HUMANITY has another shot at stopping dangerous climate change. A fresh look at temperature data from the last decade offers an unexpected opportunity to stay below the agreed international target of 2 °C of global warming.
The study took data on the rise in temperatures over the most recent decades, and worked out what this means for the coming decades. It turns out Earth will warm more slowly over this century than we thought it would, buying us a little more time to cut greenhouse gas emissions.
Climate scientists caution that this in no way means climate change is not real. Temperatures are rising faster than they have for 11,000 years. “It should not take the pressure off at all,” says of the Grantham Institute for Climate Change at Imperial College London. “Global emissions have to peak and start to come down.” But if we act soon the worst effects of climate change could yet be avoided – something many climate scientists had all but given up hope on.
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Governments have pledged to limit the world to 2 °C of warming – the agreed threshold for dangerous climate change. With emissions shooting up, this target seemed hopelessly unrealistic. “If previous estimates [of how the climate will warm] were true, keeping the world below 2 °C would have been almost impossible, however big our emission cuts,” says of the University of Leeds in the UK, who contributed to the new study. “Now it looks like we have a chance, so we should take it.”
“Prior to this, a lot of us were feeling quite gloomy that whatever we did, we would go over 2 °C,” says Forster’s colleague Myles Allen of the University of Oxford. “It’s not a foregone conclusion any more.”
“A lot of us were gloomy that we would go over 2 °C. It’s not a foregone conclusion any more”
After heating rapidly in the late 20th century, Earth warmed slowly in the last decade, partly as a result of natural cycles in the climate system.
, also of the University of Oxford, and colleagues took data on human greenhouse gas emissions since the Industrial Revolution and temperature rises in the last 40 years – including the most recent data. From this, they calculated how much greenhouse gases have warmed the Earth so far.
They then looked at what that meant for the temperature rise over the coming few decades, and found that it will be slower than expected. The team focused on how much hotter the planet will be in the year that carbon dioxide concentrations reach double their pre-industrial value. On current trends, that will happen between 2050 and 2070. Previous studies had found that temperatures would rise by 1.6 °C, but Otto found an increase of 1.3 °C ().
“It might buy us five or 10 years,” says of Penn State University, although he cautions that the problem hasn’t gone away.
Not everyone is convinced that Otto’s results change the picture. “Short-term trends are just not that useful,” says of the NASA Goddard Institute for Space Studies in New York. of the Massachusetts Institute of Technology adds that recent volcanic eruptions temporarily cooled the climate, masking some of the warming. But others say that Otto’s calculations take account of these problems, so are probably about right. “The authors have done a very careful job,” says Hoskins.
So it looks as if temperatures will rise slightly more slowly than expected in the short term. But does it change where the climate ends up the long run? That depends on how sensitive the climate is to CO2 accumulating in the atmosphere.
The 2007 report of the Intergovernmental Panel on Climate Change (IPCC) estimated that a doubling of CO2 in the atmosphere would mean temperatures eventually stabilise between 2 °C and 4.5 °C above pre-industrial temperatures, with a best estimate of about 3 °C. This long-term stabilisation is known as climate sensitivity.
A growing number of climate scientists thinks that the climate is less sensitive to CO2 than the IPCC’s best estimate, so temperatures will not rise as much as feared, even in the long run. “I’ve been arguing this for a few years,” says of the JAMSTEC Yokohama Institute for Earth Sciences in Japan.
When Otto calculated the climate sensitivity from his data, he found that it was about 2 °C – well below the IPCC’s best estimate of 3 °C.
“The observations are telling us one thing and the climate models are telling us another,” says Forest. He thinks the most likely range is between 2.5 and 3 °C, slightly below the IPCC’s estimate.
If the new figures are right, it’s a rare piece of good news for international climate talks. For the last few years, governments have been planning to sign a deal in 2015 that will come into force in 2020. That seemed far too late. Based on previous estimates of the climate sensitivity, global emissions needed to peak by 2020 and then fall to have a 50 per cent chance of avoiding 2 °C.
“If we are lucky and the climate sensitivity is at the low end, and we have a strong agreement in 2015, I think we stand a chance to limit climate change to 2 °C,” says of the Tyndall Centre for Climate Change Research in Norwich, UK. “But there are a lot of ifs.”
We can improve our chances by cutting emissions of short-lived warming agents like soot, says of the University of Exeter, UK. Otto’s research suggests that they have a bigger effect than previously thought, so getting rid of them will buy even more time.
Regardless, emissions must still peak very soon to give us even a 50:50 chance of staying below 2 °C, says of the Met Office in Reading, UK. “It was looking like the best we could attain was a 40:60 chance,” says Hoskins. “If the negotiations are done seriously, 2 °C is still on.”
Axis wobbles and wandering poles
Some of the consequences of climate change are just plain strange. Days should get a teensy bit shorter as the Earth spins faster, for instance. And now we have evidence that melting ice is tilting the planet.
Earth’s rotational axis wobbles because the planet is not a perfect immutable sphere. Erosion, plate tectonics and the weather move mass around the surface, causing the poles to wander. From 1982 to 2005, this drift averaged about 6 centimetres per year, pulling the North Pole south towards Labrador. That motion is largely attributed to the long-term effects of plate tectonics and the fact that areas covered in ice during the last ice age are popping up like corks.
In 2005, the drift abruptly shifted in an easterly direction and accelerated. This happened about the same time as melting sped up in Greenland and Antarctica, so of the University of Texas in Austin, began looking for a link. He used data from the pair of Gravity Recovery And Climate Experiment (GRACE) satellites to measure how much mass glaciers were losing. He then calculated how the poles would be affected by redistribution of that mass – around 600 gigatonnes a year from Greenland, Antarctica and mountain glaciers.
He and his team found that shifting that amount of water from glaciers to the sea can account for 90 per cent of the average polar drift since 2005, and that climate change was largely responsible for the sudden change in our planet’s tilt (). Jeff Hecht
A view to a cut
Even if the world is warming more slowly, urgent action is more pressing than ever
“The worst case scenarios are looking less likely. We still have to reduce emissions drastically. If we don’t, we are talking about crossing 2 °C for sure”
Myles Allen, University of Oxford
“I think this is overdue. I’ve been arguing it for a few years, and some powerful people have been very resistant … The most noteworthy thing about this is not what is being said, but who is saying it”
James Annan, JAMSTEC Yokohama Institute for Earth Sciences, Japan
“If anything it’s given me greater resolve. If [previous estimates] were true, keeping the world below 2 °C would have been almost impossible, however big our emission cuts. Now it looks like we have a chance”
Piers Forster, University of Leeds, UK
“It’s still collectively possible to stay within the 2 °C boundary, and we should try to do so. It’s giving some hope that we can lower the risk of long-term threats to big ice sheets”
Tim Lenton, University of Exeter, UK
“If it does mean a little breathing space, great. It should not take the pressure off at all. The major thing is that global emissions have to peak and start to come down”
Brian Hoskins, Grantham Institute for Climate Change, London
