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September 27, 2013 6:55 pm
After nearly 25 years of telling governments how the climate is changing, the world’s leading authority on the topic has produced a report unlike any that preceded it.
The 36-page paper released in Stockholm on Friday by the UN’s Intergovernmental Panel on Climate Change is a summary done for governments of a larger report to be released next week that focuses entirely on the scientific basis of climate change.
It reveals that the 259 scientists from 39 countries who drafted the full report are more convinced than ever that global warming is “unequivocal” and humans have been the main cause for the past 60 years, largely because of the greenhouse gases emitted by burning fossil fuels.
In its last big assessment in 2007, the panel said most of the temperature increases after the mid-20th century were “very likely” because of rising greenhouse gas concentrations caused by human activity.
In IPCC parlance, “very likely” means scientists think a finding has a 90 per cent chance of being correct.
The new report upgrades this to say it is “extremely likely” humans caused most of the increase in temperatures since 1951, meaning a 95 per cent probability it is correct.
It also puts much more emphasis on the distinctive nature of the changes already seen in the climate system since the 1950s, such as warming oceans, rising sea levels, melting snows and soaring greenhouse gas concentrations, noting some are “unprecedented over decades to millennia”.
Depending on the rate of future emissions, it concludes the following changes are possible:
● Global surface temperatures may rise by between 1C and 3.7C from the level of average temperatures between 1986-2005 by the final two decades of this century.
● Global sea levels, already accelerating unusually fast, could rise by between 0.4m and 0.6m over the same period, or 0.5m to 0.9m by 2100.
● Heatwaves could become more frequent and last longer in much of the world, while heavy rains could intensify in some areas.
● Arctic summer sea ice, which may have already declined faster in the last 30 years than in the previous 2,000 years, could nearly disappear entirely before the middle of this century.
● A decrease in Antarctic sea ice coverage and volume is also predicted by the end of the century, but with only low confidence.
These findings will no doubt feature in the next round of UN climate talks in Warsaw in November, where countries will be debating the shape of an international deal to tackle climate change, due to be finalised in Paris in 2015.
Some business groups, such as the Prince of Wales’s Corporate Leaders Group on Climate Change in the UK, were quick to make the link on Friday. One member, Carmen Becerril, chief international officer from Acciona, the Spanish energy and infrastructure group, said the report showed “a comprehensive, effective and ambitious global response must be agreed at the UN climate change meeting in Paris in 2015”.
Anthony Hobley, president of the Climate Markets & Investment Association, said it was clear the science on which the IPCC report was based had been categorically proven and “any further arguments around scientific consensus are for business looking to manage business risk – an unhelpful distraction”.
There is one aspect of the report, however, about which the authors admit they are far less confident: the slowdown in the rate of warming over the last 15 years, despite rising carbon dioxide concentrations.
The report released on Friday says this can be explained in part by changes in the climate system, such as a redistribution of heat within the ocean, and by other factors such as the aerosols produced by volcanic eruptions that can reflect radiation back into space and therefore have a cooling effect.
And though it says the computer models used to project future climate change have improved significantly, it says some may have overestimated the climate’s response to increasing greenhouse gases.
However, the report makes it clear that 15 years is too short a time to make a clear judgment. Because of natural changes in the climate, “trends based on short records are very sensitive to the beginning-and-end dates and do not in general reflect long-term climate trends”.
The larger trend is clearly towards warming, it says, adding that each of the last three decades has been warmer than all others since 1850 and the first decade of the 21st century was the warmest.
In the northern hemisphere, it adds, the years between 1983 and 2012 were “likely” – meaning at least 66 per cent certain – to be the warmest in the last 1,400 years.
“This is a chance to steer the climate conversation in a more realistic and constructive direction,” said Dr Bjorn Lomborg, adjunct professor at the Copenhagen Business School, who has written extensively – and controversially – on climate change.
“The IPCC’s moderate projections clearly contradict alarmist rhetoric, such as the recurring claims from activists of temperature rise of more than 5°C (9°F), and sea level rise of 1-2m (3-6ft).”
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