Covering 70% of Earth’s surface, oceans exert a major control on climate. They absorb large amounts of solar energy. Heat and water vapor are then redistributed globally through ocean currents and the circulation of the atmosphere. Jump to The Oceans
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What You Need to Know About Principle 2: Climate is Complex
This principle relates to the complex interactions that drive climate processes. Interactions between land, snow and ice, living things, oceans, and the atmosphere generate things like the greenhouse effect and a number of other climate processes. The interactions are complex and require different scientific disciplines working together to understand them. Click the tabs below to learn more about the factors that regulate climate.
Climate Varies by Region
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Earth’s climate is influenced by interactions involving the Sun, ocean, atmosphere, clouds, ice, land, and life. In other words, all elements of the Earth as well as important variables from space affect climate.
Because of local differences in these interactions, climate varies by region, and that explains for example, why parts of southern North Carolina has a mean July temperature of 71°F and receive 70 to 80 inches of precipitation a year, while parts of northwest South Carolina, just 50 miles away has a mean July temperature of 80°F and receives around 45 inches of precipitation.
The climate of southern North Carolina is influenced by the Appalachian Mountains, which have a higher elevation than the neighboring part of South Carolina. That results in lower temperatures and greater precipitation.
Temperature and Precipitation Distribution in the Southeast
￼Left: Average daily January minimum temperature. Center: Average daily July maximum temperature. Right: Annual average precipitation. Source of all three maps: Parameter-elevation Regressions on Independent Slopes Model, or PRISM; http://www.prism.oregonstate.edu/.
REGIONAL CLIMATE VARIATION AND WEATHER
In what ways does the climate vary across Antarctica and why? What weather phenomena occur in different parts of the continent?
There are large variations in climate across the continent owing mainly to differences in latitude, altitude, and distance from the Southern Ocean. The Antarctic climate as a whole can be discussed in terms of three different climate areas: the interior climate, the coastal climate and the climate of the Antarctic Peninsula.
The coldest and driest areas are inland, where the ice sheets form high plateaux (exceeding 4000m altitude on the East Antarctic Ice Sheet). In these areas, extremely cold air descends to create persistent high pressure that brings settled conditions with relatively low wind speeds. Temperatures during the austral summer rarely exceed -20°C and during the winter months temperatures are often around -60°C. Precipitation is usually snow in the form of ‘diamond dust’ – tiny ice crystals formed from the sublimation of water vapour in a clear, but intensely cold atmosphere – averaging less than 50mm (water equivalent) per year.
Winter at Halley research station where temperatures can drop below -50°C: a bulldozer covered in drifted snow © British Antarctic Survey, Martin Bell
Near the coast there is greater seasonal variation in temperature, and in the austral summer, temperatures can warm to around 0°C. Due to the lower altitude and latitude the air is warmer than inland, so enabling it to hold a lot more water vapour; and in addition, storm systems from the Southern Ocean have more influence. Hence, annual precipitation is much higher than inland, reaching levels of around 400mm in some coastal locations, and skies are often cloudy. Precipitation is almost always in the form of snow, with rain only falling extremely rarely in some areas in the summer months. Winds can reach high velocities in areas near the coast due to topographic factors and the phenomenon of katabatic winds discussed further below.
The Antarctic Peninsula extends into the Southern Ocean and is therefore more influenced by the sea than other parts of the continent. Annual precipitation varies greatly across the Peninsula, with some areas receiving as little as 250mm water equivalent, and other areas as much as 5000mm. Near the tip of the peninsula (which lies outside the Antarctic Circle) summer temperatures often rise a little above freezing.
Regional measures of temperature and precipitation
Compared with other continents, places in Antarctica where the weather is measured regularly are few and far between (although the placement of automatic weather stations and satellite-based weather measurements are improving coverage of the continent). Of the weather stations that exist, most have relatively short records. As noted in Key factors behind Antarctica’s climate, strict conditions need to be met for weather recordings to be classed as ‘official’ for statistical purposes, and climatologists like to base any statements about the climate of an area (the ‘average weather’ experienced at a locality) on at least 30 years of data (the ’30 year mean’). There are, however, some stations in Antarctica that meet these stringent requirements and allow scientists to build up a picture of how temperature, precipitation, and other climate measures vary across the continent. A few stations have records extending back well beyond 30 years, and these stations are crucial for studies of climate change as described in Climate change: past and future.
Important stations where weather is recorded in the interior of the continent include the Amundsen-Scott station (USA) at the South Pole and the Vostok station (Russia) in East Antarctica. Both stations were established in 1957 as part of the International Geophysical Year. The Amundsen-Scott station is at an elevation of 2900m above sea level and the Vostok station is at 3500m. In addition to being very cold, these stations also represent the extreme of the polar desert climate with very low levels of humidity and precipitation. Weather conditions characteristic of coastal areas of the continent are represented at Halley station (UK) bordering the Weddell Sea, which has been in operation since 1956 and McMurdo station (USA) bordering the Ross Sea, also started in 1956. Also on the coast, the Mawson station (Australia) was set up in 1954 and is the oldest continuously occupied station inside the Antarctic Circle. This station is also notable for the force of the katabatic winds (explained below) that come down off of the high ice sheet: gusts of wind here can sometimes be over 100mph. The Rothera station (UK) provides data on the climate of the Antarctic Peninsula. It is located on the west side of the peninsula at Rothera Point on Adelaide Island and has been in operation since 1975. Peninsula weather recordings have been taken over a longer period of time at Vernadsky station (Ukraine) which was previously a British station called Faraday (the climate data are sometimes referred to as being from Faraday/Vernadsky). There are also other stations along the Peninsula, notably the Palmer station (USA) and the San Martin station (Argentina). There are stations on several islands off the coast of Antarctica that provide data on the weather and climate of the Southern Ocean, for example Signy station (UK) on Signy Island in the South Orkney Islands, first occupied in 1947. Data from a selection of stations are contained in the spreadsheet attached to Student activity 2 below.
Find out the current weather conditions at various stations at the British Antarctic Survey
The dominant pattern of atmospheric circulation over Antarctica involves cold air sinking in the interior and then moving away from this area of high pressure towards the edges of the continent. The air that sinks down onto the interior is replaced by air from aloft that has travelled southwards at a higher altitude. This large-scale circulation of air is often referred to as the polar cell. (There is also a polar cell in the Arctic.) As air from the interior moves outwards across Antarctica, it doesn’t travel directly from south to north. Instead, the direction of the air is deflected by the Earth’s rotation to form polar easterlies, meaning that the prevailing wind direction is from east to west across much of the continent. This occurs because the Coriolis Force causes air to be deflected to the left of its ‘pressure gradient path’ (the most direct route from high to low pressure) in the Southern Hemisphere.
Where these easterly winds approach the coast they can reach high velocities. A katabatic wind refers to cold and relatively dense air near the surface moving downhill due to gravity. Across much of the gently sloping ice sheet katabatic winds average about 10 miles per hour; but towards the edges of the continent, slope gradients become steep and air can be funnelled down into coastal valleys causing much higher average velocities. In some places the average annual wind velocity is nearly 50 miles per hour!
High winds make life difficult at a field camp, Rutford Ice Stream © British Antarctic Survey, David Vaughan
Moving northwards, away from the continental interior, the polar easterlies eventually give way to the zone of westerly winds affecting the Southern Ocean. The westerly winds are associated with the low pressure area (circumpolar trough) that surrounds the continent owing to the large temperature difference between cold polar air and milder air from the southern mid-latitudes. The circumpolar trough exists because where warmer air meets the cold polar air (along the polar front) the warmer air is forced upwards, creating lower pressure at sea level and the frequent storm systems that affect the Southern Ocean. Air moving from the mid-latitudes towards the circumpolar trough is deflected to the left by the Coriolis force thereby producing the westerly prevailing winds. The westerly winds and Southern Ocean storm systems affect parts of the Antarctic coastline, the Antarctic Peninsula, and the islands off the coast of Antarctica.
Other weather phenomena
Antarctica is also known for several intriguing types of atmosphere and weather phenomena.
Known as the Aurora borealis in the Northern Hemisphere, this spectacular phenomenon is often described as waving or shimmering curtains of light across the night sky. It is caused by charged particles from the Sun being pulled towards the Earth’s magnetic poles and interacting with gases high in the atmosphere to illuminate the night sky.
Aurora Australis at Halley Research Station © British Antarctic Survey, Thomas Speiss
This occurs when water vapour sublimates directly out of the cold atmosphere to form ice crystals, creating a form of precipitation that occurs under clear skies.
This optical phenomenon occurs frequently in Antarctica because of ice crystals in the atmosphere that reflect and refract light. Halos are typically rings of light circling the Sun or Moon, but they can also appear as pillars and arcs of light.
A sun halo above the Laws Platform at Halley V Research Station © British Antarctic Survey, Agnieszka Fryckowska
Under whiteout conditions, it is difficult to judge distances, perceive gradients or make out the horizon. Whiteouts can occur under different weather conditions (for example blizzards or calm, overcast conditions) where light is diffuse and it is hard to distinguish the surface from the sky.
REGIONAL CLIMATE VARIATION AND WEATHER
Covering 70% of the Earth's surface, the oceans exert a major control on climate by dominating Earth's energy and water cycles.
Oceans have the capacity to absorb large amounts of solar energy. Heat and water vapor are redistributed globally through ocean currents and atmospheric circulation.
Changes in ocean circulation caused by tectonic movements or large influxes of fresh water from melting polar ice can lead to large and even abrupt changes in climate, both locally and on global scales.
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Annual global sea-surface temperature anomalies from 1880 to 2015.
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The global ocean conveyor belt.
What is the Gulf Stream?
By Kim Ann Zimmermann, Live Science Contributor | January 15, 2013 01:19pm ET
The Gulf Stream is a powerful current in the Atlantic Ocean. It starts in the Gulf of Mexico and flows into the Atlantic at the tip of Florida, accelerating along the eastern coastlines of the United States and Newfoundland. It is part of the North Atlantic Subtropical Gyre, one of the five major oceanic gyres, which are large systems of circular currents and powerful winds.
The Gulf Stream is a western boundary current; its behavior is determined by the North American coastline. Trade winds from Africa drive water in the Atlantic westward until it hits the coastline and gets pushed northward. In turn, the Gulf Stream affects the climate of the areas closest to the current by transferring tropical heat toward the northern latitudes. There is a consensus among scientists that the climate of Western and Northern Europe is warmer than it would be otherwise because of the North Atlantic Current, one of the branches of the Gulf Stream. [Video: Animation Reveals Ocean Currents]
Published: June 7, 2007, 1:14 am
Updated: March 26, 2013, 3:33 pm
Author: Michael Pidwirny
Ocean Circulation Conveyor Belt. The ocean plays a major role in the distribution of the planet's heat through deep sea circulation. This simplified illustration shows this "conveyor belt" circulation which is driven by the difference in heat and salinity
Surface Ocean Currents
An ocean current can be defined as a horizontal movement of seawater in the ocean. Ocean currents are driven by the circulation of wind above surface waters, interacting with evaporation, sinking of water at high latitudes, and the Coriolis force generated by the earth's rotation. Frictional stress at the interface between the ocean and the wind causes the water to move in the direction of the wind. Large surface ocean currents are a response of the atmosphere and ocean to the flow of energy from the tropics to polar regions. In some cases, currents are transient features and affect only a small area. Other ocean currents are essentially permanent and extend over large horizontal distances.
On a global scale, large ocean currents are constrained by the continental masses found bordering the three oceanic basins. Continental borders cause these currents to develop an almost closed circular pattern called a gyre. Each ocean basin has a large gyre located at approximately 30° North and one at 30° South latitude in the subtropical regions. The currents in these gyres are driven by the atmospheric flow produced by the subtropical high pressure systems. Smaller gyres occur in the North Atlantic and Pacific Oceans centered at 50° North. Currents in these systems are propelled by the circulation produced by polar low pressure centers. In the Southern Hemisphere, these gyre systems do not develop because of the lack of constraining land masses.
A typical gyre displays four types of joined currents: two east-west aligned currents found respectively at the top and bottom ends of the gyre; and two boundary currents oriented north-south and flowing parallel to the continental margins. Direction of flow within these currents is determined by the direction of the macro-scale wind circulation interacting with the Coriolis force. Boundary currents play a role in redistributing global heat latitudinally.
Surface Currents of the Subtropical Gyres
On either side of the equator, in all ocean basins, there are two west-flowing currents: the North and South Equatorial (Figure 1). These currents flow between 3 and 6 kilometers per day and usually extend 100 to 200 meters in depth below the ocean surface. The Equatorial Counter Current, which flows towards the east, is a partial return of water carried westward by the North and South Equatorial currents. In El Niño years, this current intensifies in the Pacific Ocean.
Flowing from the equator to high latitudes are the western boundary currents. These warm water currents have specific names associated with their location: North Atlantic - Gulf Stream; North Pacific - Kuroshio; South Atlantic - Brazil; South Pacific - East Australia; and Indian Ocean - Agulhas. All of these currents are generally narrow, jet-like flows that travel at speeds between 40 and 120 kilometers per day. Western boundary currents are the deepest ocean surface flows, usually extending 1,000 meters below the ocean surface.
Flowing from high latitudes to the equator are the eastern boundary currents. These cold water currents also have specific names associated with their location: North Atlantic - Canary; North Pacific - California; South Atlantic - Benguela; South Pacific - Peru; and Indian Ocean - West Australia. All of these currents are generally broad, shallow moving flows that travel at speeds between 3 and 7 kilometers per day.
In the Northern Hemisphere, the east-flowing North Pacific Current and North Atlantic Drift move the waters of western boundary currents to the starting points of the eastern boundary currents. The South Pacific Current, South Indian Current and South Atlantic Current provide the same function in the Southern Hemisphere. These currents are associated with the Antarctic Circumpolar Current (West Wind Drift). Because of the absence of landmass at this latitude zone, the Antarctic Circumpolar flows in continuous fashion around Antarctica and only provides a partial return of water to the three Southern Hemispheric ocean basins.
Surface Currents of the Polar Gyres
The polar gyres exist only in the Atlantic and Pacific basins in the Northern Hemisphere. They are propelled by the counterclockwise winds associated with the development of permanent low pressure centers at 50° of latitude over the ocean basins. Note that the west-flowing current forming the southern margin of the polar gyres is also the eastward-flowing flowing current forming the northen margin of the subtropical gyres. Other currents associated with these gyres are shown on Figure 1.
Figure 2: The following illustration describes the flow pattern of the major subsurface ocean currents. Near surface warm currents are drawn in red. Blue depicts the deep cold currents. Note how this system is continuously moving water from the surface to deep within the oceans and back to the top of the ocean. (Source: Arctic Climate Impact Assessment (ACIA)).
The world's oceans also have significant currents that flow beneath the surface (Figure 2). Subsurface currents generally travel at a much slower speed when compared to surface flows. The subsurface currents are driven by differences in the density of seawater. The density of seawater deviates in the oceans because of variations in temperature and salinity. Near-surface seawater begins its travel deep into the ocean in the North Atlantic. The downwelling of this water is caused by high levels of evaporation that cool and increase the salinity of the seawater as it flows poleward. The downwelling (sinking) of this cold, dense, saline water takes place between Northern Europe and Greenland and just north of of Labrador, Canada. This seawater then moves south at depth along the coast of North and South America until it reaches Antarctica. At Antarctica, the cold and dense seawater then travels eastward joining another deep current that is created by evaporation and sinking occuring between Antarctica and the southern tip of South America. Slightly into its eastward voyage, the deep cold flow splits off into two currents, one of which moves northward. In the North Pacific and in the northern Indian Ocean, these two currents are drawn up from the ocean floor to its surface by wind-induced upwelling. The water warms at the surface and forms a current that flows at the surface eventually back to the starting point in the North Atlantic, or creating a shallow flow that circles around Antarctica. One complete circuit of this flow of seawater is estimated to take about 1,000 years.
Pidwirny, M. (2013). Ocean circulation. Retrieved from http://www.eoearth.org/view/article/154990
For another, more extensive article on the oceans and climate, click here.
Soaring ocean temperature is 'greatest hidden challenge of our generation'
IUCN report warns that ‘truly staggering’ rate of warming is changing the behaviour of marine species, reducing fishing zones and spreading disease
The scale of warming in the ocean is ‘truly staggering’, the report warns. Photograph: Ralph Lee Hopkins/Alamy
Oliver Milman in Honolulu
The soaring temperature of the oceans is the “greatest hidden challenge of our generation” that is altering the make-up of marine species, shrinking fishing areas and starting to spread disease to humans, according to the most comprehensive analysis yet of ocean warming.
The oceans have already sucked up an enormous amount of heat due to escalating greenhouse gas emissions, affecting marine species from microbes to whales, according to an International Union for Conservation of Nature (IUCN) report involving the work of 80 scientists from a dozen countries.
The profound changes underway in the oceans are starting to impact people, the report states. “Due to a domino effect, key human sectors are at threat, especially fisheries, aquaculture, coastal risk management, health and coastal tourism.”
Dan Laffoley, IUCN marine adviser and one of the report’s lead authors, said: “What we are seeing now is running well ahead of what we can cope with. The overall outlook is pretty gloomy.
“We perhaps haven’t realised the gross effect we are having on the oceans, we don’t appreciate what they do for us. We are locking ourselves into a future where a lot of the poorer people in the world will miss out.”
The scale of warming in the ocean, which covers around 70% of the planet, is “truly staggering”, the report states. The upper few metres of ocean have warmed by around 0.13C a decade since the start of the 20th century, with a 1-4C increase in global ocean warming by the end of this century.
At some point, the report says, warming waters could unlock billions of tonnes of frozen methane, a powerful greenhouse gas, from the seabed and cook the surface of the planet. This could occur even if emissions are drastically cut, due to the lag time between emitting greenhouse gases and their visible consequences.
Warming is already causing fish, seabirds, sea turtles, jellyfish and other species to change their behaviour and habitat, it says. Species are fleeing to the cooler poles, away from the equator, at a rate that is up to five times faster than the shifts seen by species on land.
Even in the north Atlantic, fish will move northwards by nearly 30km per decade until 2050 in search of suitable temperatures, with shifts already documented for pilchard, anchovy, mackerel and herring.
The warming is having its greatest impact upon the building blocks of life in the seas, such as phytoplankton, zooplankton and krill. Changes in abundance and reproduction are, in turn, feeding their way up the food chain, with some fish pushed out of their preferred range and others diminished by invasive arrivals.
With more than 550 types of marine fishes and invertebrates already considered threatened, ocean warming will exacerbate the declines of some species, the report also found.
The movement of fish will create winners and losers among the 4.3 billion people in the world who rely heavily upon fish for sustenance. In south-east Asia, harvests from fisheries could drop by nearly a third by 2050 if emissions are not severely curtailed. Global production from capture fisheries has already levelled off at 90m tonnes a year, mainly due to overfishing, at a time when millions more tonnes will need to be caught to feed a human population expected to grow to 9 billion by 2050.
Humans are also set to suffer from the spread of disease as the ocean continues to heat up. The IUCN report found there is growing evidence of vibrio bacterial disease, which can cause cholera, and harmful algal bloom species that can cause food poisoning. People are also being affected by more severe, if not more numerous, hurricanes due to the extra energy in the ocean and atmosphere.
Coral reefs, which support around a quarter of all marine species, are suffering from episodes of bleaching that have increased three-fold over the past 30 years. This bleaching occurs when prolonged high temperatures cause coral to expel its symbiotic algae, causing it to whiten and ultimately die, such as the mass mortality that has gripped the Great Barrier Reef.
Ocean acidification, where rising carbon dioxide absorption increases the acidity of the water, is making it harder for animals such as crabs, shrimps and clams to form their calcium carbonate shells.
The IUCN report recommends expanding protected areas of the ocean and, above all, reduce the amount of heat-trapping gases pumped into the atmosphere.
“The only way to preserve the rich diversity of marine life, and to safeguard the protection and resources the ocean provides us with, is to cut greenhouse gas emissions rapidly and substantially,” said Inger Andersen, director general of the IUCN.
Our atmosphere effects the amount of solar energy absorbed by the Earth and the amount of that energy that the Earth radiates back out into space.
Greenhouse gases — water vapor, carbon dioxide, and methane — occur naturally in small amounts in our atmosphere. They absorb and release heat energy more efficiently than other gases like nitrogen and oxygen, which are actually more abundant.
Indeed, the greenhouse gases are so efficient that even a small increase in their concentration can have an enormous effect on our climate. Human released CO2 and methane are two greenhouse gases that are dramatically changing Earth’s climate. Read more…
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1. The first involves the sediments at the bottom of the oceans: Carbon dioxide dissolves into cold ocean water at high latitudes. That CO2 is then carried to the deep ocean by sinking currents where it stays in sediments for hundreds of years. Thus deep ocean currents pump carbon from the atmosphere into the sea for storage.
2. Plants also reduce carbon in the atmosphere through photosynthesis: They use energy from the sun to combine CO2 from the atmosphere and water from the soil to make carbon-rich carbohydrates like glucose.Thus plants extract CO2 from the atmosphere and accumulate it in their tissues. Conversely, cutting down trees, or deforestation, and the burning of fossil fuels increases CO2 in the atmosphere.
3. Some carbon is transformed into calcium carbonate (limestone), the largest carbon reservoir on Earth. Read more…
Aerosols are simply particles that are airborne. They have a complex effect on the Earth's energy balance: (1) They can cause cooling, by reflecting incoming sunlight back out to space. (2) They can cause warming, by absorbing and releasing heat energy in the atmosphere.
Small solid and liquid particles can be carried into the atmosphere through a variety of natural and man-made processes, including volcanic eruptions, sea spray, forest fires, and emissions generated through human activities (things like exhaust from your car or a power plant). Read more…
watch the video
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A big change in any one component of the climate system can influence the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system—changes more rapid and on a larger scale than projected by current climate models.
Feedback loops are found in many natural processes. For example: The relationship between snow and ice cover and greenhouse gases trapped under snow and ice generates a positive feedback loop that releases additional greenhouse gases as the planet warms (see the diagram at right). Read more…
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Gulf of Mexico waters are freakishly warm, which could mean explosive springtime storms
By Jason Samenow March 22
Sea surface temperature difference from average. (WeatherBell.com)
Water temperatures at the surface of the Gulf of Mexico and near South Florida are on fire. They spurred a historically warm winter from Houston to Miami and could fuel intense thunderstorms in the spring from the South to the Plains.
In the Gulf, the average sea surface temperature never fell below 73 degrees over the winter for the first time on record, reported Eric Berger of Ars Technica.
Galveston, Tex., has tied or broken an astonishing 33 record highs since Nov. 1, while neighboring Houston had its warmest winter on record. Both cities have witnessed precious few days with below-normal temperatures since late fall.
Average temperature rankings along the coast of the western Gulf of Mexico this winter. (Southeast Regional Climate Center)
More often than not, temperatures have averaged at least 10 degrees warmer than normal. “The consistency and persistence of the warmth was the defining element of this winter,” said Matt Lanza, a Houston-based meteorologist, who has closely tracked the region’s temperatures.
Warmer-than-normal weather is predicted to continue in Galveston and Houston, with afternoon temperatures of 80 to 85 degrees through the weekend (normal highs are in the mid-70s).
“A steamy Gulf has meant that any time winds blow out of the south, we’re not going to cool down that much overnight, and daytime temperatures can warm pretty quickly,” wrote Berger, who also pens the Houston weather blog Space City Weather.
To the south of Galveston and Houston, Brownsville, McAllen and Harlingen all posted their warmest winters on record, by large margins. “Call it the ‘Usain Bolt’ of records: Leaving the others in the dust!” tweeted the National Weather Service forecast office in Brownsville.
The abnormally warm temperatures curled around the Gulf, helping Baton Rouge and New Orleans reach their warmest Februaries on record.
Meanwhile, a ribbon of toasty sea surface temperatures streamed north through the Straits of Florida supporting record-setting warmth over parts of the Florida peninsula.
Miami and Fort Lauderdale both posted their warmest winters on record. Climate Central, a nonprofit science communications firm in Princeton, N.J., found 80 percent of the winter days in Miami, Orlando and Tampa were above normal.
“Out of 90 days this winter, Miami saw a record setting 69 of them reach 80°F or warmer!” wrote Miami broadcast meteorologist John Morales for the website WxShift, a project of Climate Central. “In addition, 11 daily record high temperatures were set as were 8 daily record warm low temperatures and 2 monthly record warm low temperatures.”
[Forty years ago Miami saw its only snow. These days, it’s simmering in record heat.]
Brian McNoldy, a tropical weather researcher at the University of Miami, said that in addition to the warm water temperatures, a lack of cold fronts penetrating into Florida played a big role in the warmth. “We’ve not had strong, long-lasting cold fronts make it this far south,” he said.
Effects of warm Gulf waters on thunderstorms and hurricanes
The warm water temperatures in the Gulf of Mexico, in particular, could mean that thunderstorms that erupt over the southern and central United States are more severe this spring. Berger explained in his Ars Technica piece: “While the relationship is far from absolute, scientists have found that when the Gulf of Mexico tends to be warmer than normal, there is more energy for severe storms and tornadoes to form than when the Gulf is cooler.”
A study published in the journal Geophysical Research Letters in December found: “The warmer (cooler) the Gulf of Mexico sea surface temperatures, the more (less) hail and tornadoes occur during March–May over the southern U.S.”
Victor Gensini, a professor of meteorology at the College of DuPage, agreed that the warm Gulf could intensify storms this spring but cautioned that additional ingredients will need to come together. “The water is only one piece,” he said.
An additional key component for severe thunderstorms is a phenomenon known as the elevated mixed layer, a zone of hot and dry air at high altitudes that develops over Mexico’s high plateau and can flow into the southern and central United States. When it interacts with the warm, moist air from the Gulf, the resulting instability can give rise to explosive thunderstorms.
“This year we have both ingredients,” Gensini said. “With them coming together, we’re already seeing tornado levels as high as they’ve been since 2008.”
Another favorable ingredient for severe weather this spring is the configuration of water temperatures in the eastern Pacific Ocean. When there is a warm pool of water off the coast of Peru (which has contributed in extreme flooding there) and a cold pool off the U.S. West coast, such a pattern strongly correlates with high tornado activity, according to research conducted at the National Oceanic and Atmospheric Administration.
Gensini, who leads a team that produces severe weather outlooks up to three weeks into the future, is calling for above-average thunderstorm activity for the week beginning March 26, with high confidence.
A vigorous jet stream disturbance, originating from the Pacific Ocean, will crash into the southwestern United States around March 28. Once it enters the Plains around March 29 and March 30, it is likely to tap into the warm Gulf water and encounter the elevated mixed layer. Then severe storms may erupt.
Mean trough position over interior West w/East Coast ridging is classic setup for active #severe wx Plains/Midwest next 2 weeks. Get ready! pic.twitter.com/lF9dUjYglW
— Michael Palmer (@MPalmerTWC) March 21, 2017
Such conducive environments for severe weather may increase due to climate change, Gensini said, although he expects high year-to-year to variability — something already being observed.
[Studies: Tornado seasons peaking earlier, becoming more volatile]
The implications of the warm water for hurricane season, June 1 to Nov. 30, are less clear. Warmer-than-normal water temperatures can make tropical storms and hurricanes more intense, but wind shear and atmospheric moisture levels often play more important roles in hurricane formation, Berger reported.
Misconceptions about this Principle
Isn’t it true that the planet cooled mid-century during a period of post World War II industrialization when CO2 emissions were rising?
The misconception goes something like this: If CO2 really is responsible for global warming, then why don’t we see a consistent rise in temperatures during the 20th century since CO2 levels were rising throughout the century and especially during the post WWII period? Instead we see a cooling period from the 1940s to the 1970s.
CO2 was increasing during the period following WWII, but so were sulphate aresols, which had a pronounced cooling effect because they reflect incoming solar energy back into space and lead to cooling.
The science says: Although temperatures increased overall during the 20th century, three distinct periods can be observed. Global warming occurred both at the beginning and at the end of the 20th century, but a cooling trend is seen from about 1940 to 1975. As a result, changes in 20th century trends offer a good framework through which to understand climate change and the role of numerous factors in determining the climate at any one time. Read more…
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