Thousands of scientists are convening in Vienna this week for a major international conference held by the European Geophysical Union (EGU). The conference is huge, spanning topics from space weather to sea level rise. This week, we’ll bring you some of the best climate bits.
An abrupt start
The science community is unequivocal that human activity is changing the climate. Last September’s report from the Intergovernmental Panel on Climate Change (IPCC) concluded global temperatures have risen by 0.85 degrees Celsius since 1880 and if emissions stay high, we could be looking at warming of at least three degrees by the end of the century.
Professor James White from the Institute for Arctic and Alpine Research at the University of Colorado opened proceedings at the EGU conference today with a talk on abrupt climate change. Abrupt climate change refers to the idea that steady changes in temperature could trigger sudden and rapid shifts in the climate system, perhaps irreversibly.
White asked if the changes in climate we encounter will be slow enough to allow time to adapt or whether there will be tipping points.
Earth has been through abrupt changes in climate before, when temperatures changed 10 to 15 degrees in less than a decade, White explained. He and other scientists are interested in whether we could cause similar abrupt changes to occur through greenhouse gas warming.
White defines “abrupt” climate change as an impact that is “unfolding faster than expected, planned or budgeted for” – one which leaves society little time to adapt.
Using these criteria, White argues we’re already seeing abrupt climate change – notably in the loss of sea ice in the Arctic.
Arctic sea ice is disappearing at a rate of about five per cent per decade. The biggest losses occur when the sea ice reaches a seasonal low in September, when the rate of loss is more like 14 per cent per decade.
The graph below from the recent IPCC report shows how summer sea ice has changed since 1900, and the acceleration in ice loss in recent decades.
Taken from Figure SPM.3 from the IPCC report (p.8): extent of Arctic July-August-September (summer) average sea ice.
White classifies the change as “abrupt” because the disappearance of sea ice is happening much faster than scientists anticipated, White explains. Climate models suggest that at the current rate of melting, the Arctic will be sea ice free in summer by mid century.
Ice loss is causing other changes to occur quicker than expected, too. New shipping routes being are carved through the Arctic, geopolitics in the region are changing and mining for resources is set to scale up. White warned:
“We’re not ready for the impacts we’re causing in the Arctic.”
In another session at today’s conference, Dr Julienne Stroeve from the National Snow and Ice Data Centre (NSIDC) explained the length of the Arctic melt season is increasing by five or six days per decade.
Not only is more sea ice in the Arctic disappearing in summer, it’s starting to melt earlier in the year and refreeze late, she said.
Stroeve’s research shows interesting details within that trend, however. Natural variation in Arctic weather causes big differences in the length of the melt season from year to year.
In the recent record, 2007 saw the longest melt season – at around 130 days. Summer Arctic sea ice reached the second lowest extent on record that year. In 2013, however, conditions were much more favourable for ice formation and the melt season was shorter, more like 100 days.
Since ice is reflective, the dark open ocean absorbs more of the sun’s heat as the ice retreats. Stroeve’s research suggests the region’s reflectivity – known as the “albedo” – is reducing at a rate of nine per cent per decade.
Stroeve is cautious about calling these changes in the Arctic “abrupt”, however. She tells us that at the moment, scientists aren’t seeing clues in their models of sudden and complete loss of summer sea ice.
However, the ice is getting thinner and becoming more vulnerable to breaking up, Stroeve explained. It’s not impossible that we could see a disappearance of summer sea ice if the same weather conditions that caused such rapid loss in 2007 were to combine with the thinner ice we have now, she suggested.
But natural variation mean the picture may look different the following year, so we should look at long term trends not single years, she warned.
Some scientists have raised concerns that a warming Arctic could release methane from carbon-rich permafrost as it starts to thaw.
White said while this is something the average non-scientist gets worried about, most scientists agree it’s a very slow process – the release of enough methane to have a significant impact on global temperature would take centuries, rather than decades.
That doesn’t mean we should ignore it, warned White, adding that permafrost methane is still a concern and continued monitoring is needed.
A more pressing cause for concern is the possibility that the West Antarctic ice sheet destabilising and disappearing completely. This would lead to a rise in sea level of about a metre in 30 years rather than 100 years, which is what we might expect at current rates of warming, White added.
While this is a high risk scenario, there’s considerable scientific uncertainty about when it could occur. The IPCC report concludes:
“Abrupt and irreversible ice loss from a potential instability of marine-based sectors of the Antarctic ice sheet in response to climate forcing is possible, but current evidence and understanding is insufficient to make a quantitative assessment.”
Time to get serious
There’s still uncertainty about what the consequences of passing climatic thresholds would be – as well as how close they really are. But abrupt climate change is an economic, social and environmental prospect that’s much better avoided than dealt with, said White.
Research should focus on the development of early warning systems that combine the physical and social sciences, White said. He added:
“We know how to do this much better than we used to … the time is here to be serious about the threat of tipping points so as to better anticipate and better prepare ourselves for inevitable surprises.”