HERE IS WHAT THE BBC SAYS BOTH SIDES ARE SAYING
Fred Singer contributed & Gavin Schmidt
The 'Skeptical' View The IPCC 'Consensus'
Compiled by Richard Black of the BBC
IT WOULD OF COURSE BE MORE SPORTING IF DICK LINZEN
WOULD PITCH IN AND REWRITE SINGER'S HALF
1. It Is unclear what climate has been doing for the last century
Singer: Instruments show there has been some warming of the Earth's surface since 1979, but the actual value is subject to large errors. Most long-term data comes from surface weather stations. Many of these are in urban centres which have expanded in both size and energy use. When these stations observe a temperature rise, they are simply measuring the "urban heat island effect". In addition, coverage is patchy, with some regions of the world almost devoid of instruments. Data going back further than a century or two is derived from "proxy" indicators such as tree-rings and stalactites which, again, are subject to large errors.
Schmidt Warming is unequivocal. Weather stations, ocean measurements, decreases in snow cover, reductions in Arctic sea ice, longer growing seasons, balloon measurements, boreholes and satellites all show results consistent with the surface record of warming. The urban heat island effect is real but small; and it has been studied and corrected for. Analyses by Nasa for example use only rural stations to calculate trends. Recently, work has shown that if you analyse long-term global temperature rise for windy days and calm days separately, there is no difference. If the urban heat island effect were large, you would expect to see a bigger trend for calm days when more of the heat stays in the city. Furthermore, the pattern of warming globally doesn't resemble the pattern of urbanisation, with the greatest warming seen in the Arctic and northern high latitudes. Globally, there is a warming trend of about 0.8C since 1900, more than half of which has occurred since 1979.
2. IF THE AVERAGE TEMPERATURE WAS RISING, IT HAS NOW STOPPED
Since 1998 - almost a decade - the record, as determined by
observations from satellites and balloon radiosondes, shows no warming.
1998 was an exceptionally warm year because of the strong El Nino
event. Variability from year to year is expected, and picking a
specific warm year to start an analysis is "cherry-picking"; if you
picked 1997 or 1999 you would see a sharper rise. Even so, the linear
trends since 1998 are still positive.
3. THE EARTH HAS BEEN WARMER IN THE RECENT PAST
The beginning of the last Millennium saw a "Mediaeval Warm Period" when
temperatures, certainly in Europe, were higher than they are now.
Grapes grew in northern England. Ice-bound mountain passes opened in
the Alps. The Arctic was warmer in the 1930s than it is today.
There have been many periods in Earth history that were warmer than
today - if not the MWP, then maybe the last interglacial (125,000 years
ago) or the Pliocene (three million years ago). Whether those
variations were caused by solar forcing, the Earth's orbital wobbles or
continental configurations, none of those causes apply today. Evidence
for a Mediaeval Warm Period outside Europe is patchy at best, and is
often not contemporary with the warmth in Europe. As the US National
Oceanographic and Atmospheric Administration (Noaa) puts it: "The idea
of a global or hemispheric Mediaeval Warm Period that was warmer than
today has turned out to be incorrect". Additionally, although the
Arctic was warmer in the 1930s than in the following few decades, it is
now warmer still.
4. COMPUTER MODELS ARE NOT RELIABLE
Computer models are the main way of forecasting future climate change.
But despite decades of development they are unable to model all the
processes involved; for example, the influence of clouds, the
distribution of water vapour, the impact of warm seawater on
ice-shelves and the response of plants to changes in water supply.
Climate models follow the old maxim of "garbage in, garbage out".
Models are simply ways to quantify understanding of climate. They will
never be perfect and they will never be able to forecast the future
exactly. However, models are tested and validated against all sorts of
data. Over the last 20 years they have become able to simulate more
physical, chemical and biological processes, and work on smaller
spatial scales. The 2007 IPCC report produced regional climate
projections in detail that would have been impossible in its 2001
assessment. All of the robust results from modelling have both
theoretical and observational support.
5. THE ATMOSPHERE IS NOT BEHAVING AS MODELS WOULD PREDICT
Computer models predict that the lower levels of the atmosphere, the
troposphere, should be warming faster than the Earth's surface.
Measurements show the opposite. So either this is another failing of
the models, or one set of measurements is flawed, or there are holes in
our understanding of the science.
Lower levels of the troposphere are warming; but measuring the exact
rate has been an uncertain process, particularly in the satellite era
(since 1979). Readings from different satellites need to be tied
together, and each has its own problems with orbital decay and sensor
drift. Two separate analyses show consistent warming, one faster than
the surface and one slightly less. Within the uncertainties of the
data, there is no discrepancy that needs to be dealt with. Information
from balloons has its own problems but the IPCC concluded this year:
"For the period since 1958, overall global and tropical tropospheric
warming estimated from radiosondes has slightly exceeded surface
6. CLIMATE IS MAINLY INFLUENCED BY THE SUN
Earth history shows climate has regularly responded to cyclical changes
in the Sun's energy output. Any warming we see can be attributed mainly
to variations in the Sun's magnetic field and solar wind.
Solar variations do affect climate, but they are not the only factor.
As there has been no positive trend in any solar index since the 1960s
(and possibly a small negative trend), solar forcing cannot be
responsible for the recent temperature trends. The difference between
the solar minimum and solar maximum over the 11-year solar cycle is 10
times smaller than the effect of greenhouse gases over the same
7. A CARBON DIOXIDE RISE HAS ALWAYS COME AFTER A TEMPERATURE INCREASE NOT BEFORE
Ice-cores dating back nearly one million years show a pattern of
temperature and CO2 rise at roughly 100,000-year intervals. But the CO2
rise has always come after the temperature rise, not before, presumably
as warmer temperatures have liberated the gas from oceans.
This is largely true, but largely irrelevant. Ancient ice-cores do show
CO2 rising after temperature by a few hundred years - a timescale
associated with the ocean response to atmospheric changes mainly driven
by wobbles in the Earth's orbit. However, the situation today is
dramatically different. The extra CO2 in the atmosphere (35% increase
over pre-industrial levels) is from human emissions. Levels are higher
than have been seen in 650,000 years of ice-core records, and are
possibly higher than any time since three million years ago.
8. LONG-TERM DATA ON HURRICANES AND ARCTIC ICE IS TOO POOR TO ASSESS TRENDS
Before the era of satellite observation began in the 1970s,
measurements were ad-hoc and haphazard. Hurricanes would be reported
only if they hit land or shipping. Arctic ice extent was measured only
during expeditions. The satellite record for these phenomena is too
short to justify claims that hurricanes are becoming stronger or more
frequent, or that there is anything exceptional about the apparent
shrinkage in Arctic ice.
The Arctic Climate Impact Assessment project notes that systematic
collection of data in parts of the Arctic began in the late 18th
Century. The US National Hurricane Center notes that "organised
reconnaissance" for Atlantic storms began in 1944. So although
historical data is not as complete as one might like, conclusions can
be drawn. And the IPCC does not claim that global warming will make
hurricanes more frequent - its 2007 report says that if anything, they
are likely to become less frequent, but more intense.
9. WATER VAPOUR IS THE MAJOR GREENHOUSE GAS; CO2 IS RELATIVELY UNIMPORTANT
The natural greenhouse effect keeps the Earth's surface about 33C
warmer than it would otherwise be. Water vapour is the most important
greenhouse gas, accounting for about 98% of all warming. So changes in
carbon dioxide or methane concentrations would have a relatively small
impact. Water vapour concentrations are rising, but this does not
necessarily increase warming - it depends how the water vapour is
Water vapour is essentially in balance with the planet's temperature on
annual timescales and longer, whereas trace greenhouse gases such as
CO2 stay in the atmosphere on a timescale of decades to centuries. The
statement that water vapour is "98% of the greenhouse effect" is simply
false. In fact, it does about 50% of the work; clouds add another 25%,
with CO2 and the other greenhouse gases contributing the remaining
quarter. Water vapour concentrations are increasing in response to
rising temperatures, and there is evidence that this is adding to
warming, for example in Europe. The fact that water vapour is a
feedback is included in all climate models.
10. PROBLEMS SUCH AS HIV/AIDS AND POVERTY ARE MORE PRESSING THAN CLIMATE CHANGE
The Kyoto Protocol will not reduce emissions of greenhouse gases
noticeably. The targets were too low, applied only to certain
countries, and have been rendered meaningless by loopholes. Many
governments that enthuse about the treaty are not going to meet the
reduction targets that they signed up to. Even if it is real, man-made
climate change is just one problem among many facing the world's rich
and poor alike. Governments and societies should respond
proportionately, not pretend that climate is a special case. And some
economists believe that a warmer climate would, on balance, improve
Arguments over the Kyoto Protocol are outside the realms of science,
although it certainly will not reduce greenhouse gas emissions as far
or as fast as the IPCC indicates is necessary. The latest IPCC Working
Group 2 report suggest that the impact of man-made climate change will
on balance be deleterious, particular to the poorer countries of the
tropics, although colder regions may see benefits such as increased
crop yields. Investment in energy efficiency, new energy technologies
and renewables are likely to benefit the developing world.