New research indicates the impact of rising CO2 levels in the
Earth’s atmosphere will cause unstoppable effects to the climate
for at least the next 1,000 years, causing researchers to estimate
a collapse of the West Antarctic ice sheet by the year 3000 and an
eventual rise in the global sea level of at least four
metres. 

The study, published in the Jan. 9 Advanced Online
Publication of the journal Nature Geoscience, is the first full
climate model simulation to make predictions out to 1,000 years
from now.

It is based on best-case, ‘zero-emissions’ scenarios
constructed by a team of researchers from the Canadian Centre for
Climate Modelling and Analysis (an Environment Canada research lab
at the University of Victoria) and the University of
Calgary.

“We created ‘what if’
scenarios,” says Dr. Shawn Marshall, co-author of the paper, Canada
Research Chair in Climate Change and University of Calgary geography professor

“What if we completely stopped using fossil fuels and put
no more CO2 in the atmosphere? How long would it then take to
reverse current climate change trends and will things first become
worse?” The research team explored zero-emissions scenarios
beginning in 2010 and in 2100.

The Northern Hemisphere fares better than the south in the
computer simulations, with patterns of climate change reversing
within the 1,000-year timeframe in places, such as
Canada.

At the same time, parts of North Africa experience
desertification as land dries out by up to 30 percent and ocean
warming of up to 5°C off of
Antarctica is likely to trigger widespread collapse of the West
Antarctic ice sheet, a region the size of the Canadian
prairies.

Researchers hypothesize that one reason for the
variability between the North and South is the slow movement of
ocean water from the North Atlantic into the South
Atlantic.

“The global ocean and parts of the Southern Hemisphere
have much more inertia, such that change occurs more slowly,” says
Marshall. “The inertia in intermediate and deep ocean currents
driving into the Southern Atlantic means those oceans are only now
beginning to warm as a result of CO2 emissions from the last
century. The simulation showed that warming will continue rather
than stop or reverse on the 1,000-year time scale.”

Wind currents in the Southern Hemisphere may also have an
impact. Marshall says that winds in the global south tend to
strengthen and stay strong without reversing. “This increases the
mixing in the ocean, bringing more heat from the atmosphere down
and warming the ocean.”

Researchers will next begin to investigate more deeply the
impact of atmosphere temperature on ocean temperature to help
determine the rate at which West Antarctica could destabilize and
how long it may take to fully collapse into the water.

The paper “Ongoing climate change following a complete
cessation of carbon dioxide emissions” by Nathan P. Gillett, Vivek
K. Arora, Kirsten Zickfeld, Shawn J. Marshall and William J.
Merryfield is available online at
http://www.nature.com/ngeo/index.html