Warming trend continues

Lord Stern, who completed a review of the economics of climate change for the British government in 2006, says he should have been fiercer in his report.

Speaking at the start of the World Economic Forum in Davros, Switzerland, this week he said governments are “fooling themselves” if they think global temperature rises will only have modest economic impacts.

Stern says things have moved on in the eight years since his review. "I would have been much fiercer,” he admits. "Emissions have gone up faster than I thought and some of the effects of global warming are coming through more quickly, such as melting of the glaciers and the polar ice caps.”

He estimates global temperatures will be 4-5 C higher in the next century on present trends and that governments are being unrealistic if they think this will only have a modest impact on economies.

"The last time we had a change in global temperatures of this order of magnitude it was in the other direction. It was called the Ice Age,” Stern added.

According to new figures released by NASA the year just past tied with 2009 and 2006 for the seventh warmest year since 1880, continuing the long-term trend of rising global temperatures.

With the exception of 1998, the 10 warmest years in the 134 year record all have occurred since 2000, with 2010 and 2005 ranking as the warmest years on record.

NASA's Goddard Institute for Space Studies (GISS) in New York, which analyses global surface temperatures on an ongoing basis, released an updated report this week on temperatures around the globe in 2013. 

The comparison shows how Earth continues to experience temperatures warmer than those measured several decades ago.

The average temperature in 2013 was 14.6 Celsius, which is 0.6 C warmer than the mid-20th century baseline. The average global temperature has risen about 0.8 C since 1880, according to the new analysis. Exact rankings for individual years are sensitive to data inputs and analysis methods.

"Long-term trends in surface temperatures are unusual and 2013 adds to the evidence for ongoing climate change," said GISS climatologist Gavin Schmidt at a NASA press conference on Tuesday.

"While one year or one season can be affected by random weather events, this analysis shows the necessity for continued, long-term monitoring.”

Scientists emphasise that weather patterns will always cause fluctuations in average temperatures from year to year but say the continued increases in greenhouse gas levels in Earth's atmosphere are driving a long-term rise in global temperatures. 

Each successive year will not necessarily be warmer than the year before, but with the current level of greenhouse gas emissions, scientists expect each successive decade to be warmer than the previous.

Carbon dioxide is a greenhouse gas that traps heat and plays a major role in controlling changes to Earth's climate. It occurs naturally and is also emitted by the burning of fossil fuels for energy. 

Driven by increasing man-made emissions, the level of carbon dioxide in Earth's atmosphere at present is higher than at any time in the last 800,000 years.

The carbon dioxide level in the atmosphere was about 285 parts per million in 1880, the first year in the GISS temperature record. By 1960, the atmospheric carbon dioxide concentration, measured at the National Oceanic and Atmospheric Administration's (NOAA) Mauna Loa Observatory in Hawaii, was about 315 parts per million. This measurement peaked last year at more than 400 parts per million.

While the world experienced relatively warm temperatures in 2013, the continental United States experienced the 42nd warmest year on record, according to GISS analysis. For some other countries, such as Australia, 2013 was the hottest year on record.

The temperature analysis produced at GISS is compiled from weather data from more than 1,000 meteorological stations around the world, satellite observations of sea-surface temperature and Antarctic research station measurements, taking into account station history and urban heat island effects. 

Software is used to calculate the difference between surface temperature in a given month and the average temperature for the same place from 1951 to 1980. This three-decade period functions as a baseline for the analysis. It has been 38 years since the recording of a year of cooler than average temperatures.

The GISS temperature record is one of several global temperature analyses, along with those produced by the Met Office Hadley Centre in the UK and NOAA's National Climatic Data Center in the US. These three primary records use slightly different methods but overall their trends show close agreement.