2001-2010: Warmest decade on record

Climate change is happening now and is not some distant future event: World Meteorological Organization general secretary

 
By Indrajit Bose
Last Updated: Thursday 17 September 2015

The rate of climate change accelerated in the period 2001-2010—the warmest decade ever recorded worldwide, the World Meteorological Organization (WMO) said in its preliminary findings for its report titled Decadal Global Climate Summary. 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 (see 'Decade of extreme weather events', and map).
   
imageAlso, the year gone by, 2011, was the 11th warmest year since 1850, WMO said in its recently-released Status on the Global Climate report. Globally-averaged temperatures in 2011 were estimated to be 0.4°C above the 1961-1990 annual average of 14°C. This was despite La Nina, a weather event where the sea surface temperature is lower than usual in the tropical Pacific Ocean and has a cooling influence. It was not just temperatures though; significant flooding occurred in many places throughout the world, while major droughts affected parts of east Africa and North America.

Wrong question to ask

But are these changes a result of climate change or are these a result of natural variabilities? It is believed that science is not advanced enough to distinguish between the two in quantitative terms. The 2011 annual assessment confirms that climate change is happening now and is not some distant future threat, said Michel Jarraurd, secretary general, WMO.

Kevin E Trenberth of the National Center for Atmospheric Research, in his recent paper—Framing the way to relate extremes to climate change—says it is a wrong question to ask in the first place. No events are “caused by climate change” or global warming; all events make a contribution. Moreover, a small shift in the mean temperature can still lead to very large percentage changes in extremes. Thus, all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be. While Trenberth admits that extremes are expected to happen as the climate record gets longer, he also adds that certain extremes related to heating are becoming more evident. 

He explains in his paper: “Climate extremes are typically treated individually, but many are not unrelated. As climate varies or changes, several direct influences alter precipitation amount, intensity, frequency and type. Warming accelerates land-surface drying as heat goes into evaporation of moisture, and this increases the potential incidence and severity of droughts, which has been observed in many places worldwide.”

Climate model simulations and empirical evidence confirm that warmer climates, because of increased water vapour, lead to more intense precipitation events even when the total annual precipitation is reduced slightly. A warmer climate therefore increases risks of both drought—where it is not raining—and floods—where it is—but at different times and/or places.
 

Decade of extreme weather events
 
Temperature:
  • The decade 2001-2010 was the warmest since records began to be maintained 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. 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
  • 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
Precipitation:
  • Global precipitation 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 US, 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 US, 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
Extreme events:
  • Numerous weather and climate extremes affected almost every part of the globe with floods, droughts, cyclones, heat waves, and cold waves. Two exceptional heat waves hit Europe and Russia during the summer of 2003 and 2010 with disastrous impacts and thousands of deaths and outbreaks of prolonged bush fires
  • Flooding was the most reported extreme event during the decade. 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
  • Several countries reported extreme drought conditions, including Australia, eastern Africa, the Amazonian region and the western US. 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
  • 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 US, 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
Sea ice
  • 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 km (35 per cent below the 1979-2000 average), according to the US 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 dipped further and was estimated at a new record low of 4,200 cubic km, surpassing the record of 4,580 cubic km set in 2010
  • The thickness and sea ice extent in the Arctic have shown a marked decline over the past 35 years. Data indicate 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 per cent below the 1979-2000 reference period

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