The
Oceans
Scientists have long understood the key role that oceans play in regulating
the Earth's climate. Oceans cover 70 percent of the globe and store a thousand
times more heat than the atmosphere does. What's newer is the understanding of
how this key component of our climate system responds to global warming.
"Even
five years ago most scientists had no inkling of the extent to which global warming
was affecting the oceans-but slowly over the years a consensus has been building,"
says Environmental Defense marine ecologist Rod Fujita. Today, the scientific
community believes there's plenty to worry about: changes are afoot in global
ocean dynamics that could have profound ecological impacts.
A brake on
global warming-for now
One of the ocean's most important climate functions
is absorbing heat and carbon dioxide (CO2), one of the gases that causes global
warming. Acting as a heat sponge, the oceans have absorbed huge amounts of heat
and CO2 in the last forty years.
Fujita explains that "the oceans are
saving us from faster climate change-in essence, they are a big flywheel that
delays rapid overheating of the earth, putting a brake on the climate system."
"That's
the good news," he adds. "The bad news is that the oceans only slow
the atmospheric warming down. Once the oceans come to equilibrium with a greenhouse-gas
warmed earth, the excess heat will remain in the atmosphere and things will get
much hotter."
In effect, the oceans are taking up the slack for the atmosphere
and delaying the full impacts of global warming. But where and how the oceans
release this accumulated heat is uncertain. And as the ocean stores heat, fragile
underwater ecosystems are struggling.
The most recent scientific report from
the Intergovernmental Panel on Climate Change (IPCC) also notes with concern that
the ocean is acidifying because of increased absorption of atmospheric CO2, and
thus posing a threat for shell-forming species, which are an essential part of
the marine food web. Projected increases in carbon dioxide levels will cause further
acidification of the ocean.
Currents Distributing Heat
Another important
role the oceans play is that of distributor. Oceans deliver heat and life-sustaining
nutrients around the globe.
Just as blood vessels and capillaries bring oxygen
and nutrients to cells in the human body, the ocean's currents carry oxygen, nutrients
and heat throughout the Earth. The ocean distributes 25 to 50 percent of the energy
the planet receives from the sun.
For example, the Gulf Stream carries heat
across the Atlantic. This warm current gives northwestern Europe a milder climate
than it would normally have so far north.
A change to the ocean's circulation
patterns could plunge Europe into a colder era, even as the rest of world experiences
warmer temperatures. (Find out more about the ocean's circulation system on oceansalive.org.)
Currents
Circulating Food
Changing ocean circulation patterns would also affect the
nutrient delivery system for marine life. Colder waters are more productive than
warm waters. The warming of the oceans may be starting to break the ocean's food
chain.
The system of currents replenishes deep waters with oxygen and carries
nutrients to surface waters where microscopic plants known as phytoplankton can
use them. When cold, nutrient-rich waters rise to the surface seasonally and mix
with sunlit surface waters, the upwellings trigger the growth of phytoplankton.
The
areas where these upwellings occur are often rich fishing grounds, the sea's "gardens
of Eden" where an abundance of marine life flourishes.
As oceans absorb
more heat, upwellings of cold, nutrient-rich waters can become less frequent.
Without this nourishment, blooms of plant plankton, which are the base of the
marine food chain, are disrupted and so food for sea life up the food chain, like
krill, larger fish and seabirds, is cut off.
To make things worse, phytoplankton
use carbon dioxide for photosynthesis. With fewer plankton, the oceans could not
remove as much carbon dioxide from the atmosphere.
An Example: Starving
Sea Birds
Some signs already show that the marine food web is fraying. In 2005
on the U.S. West Coast and 2004 in Britain, hundreds of thousands of seabirds
failed to breed. Dead seabirds like cormorants and Cassin's auklets have washed
up on West Coast beaches.
Juvenile rockfish counts were the lowest they had
been off California in more than 20 years. Most alarming, small crustaceans like
krill -- a critical link in the ocean's food web -- suffered steep declines.
The
culprit for the collapse appears to be slackening upwellings, which decreased
phytoplankton blooms in these coastal areas. Fewer phytoplankton mean fewer fish,
leaving the birds to face mass starvation.
Monitoring of the oceans off Hawaii
over the last 20 years shows that upwellings are decreasing. Scientists suspect
that this is an effect of global warming.
The debate over global warming has
shifted from whether it is happening to how to avoid catastrophic damage. Significant
changes loom for seabird and fish communities, ocean circulation patterns and
basic processes of ocean chemistry.
"We're facing warming waters and major
alterations in many oceanic processes and ocean chemistry, damage to coral reefs,
and effects from sea level rise on marine ecosystems," says Environmental
Defense scientist Doug Rader.
Without emissions cuts, the effects will be even
worse.
"The ship is already in motion, and it will take immediate action
to turn it away from the danger ahead," sums up Environmental Defense climate
scientist Dr. James Wang.
Sources for the Oceans and Global Warming
Fujita.
Rod. Heal the Ocean: Solutions for Saving our Seas. New Society Publishers, Gabriola
Island, B.C., Canada. 55-57, 75-78.
The Heat Is On: A White Paper on Climate
Action (PDF). Environmental Defense, 2004.
Intergovernmental Panel on Climate
Change (IPCC). "Climate Change 2007: The Physical Scientific Basis":
Summary for Policymakers (PDF).
Martin, Glen. "Sea Life in Peril - Plankton
Vanishing: Usual Seasonal Influx of Cold Water Isn't Happening." San Francisco
Chronicle. 12 July 2005.
McCarthy, Michael. "Disaster at Sea: Global Warming
Hits UK Birds." The Independent. 30 July 2004.
The National Assessment
Synthesis Team. Climate Change Impacts on the United States: The Potential Consequences
of Climate Variability and Change (PDF). US Global Change Research Program, Washington
D.C. 2000.
Sarmiento, J. L. ; Gruber, N. ; Brzezinski, M. A. ; Dunne, J. P.
"High-Latitude Controls of Thermocline Nutrients and Low Latitude Biological
Productivity" (PDF). Nature, Vol. 427, 1 January 2004.