No one said that there is no need for more studies. What they did say, among other things, was:
There is high agreement and much evidence that with
current climate change mitigation policies and related sustainable
development practices, global GHG emissions
will continue to grow over the next few decades. {3.1}
The IPCC Special Report on Emissions Scenarios (SRES,
2000) projects an increase of global GHG emissions by 25 to
90% (CO2-eq) between 2000 and 2030 (Figure SPM.5), with
fossil fuels maintaining their dominant position in the global energy
mix to 2030 and beyond. More recent scenarios without
additional emissions mitigation are comparable in range.8,9 {3.1}
Continued GHG emissions at or above current rates
would cause further warming and induce many changes
in the global climate system during the 21st century that
would very likely be larger than those observed during
the 20th century (Table SPM.1, Figure SPM.5). {3.2.1}
For the next two decades a warming of about 0.2°C per decade
is projected for a range of SRES emissions scenarios. Even
if the concentrations of all GHGs and aerosols had been kept
constant at year 2000 levels, a further warming of about 0.1°C
per decade would be expected. Afterwards, temperature projections
increasingly depend on specific emissions scenarios. {3.2}
The range of projections (Table SPM.1) is broadly consistent
with the TAR, but uncertainties and upper ranges for
temperature are larger mainly because the broader range of
available models suggests stronger climate-carbon cycle feedbacks.
Warming reduces terrestrial and ocean uptake of atmospheric
CO2, increasing the fraction of anthropogenic emissions
remaining in the atmosphere. The strength of this feedback
effect varies markedly among models. {2.3, 3.2.1}
Because understanding of some important effects driving
sea level rise is too limited, this report does not assess the
likelihood, nor provide a best estimate or an upper bound for
sea level rise. Table SPM.1 shows model-based projections of global average sea level rise for 2090-2099.10 The projections
do not include uncertainties in climate-carbon cycle feedbacks
nor the full effects of changes in ice sheet flow, therefore
the upper values of the ranges are not to be considered
upper bounds for sea level rise. They include a contribution
from increased Greenland and Antarctic ice flow at the rates
observed for 1993-2003, but this could increase or decrease
in the future.11 {3.2.1}
There is now higher confidence than in the TAR in projected
patterns of warming and other regional-scale
features, including changes in wind patterns, precipitation
and some aspects of extremes and sea ice. {3.2.2}
Regional-scale changes include: {3.2.2}
warming greatest over land and at most high northern latitudes
and least over Southern Ocean and parts of the North
Atlantic Ocean, continuing recent observed trends (Figure
SPM.6)
contraction of snow cover area, increases in thaw depth
over most permafrost regions and decrease in sea ice extent;
in some projections using SRES scenarios, Arctic
late-summer sea ice disappears almost entirely by the latter
part of the 21st century
very likely increase in frequency of hot extremes, heat
waves and heavy precipitation
likely increase in tropical cyclone intensity; less confidence
in global decrease of tropical cyclone numbers
poleward shift of extra-tropical storm tracks with consequent
changes in wind, precipitation and temperature patterns
very likely precipitation increases in high latitudes and
likely decreases in most subtropical land regions, continuing
observed recent trends.
There is high confidence that by mid-century, annual river
runoff and water availability are projected to increase at high
latitudes (and in some tropical wet areas) and decrease in some
dry regions in the mid-latitudes and tropics. There is also high confidence that many semi-arid areas (e.g. Mediterranean
Basin, western United States, southern Africa and
north-eastern Brazil) will suffer a decrease in water resources
due to climate change. {3.3.1, Figure 3.5}
Studies since the TAR have enabled more systematic
understanding of the timing and magnitude of impacts
related to differing amounts and rates of climate
change. {3.3.1, 3.3.2}
Figure SPM.7 presents examples of this new information
for systems and sectors. The top panel shows impacts increasing
with increasing temperature change. Their estimated magnitude
and timing is also affected by development pathway
(lower panel). {3.3.1}
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