Past , 7 , — , doi: Klein Tank , , and G. Lenderink , , M. Collins , , and W. Hazeleger , : SST and circulation trend biases cause an underestimation of European precipitation trends. Past , 3 , — , doi: Drijfhout , , A. Haarsma , , A. Sterl , , C. Severijns , , W. Hazeleger , , and H. Dijkstra , : Western Europe is warming much faster than expected. Return time yr of a the mean of December—February minimum winter temperature of —14 in the climate of and b at GDCN-D stations in the Great Lakes area with at least years of data.
All trends are defined as the regression on the GISTEMP global mean temperature, low-pass filtered with a 4-yr running mean, and exclude the winter of — For surface air temperature and sea level pressure, the same 42 CMIP5 models were used as in van Oldenborgh et al. The annual minimum of minimum temperature used the 25 models of Sillmann et al. The winter of —14 had unusual weather in many parts of the world.
Here we analyze the cold extremes that were widely reported in North America and the lack of cold extremes in western Europe.
We perform a statistical analysis of cold extremes at two representative stations in these areas: Chicago, Illinois, and De Bilt, the Netherlands. This shows that the lowest minimum temperature of the winter was not very unusual in Chicago, even in the current warmer climate.
Around it would have been completely normal. The same holds for multiday cold periods. Only the whole winter temperature was unusual, with a return time larger than 25 years. In the Netherlands, the opposite holds: the absence of any cold waves was highly unusual even now, and would have been extremely improbable halfway through the previous century.
These results are representative of other stations in the regions. The difference is due to the skewness of the temperature distribution. In both locations, cold extremes are more likely than equally large warm extremes in winter.
Severe cold outbreaks and cold winters, like the winter of —14 in the Great Lakes area, are therefore not evidence against global warming: they will keep on occurring, even if they become less frequent. The absence of cold weather as observed in the Netherlands is a strong signal of a warming trend, as this would have been statistically extremely improbable in the s.
Here we analyze the cold extremes that were widely reported in North America and the lack of cold extremes in Western Europe. We study the winter weather and cold extremes in these two regions statistically and investigate how this winter fits in with the climate model representation of global warming.
This was balanced by above-average temperatures over the Arctic, Europe, and the North Pacific. The deviations were more pronounced and farther south in other aspects that represent the severity of winter weather: the coldest day of the year Fig.
The anomalous temperature pattern was caused by large deviations from normal in the circulation. In January, the jet stream that normally circles the cold air over the Arctic was displaced to North America a wavenumber-1 anomaly. In January and February, it was split in two, with a second pole over Siberia wavenumber Citation: Bulletin of the American Meteorological Society 96, 5; Two features of the winter of —14 that stood out were cold outbreaks in North America that caused extensive problems and the very low winter-averaged temperatures in the Great Lakes area.
A widely reported extreme occurred on January 6, in Chicago, Illinois. The minimum temperature at Midway Airport reached — The outbreak was due to Arctic air flowing south into the Midwest Fig. A second cold outbreak at the end of January brought unusually cold weather to the southeastern United States Fig. In parts of the northern United States and Canada, below-normal temperatures persisted for much of the winter.
This led to an almost complete freezing over the Great Lakes, which had not occurred in 35 years. In Chicago, the December—February winter mean minimum temperature was the sixth coldest on record. The extended winter December—March temperature was the coldest on record within observational errors. The severe winter was associated with large economic losses. In contrast, the winter in most of Europe was notable for its lack of cold outbreaks. In the Netherlands, it was the first recorded winter with no days with a daily mean temperature below zero.
The winter-mean temperature was also among the highest recorded there. We do not discuss the extreme precipitation that also occurred in North America and Europe that winter, such as the record winter precipitation in northern Italy and in England due to a very persistent low-pressure area just west of Scotland and the drought in the western United States.
To look at the statistics of the cold outbreaks, we consider the lowest minimum temperature of the year from July to June. For the winter temperature we take the conventional December—February season of the daily minimum temperature.
These are first analyzed in some detail at two meteorological stations with relatively long time series in the areas with the reportedly most extreme weather. The very nonstandard thermometer hut at De Bilt prior to does not appear to affect the monthly means of the minimum temperatures in winter, and we assume this also holds for the daily temperatures.
In a second step, we check that the results are representative of the Midwest and continental Europe, respectively. Figures 2a,b show the winter mean minimum T2m and the lowest minimum temperature in Chicago. This station has a continental climate, with low temperatures in winter, large day-to-day variability and a large negative skewness —0. The winter mean minimum temperature has a significant positive trend of 1.
The maximum temperature has a smaller, nonsignificant trend 0. The trend in the lowest minimum temperature of the year is even more pronounced, but of course has larger uncertainties as well 3. To determine the return time of the coldest outbreak in the winter of —14, the annual minima T n are fitted to a Generalized Extreme Value GEV distribution, excluding the winter to be studied. This distribution describes the tail of extremes within a larger dataset with three parameters.
A negative shape parameter indicates a threshold above which the probability is zero. Snow sometimes comes on the heels of rain and the temperature can dip into the negatives, especially in the mountains. Along the Atlantic seaboard, in the West of France, there is an oceanic climate. Temperature differences are moderate and the winters are mild but damp.
It rains relatively frequently. In the East, the climate is continental. Summers are warm, with some thunderstorms, and winters are cold. Temperatures can drop below 0 degrees Celsius and, in the mountains, are frequently accompanied by snow. In the South, the climate is Mediterranean. However, when approaching the Mediterranean or Black Sea the climate becomes milder due to influences from the sea.
The climate usually has mild, wet winters and cool, humid summers. Long harsh frost periods are rare just like hot summers. Due to the longer growing period there are many possibilities and solutions to choose from. Barenbrug has a wide range of varieties that are suitable for your specific situation in the Atlantic climate. The Mediterranean climate can be experiences around the Mediterranean sea. Countries like Spain, Portugal, Southern France, Italy, Greece and Turkey do all face hot dry summers and mild winters with hardly any frost.
Drought and a lack of quality irrigation water are the biggest problems turf managers to deal with. Therefore Barenbrug included drought tolerant species and varieties in their mixtures for the southern areas. This assertion has the benefit of being both correct and misleading. Because it does not specify what European climate is ameliorated relative to the climate of eastern North America?
The idea that the Gulf Stream is responsible for Europe's mild winters seems to have originated with Matthew Fontaine Maury, an American naval officer who in published The Physical Geography of the Sea , which is often considered the first textbook of physical oceanography. The book was a huge success, went through many printings and was translated into three languages.
The role of the Gulf Stream in shaping climate is a recurring theme in Maury's book. For example, he stated:. According to Maury, if this transport of heat did not take place, "… the soft climates of both France and England would be as that of Labrador, severe in the extreme, and ice bound.
Maury thought that God set the ocean up to work this way apparently as part of His design to keep Europe warm for unspecified reasons. But holding such religious beliefs did not stop Maury from also providing a scientific explanation for the Gulf Stream. His idea was that it was the oceanic equivalent of what in the atmosphere is known as a Hadley cell , a convection cell wherein warm air flows upward and poleward, and cold material flows downward and equatorward.
In the ocean, heated surface waters take a northeastward route, in Maury's view, because of the need to conserve angular momentum as they move north and, hence, closer to the axis of the Earth's rotation. Maury did not recognize that winds drive ocean currents. And it was not until a century later that a valid explanation of the Gulf Stream emerged: In the jargon of oceanographers, it is a westward-intensified boundary current within a subtropical gyre a large circular current system driven by the trade winds, which blow from east to west in the tropics, and mid-latitude westerlies, which move in the opposite direction.
After completing my Ph. Seattle and British Columbia, just to the north, I discovered, have a winter climate with which I was very familiar—mild and damp, quite unlike the very cold conditions that prevail on the Asian side of the Pacific Ocean. This contrast exists despite the fact that the circulation of currents in the Pacific Ocean is very different from the situation in the Atlantic. Figure 2. Average January air temperatures are warmer over oceans than they are over land, because the sea retains more summer heat, which can then be released to the overlying air in winter.
Sites located close to the coasts thus tend to enjoy mild "maritime" climates. And because prevailing winds over the midlatitudes blow from west to east, coastal areas on the eastern side of ocean basins experience especially mild temperatures.
Conversely, the coasts bordering the western side of ocean basins experience winters that are intermediate between typical maritime conditions and the frigid "continental" climates found in interior regions. The difference in January temperatures across the North Atlantic at the latitude of London, for example, amounts to between 15 and 20 degrees Celsius.
The analogue of the Gulf Stream in the Pacific Ocean is the Kuroshio Current , which flows north along the coast of Asia until it shoots off into the interior of the Pacific Ocean east of Japan.
From there, it heads due east unlike the Gulf Stream, which heads northeast toward Oregon and California. As such, there is almost no heat carried northward into the Pacific Ocean at the latitudes of Washington and British Columbia. Hence oceanic heat transport cannot be creating the vast difference in winter climate between the Pacific Northwest and similar latitudes in eastern Asia—say, chilly Vladivostok.
Strangely, experiencing a Seattle winter firsthand was not enough to make me question the myth. However, in Seattle I did become good friends with David S.
Battisti, a professor of atmospheric sciences at the University of Washington. Battisti is one of those great scientists who, with relish and an air of mischief, loves to question conventional wisdom. Over the years he and I have enjoyed many a long evening indulging our shared passions for Italian cooking and wine while talking about climate research.
During one of those conversations, sometime in as I recall, he brought up that he wanted to test the Gulf Stream-European climate idea. It was perfect timing, because just then I had been conducting a series of experiments with a numerical climate model, ones designed to examine the role the ocean plays in determining the global and regional features of the Earth's climate.
So Battisti and I went to work. First we had to consider the range of possibilities. If oceanic heat transport does not create the differences in regional climate across the North Atlantic or North Pacific , what does? An obvious alternative explanation is that standard of high school geography education: Because the heat capacity of water is so much greater than that of rock or soil, the ocean warms more slowly in summer than does land.
For the same reason, it cools more slowly in winter. That effect alone means that the seasonal cycle of sea-surface temperature is considerably less than that of land surfaces at the same latitude, which is why summers near the sea are cooler and winters are warmer than at equivalent sites located inland.
Figure 3. Thermohaline circulation—often dubbed "the ocean conveyor belt"—carries warm surface waters pink from the tropics to the North Atlantic, with the return flow at depth purple. But contrary to many accounts summarized by diagrams such as this , this heat conveyor plays only a minor role in keeping European countries warm during winter months.
The effect of differing heat capacities is augmented by the fact that the Sun's heat is stored within a larger mass in the ocean than on land. The heat reservoir is bigger because, as the Sun's rays are absorbed in the upper several meters of the ocean, the wind mixes that water downward so that, in the end, solar energy heats several tens of meters of water. On land, the absorbed heat of the Sun can only diffuse downward and does not reach deeper than a meter or two during a season.
The greater density of soil and rock which ranges up to three times that of water cannot make up for this difference in volume of material that the Sun heats and for the difference in heat capacity of water compared with soil or rock.
Because sea-surface temperatures vary less through the seasonal cycle than do land-surface temperatures, any place where the wind blows from off the ocean will have relatively mild winters and cool summers. Both the British Isles and the Pacific Northwest enjoy such "maritime" climates. Central Asia, the northern Great Plains and Canadian Prairies are classic examples of "continental" climates, which do not benefit from this moderating effect and thus experience bitterly cold winters and blazingly hot summers.
The northeastern United States and eastern Canada fall somewhere in between. But because they are under the influence of prevailing winds that blow from west to east, their climate is considerably more continental than maritime. Battisti and I naturally wondered whether we could explain the difference in winter conditions between Europe and eastern North America as simply the difference between a maritime climate and a more continental one.
To find the answer, he and I used two climate models, ones that normally serve for studies of natural climate variability or for assessments of future climate change. As in all such models, Earth's atmosphere is represented on a three-dimensional grid latitude, longitude and pressure level in the vertical. For each grid point, the computer solves the relevant equations for the winds, temperature, specific humidity, fluxes of solar and terrestrial radiation and so forth while keeping track of the precipitation and energy fluxes at Earth's surface.
The packing of the grid points was sufficiently dense so that we could accurately capture the endless progression of storm systems, which transport vast quantities of heat and moisture poleward. As with the computer models used to forecast the weather which are basically the same as climate models , the computer code we used calculated conditions forward in time until, for these experiments, a statistical steady state was achieved.
To get a representative picture of overall climate, we averaged together many years of simulated weather. Figure 4. Gulf Stream currents carry an enormous amount of heat from the Gulf of Mexico, around the tip of Florida and up along the East Coast before heading northeast toward Europe top. Arrows indicate speed and direction. Measurements of less than 15 centimeters per second are not shown. So at first glance the supposition that the Gulf Stream is responsible for mild European winters seems reasonable.
But the current pattern found in the Pacific bottom argues otherwise: The equivalent boundary current, the Kuroshio, heads almost due east after it departs from the coast of Japan, meaning that it transports almost no heat northward to warm such places as Seattle or Vancouver on the eastern side of the Pacific.
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