20 3 月 2012 at 6:49 上午 #3621
Till lately, 1998 had been thought to be the hottest year on record, maybe tying with 2005. Now, however a new revised dataset – which includes more Arctic measurements – gives 2010 that dubious honour. Info from UK Met Office:引用：The global temperature dataset compiled by the Met Office and the University of East Anglia's Climatic Research Unit has been updated.
Compiled from temperature observations obtained over land and sea, HadCRUT is used as a basis for a global temperature record going back to 1850.
The latest version of the dataset, called HadCRUT4, includes newly available data – notably adding much more information from the sparsely observed northern higher latitude region.
Differences in the way sea surface temperature observations have been collected have been taken account of and the new version also provides much more detail on uncertainty.
Colin Morice, Climate Monitoring Research Scientist at the Met Office said: "The new study brings together our latest and most comprehensive databases of land and marine temperature observations, along with recent advances in our understanding of how measurements were made at sea. These have been combined to give us a clearer picture of what the historical data can tell us about global climate change over the past 161 years.
"Updates have resulted in some changes to individual years in the nominal global mean temperature record, but have not changed the overall warming signal of about 0.75 °C since 1900."
One of the key reasons for slight changes to mean temperature for later years in HadCRUT4 is the inclusion of much more data from the Arctic, an area which is warming faster than other parts of the world.
Phil Jones, Director of the Climatic Research Unit, said: "HadCRUT is underpinned by observations and we've previously been clear it may not be fully capturing changes in the Arctic because we have had so little data from the area.
"For the latest version we have included observations from more than 400 stations across the Arctic, Russia and Canada. This has led to better representation of what's going on in the large geographical region."
Another change relates to dealing with the different ways sea-surface temperatures have been measured. This has had an effect on some years further back in the record, particularly in the mid 20日 世紀。
Peter Stott, Head of Climate Monitoring and Attribution at the Met Office, said: "An example of this is the rapid changes in the kinds of measurements we see in the digital archives around the Second World War. Some sea surface temperature observations were taken from buckets hauled on board ships and others were made in the engine rooms.
"Research has shown readings from buckets were generally cooler so when the database changes from one source to another you see artificial jumps in the raw data. We've quantified these effects and corrected for them providing a clearer view of the evolution of global temperatures."
Annual global mean temperature record under HadCRUT3 and HadCRUT4
Uncertainty (HadCRUT4) (°C)
0.0925 3 月 2012 at 4:09 下午 #4841
The World Meteorological Agency instead rates 2010 as 11th warmest year on record. But still, says 2001-2010 was the warmest decade on record; climate change is accelerating
Press release:引用：GENEVA, 23 MARCH 2012 (WMO) – The World Meteorological Organization’s Annual Statement on the Status of the Global Climate said that 2011 was the 11th warmest since records began in 1850. It confirmed preliminary findings that 2011 was the warmest year on record with a La Niña, which has a cooling influence. Globally-averaged temperatures in 2011 were estimated to be 0.40° Centigrade above the 1961-1990 annual average of 14°C.
Precipitation extremes, many of them associated with one of the strongest La Niña events of the last 60 years, had major impacts on the world. Significant flooding occurred on all continents, whilst major droughts affected parts of east Africa and North America. Arctic sea ice extent fell to near record-low levels. Global tropical cyclone activity was below average, but the United States had one of its most destructive tornado seasons on record.
The annual statement for 2011 was released for World Meteorological Day 23 March. In addition, WMO also announced preliminary findings of the soon to be released Decadal Global Climate Summary, showing that climate change accelerated in 2001-2010, which was the warmest decade ever recorded in all continents of the globe.
The rate of increase since 1971 has been “remarkable” according to the preliminary assessment. Atmospheric and oceanic phenomena such as La Niña events had a temporary cooling influence in some years but did not halt the overriding warming trend.
The “dramatic and continuing sea ice decline in the Arctic” was one of the most prominent features of the changing state of the climate during the decade, according to the preliminary findings. Global average precipitation was the second highest since 1901 and flooding was reported as the most frequent extreme event, it said.
The full report will be released later in the year following further analysis of data received from National Meteorological and Hydrological Services and collaborating monitoring agencies. The decadal summary aims to increase understanding of our varying and changing climate from a longer-term perspective and complements WMO’s annual reports.
“This 2011 annual assessment confirms the findings of the previous WMO annual statements that climate change is happening now and is not some distant future threat. The world is warming because of human activities and this is resulting in far-reaching and potentially irreversible impacts on our Earth, atmosphere and oceans,” said WMO Secretary-General Michel Jarraud.
The decade 2001-2010 was the warmest since records began in 1850, with global land and sea surface temperatures estimated at 0.46°C above the long-term average (1961-1990) of 14.0°C. Nine of these years were among the ten warmest on record. The warmest year on record was 2010, closely followed by 2005, with a mean temperature estimated at 0.53°C above the long-term average. It was the warmest decade ever recorded for global land surface, sea surface and for every continent.
Most parts of Canada, Alaska, Greenland, Asia and northern Africa recorded temperatures for the decade between 1°C and 3°C above the 1961-1990 average.
Nearly 90% of the countries involved in the assessment experienced their warmest decade on record.
The global temperature increase rate has been “remarkable” during the previous four decades, according to the preliminary summary. The global temperature has increased since 1971 at an average estimated rate of 0.166°C per decade compared to the average rate of 0.06 °C per decade computed over the full period 1881-2010.
(See Figures 1-3)
Global precipitation (rain, snow etc) over land in 2001-2010 was the second highest average after 1951-60 since 1901. Within this global average, there were big regional and annual differences.
Large parts of the Northern Hemisphere recorded wetter-than-average conditions during the decade, especially the eastern United States of America, northern and eastern Canada, and many parts of Europe and central Asia. South America, including Colombia, parts of northern and southern Brazil, Uruguay and northeastern Argentina experienced wetter-than-average conditions, as did most parts of South Africa, Indonesia and northern Australia.
In contrast, other regions experienced, on average, below normal precipitation. The western United States, southwestern Canada, Alaska, most parts of southern and western Europe, most parts of southern Asia, central Africa, central South America, and eastern and southeastern Australia were the most affected.
(See Figures 4 and 5)
Numerous weather and climate extremes affected almost every part of the globe with flooding, droughts, cyclones, heat waves, and cold waves. Two exceptional heat waves hit Europe and Russia during summer 2003 and 2010 respectively with disastrous impacts and thousands of deaths and outbreaks of prolonged bush fires.
Flooding was the most reported extreme event during the decade with many parts of the world affected. Historical widespread and prolonged flooding affected Eastern Europe in 2001 and 2005, Africa in 2008, Asia (in particular Pakistan) in 2010 and India in 2005, and Australia in 2010.
A large number of countries reported extreme drought conditions, including Australia, eastern Africa, the Amazonia region and the western United States. Humanitarian consequences were significant in eastern Africa during the first half of the decade, with widespread shortage of food and loss of lives and livestock.
Forty-eight out of 102 countries (47 per cent) reported that their highest national maximum temperature was recorded in 2001-2010, compared to 20 per cent for 1991-2000 and around 10 per cent for the earlier decades.
The decade saw the highest level of tropical cyclone activity on record for the North Atlantic basin. In 2005 category 5 hurricane Katrina was the most costly hurricane to hit the United States, with a significant human toll of more than 1 800 deaths. In 2008, tropical cyclone Nargis was the worst natural disaster in Myanmar and the world’s deadliest tropical cyclone during the decade, killing more than 70 000 people.
(See Figures 6 and 7)
The decline in the Arctic sea-ice, observed since the end of the 1960s, continued throughout 2001-2010. A historical low Arctic sea-ice extent at the melting period in September was recorded in 2007.
Arctic sea ice extent was again well below average in 2011. The seasonal minimum, reached on 9 September, was 4.33 million square kilometres (35% below the 1979-2000 average) according to the U.S. National Snow and Ice Data Center. This was the second-lowest seasonal minimum on record, 0.16 million square kilometres above the record low set in 2007. Sea ice volume was even further below average and was estimated at a new record low of 4200 cubic kilometres, surpassing the record of 4580 cubic kilometres set in 2010.
Satellites have shown the fluctuation in sea ice from year to year since 1972. According to scientific measurements, both the thickness and sea ice extent in the Arctic have shown a marked decline over the past 35 years. Data indicate, however, an even more dramatic reduction in Arctic sea ice cover in recent years. The last six years of the decade (2005 to 2010) recorded the lowest five September extents, with 2007 recording the record minimum extent with 4.28 million km2, 39 % below the 1979-2000 reference period.