Times the contails effect by 8. Also stratospheric water vapor plays a far more importen role than indecated in the graph. In the 80's and 90's stratospheric water vapor caused one third of the observed warming and have caused surface temperatures to increase about 25 percent more slowly since 2000.
How do you know it is incorrect? Do you have a source?
As far as I understand about stratospheric water vapor, you are right, in the 80's and 90's it was pretty bad. But after year 2000, there was a significant drop of it's concentration especially in the lower-stratosphere. So since the graph shows the diffrence between 1750 and 2005, it might very well (and most probably) be less important than if it was between let's say 1750 and 1990.
Now for the contrails, I know that they both reflect incoming radiations and trap outgoing radiations. Since the lastest is more important, the net result is an increase in forcing. But since it also reflects incoming radiations as said, the positive effect is diminished.
But I haven't gotten to deep in both these mechanisms yet.
Here's what I found about it in the IPCC report (graph comes from it).
STRATOSPHERIC WATER VAPOR
"The TAR noted that several studies had indicated long-term increases in stratospheric water vapour and acknowledged that these trends would contribute a significant radiative impact. However, it only considered the stratospheric water vapour increase expected from CH4 increases as an RF, and this was estimated to contribute 2 to 5% of the total CH4 RF (about +0.02 W m–2).
Section 3.4 discusses the evidence for stratospheric water vapour trends and presents the current understanding of their possible causes. There are now 14 years of global stratospheric water vapour measurements from Halogen Occultation Experiment (HALOE) and continued balloon-based measurements (since 1980) at Boulder, Colorado. There is some evidence of a sustained long-term increase in stratospheric water vapour of around 0.05 ppm yr–1 from 1980 until roughly 2000, since then water vapour concentrations in the lower stratosphere have been decreasing (see Section 3.4 for details and references). As well as CH4 increases, several other indirect forcing mechanisms have been proposed, including: a) volcanic eruptions (Considi ne et al., 2001; Joshi and Shine, 2003); b ) biomass burning aerosol (Sherwood, 2002); c) tropospheric (SO2; Notholt et al., 2005) and d) changes in CH4 oxidation rates from changes in stratospheric chlorine, ozone and OH (Rockmann et al., 2004). These are mechanisms that can be linked to an external forcing agent. Other proposed mechanisms are more associated with climate feedbacks and are related to changes in tropopause temperatures or circulation (Stuber et al., 2001a; Fueglistaler et al., 2004). From these studies, there is little quantification of the stratospheric water vapour change attributable to different causes. It is also likely that different mechanisms are affecting water vapour trends at different altitudes.
Since the TAR, several further calculations of the radiative balance change due to changes in stratospheric water vapour have been performed (Forster and Shine, 1999; Oinas et al., 2001; Shindell, 2001; Smith et al., 2001; Forster and Shine, 2002). Smith et al. (2001) estimated a +0.12 to +0.2 W m–2 per decade range for the RF from the change in stratospheric water vapour, using HALOE satellite data. Shindell (2001) estimated an RF of about +0.2 W m–2 in a period of two decades, using a GCM to estimate the increase in water vapour in the stratosphere from oxidation of CH4 and including climate feedback changes associated with an increase in greenhouse gases. Forster and Shine (2002) used a constant 0.05 ppm yr–1 trend in water vapour at pressures of 100 to 10 hPa and estimated the RF to be +0.29 W m–2 for 1980 to 2000. GCM radiation codes can have a factor of two uncertainty in their modelling of this RF (Oinas et al., 2001). For the purposes of this chapter, the above RF estimates are not readily attributable to forcing agent(s) and uncertainty as to the causes of the observed change precludes all but the component due to CH4 increases being considered a forcing. Two related CTM studies have calculated the RF associated with increases in CH4 since pre-industrial times (Hansen and Sato, 2001; Hansen et al., 2005), but no dynamical feedbacks were included in those estimates. Hansen et al. (2005) estimated an RF of +0.07 ± 0.01 W m–2 for the stratospheric water vapour changes over 1750 to 2000, which is at least a factor of three larger than the TAR value. The RF from direct injection of water vapour by aircraft is believed to be an order of magnitude smaller than this, at about +0.002 W m–2 (IPCC, 1999). There has been little trend in CH4 concentration since 2000 (see Section 2.3.2); therefore the best estimate of the stratospheric water vapour RF from CH4 oxidation (+0.07 W m–2) is based on the Hansen et al. (2005) calculation. The 90% confidence range is estimated as ±0.05 W m–2, from the range of the RF studies that included other effects. There is a low level of scientific understanding in this estimate, as there is only a partial understanding of the vertical profile of CH4-induced stratospheric water vapour change (Section 2.9, Table 2.11). Other human causes of stratospheric water vapour change are unquantified and have a very low level of scientific understanding."
"Aircraft produce persistent contrails in the upper troposphere in ice-supersaturated air masses (IPCC, 1999). Contrails are thin cirrus clouds, which reflect solar radiation and trap outgoing longwave radiation. The latter effect is expected to dominate for thin cirrus (Hartmann et al., 1992; Meerkötter et al., 1999), thereby resulting in a net positive RF value for contrails. Persistent contrail cover has been calculated globally from meteorological data (e.g., Sausen et al., 1998) or by using a modified cirrus cloud parametrization in a GCM (Ponater et al., 2002). Contrail cover calculations are uncertain because the extent of supersaturated regions in the atmosphere is poorly known. The associated contrail RF follows from determining an optical depth for the computed contrail cover. The global RF values for contrail and induced cloudiness are assumed to vary linearly with distances flown by the global fleet if flight ambient conditions remain unchanged. The current best estimate for the RF of persistent linear contrails for aircraft operations in 2000 is +0.010 W m–2 (Table 2.9; Sausen et al., 2005). The value is based on independent estimates derived from Myhre and Stordal (2001b) and Marquart et al. (2003) that were updated for increased aircraft traffic in Sausen et al. (2005) to give RF estimates of +0.015 W m–2 and +0.006 W m–2, respectively. The uncertainty range is conservatively estimated to be a factor of three. The +0.010 W m–2 value is also considered to be the best estimate for 2005 because of the slow overall growth in aviation fuel use in the 2000 to 2005 period. The decrease in the best estimate from the TAR by a factor of two results from reassessments of persistent contrail cover and lower optical depth estimates (Marquart and Mayer, 2002; Meyer et al., 2002; Ponater et al., 2002; Marquart et al., 2003). The new estimates include diurnal changes in the solar RF, which decreases the net RF for a given contrail cover by about 20% (Myhre and Stordal, 2001b). The level of scientific understanding of contrail RF is considered low, since important uncertainties remain in the determination of global values (Section 2.9, Table 2.11). For example, unexplained regional differences are found in contrail optical depths between Europe and the USA that have not been fully accounted for in model calculations (Meyer et al., 2002; Ponater et al., 2002; Palikonda et al., 2005)."