2 posts • joined Tuesday 6th December 2011 14:12 GMT
Where on Earth have you got the idea that anyone thinks these factors won't continue to have effects in the future?
The 3 things mentioned are considered the most important factors in determining subdecadal global average surface temperature fluctuations. However, since they essentially oscillate around 0 their effect on multi-decadal trends is minimal, hence the overall trends in the full 1979-present reference period are unchanged.
Where they have a large effect is in shorter-term trends. For example, in the NOAA record the decadal trend from 1974-84 was 0.29ºC/Decade, from 1992-2002 0.33ºC/Decade; Conversely 1986-96 was only 0.08ºC/Decade and 1998-2008 0.06ºC/Decade. Even though the trends across the whole period are around 0.15ºC/Decade plotting across shorter periods reveals much greater variability - sometimes warming is 'faster', sometimes warming is 'slower' or perhaps even 'stopped'. What this paper has shown is that simply adjusting for these 3 factors leaves a much more consistent temperature progression. What that consistency means can be left to you as an exercise.
There are certainly potential problems with this approach, which may be worked out later in the literature, but it's a useful contribution to scientific understanding.
'Using a range of simulations the authors estimate that global temperature trends have inched up by between 0.014C and 0.018C a year in recent times. They say that the total rise since 1979 is 0.4C. The authors arrived at this figure by adding or subtracting so as to remove much larger climatic factors such as El Nino and volcanic effects...'
I'm not sure the author understands the study. The overall trends across the 1979-present reference period from different global temperature indexes are barely affected by the analysis. The trends and total increase quoted here can be obtained simply by looking at the raw data (though 0.4ºC is at the low end).
What the study has found is a clear and consistent underlying trend in the data, instead of the collection of large bumps and spikes in the raw data, by accounting for known factors which cause short-term surface and tropospheric temperature fluctuations (volcanic eruptions, ENSO, solar cycle).
To sum up, the important finding in this study is the consistency of the trends, not the magnitude of them.
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