect only against saltwater flooding and infiltration at the surface, not underground. Pumping out saline groundwater or installing underground barriers can keep deeper salt water from moving inland.

Being proactive is best, because once groundwater is contaminated, it’s hard to remove the salt. If salt water does penetrate inland, communities can manage water quality by constructing desalination plants and switching to salt-tolerant crops.

Another option is to let nature take its course. Allowing marshes to migrate inland can compensate for losses at the coastline as sea level rises. This preserves critical habitats, enhances flood protection and stores carbon at rates far exceeding most terrestrial ecosystems – dialing back the acceleration of climate change.

Holly Michael receives funding from the US National Science Foundation, the US Geological Survey, and the US National Park Service.