Climate change may be closer than you think

Blog - June 5, 2014 - By John Stone

With climate change there will be surprises.

The Intergovernmental Panel on Climate Change (IPCC) recognized this in its 2nd Assessment Report. This report was finalized at a landmark meeting held in Madrid in 1995, which the journal Nature identified as one of the 10 “meetings that changed the World”.

World-changing, because it was the first time there was scientific evidence showing “that there is a discernible human influence on global climate.”

The last part of the report was drafted by scientists and government representatives gathered around an overhead projector in the small hours of the night. It notes that surprises will naturally arise because of the physical nature of the climate system. When it is forced rapidly, as it is today, it will be subject to unexpected behaviour — surprises.

For a long time, climate scientists have been concerned with the possible decline of the ice sheet that covers Antarctica and is as much as three kilometres thick. We know from looking at past climates that the ice sheet has declined before. What we don’t know is: will it, as a result of the way we are changing the climate, decline again and when?

What is the probability of a surprise?

While, overall, the ice cover over Antarctica seems to be stable, the worry is that the glaciers that drain into the surrounding ocean may not be so stable. Melting of these glaciers could lead to a global rise in sea level of several meters. This would threaten the vulnerability of millions of people living in coastal cities, including here in North America.

A couple of recent research papers have provided evidence that a surprise may be closer then we had thought. The papers suggest that the West Antarctic Ice Sheet, which drains six massive glaciers (as much as 100 km across) into the Amundsen Sea, is declining and at an accelerated rate.

YouTube video by NASA explaining the decline in Antarctic sea ice

These glaciers flow off the land and onto the sea where they float. Their decline has been held back by the grounding of the glaciers on ridges in the bedrock below. These ridges can be as much as 600 metres below sea level. The relatively warm ocean water flows underneath the glaciers and slowly melts them, making them thinner and hence weaker. The thinnest parts of the glacier break off and lead to an inland retreat.

Figure: Melting of an ice sheet. Source: “Ice sheet mass balance and climate change,” Nature 498, 51–59 (06 June 2013).

Once the retreat passes the underwater ridge, there is nothing to hold back the glaciers and the flow accelerates. In some places the seabed descends downwards on the inland side of the ridge. Warm water then floods in, raising the level of the ice. The decline of the ice sheet becomes virtually unstoppable.

At the other end of the globe it has been evident for some years that the Greenland Ice Sheet has been shrinking, particularly around its edges where the glaciers flow into the sea. Some of these glaciers have been accelerating at surprisingly fast rates — you can actually see the flow in some places. We are still trying to fully understand the mechanisms responsible for this rapid decline. In fact, we have been forced to rethink the physics of glacier flow.

During the summer, ice on the surface of the ice sheets melts and forms large pools of water. As those pools get warmer, they in turn melt more ice. Eventually some of this water finds its way into deep crevices and flows down to the bedrock. The surprising thing is that this water stays liquid, pushes up the ice and lubricates the flow of the glacier. Like the decline of the West Antarctic Ice Sheet, the melting of the Greenland Ice Sheet will take millennia — but there could be surprises. There is enough water in the Greenland Ice Sheet to raise global sea levels by five metres.

It has been said in discussing climate change, that the Arctic is the canary in the coalmine. This is a good analogy. Changes are happening faster and sooner in the Arctic than elsewhere.

Amongst the more surprising changes has been the decline in the Arctic sea ice. The extent of Arctic sea ice has been below the long-term average for much of the past decade. The 2013-14 extent is amongst the lowest on record. We may have had a colder than average winter, but temperatures in much of the Arctic were above normal.

A plot of sea ice extent is clearly non-linear — you can’t put a straight line through the observations. Summer ice volume is now only 30 per cent of what it was in the 1980s. This decline has occurred faster than any of our models predicted. The result is that we might see an ice-free Arctic ocean within the next two decades rather than the end of the century as was previously estimated.

The most recent surprise is that the iconic Athabasca glacier that so many tourists visit every year may be in terminal decline. The glacier has shrunk by almost a third since reliable measurements have been taken. Studies by Parks Canada suggest that much of it could be gone within a generation.

Retreat of the Athabasca Glacier.

It is not only this glacier that is retreating, but almost all those in the Rockies. To quote from the film Chasing Ice by James Balog, “the glaciers are dying.” In the past we have relied on the summer melting of the glaciers and their replenishment in the winter to supply Prairie farmers with the necessary moisture to grow their crops. Unfortunately, more of the winter precipitation is falling as rain and not snow, leading to smaller glaciers and less snow pack and ultimately reducing the summer run-off. There is also a greater likelihood of earlier Spring run-off and heightened danger of flooding downstream, as we saw last year across southern Alberta.

The more we observe and understand the climate system, the more surprises there seem to be.

Despite our best scientific modelling and predictions, surprises will certainly happen. They have happened in the past and are now more likely to occur for we have loaded the dice as a result of modifying our climate.

The question is: when will the next surprise happen, and will we be prepared?

John Stone

John Stone is an adjunct research professor in the Department of Geography and Environmental Studies at Carleton University, and is widely regarded as an expert on climate change and international affairs. He serves as Secretary of the Pembina Institute's Board of Directors.


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