Extra Tropical Northern Hemisphere Climate | Climatology

In this article, we present the major aspects of extra-tropical northern hemisphere climate of North America, Europe and Asia.

The Climatic Setting of North America:

North America, extending to within 10° of latitude of both the equator and the North Pole, embraces every climatic zone, from tropical rain forest and savanna on the lowlands of Central America to areas of permanent ice cap in central Greenland.

Subarctic and tundra climates prevail in N Canada and N Alaska, and desert and semiarid conditions are found in interior regions cut off by high mountains from rain-bearing westerly winds. However, a high proportion of the continent has temperate climates very favourable to settlement and agriculture.

Climatic Regions:

Differing continental climatic regions reflect the considerable amount of Arctic land, the great spread of temperate conditions, and the small but significant tropical area; dry climates also stand out in strong contrast to the prevailingly humid ones.

The Arctic Zone:

Including the northern parts of the Canadian Shield and Alaska, the Canadian Arctic Archipelago, and Greenland, the Arctic zone is dominated by Arctic and polar continental air masses and is perennially cold or cool. Temperatures below 0°F (“18°C) last 5 to 7 months, and subfreezing temperatures can persist for 8 to 10 months. Only between June and September do temperatures frequently rise above 32°F (0°C). The frost- free season does not exceed 60 days. Precipitation is low—especially in the far north—with 2 to 4 in (50 to 100 mm) of summer rain, plus 30 to 60 in (760 to 1,500 mm) of winter snow.

The Cool Temperate Zone:

The cool temperate zone extends from Newfoundland to Alaska and from Hudson Bay to the Ohio River. It is dominated by the polar continental air mass, especially during the long, cold winters. After the period of “Indian summer” that continues into October, temperatures fall quickly and do not rise substantially until April or early May. In January and February they drop to below 32°F (0°C) in the Ohio River valley and below 0°F (“18°C) north of the Great Lakes, with minimum temperatures as low as “20 to “80°F (“29 to “62°C).

Winter killing of crops and spring and autumn frosts are a hazard in the Canadian parts of the region, where the frost-free season is from 90 to 120 days. A swift transition occurs with spring; tropical gulf air raises monthly mean temperatures to more than 50°F (10°C) in June and to more than 60°F (16°C) in July. Precipitation is moderate, from 15 to 35 in (380 to 900 mm); as evaporation is low, however, most precipitation is effective for plant growth.

The Warm Temperate Zone:

On the southeast coasts of the United States, the warm temperate zone extends to the Mississippi River and over the Gulf Coast; the zone is strongly influenced by the warm, moist tropical air mass that originates over the Gulf of Mexico. The long frost-free season exceeds 200 days. Tropical air spreads north in February and dominates the region until November, when polar continental air occasionally invades. Winters are mild, with January means of 40 to 54°F (4 to 12°C). July averages are tropical, with highs exceeding 80°F (28°C).

This warmth and the long growing season allow subtropical crops such as cotton and peanuts (groundnuts) to be grown. Rainfall is ample (40 to 60 in [1,000 to 1,500 mm]) and benefits from the presence of the Colorado and Texas low-pressure systems and from thunderstorms that flare up on warm afternoons in the tropical maritime air. Because the landmass is intensely heated, frequent thunderstorms dot the landscape in this region, especially in early summer.

In the American Southwest a Mediterranean type of climate is found. Summers are dry there, because tropical continental air is dominant. July means of 70 to 80°F (21 to 27°C) are typical, with bright, sunny skies. Winters are mild (45 to 50°F [7 to 10°C]) and somewhat wet, with polar Pacific airs swinging south and bringing occasional heavy rain.

Frost and snowfall are rare but may occur when polar continental air thrusts through to the coast. Los Angeles has a record low temperature of only 23°F (5°C). Annual rainfall totals of 15 to 30 in (380 to 760 mm), along with high evaporation rates, often are insufficient for growing crops during the summer; supplemental irrigation is necessary.

The Tropical Humid Climate:

Central America, with its tropical humid climate, has no real winter; even the coldest month averages above 64°F (18°C). With summers of 80 to 82°F (27 to 28°C), the mean annual temperature range is lower than the usual daily range, a characteristic which is markedly different from most of North America. Rainfall is ample and regular, with 45 to 80 in (1,100 to 2,000 mm) where the easterly trade winds blow onshore.

Dry Climates:

About one-third of North America, including the high Arctic latitudes, has a dry climate. Chief dry areas lie in the American Southwest, where a combination of the mid-latitude high-pressure belt, the tropical continental air mass, and rain shadow effects behind the high Sierra Nevada has led to lack of rainfall. Summer winds blow from the continent outward, discounting the effect of Pacific subtropical air. As the winds move down in altitude from high interior plateaus, they become drier and warmer.

The inter-montane region of the United States and Mexico, from the Columbia River basin to Guadalajara, and the Pacific coast from San Diego, Calif., south to Mazatlan, Mex., are therefore arid, receiving less than 10 in (250 mm) of rain per year.

Some years have no rain. The Great Plains, from the South Saskatchewan River to Mexico, are semiarid, with 8 to 15 in (200 to 380 mm) of rainfall; the high mid-continental jet stream usually is depressed southward over them, strengthening down-moving dry wind from across the Rockies and tending to fend off cyclones from tropical gulf or polar continental air masses. The high Arctic areas are dry because most of the open water (which could act as a source of moisture) is frozen for six to nine months of the year and because the cold air that dominates the region can hold little moisture.

Weather of North America:

The continent of America is one of the largest and also one of the most diverse continents across the globe. Over the ages the weather of North America has been a subject of interest among weather specialists. Such is the weather of North America, that it traverses a climatic range from the Arctic climatic conditions to the Equatorial; and between the tropical weather conditions to the arid climate. In fact, of all the types of weather in America, it is the North American weather that has so much variety.

While ice caps are to be found permanently found in the country of Greenland, the temperatures in the northern regions of North America are never known to rise above the freezing point. Most of the north most regions of North America remains in freezing conditions all year round. Just below the Arctic region of North America lies the treeless and grassy tundra region.

A spectacular feature of the weather in North America, the Tundra is more than just a marvelous sight. Below the tundra comes the sub-arctic belt in North America, which in turn followed by the continental type of climate. Continental climate is pleasant, though with marked changes in seasonal changes. Of course, the coastal climate in these regions is pretty pleasant too. In the coastal regions in this belt, the climatic is more of Tropical.

Role of the Gulf of Mexico and Low-Level Jet:

The Gulf of Mexico is a Mediterranean-type sea located at the southeastern corner of North America. The Gulf is bordered by the United States to the north (Florida, Alabama, Mississippi, Louisiana, Texas), five Mexican states to the west (Tamaulipas, Veracruz, Tabasco, Campeche, Yucatan), and the island of Cuba to the southeast.

The Gulf measures approximately 1,600 kilometers from east to west, 900 kilometers from north to south, and has a surface area of 1.5 million square kilometers. The marine shoreline from Cape Sable, Florida to the tip of the Yucatan peninsula extends ∼5,700 kilometers, with another 380 kilometers of shore on the northwest tip of Cuba. If bays and other inland waters are included, the total shoreline increases to over 27,000 kilometers in the U.S. alone.

Depth:

The Gulf of Mexico basin resembles a large pit with a broad shallow rim. Approximately 38% of the Gulf is comprised by shallow and intertidal areas (< 20 m deep). The area of the continental shelf (< 180 m) and continental slope (180 – 3,000 m) represent 22% and 20% respectively, and abyssal areas deeper than 3,000 m comprise the final 20%.

The Sigsbee Deep, located in the southwestern quadrant, is the deepest region of the Gulf of Mexico. Its exact maximum depth is controversial, and reports by different authors state maximum depths ranging from 3,750 m to 4,384 m. Mean (average) water depth of the Gulf is ∼1,615 m and the basin contains a volume of 2,434,000 cubic kilometers of water (6.43* 10¹⁷ or 643 quadrillion gallons).

Origins and Geologic History:

The Gulf of Mexico basin is a relatively simple, roughly circular structural basin approximately 1,500 km in diameter, filled in its deeper part with 10 to 15 km of sedimentary rocks that range in age from Late Triassic to Holocene (approximately 230 m.y. to present). Little is known about the geologic history of the Gulf of Mexico Basin before Late Triassic time. Since pre-Triassic rocks are known from only a few widely separated outcrop areas and wells, much of the geologic history of the basin during Paleozoic time needs to be inferred from the study of neighboring areas.

Some authors have postulated the presence of a basin in the area during most of Paleozoic time, but most evidence seems to indicate that Paleozoic rocks do not underlie most of the Gulf of Mexico basin and that the area was, at the end of Paleozoic time, part of the large supercontinent of Pangea, the result of the collision of several continental plates.

The present Gulf of Mexico basin, in any case, is believed to have had its origin in Late Triassic time as the result of rifting within the North American Plate at the time it began to crack and drift away from the African and South American plates. Rifting probably continued through Early and Middle Jurassic time with the formation of “stretched” or “transitional” continental crust throughout the central part of the basin.

Intermittent advance of the sea into the continental area from the west during late Middle Jurassic time resulted in the formation of the extensive salt deposits known today in the Gulf of Mexico basin. It appears that the main drifting episode, during which the Yucatan block moved southward and separated from the North American Plate and true oceanic crust formed in the central part of the basin, took place during the early Late Jurassic, after the formation of the salt deposits.

Since Late Jurassic time, the basin has been a stable geologic province characterised by the persistent subsidence of its central part, probably due at first to thermal cooling and later to sediment loading as the basin filled with thick pro-grading clastic wedges along its northwestern and northern margins, particularly during the Cenozoic. To the east, the stable Florida, platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatan platform was emergent until the mid-Cretaceous.

After both platforms were submerged, the formation of carbonates and evaporites has characterised the geologic history of these two stable areas. Most of the basin was rimmed during the Early Cretaceous by carbonate platforms, and its western flank was involved during the latest Cretaceous and early Tertiary in a compressive deformation episode, the Laramide Orogeny, which created the Sierra Madre Oriental of eastern Mexico.

Geology:

Today, the Gulf of Mexico is a small oceanic basin surrounded by continental land masses. Due to their physical structure, the Gulf and the Caribbean Sea are sometimes combined and referred to as the ‘American Mediterranean’. Uchupi (1975) divides the Gulf into two distinct geographical provinces (Terrigenous and Carbonate) while Antoine (1972) recognizes seven. The scheme proposed by Antoine is presented here, with additional information derived from other sources.

i. Gulf of Mexico Basin:

This portion of the Gulf of Mexico contains the Sigsbee Deep and can be further divided into the continental rise, the Sigsbee Abyssal Plain, and the Mississippi Cone. Located between the Sigsbee escarpment and the Sigsbee Abyssal Plain, the continental rise is composed of sediments transported to the area from the north. The Sigsbee Abyssal Plain is a deep, flat portion of the Gulf bottom located northwest of Campeche Bank.

In this relatively uniform area of the Gulf bottom, the Sigsbee Knolls and other small diapiric (salt) domes represent the only major topographical features. The Mississippi Cone is composed of soft sediment and extends southeast from the Mississippi Trough, eventually merging with other sediments of the central basin. The cone is bordered by the DeSoto Canyon to the east and the Mississippi Trough to the west, and has been described in detail by Ewing et al. (1958).

ii. Northeast Gulf of Mexico:

Extending from just east of the Mississippi Delta near Biloxi to the eastern side of Apalachee Bay, this region of the Gulf bottom is characterised by soft sediments. To the west of the DeSoto Canyon, terrigenous (land-derived) sediments are thick and fill the remnants of the Gulf basin. In the eastern portion of the region, Mississippi-derived sediments cover the western edge of the Florida Carbonate Platform and a transition towards carbonate sediments begins. The Florida Escarpment separates the Florida Platform from the Gulf Basin and also forms the southeastern side of the DeSoto Canyon.

iii. South Florida Continental Shelf and Slope:

A submerged portion of the larger emergent Florida Peninsula, this region of the Gulf of Mexico extends along the coast from Apalachee Bay to the Straits of Florida and includes the Florida Keys and Dry Tortugas. A generalized progression towards carbonate sediments occurs from north to south ending in the thick carbonate sediments of the Florida Basin. Evidence suggests that this basin – was at one time enclosed by a barrier reef system. In the Straits of Florida the Jordan Knoll appears to be composed of remnants from this ancient reef system.

iv. Campeche Bank:

Campeche Bank is an extensive carbonate bank located to the north of the Yucatan Peninsula. The bank extends from the Yucatan Straits in the east to the Tabasco-Campeche Basin in the west and includes Arrecife Alacran. The region shows many similarities to the south Florida platform and some evidence suggests that the two ancient reef systems may have been continuous.

v. Bay of Campeche:

The Bay of Campeche is an isthmian embayment extending from the western edge of Campeche Bank to the offshore regions just east of Veracruz (∼96 degrees W). The Sierra Madre Oriental forms the south-southwestern border, and the associated coastal plain is similar to the Texas-Louisiana coast in the northern Gulf.

The bottom topography is characterised by long ridges parallel to the exterior of the basin. Salt domes are prevalent in the region, and the upward migration of salt is theorized to be a cause of the complex bottom profiles. Similar to the northern Gulf, large quantities of oil are produced here, and thick terrigenous sediments predominate.

vi. Eastern Mexico Continental Shelf and Slope:

Located between Veracruz to the south and the Rio Grande to the north, this geological province spans the entire eastern shore of Mexico. The Gulf bottom of the region is characterised by sediment- covered folds that parallel the shore. Apparently created by sediment-covered evaporites, evidence suggests that the folds have impeded sediment transport from the Mexican coast to the Gulf Basin.

vii. Northern Gulf of Mexico:

The northern Gulf of Mexico extends from Alabama to the U.S. Mexico border. North to south, the province extends from 200 miles inland of the present day shoreline to the Sigsbee escarpment. Sediments in the region arc generally thick with the greatest sediment load provided by the Mississippi River. Widespread salt deposits are present throughout the region and these structures act to create subsurface and emergent topographic features on the continental slope such as the Flower Garden Banks off the Texas/Louisiana coast, and the pinnacles region offshore of the Mississippi/Alabama coast.

Circulation and Currents:

Water enters the Gulf through the Yucatan Strait, circulates as the Loop Current, and exits through the Florida Strait eventually forming the Gulf Stream. Portions of the Loop Current often break away forming eddies or ‘gyres’ which affect regional current patterns. Smaller wind driven and tidal currents are created in near-shore environments.

Drainage into the Gulf of Mexico is extensive and includes 20 major river systems (> 150 rivers) covering over 3.8 million square kilometers of the continental United States. Annual freshwater inflow to the Gulf is approximately 10.6 x 10¹¹ m³ per year (280 trillion gallons). 85% of this flow comes from the United States, with 64% originating from the Mississippi River alone. Additional freshwater inputs originate in Mexico, the Yucatan Peninsula, and Cuba.

Effect of the Great Lakes:

As the single largest source of surface fresh water in the world, the Great Lakes region supports a burgeoning economy in the US. While being the linchpin for drinking water, hydroelectric power, commercial shipping, and recreation, the region also houses an amazingly diverse array of plants and wildlife. With scenic lakeshores, unique wildlife, and diverse recreational opportunities drawing millions of tourists annually, problems such as urban sprawl, air and water pollution, and habitat fragmentation are already stressing ecosystems of the Great Lakes region.

Global climate change looms as an additional threat on the region’s economy, population and wildlife by changing climate patterns and compounding the negative effects of current environmental problems. Given the heavy pressure from development on the hundreds of miles of delicate lakeshore and ecosystems, the Great Lakes region is particularly susceptible to the effects of rapid global warming.

According to the scenarios used in the National Assessment, scientists expect average temperatures in the Upper Great Lakes region to warm by 2 to 4°C, while precipitation could increase by 25% by the end of the 21^th century. Despite this significant increase in precipitation, lake water levels are expected to fall by 1.5 to 8 feet by 2100 because of the higher temperatures, with serious implications for ecosystems and the economy.

Although not necessarily due to global warming, the recent series of unusually warm years is already to blame for a drop of 3.5 feet in water levels for Lakes Huron, Michigan and Erie since 1997, and record low levels are expected later this summer. These lake-level declines from record high levels in the 1980s have caused concern among commercial shippers, hydroelectric companies, and recreational boaters. Fewer cold air outbreaks and less lake-effect snow (especially around Lake Erie and Lake Ontario) may decrease annual snowfall significantly, a trend that has already been observed in the past few years.

Although uncertainties remain, the research conducted through the National Assessment is an important first step in helping policymakers and residents understand the possible impacts of global warming on their region. Identifying risks specific to the people and ecosystems of the Great Lakes will help them make better informed decisions about how to address the problem.

Key Findings:

Water Ecology:

Aquatic ecosystems of the Great Lakes region support delicate, deeply interconnected webs of life which are highly adapted to the physical (and biochemical) characteristics and cycles of the lakes themselves. Climate computer models suggest that the waters of the Great Lakes will be warmer by the end of the 21^st century.

In addition, models suggest that lengthening warm seasons will reduce the seasonal mixing that replenishes critical oxygen to biologically productive lake zones, possibly shrinking lake biomass productivity by around 20%. This will include losses of zooplankton and phytoplankton that form the very base of aquatic food chains, and are critical to the survival of the many species of fish that live in the Great Lakes.

Changes in precipitation patterns may alter seasonal flow and volume patterns in streams and rivers feeding the Great Lakes. The National Assessment reiterates earlier findings that cold water stream habitats could be significantly altered by a warming climate, threatening cold-water species such as walleye and trout, and even some warm-water species such as smallmouth bass.

Wetlands and Coastal Ecosystems:

Climate change poses a significant threat to the remaining wetlands in the Great Lakes region, from the prairie potholes of Minnesota to the coastal marshes of northern Lake Huron. These delicate ecosystems are critical to declining migratory bird populations, providing food, breeding grounds, and resting stops along major migration routes. For example, Minnesota and Wisconsin may lose important duck habitat in prairie potholes.

Already, the region has lost up to 60 % of its prairie pothole wetlands, and under dryer climate conditions, the size and number of those that remain could be further reduced. Additionally, at least 32 of the 36 species of fish in the Great Lakes are dependent on coastal wetlands for successful reproduction. Declines in water levels caused by climate change will reduce fish’s access to the emergent vegetation of coastal marshes, which provide breeding habitat, shelter for young fish, and plenty of food in the form of vegetation and invertebrates.

With only 50 % of original wetlands remaining in the Great Lakes region, and much of these areas already stressed by pollution and development, it is imperative that Great Lakes authorities take meaningful steps to preserve wetlands ecosystems under the compounding effects of climate change.

Forest Ecosystems and Bird Habitat:

Forest ecosystems have contributed greatly to the prosperity and quality of life in the region as well as to cleaning its air and water, and the reduction of soil erosion. Their diversity has also provided important habitat to wildlife. If global warming occurs rather rapidly, both plants and animals are likely to face difficult challenges in adapting to changing conditions.

Several species of trees may no longer be able to grow in the Great Lakes region as summers become too warm, including economically important species such as quaking aspen, yellow birch, jack pine, red pine and white pine. Both broadleaf and conifer forests are in danger of declining by as much as 50 to 70% in the Upper Great Lakes region, although uncertainties in altered precipitation patterns make exact predictions impossible at this time.

Other trees such as black walnut and black cherry may eventually migrate northward into the region. Although productivity may ultimately increase after an initial dieback phenomenon, current mixed forest communities could give way to grasslands, savanna, or hardwood forests consisting of more oak, elm, ash and pines. This will have serious implications for species dependent on very specific habitats, including the endangered Kirtlands warbler, which breeds in the sandy jack pine barrens of Michigan.

Migratory birds are especially threatened by climate change in the Great Lakes. Michigan and Wisconsin whose secluded woodlands provide preferred habitat for wood warblers could each lose up to 32% of neo-tropical bird species. The assessment indicates that 67% of wood warbler species may be lost from Wisconsin, 61% from Michigan, and 52% from Minnesota, respectively. Changes in the distributions of upland game birds such as Northern pintails and mallards may also occur.

Agriculture:

Agriculture ranks among the most important economic activities in the Great Lakes region, accounting for more than $15 billion in annual cash receipts. Livestock, including dairy, is the number one agricultural commodity group, comprising over half of the total. Dairy production alone produces $5 billion in receipts. Crop diversity is an important characteristic of agriculture in the region, at least in part reflecting the moderating influence of the Great Lakes on regional climate. Over 120 commodities are grown or raised in this region.

The warmer and wetter climate across the region portrayed by the global climate models used in the assessment and the positive effects of CO₂ enrichment suggest that future crop yields may be greater than historical yields. Some crop yields may increase through 2050, but then decrease overtime from 2051 to 2100, especially at western and southern locations.

Quality of Life:

Heat waves in the Great Lakes region are still relatively rare but the climate models used in the assessment suggest significant increases in the number of days above 90°F. Thus, a major quality of life issue in the region will be human health and well-being. People who lack protection to high temperature extremes may suffer from heat stress, dehydration, respiratory distress, and occasionally heat stroke or cardiac malfunction.

On the other hand, winters will be warmer, decreasing illness and mortality related to extreme cold. Additionally, inter-annual variability may decrease, for example, cool summers may not occur as frequently as they do now. Other impacts from short-term, extreme weather events such as floods, tornadoes, and blizzards may also increase in the region, particularly heavy precipitation events.

Water Resources and Ecology:

The development of water conservation and regulation strategies robust enough for both high and low water levels would give Great Lakes water managers a more flexible, adaptive framework for decision-making. This would be aided by water management approaches that can deal with the lake level changes thought to be possible from climate change. If primary production in lakes declines as projected, stocking strategies may be required to rebuild stocks of native species that have survived in the lakes through centuries of post-glacial change. Appropriate public education programs to explain these changes could assist such efforts.

Forests and Land Management:

Possible adaptive strategies used within the forestry and land management communities include monitoring the health and productivity of forests as climate and other environmental parameters change; using land use planning and other tools to minimise land use conflicts; facilitating the migrations of plant species as the most hospitable climate conditions shift north; and planting tree species that are better suited to a changed climate.

Agriculture:

Improvements in technology, the CO2 fertilization effect, and the use of adaptive farm management strategies can possibly mitigate some of the negative effects of climate change for the majority of farm operations in the Great Lakes region.

Additional adaptive farm strategies include – changes in crop selection to varieties currently used in more southern regions; changes in the timing of planting and harvesting; improved soil management to retain soil moisture and prevent soil erosion; and the development of new varieties of crops that is more adaptable to inter-annual variations of weather.

Quality of Life:

Improved weather forecasting, information distribution, special assistance, and improving economic well-being will help at-risk populations to better cope with high temperature extremes. Better insulation of homes against heat and cold, and other construction improvements, as well as preventing construction too close to lakeshores will help reduce some of the weather-related risks, especially those related to extreme heat, floods, and storms. Efforts to reduce air pollution at the source and timely health advisories for susceptible people, such as the elderly, will help reduce the impacts of air pollutants on health.

The Climatic Setting in Europe:

The climate of Europe is of a temperate, continental nature, with a maritime climate prevailing on the western coasts and a Mediterranean climate in the south. The climate is strongly conditioned by the Gulf Stream, which warms the western region to levels unattainable at similar latitudes on other continents. Western Europe is oceanic, while Eastern Europe is continental and dry.

Four seasons occur in Western Europe, while southern Europe experiences a wet season and a dry season. Southern Europe is hot and dry during the summer months. The heaviest precipitation occurs downwind of water bodies due to the prevailing westerlies, with higher amounts also seen in the Alps.

Gulf Stream:

The climate is milder in comparison to other areas of the same latitude around the globe due to the influence of the Gulf Stream. The Gulf Stream is nicknamed “Europe’s central heating”, because it makes Europe’s climate warmer and wetter than it would otherwise be.

The extent of the Gulf Stream’s contribution to the actual temperature differential between North America and Europe is a matter of dispute as there is a minority opinion within the science community that this temperature difference is mainly due to the Atlantic Ocean being upwind of western Europe (producing an oceanic climate) and a landmass being upwind of the east coast of North America.

The average temperature throughout the year of Naples is 16°C (60.8°F), while it is only 12°C (53.6°F) in New York City which is almost on the same latitude. Berlin, Germany; Calgary, Canada; and Irkutsk, in the Asian part of Russia, lie on around the same latitude; January temperatures in Berlin average around 8°C (15°F) higher than those in Calgary, and they are almost 22°C (40°F) higher than average temperatures in Irkutsk.

This difference is even larger on the northern part of the continent; the January average in Brannaysund, Norway, is almost 15°C warmer than the January average in Nome, Alaska, even if both towns are situated upwind on the west coast of the continents at 65°N, and as much as 42°C warmer than January average in Yakutsk which is actually slightly further south.

Precipitation:

On an annual basis, rainfall across the continent is favoured within the Alps, and from Slovenia southward to the western coast of Greece. Other maxima exist in western Georgia, northwest Spain, western Great Britain, and western Norway. The maxima along the eastern coasts of water bodies are due to the westerly wind flow which dominates across the continent. A bulk of the precipitation across the Alps falls between March and November.

The wet season in lands bordering the Mediterranean Sea lasts from October through March, with November and December typically the wettest months. For example, the monthly rainfall at Athens ranges from 6 mm (July) during their dry season to 71 mm (December) during their wet season. Summer rainfall across the continent evaporates completely into the warm atmosphere, leaving winter precipitation to be the source of groundwater for Europe.

The European Monsoon (more commonly known as the Return of the Westerlies) is the result of a resurgence of westerly winds from the Atlantic, where they become loaded with wind and rain. These Westerly winds are a common phenomenon during the European winter, but they ease as spring approaches in late March and through April and May. The winds pick up again in June, which is why this phenomenon is also referred to as “the return of the westerlies”.

The rain usually arrives in two waves, at the beginning of June and again in mid to late June. The European monsoon is not a monsoon in the traditional sense in that it doesn’t meet all the requirements to be classified as such. Instead the Return of the Westerlies is more regarded as a conveyor belt that delivers a series of low pressure centres to Western Europe where they create unseasonable weather.

These storms generally feature significantly lower than average temperatures, fierce rain or hail, thunder and strong winds. The Return of the Westerlies affects Europe’s Northern Atlantic coastline, such as Ireland, Great Britain, the Benelux countries, Western Germany, Northern France and parts of Scandinavia.

Rainfall averages between 36 mm (March) to 54 mm (November) in London and from 36 mm (March) to 88 mm (July) in Moscow.

Blocking Anticyclones:

Time evolutions of prominent blocking flow configurations over the North Pacific and Europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons. Fluctuations associated with synoptic-scale migratory eddies have been filtered out before the compositing. A quasi-stationary wave train across the Atlantic is evident during the blocking amplification over Europe, while no counterpart is found to the west of the amplifying blocking over the North Pacific.

Correlation between the tropopause-level potential vorticity (PV) and meridional wind velocity associated with the amplifying blocking is found to be negative over Europe in association with the anti-cyclonic evolution of the low-P V center, but it is almost zero over the North Pacific. Feedback from the synoptic-scale eddies, as evaluated in the form of 250-mb geo-potential height tendency due to the eddy vorticity flux convergence, accounts for more than 75% of the observed amplification for the Pacific blocking and less than 45% for the European blocking.

This difference is highlighted in two types of contour advection with surgery experiments. In one of them PV contours observed four days before the peak blocking time were advected by composite time series of the low-pass-filtered observational wind, and in the other experiment they were advected by the low-pass-filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step.

Hence, the latter data should be dominated by low-frequency dynamics. For the European blocking both experiments can reproduce the anti-cyclonic evolution of low-PV air within a blocking ridge as observed. For the Pacific blocking, in contrast, the observed intrusion of low-PV air into the higher latitudes cannot be reproduced without the transient feedback.

Furthermore, in a barotropic model initialized with the composite 250-mb flow observed three days before the peak time, a simulated blocking development over the North Pacific is more sensitive to the insertion of the observed transient feedback than that over Europe. These results suggest that the incoming wave activity flux associated with a quasi- stationary Rossby wave train is of primary importance in the blocking formation over Europe, whereas the forcing by the synoptic-scale transients is indispensable to that over the North Pacific.

Climate is Changing and the Impacts:

The earth’s climate is changing and the impacts are already being felt in Europe and across the world.

Global temperatures are predicted to continue rising, bringing changes in weather patterns, rising sea levels and increased frequency and intensity of extreme weather events such as storms, floods, droughts and heat waves. Such climatic events can have a major impact on households, businesses, critical infrastructure (transport, energy and water supply) and vulnerable sections of society (elderly, disabled, poor income households) as well as having a major economic impact. We must therefore prepare to cope with living in a changing climate. This process is known as adaptation.

In April 2009 the European Commission presented a policy paper known as a White Paper which presents the framework for adaptation measures and policies to reduce the European Union’s vulnerability to the impacts of climate change. Decisions on how best to adapt to climate change must be based on solid scientific and economic analysis.

It is therefore important to increase the understanding of climate change and the impacts it will have. The White Paper outlines the need to create a Clearing House Mechanism by 2011 where information on climate change risks, impacts and best practices would be exchanged between governments, agencies, and organisations working on adaptation policies.

Since the impacts of climate change will vary by region – with coastal and mountain areas and flood plains particularly vulnerable – many of the adaptation measures will need to be carried out nationally or regionally. The role of the European Union will be to support and complement these efforts through an integrated and coordinated approach, particularly in cross-border issues and policies which are highly integrated at EU level.

The Climatic Setting in Asia:

Asia stretches about 5,000 miles from north of the Arctic Circle to south of the equator. From east to west Asia stretches nearly halfway around the world. This vast area has many different kinds of climate. Asia has some of the coldest and some of the hottest, some of the wettest and some of the driest places on earth.

The great interior lands of Asia are far from the ocean. Winds from the oceans cut off by the high mountain chains which surround the interior. Because of this, the climate of central Asia is one of extremes. Winters are long and cold, chilled by cold winds from the polar-regions. Summers everywhere but the highlands are short and hot. Except in the mountains, there is little rainfall. Consequently, much of the region is desert.

Northern Asia has much the same sort of climate as central Asia, except that is has more rainfall. Winters are extremely cold – the coldest inhabited place in the world is a village in Siberia called Verkhoyansk. The temperature there sometimes drops to 90 degrees below zero. In southern Asia the climate is quite different. Here is hot all year round, except in the mountains. The temperature in the lowlands may reach as high as 125 degrees. There are no summer and winter as we know them. Instead, there is a rainy season and a dry season.

The rainy season usually lasts from June through October. During that period it rains heavily every day. More rain falls in this part of the Asia than in any other place in the world. Some areas in India get more than 450 inches of rainfall during the rainy season. The rainy and dry seasons are caused by winds called monsoons, which blow from central Asia toward the southern and eastern edges of the continent. Winter monsoons are dry winds because they blow over dry land. They are cold because they come from a cold region.

The summer monsoons blow inland from the oceans, bringing moisture as far inland as they reach. The rainy season is very important to the millions of people who live in southern and eastern Asia. This is the reason when they planted the crops on which they depend for their food. Without the rains the plants will not grow. Drought brings famine, and thousands of people starve.

Sometimes the monsoons are late, and crops cannot be planted in time to ripen. Sometimes the monsoons bring floods. Southwestern Asia is another very dry region. Summers there are long and very hot. Winters are relatively mild except in the far interior. In certain areas of southwestern Asia, winter is the rainy season. It is also the growing season, because crops would die in the hot, dry summers.

Climate Characteristics and Trends:

Climate in Tropical Asia is characterised by seasonal weather patterns associated with the two monsoons and the occurrence of tropical cyclones in the two core areas of cyclogenesis (the northern Indian Ocean and the northwestern Pacific Ocean). Over the past 100 years, mean surface temperatures across the region have increased in the range of 0.3 – 0.8°C.

No long-term trend in mean rainfall has been discernible over that period, although many countries have shown a decreasing trend in the past three decades. Similarly, no identifiable change in the number, frequency, or intensity of tropical cyclones has been observed in the region over the past 100 years; however, substantial decadal-scale variations have occurred.

Ecological Systems:

Substantial elevational shifts of ecosystems in the mountains and uplands of Tropical Asia are projected. At high elevations, weedy species can be expected to displace tree species, although the rates of vegetation change could be slow and constrained by increased erosion in the Greater Himalayas. Changes in the distribution and health of rainforest and drier monsoon forest will be complex. In Thailand, for instance, the area of tropical forest could increase from 45% to 80% of total forest cover; in Sri Lanka, a significant increase in dry forest and a decrease in wet forest could occur.

Projected increases in evapotranspiration and rainfall variability are likely to have a negative impact on the viability of freshwater wetlands, resulting in shrinkage and desiccation. Sea-level rise and increases in sea-surface temperature are the most probable major climate change-related stresses on coastal ecosystems. Coral reefs may be able to keep up with the rate of sea-level rise but may suffer bleaching from higher temperatures. Landward migration of mangroves and tidal wetlands is expected to be constrained by human infrastructure and human activities.

Hydrology and Water Resources:

The Himalayas play a critical role in the provision of water to continental monsoon Asia. Increased temperature and increased seasonal variability in precipitation are expected to result in accelerated recession of glaciers and increasing danger from glacial lake outburst floods. A reduction in flow of snow-fed rivers, accompanied by increases in peak flows and sediment yields, would have major impacts on hydropower generation, urban water supply, and agriculture. Availability of water from snow-fed rivers may increase in the short term but decrease in the long term.

Runoff from rain-fed rivers may change in the future, although a reduction in snowmelt water would result in a decrease in dry-season flow of these rivers. Larger populations and increasing demands in the agricultural, industrial, and hydropower sectors will put additional stress on water resources. Pressure will be most acute on drier river basins and those subject to low seasonal flows. Hydrological changes in island and coastal drainage basins are expected to be small, apart from those associated with sea-level rise.

Agriculture:

The sensitivity of major cereal and tree crops to changes in temperature, moisture, and carbon dioxide (CO₂) concentration of the magnitudes projected for the region has been demonstrated in many studies. For instance, projected impacts on rice, wheat, and sorghum yields suggest that any increases in production associated with CO₂ fertilization will be more than offset by reductions in yield resulting from temperature and/or moisture changes.

Although climate change impacts could result in significant changes in crop yields, production, storage, and distribution, the net effect of the changes region-wide is uncertain because of varietal differences and local differences in growing season, crop management, and so forth; non-inclusion of possible diseases, pests, and microorganisms in crop model simulations; and the vulnerability of agricultural areas to episodic environmental hazards, including floods, droughts, and cyclones. Low-income rural populations that depend on traditional agricultural systems or on marginal lands are particularly vulnerable.

Coastal Zones:

Sea-level rise is the most obvious climate-related impact in coastal areas. Densely settled and intensively used low-lying coastal plains, islands, and deltas are especially vulnerable to coastal erosion and land loss, inundation and sea flooding, upstream movement of the saline/freshwater front, and seawater intrusion into freshwater lenses.

Especially at risk are the large deltaic regions of Bangladesh, Myanmar, Vietnam, and Thailand, and the low-lying areas of Indonesia, the Philippines, and Malaysia. Socioeconomic impacts could be felt in major cities, ports, and tourist resorts; artisanal and commercial fisheries; coastal agriculture; and infrastructure development.

Human Health:

The incidence and extent of some vector-borne diseases are expected to increase with global warming. Malaria, schistosomiasis, and dengue-which are significant causes of mortality and morbidity in Tropical Asia- are very sensitive to climate and are likely to spread into new regions on the margins of presently endemic areas as a consequence of climate change. Newly affected populations initially would experience higher case fatality rates.

In presently vulnerable regions, increases in epidemic potential of 12–27% for malaria and 31–47% for dengue are anticipated, along with an 11–17% decrease for schistosomiasis. Waterborne and water-related infectious diseases, which already account for the majority of epidemic emergencies in the region, also are expected to increase when higher temperatures and higher humidity are superimposed on existing conditions and projected increases in population, urbanisation rates, water quality declines, and other factors.

Adaptation and Integration:

Strategies for adapting to different climatic conditions will be quite diverse. For example, responses to impacts on agriculture will vary from region to region, depending on the local agro-climatic setting as well as the magnitude of climate change. New temperature- and pest-resistant crop varieties may be introduced, and new technologies may be developed to reduce crop yield losses. Countries in Tropical Asia could improve irrigation efficiency from current levels, to reduce total water requirements.

Integrated approaches to river basin management, which already are used in a number of countries in the region, could be adapted region-wide. Such approaches could increase the effectiveness of adapting to the often-complex potential impacts of climate change that generally transcend political boundaries and encompass upstream and downstream areas. Similarly integrated approaches to coastal zone management can include current and longer-term issues, including climate change and sea-level rise.

Regional Climate:

Present Climate Characteristics:

The climate of Tropical Asia is dominated by the two monsoons – The summer South-West monsoon influences the climate of the region from May to September, and the winter northeast monsoon controls the climate from November to February. The monsoons bring most of the region’s precipitation and are the most critical climatic factor in the provision of drinking water and water for rain-fed and irrigated agriculture.

As a result of the seasonal shifts in weather, a large part of Tropical Asia is exposed to annual floods and droughts. The average annual flood covers vast areas throughout the region; in India and Bangladesh alone, floods cover 7.7 million ha and 3.1 million ha, respectively.

At least four types of floods are common – riverine flood, flash flood, glacial lake outburst flood, and breached landslide-dam flood (bishayri); the latter two are limited to mountainous regions of Nepal, Bhutan, Papua New Guinea, and Indonesia. Flash floods are common in the foothills, mountain borderlands, and steep coastal catchments; riverine floods occur along the courses of the major rivers, broad river valleys, and alluvial plains throughout the region.

Tropical cyclones also are an important feature of the weather and climate in parts of Tropical Asia. Two core areas of cyclogenesis exist in the region – one in the northwestern Pacific Ocean, which particularly affects the Philippines and Viet Nam, and the other in the northern Indian Ocean, which particularly affects Bangladesh. Other extreme events include high-temperature winds, such as those that blow from the North-West into the Ganges valley during January.

In the megacities and large urban areas, high temperatures and heat waves also occur. These phenomena are exacerbated by the urban heat- island effect and air pollution. Geographically much more extensive is the El Nino-Southern Oscillation (ENSO) phenomenon, which has an especially important influence on the weather and inter-annual variability of climate and sea level, especially in the western Pacific Ocean, South China Sea, Celebes Sea, and northern Indian Ocean.

Indeed, the original historical record of El Niño events compiled by Quinn et al. (1978) considered the relationships among Indonesian droughts, the Southern Oscillation, and El Niño. The strength of such connections has been demonstrated in several other studies. Suppiah (1997) has found a strong correlation between the Southern Oscillation Index (SOI) and seasonal rainfall in the dry zone of Sri Lanka; Clarke and Liu (1994) relate recent variations in south Asian sea-level records to zonal ENSO wind stress in the equatorial Pacific.

The influences of Indian Ocean sea-surface temperature on the large-scale Asian summer monsoon and hydrological cycle and the relationship between Eurasian snow cover and the Asian summer monsoon also have been substantiated. Kripalani et al. (1996) studied rainfall variability over Bangladesh and Nepal and identified its connections with features over India.