In order to
understand the world’s climate and how it has changed through centuries, we
need long-term worldwide observations of the atmosphere, oceans and lands
surface. But we have a lack of information, some of the problems related with
it, are exposed below:
Geographical
coverage and gaps in the historical record
The main
obstacle in assessing past climate change has been the fact that a lot of
observations aren’t complete. Climate observations were mainly limited to
weather stations and vessels, and only included measurements made at or near
the land or the ocean surface. In the 19th century, many parts of
the world were not monitorated at all. In the last years this have changed,
- Since the 1950’s weather balloon sounding have been widespread over land.
- Satellites are used for monitoring the climate; it gives us a worldwide coverage since 1970s. The measures include Sea surface temperature (SST), Sea Ice extension, Chlorophyll, etc.
- More than 3611 free-drifting profiling floats that measures the temperature and the salinity of the upper 2000m of the ocean in the Argo project. This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all the data transferred and published in a global platform.
Profiling float, Argo project - Malaspina Leg 3 Indian Ocean
For the
last two centuries, the scientists have improved the availability of
instrumental data. Many data was only available from paper logbooks, some of
these data has been put in computer databases. Nowadays, most data collected is
recorded on databases.
Using
indirect or proxy measurements
Before
1600’s we don’t have direct measurements of changes in climate, so scientists
have used indirect or proxy methods, such as,
- Tree-ring and ice-cores for inferring changes in temperature and precipitation.
- Depth profiles of temperature in oil-drilling boreholes to estimate the changes in air temperature.
- Corals to estimate the ocean temperature and the sea-level changes.
These
indirect or proxy methods are not as precise as direct instrument measurements,
however, long-term temperatures trends confirms climate in the past two
thousand years was no as warm as it has been in recent decades.
Varying
standards for taking observations
When we are
comparing data from different sources, we have to take into account that the
different measurements have been taken with different methods and that those
methods have changed through the time. That’s the reason why International
standards have been developed for observing practices. Those standards, for
both satellite and ground-based data, include the requirement to overlap records in order to have more reliable information.
Useful
links:
Argo
information centre - http://wo.jcommops.org/cgi-bin/WebObjects/Argo
Argo
steering team - http://www.argo.ucsd.edu/
Argo - España - http://www.oceanografia.es/argo/
Met Office
- Climate change and observations
NOAA Ocean
Products – Environmental Satellite data and information service http://www.ospo.noaa.gov/Products/ocean/index.html
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