Natural causes responsible for slowing temperature rise, but overall trends suggest we’ll still hit 2 degrees
Temperatures have increased at a lower rate in the past 10 to 15 years than in previous decades, experts at the UK Met Office say (Pic: NASA)
By Sophie Yeo
There has been a pause in the rate of global warming, climate scientists say, but that does not mean an end to the problem.
Scientists expect the rise in temperatures to ebb and flow, while the overall upward trend continues, due to the continuing emissions of greenhouse gases.
Between 1998 and 2012, the average rate of warming was 0.04°C per decade, compared to 0.17°C from 1970 to 1998.
At a briefing for journalists in London on July 22, leading climate scientists explained that the time period over which this slower pace of temperature rise has occurred is so short that it does not impact upon their long term expectations that the world will continue to warm.
The briefing was held to introduce three new papers published today by the Met Office, which explain the temporary lull in climate change.
“We expect to get periods of slower warming. This is absolutely what we expect. Global temperatures remain high: 12 out of the 14 hottest years on record have occurred since 2000,” said Dr Peter Stott from the UK Met Office’s Hadley Centre.
Natural causes
Natural causes account for the current hiatus in the upward trend.
The oceans have absorbed much of the heat, veiling the effects of global warming on the land, though it is still measurable from the rising sea levels. Scientists believe that energy is being absorbed deeper down than in previous decades.
The pause in warming can also be accounted for by a series of small volcanic eruptions since 2000. Volcanic activity ejects reflective particles into the atmosphere, helping to slow temperature rise.
Between 2008 and 2009, the sun went through a phase of lower than usual activity, which has also contributed to the pause.
The slowed warming could delay the planet from reaching 2°C warming, but only by between five to ten years, according to Professor Piers Forster, a climate scientist at the University of Leeds.
He said, “If we do continue on this emissions trajectory we’re currently on, we’ll reach 2°C in 2060 or so.”
Measuring climate change
While the graphs do simulate these periods of less rapid warming, and even cooling, in their predictions, these cannot be expected to line up exactly to when they occur in real life.
Although the temperature has been increasing less rapidly, there are many other factors consistent with continued global warming, including sea level change, sea ice cover in the Arctic, glacier volume and ocean temperatures.
These indicators can be more informative in measuring climate change over short timescales, since computer models measuring temperature are designed to predict long term trends, rather than short term anomalies.
Key points on recent warming slowdown: (1) needs to be put in longer term context & considering other climate indicators such as sea level
— Ed Hawkins (@ed_hawkins) July 22, 2013
Key points on recent warming slowdown: (2) Explanation is partly radiative forcing & partly ocean heat uptake. (3) Models simulate pauses.
— Ed Hawkins (@ed_hawkins) July 22, 2013
IPCC report
A leaked version of the Intergovernmental Panel on Climate Charge Fifth Assessment report last December suggested that the link between the sun’s activity and the climate is slightly stronger than before – a claim which sceptics said undermined the main conclusion of human caused climate change, but which scientists were quick to refute.
The final version of the report is due to be released in September, which is expected to provide detailed information on the exact state of climate change.
The last report was in 2007, and the updated version will likely play a key role in upcoming global emissions negotiations.