Global Warming

Global Warming is Irreversible, According to New Study

| by NOAA

A new scientific study led by the National Oceanic and Atmospheric
Administration reaches a powerful conclusion about the climate change
caused by future increases of carbon dioxide:  to a large extent,
there’s no going back.

The pioneering study, led by NOAA
senior scientist Susan Solomon, shows how changes in surface
temperature, rainfall, and sea level are largely irreversible for more
than 1,000 years after carbon dioxide (CO2) emissions are
completely stopped. The findings appear during the week of January 26
in the Proceedings of the National Academy of Sciences.

“Our
study convinced us that current choices regarding carbon dioxide
emissions will have legacies that will irreversibly change the planet,”
said Solomon, who is based at NOAA’s Earth System Research Laboratory in Boulder, Colo.

“It has long been known that some of the carbon dioxide emitted by
human activities stays in the atmosphere for thousands of years,”
Solomon said. “But the new study advances the understanding of how this
affects the climate system.” 

The study examines the consequences of allowing CO2
to build up to several different peak levels beyond present-day
concentrations of 385 parts per million and then completely halting the
emissions after the peak. The authors found that the scientific
evidence is strong enough to quantify some irreversible climate
impacts, including rainfall changes in certain key regions, and global
sea level rise.

If CO2 is allowed to peak at
450-600 parts per million, the results would include persistent
decreases in dry-season rainfall that are comparable to the 1930s North
American Dust Bowl in zones including southern Europe, northern Africa,
southwestern North America, southern Africa and western Australia.

The
study notes that decreases in rainfall that last not just for a few
decades but over centuries are expected to have a range of impacts that
differ by region. Such regional impacts include decreasing human water
supplies, increased fire frequency, ecosystem change and expanded
deserts. Dry-season wheat and maize agriculture in regions of rain-fed
farming, such as Africa, would also be affected.

Climate
impacts were less severe at lower peak levels. But at all levels added
carbon dioxide and its climate effects linger because of the ocean.

“In
the long run, both carbon dioxide loss and heat transfer depend on the
same physics of deep-ocean mixing. The two work against each other to
keep temperatures almost constant for more than a thousand years, and
that makes carbon dioxide unique among the major climate gases,” said
Solomon.

The scientists emphasize that increases in CO2
that occur in this century “lock in” sea level rise that would slowly
follow in the next 1,000 years. Considering just the expansion of
warming ocean waters—without melting glaciers and polar ice sheets—the
authors find that the irreversible global average sea level rise by the
year 3000 would be at least 1.3–3.2 feet (0.4–1.0 meter) if CO2 peaks at 600 parts per million, and double that amount if CO2 peaks at 1,000 parts per million.

“Additional
contributions to sea level rise from the melting of glaciers and polar
ice sheets are too uncertain to quantify in the same way,” said
Solomon. “They could be even larger but we just don’t have the same
level of knowledge about those terms. We presented the minimum sea
level rise that we can expect from well-understood physics, and we were
surprised that it was so large.”

Rising sea levels would
cause “…irreversible commitments to future changes in the geography of
the Earth, since many coastal and island features would ultimately
become submerged,” the authors write.

Geoengineering to
remove carbon dioxide from the atmosphere was not considered in the
study. “Ideas about taking the carbon dioxide away after the world puts
it in have been proposed, but right now those are very speculative,”
said Solomon.

The authors relied on measurements as well as
many different models to support the understanding of their results.
They focused on drying of particular regions and on thermal expansion
of the ocean because observations suggest that humans are contributing
to changes that have already been measured.  

Besides
Solomon, the study’s authors are Gian-Kasper Plattner and Reto Knutti
of ETH Zurich, Switzerland, and Pierre Friedlingstein of Institut
Pierre Simon Laplace, Gif-Sur-Yvette, France.

NOAA understands and
predicts changes in the Earth's environment, from the depths of the
ocean to the surface of the sun, and conserves and manages our coastal
and marine resources.

POST YOUR COMMENTS BELOW