Understanding how humans are changing the climate requires
experts from many different areas.
Physicists, chemists, engineers,
mathematicians, biologists, atmospheric scientists, oceanographers,
social scientists, the list goes on.
Scientists studying the Earth's
climate work out descriptions of how humans are interacting with the
environment, how those interactions cause changes, and how measurements
can be made.
The methods that have been developed to measure the
Earth's climate include true engineering marvels.
There are instruments
on satellites that measure the rising sea levels and surface
temperatures of
oceans, land surfaces, and atmosphere.
But satellite instruments can't see below the surface.
Perhaps
the most important component of the Earth's climate, and perhaps the
hardest to measure, is the oceans that cover over 70 percent of the
Earth's surface.
Over the past decades and even centuries, humans have
used various techniques to measure oceans, from buckets that were
dragged through the ocean waters to collect samples, to modern
autonomous devices that measure the oceans day and night throughout the
year and report data by satellite.
A major new development since about
2005 is use of floats that pop up and down to sample the top 2000 meters
of the ocean for temperature and salinity.
These enable us to
calculate the increase in heat and the changes to the acidity of the
ocean waters.
It seems logical that throughout the decades, as
our measurements have become more sophisticated, our understanding of
the oceans has improved.
That much is true.
But, from a climate
perspective, we must address how today's oceans differ from the oceans
10, 20, or 100 years ago.
Sure, the oceans are warmer now because
humans have loaded the atmosphere with heat-trapping gases, but how much
warmer?
How do we compare today's sophisticated measurements with
yesteryears crude ones?
For instance, if measurements in past decades
were biased or their assessed depth was off, it could appear that the
oceans have not warmed much in certain periods.
Such errors would also
have tremendous consequences for our predictions of what the climate
will be like in the future.
This complicated topic is the subject of a recent
paper my colleagues and I published
in the journal Reviews of Geophysics.
Nearly 30 of the world's top
oceanographers collaborated on a massive study that not only went back
through the history books to describe the evolution of ocean temperature
measuring methods, but also looked forward to future measuring
techniques.
The paper found that while all the evidence shows the Earth is warming,
without pause,
there are still unanswered questions and unmeasured parts of the
oceans.
Underneath ice sheets and deep in ocean basins are just two
regions that need more attention.
One of the world's pre-eminent
oceanographers for, among other things,
his important work measuring heat transferred to very deep ocean waters,
is Dr. Gregory C. Johnson.
Dr. Johnson works as an oceanographer at
NOAA's Pacific Marine Environmental Laboratory in Seattle, Washington;
he is also a co-author on the paper. He notes,
"This
review points to the need to expand the innovative, year-round,
broad-scale measurements of the upper half of the open ocean volume so
successfully pioneered by the international Argo Program all the way
down to the ocean floor and into the ice-covered polar regions, so we
can make well-resolved, timely, and truly global assessments of the
amount of heat being absorbed by the ocean."
Arctic Sea Ice Minimum
After an unusually cold summer in the northernmost latitudes, Arctic sea ice appears to have reached its annual minimum summer extent for 2013 on Sept. 13, the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado in Boulder has reported.
Analysis of satellite data by NSIDC and NASA showed that the sea ice extent shrunk to 1.97 million square miles (5.10 million square kilometers), the sixth-lowest on record.
This animation shows daily Arctic sea ice extent and seasonal land cover change from May 16 through Sept. 12, 2013, the day before the sea ice reached its minimum area of coverage for the year.
The data was provided by the Japan Aerospace Exploration Agency (JAXA) from their AMSR2 instrument aboard the GCOM-W1 satellite.
In short, we are doing well, but we could do better with more deep-ocean measuring equipment.
A similar reaction comes from
Dr. Kevin Trenberth, who not only is one of the world's top climate scientists, but is also recognized as a top communicator,
winning the 2013 American Geophysical Union Climate Communication Award.
Dr. Trenberth has been quite active in ocean heating studies, most recently publishing
an important paper which calculated significant rates of heating in the ocean.
He described this new study as,
"an
excellent review of the history of ocean observations and very
revealing about the problems, the issues, and the advances. Most people
don't realize the state of the science of ocean observations and this
paper is in that sense an expose."
Drs. Johnson, Trenberth, and others who study
climate change
every day are hopeful that their work will help us quantify how much
climate change has occurred and what the future may hold.
While climate
science, like other scientific endeavors does not package answers in
neatly wrapped exacting answers, what we can say with certainty that is
the Earth is warming and the best place to measure that warming is in
the oceans.
The best ocean measurements show a continuous
heating that is largely from human-emitted greenhouse gases, and it is
an important component of sea level rise.
Indeed sea level rise may be
the best single indicator of a warming planet: the other major
contributor is additional water from melting land ice.
Since satellite
altimeters were placed in orbit in 1992, sea level has risen at 3.2
mm/year.
That should be alarming to everyone.
Links :
- AWI : Long-term data reveal: The deep Greenland Sea is warming faster than the World Ocean
