fredag den 6. juni 2014



 Full 8-Century Record
] The complete 8-century Mg/Ca-derived SST record
(Figure 4a) shows an unexpectedly large amount of vari-
ability for a tropical location during the late Holocene. The
base of the record captures the latter part of the Medieval
Warm Period (MWP), approximately A.D. 1200 and 1425,
during which spring SSTs gradually cooled by 0.75ºC. 
This cooling was followed by more than 1.0ºC warming between
A.D. 1425 and 1500. The Little Ice Age (LIA) is charac-
terized by a pronounced 1.5ºC SST decrease between A.D.
1500 and 1640, with a particularly steep drop between
approximately 1630 and 1640, almost exactly coincident
with the beginning of the Maunder Minimum in 1645
. SSTs gradually rose again until about A.D.
1800, after which temperatures fluctuate around a mean that
is slightly cooler than SSTs observed for the late Medieval
Warm Period. A brief 0.5ºC cooling occurred in the late
1800s and early 1900s followed by a strong 1ºC warming
during the twentieth century. The resolution of this data
set is sufficient to capture even short transient events such
as the brief but notable cooling that occurred in the Atlantic

Nearly 50 years ago Bjerknes suggested that the character of large-scale air–sea interaction over the mid-latitude North Atlantic Ocean differs with timescales: the atmosphere was thought to drive directly most short-term—interannual—sea surface temperature (SST) variability, and the ocean to contribute significantly to long-term—multidecadal—SST and potentially atmospheric variability. Although the conjecture for short timescales is well accepted, understanding Atlantic multidecadal variability (AMV) of SST remains a challenge as a result of limited ocean observations. AMV is nonetheless of major socio-economic importance because it is linked to important climate phenomena such as Atlantic hurricane activity and Sahel rainfall, and it hinders the detection of anthropogenic signals in the North Atlantic sector
 Direct evidence of the oceanic influence of AMV can only be provided by surface heat fluxes, the language of ocean–atmosphere communication. Here we provide observational evidence that in the mid-latitude North Atlantic and on timescales longer than 10years, surface turbulent heat fluxes are indeed driven by the ocean and may force the atmosphere, whereas on shorter timescales the converse is true, thereby confirming the Bjerknes conjecture. This result, although strongest in boreal winter, is found in all seasons. Our findings suggest that the predictability of mid-latitude North Atlantic air–sea interaction could extend beyond the ocean to the climate of surrounding continents.

 We present the first direct comparison and calibration of a downcore foraminiferal Mg/Ca record to
historical instrumental sea surface temperature (SST). Mg/Ca measured on the planktic foraminifer
from a Cariaco Basin sediment core strongly correlate with spring (March–May) instrumental SSTs
between A.D. 1870 and 1990. A Mg/Ca SST equation is derived and a paleo-SST record is presented spanning
the last 8 centuries, an interval that includes the end of the Medieval Warm Period and the Little Ice Age. The
long-term record displays a surprising amount of variability. The temperature swings are not necessarily related
to local upwelling variability but instead represent wider conditions in the Caribbean and western tropical
Atlantic. The Mg/Ca SST record also captures the decadal and multidecadal variability observed in records of
global land and sea surface temperature anomalies and Atlantic tropical storm and hurricane frequency over the
late nineteenth and twentieth centuries. A divergence between the SST proxy record and Atlantic storm
frequency around 1970 appears to reflect a fundamental change in Atlantic hurricane behavior noted in historical
data. On average, twentieth-century temperatures are not the warmest in the entire record, but they do show the
largest increase in magnitude and fastest rate of SST change over the last 800 a

4 kommentarer:

  1. June 2001

    The averaging period used for the following assessment was 1961-1990.
    UK overview

    A cool and dull month over Northern Ireland and Scotland, whilst England and Wales were warmer than normal and rather sunny. Although it was a generally dry month over England and Wales, heavy thundery rainfall over the south-west on the 5th produced two inches of rainfall at Newquay.

    Eskdalemuir received just 66% of their normal sunshine. Barbourne, near Worcester, recorded a high of 32.6 °C on the 26th.

  2. The weather was dominated by low pressure over or close to the UK, with associated weather fronts. These brought rather cool days, some very large rainfall totals and also some strong winds early in the month.

    Persistent, and often heavy, rainfall for much of the 22nd caused significant flooding across parts of Lancashire, Cumbria and West Yorkshire with around 500 properties affected by both surface water flooding and where rivers burst their banks. Roads were closed and train services on the West Coast main line were suspended.

    On the 27th, torrential rain resulted in more than 700 flood-related call-outs in Belfast and County Antrim. At the height of the flooding, many roads were impassable and about 1,000 homes were left without power.

    Perhaps the most widespread and serious flooding occurred following thunderstorms and torrential rain on the 28th. Areas affected included the Midlands, NE England and parts of Northern Ireland and southern Scotland. As well as the flooding of properties and roads, thousands of homes were without power and both rail routes between England and Scotland were cut. Worst affected was NE England, where hundreds of homes were flooded, some 23,000 properties lost power after sub-stations
    The mean temperature was 0.6 °C below the 1981–2010 average, making it the coolest June since 1991. It was very wet across almost all areas, especially in Cumbria, Northumberland and counties in central southern England and the south-west Midlands where over 250% of the normal amount was recorded. It was the wettest June on record, just wetter than June 2007. The number of days with rain was the third highest for June in the last 50 years. Sunshine amounts were well below normal and it was the equal-dullest June on record.

    1st to 4th:
    After a dry, warm start to the month, slow-moving fronts lay across the south producing rain or drizzle. On 3rd, persistent rain across the Midlands and south-east gave totals of more than 15 mm, with 26 mm at Hampstead (Greater London), and temperatures from the Midlands northwards struggled to rise above 11 °C.
    5th to 9th:
    After a chilly start to 5th in the north and east, with temperatures as low as 2 °C in parts of East Anglia, rain moved north-eastwards bringing more than 15 mm across southernmost counties; 23.6 mm was recorded at Shanklin (Isle of Wight). There was a very wet and windy spell from 7th to 9th with southern and south-western parts bearing the brunt of the weather from the Atlantic. More than 20 mm of rainfall was recorded in much of the west and north on 7th; 36.7 mm at Buxton (Derbyshire) and 40.8 mm at Liscombe (Somerset). Gusts of 62 mph. were recorded at Plymouth (Devon) on 7th and of 82 mph. at the Needles (Isle of Wight) in the early hours of 8th. As rain cleared north-eastwards on 9th conditions turned more showery.
    10th to 13th:
    A shallow but active depression ran across southern areas on 10th and 11th with over 15 mm rainfall recorded widely each day; 57.2 mm fell at Shoreham (West Sussex) on 10th and 47.2 mm was recorded at Otterbourne (Hampshire) on 11th. Further north it was more showery and the rain in the south-east eased on 12th. After a chilly start on 13th when Santon Downham (Suffolk) dipped to 0.4 °C, many places saw showers 22nd, heavy persistent rainfall across the north-west resulted in totals of over 50 mm widely with 208.4 mm at Honister Pass (Cumbria).
    25th to 28th:
    Warm, humid air moving northwards brought rather cloudy, muggy conditions.low pressure over or close to the UK for the whole month, the weather was generally cool and unsettled with showers or longer periods of rain making it exceptionally wet in the south and east.
    The mean temperature was 0.9 °C below the 1981–2010 average, making it the coolest June since 1998. It was much wetter than normal across much of southern and eastern Scotland, especially in the Borders, Lothians and Fife where 250% to 300% of the normal amount fell.

  3. The latest value: 11,012,921 km2 (June 7, 2014)

    The 2012 has plunged below all previous minimums, but I have to add the caveat that this is based on a preliminary data point for August 24th, which will be revised tomorrow. It needs to be revised upwards by 66 thousand square km for this record not to remain standing. Even if this happens, the record will almost certainly be broken tomorrow.

    Here are the numbers for the IJIS SIE minimums in the 2005-2012 period:

    2005: 5.315 million square km
    2006: 5.781 million square km
    2007: 4.255 million square km
    2008: 4.715 million square km
    2009: 5.250 million square km
    2010: 4.814 million square km
    2011: 4.527 million square km
    2012: 4.189 million square km (and running)

    Another caveat is that the IARC-JAXA Information System (IJIS) - an international collaboration between the International Arctic Research Center (IARC) in corporation with the Japan Aerospace Exploration Agency (JAXA) - has switched from the AMSR-E to the WindSat sensor, when AMSR-E stopped functioning last year. WindSat isn't as sophisticated as AMSR-E, so this could cause slight inconsistencies