CLEAR ….. HUMAN IMPACT ON CLIMATE

[Anonymous]

‘Clear’ human impact on climate
A
scientific report commissioned by the US government has concluded there
is “clear evidence” of climate change caused by human activities.
The
report, from the federal Climate Change Science Program, said trends
seen over the last 50 years “cannot be explained by natural processes
alone”.It found that temperatures have increased in the lower
atmosphere as well as at the Earth’s surface.However, scientists
involved in the report say better data is badly needed.Observations
down the years have suggested that the troposphere, the lower
atmosphere, is not warming up, despite evidence that temperatures at
the Earth’s surface are rising.This goes against generally accepted
tenets of atmospheric physics, and has been used by “climate sceptics”
as proof that there is no real warming.The new report, Temperature
Trends in the Lower Atmosphere, re-analyses the atmospheric data and
concludes that tropospheric temperatures are rising.This means, it
says, that the impact of human activities upon the global climate is
clear.”The observed patterns of change over the past 50 years cannot be
explained by natural processes alone, nor by the effect of short-lived
atmospheric constituents (such as aerosols and tropospheric ozone)
alone,” it says.
Holes in the data
But there are some big uncertainties which still need resolving.
Globally,
the report concludes, tropospheric temperatures have risen by 0.10 and
0.20C per decade since 1979, when satellite data became generally
available.
The wide gap between the two figures means, says the
report, that “…it is not clear whether the troposphere has warmed
more or less than the surface”.Peter Thorne, of the UK Meteorological
Office, who contributed to the report, ascribes this uncertainty to
poor data.”Basically, we’ve not been observing the atmosphere with
climate in mind,” he told the BBC News website.”We’re looking for very
small signals in data that are very noisy. From one day to the next,
the temperature can change by 10C, but we’re looking for a signal in
the order of 0.1C per decade.”
The report shows up a particular
discrepancy concerning the tropics, where it concludes that
temperatures are rising by between 0.02 and 0.19C per decade, a big
margin of error.Additionally, the majority of the available datasets
show more warming at the surface than in the troposphere, whereas most
models predict the opposite.
For Fred Singer, of the Science and
Environmental Policy Project, a prominent climate sceptic, this
suggests that the report’s support for the concept of human-induced
climate change is spin rather than substance.
“The basic data in the
report is quite OK,” he said, “but the interpretation that’s been given
is different from what the data says.”In particular, [the authors]
suppress the major result of the report; that data do not agree with
models.”
‘No inconsistency’
Measuring tropospheric temperatures is far from a simple business.
Satellites
sense the “average” temperature of the air between themselves and the
Earth, largely blind to what is happening at different altitudes.To
compound matters, instruments on board satellites degrade over time,
orbits subtly drift, and calibration between different satellites may
be poor.Weather balloons (or radiosondes) take real-time measurements
as they ascend, but scientists can never assess instruments afterwards;
they are “fire-and-forget” equipment.
Correcting for all these potential sources of error is a sensitive and time-consuming process.
The
report makes clear recommendations for the kind of infrastructure
needed to produce higher-quality data and resolve remaining
uncertainties.
Key recommendations include:
* establishing reference sites for radiosonde measurements which would increase consistency between datasets
* making sure the operating periods of satellites overlap so instruments can be cross-calibrated
*
observing factors such as wind, clouds, and humidity in the troposphere
to make sure they are consistent with temperature data ,Such
observations could produce an unambiguous picture of tropospheric
warming, removing discrepancies over the scientific picture and
providing better data which can be used to improve computer models.”I
would be reticent to say the report provides a clear answer,” said
Peter Thorne, “but I would say it provides a clear road-map.”But we do
now have overlap between what is happening and what we believe ought to
be happening.

[Author]

May 4, 2006 at 10:21 AM