The ecologically tumultuous year saw record greenhouse gas emissions, melting Arctic sea ice, natural disasters and extreme weather - and the world's second worst nuclear disaster
The year 2011 was another ecologically tumultuous year with greenhouse gases rise to record levels, Arctic sea ice nearly equalling 2007's record melt, and temperatures the 11th highest ever recorded.
It was marked on the ground by unparalleled extremes of heat and cold in the US, droughts and heatwaves in Europe and Africa and record numbers of weather-related natural disasters.
The 41 sea, land and air indicators used by the US government's National Oceanic and Atmospheric Administration (NOAA) to measure sea and land temperatures showed unequivocally that the world continued to warm throughout 2011. In July, NOAA reported that the last 300 months had all been above average temperature and that the 13 warmest years had all occurred in the 15 years since 1997. 2011 was additionally remarkable, it said, because a "La Niña" event was taking place, a naturally occurring oceanic cooling phenomenon that would normally bring temperatures down.
Despite stagnation or economic recession in many industrialised countries, concentrations of CO2, measured at Mauna Loa in Hawaii, peaked at more than 394 parts per million in May and are now 39% above where they were at the start of the industrial era and approaching the point when some scientists say it will be nearly impossible to contain global warming.
In September, Germany's University of Bremen reported that Arctic sea ice had hit a record low, based on data from a Japanese sensor on Nasa's Aqua satellite. Days later, the US National Snow and Ice Data Centre, using a different satellite data set, reported that ice coverage in 2011 was marginally greater, making 2011 the second-lowest on record.
Christophe Kinnard, of the Centre for Advanced Studies in Arid Zones in La Serena, Chile reported in November that both the duration and magnitude of the current decline in sea ice "seem to be unprecedented for the past 1,450 years".
"Everything is trending up - surface temperature, the atmosphere, and it seems also that the ocean is warming and there is more warm and saline water that makes it into the Arctic. The sea ice is eroded from below and melting from the top," said Kinnard.
While eastern Europe, Russia, Pakistan and the Middle East suffered the most from weather extremes in 2010, it was the turn of North America in 2011. The continent experienced massive flooding along the Mississippi and Missouri rivers, record wildfires and a crippling drought in the south.
More than 2,941 monthly records for extreme heat and extreme cold were broken in all 50 US states in 2011, said the Natural Resources Defense Council.
The costs of weather-related disasters spiralled. The US experienced 14 separate disasters each costing over $1bn. In total, financial losses were estimated at over $50bn.
"In many ways, 2011 rewrote the record books. From crippling snowstorms to the second deadliest tornado year on record to epic floods, drought and heat, and the third busiest hurricane season on record, we've witnessed the extreme of nearly every weather category," said NOAA spokesman Christopher Vaccaro.
2011 was described by many commentators as the "year of the tornado". Between January and June, 43 major thunderstorms released nearly 1,600 tornadoes in the central, southern and eastern United States. Half happened in April, and 226 of them on April 27.
But 2011 was also the year of too much or too little water. It began with devastating floods in Australia which covered an area the size of France and Germany combined, and ended with tropical storm Washi killing nearly 1,000 people and making 300,000 homeless in the Philippines.
Thailand's worst floods in 50 years claimed 730 lives, northern China's drought that started in 2010 continued well into 2011 and was the worst drought to hit the country in 60 years.
Massive droughts affected some of the world's richest and poorest communities. The worst drought in 60 years gripped more than 10 million people and led to the death of thousands of people and millions of animals in Somalia and the Horn of Africa.
Meanwhile, Texas was badly hit by heatwaves and drought. The city of Austin had 27 consecutive days where the temperature was over 100F and 90 days in total when it reached that level. The Texas Forest Service said the continuing drought had killed 100-500 million trees, a figure that did not include the ones killed in wildfires that scorched around 4m acres of the state.
The year began and ended with drought and record temperatures in Europe. The average temperature for northern Norway in November was 5.3C (9.5F) above normal, the Danube was at its lowest levels in 60 years, and Germany and much of northern Europe had the driest end to a year since recordkeeping began in 1881.
2011 was also an extraordinary year for major earthquakes. In the seven weeks between 1 January and 21 February, Argentina, Chile, Iran, Pakistan, Tajikistan, Tonga, Burma, the Solomon Islands, Tonga, Sulawesi, Fiji and New Zealand were all hit.
But by far the most damaging quake was the one that led to Japan's deadly tsunami on 11 March. This killed 15,500 people, caused the meltdowns of three nuclear reactors at the Fukushima Daiichi power plant, and led to 160,000 people fleeing the area or being moved away. By the end of the year, it was estimated to have cost around $210bn in lost production and physical damage. Decommissioning the station is expected to cost a further $15bn.
Arguments still rage over the radioactivity levels, but while the industry, backed some western commentators, played down the consequences, levels of radioactive caesium were shown to have reached 50m times normal levels off the coast. As 2011 ended, it was still hard to accurately gauge the level of devastation, the amount of the meltdown and the exact radiation levels. Last week, the Japanese prime minister, Yoshihiko Noda, said its owners had at last brought the station into a state known as "cold shutdown".
One clear fallout of the Fukushima disaster has been European countries turning their backs on nuclear power. Most significantly, the German chancellor, Angela Merkel, said in May that she would bring forward the phase-out of Germany's nuclear power stations to 2022. Italians voted overwhelmingly against new nuclear reactors and the Swiss government moved to phase out its reactors.
Now for the good news. In July, the UN Environment Programme announced that investments in renewable energy had grown 32% in 2010, reaching a record $211bn since 2004. For the first time, investment in faster-growing developing economies was greater than that in developed economies.
Bloomberg New Energy Finance said renewable energy investments were projected to double over the next eight years and reach $395bn per year by 2020. The bad news is that the International Energy Agency (IEA) says even this will not be enough to stabilise emissions and control climate change.
The IEA's sense of realism was underlined at the UN's annual climate conference in December. The talks in Durban, South Africa, avoided a major split between big emitters and others, with an agreement between 194 countries to work towards a legally binding deal to cut emissions in the future, leaving only voluntary pledges in the meantime.
"Without much stronger commitments for the next 5-10 years the Durban outcome will stay nothing more than smoke and mirrors - an illusion of ambition with no real targets or clear timelines," said Nnimmo Bassey, head of Friends of the Earth International.
Negotiators also concentrated on establishing carbon markets for forest protection and transport.
Conservationists battling the worldwide loss of forests welcomed satellite data from Brazil showing deforestation in the Amazon region had fallen to the lowest level for 23 years. However, new laws were passed in December that, if enacted, will allow ranchers to fell more trees near rivers and on mountaintop watersheds.
Tigers and other charismatic mega-fauna appeared to do better in 2011. Cambodia, India, Indonesia, Laos, Burma and Nepal protected a further 2m hectares of land for tigers. India - which holds half of the world's tigers - estimated an increase in the population from 1,411 in 2007 to 1,706 today. However, the WWF announced that only 18-22 Siberian tigers remained in the wild in north-east China.
Unexpectedly, a significant increase was recorded in the Virunga mountains that are shared between Rwanda, The Democratic Republic of the Congo and Uganda. A WWF survey counted 480, an increase of 100 since the last count in 2003.
And in a small triumph for conservation, the UN Development programme declared in December that more than $100m had been raised, mostly by Latin American countries, to temporarily leave in the ground the estimated 900m barrels of oil believed to be below the Yasuni national park in the Ecuadorian Amazon.