Meteorological data from the manned stations in the Antarctic Peninsula show a strong warming trend over the past 50 years, with a warming of about 2°C. This makes the region one of the fastest warming areas on earth.
Dr Robert Mulvaney
Appearing in the journal Nature
this week, the results of research from British, French and Australian polar scientists provides the most complete picture to date of the climate of the Antarctic Peninsula. The team fears that if warming continues at the unprecedented rate of the last 100 years, further ice shelves in this region will follow the fate of those that have already been lost, such as Larsen A which broke up in 1995, and Larsen B which broke up in 2002.
The study constitutes a small component of a much bigger programme to understand the mass balance of both the Greenland and Antarctic ice sheets, hence determining their likely contribution to sea level rise. A 364 m ice core was drilled from James Ross Island on the Antarctic Peninsula and chemically analysed by the British Antarctic Survey (BAS) and the NERC Isotope Geosciences Laboratory (part of the British Geological Survey) to create a temperature record.
Dr Robert Mulvaney, OBE, of the BAS spoke to ScienceOmega.com
to give more detail on what the study reveals about climate history and how this could influence climate predictions for the future. He commenced with an explanation of the two factors which suggest that something ‘out of the ordinary’ is going on in the Antarctic Peninsula.
"Meteorological data from the manned stations in the Antarctic Peninsula show a strong warming trend over the past 50 years, with a warming of about 2°C. This makes the region one of the fastest warming areas on earth.
"Secondly, there is the loss of ice shelves – floating ice that has flowed off ice sheets on land (as opposed to sea ice which is frozen sea water). Ice shelves can be hundreds of metres thick. Several ice shelves in the northern Antarctic Peninsula have disintegrated and been lost in the last couple of decades."
The disintegration of ice sheets and shelves is a cause for concern as they are critical to the circulation of heat around the Earth. Sea ice in the Arctic and ice shelves and sea ice in the Antarctic contribute cold, dense water which drives meridional ocean circulation to move heat from the equator and towards the poles.
Operating from the Royal Navy’s HMS Endurance, two Lynx helicopters (one of which is pictured above) were the means by which the seven scientists on the team and six tonnes of ice core drilling equipment were transported to the northernmost tip of the Antarctic Peninsula. It was there that the scientists collected their samples.
"Using an ice core drilled on James Ross Island (formerly bounded on its west by the Prince Gustav Channel), we were able to recover a record of climate spanning 50,000 years," said Dr Mulvaney. "In the new paper, we look in detail at the last 15,000 years. We wanted to do this to get the longer term climate record to compare with the rather short meteorological record."
A core of ice was collected continuously through the James Ross Island ice cap.
The dataset was dated to within a few years for the last few centuries, but less accuracy was possible for the older samples.
"We used the ratio of heavy to light water stable isotopes to determine temperature," Dr Mulvaney explained. "In the upper parts of the core we have a dozen or more samples per year, while deeper in the core – where the layers are squeezed thinner – each sample contains several years. We normalised for this change in resolution by taking ten and 100 year running means."
I asked Dr Mulvaney what we can glean about the future of the climate from the ice sheets of the Antarctic Peninsula. Despite the fact that we cannot say for certain that the current, more rapid, warming is human-induced, the team suspects that the effects are down to a combination of human-induced and natural warming.
"The ice sheets record the change in climate in terms of temperature and rate of ice accumulation, and the changes in the atmosphere. They don’t really predict the future climate directly, though the rate of glacier flow will help predict likely sea level rise. What we do get from the ice cores is the range and rate of climate change in the past.
"We can confidently say that the Antarctic Peninsula warmed by 6°C from the glacial period, or the last ‘ice age’, to the early part of the Holocene – the last 12,000 years of relatively stable warm climate. We can see that the early part of the Holocene in this region was warmer than today by about 1.3°C, but by 9000 years ago, the climate was about the same as today.
"Between about 2500 and 600 years ago, the climate cooled by about 1°C, then began warming 600 years ago. The rate of warming in the early part was around 0.2°C per century, but over the past 100 years, the rate is closer to 1.5°C per century. Our ice cores show an increase rate of about 2.5°C per century for the past 50 years, which is similar to the meteorological records."
Although it is not as pronounced as in the Peninsula, there is evidence – both meteorological and from ice cores – that warming is taking place elsewhere in Antarctica. This is the next area of focus for Dr Mulvaney research.
"My next ice core drilling project will take me to an area in the West Antarctic Ice Sheet called Pine Island Glacier where satellites have shown that the ice is getting thinner, and the ice streams that drain the ice sheet are flowing faster," he told us. "I will take some ice cores in the area to try to determine whether the amount of precipitation has changed in the past 50 years or so (one half of the mass balance equation) while others will be making measurements of the ice flow and so on."