In the AR5 The IPCC tried to explain that ENSO oscillation is the main reason temperatures deviate from projections in the short term. ENSO is not a forcing. It oscillates around a nuetral state and has no effect on long term trends.
ENSO oscillation certainly is one of the known factors in significant deviations of temperatures on the dacadal scale. If it were true that this specific, well documented phenomenon was the only oscillation that affected climate, then it would be correct to assume that it "has no effect on long term trends". However, the source of ENSO oscillation is an emergent behavior that exhibits chaotic tendencies. One characteristic of such systems is that they sometimes occur on multiple scales (physical or temporal or both) and if this is the case with the Earth's climate, then it is likely that other oscillations that we haven't discovered yet occur on multi-decadal or even multi-century scales.
These describe the known patterns (page 2003, IPCC AR5) :
1 AMO: Atlantic Multi-decadal Oscillation
2 AN: Atlantic Niño pattern
3 BLC: Blocking events
4 ENSO: El Niño-Southern Oscillation
5 IOB: Indian Ocean Basin pattern
6 IOD: Indian Ocean Dipole pattern
7 IPO: Interdecadal Pacific Oscillation
8 MJO: Madden-Julian Oscillation
9 NAM: Northern Annular Mode
10 NAO: North Atlantic Oscillation
11 NPO: North Pacific Oscillation
12 PDO: Pacific Decadal Oscillation
13 PNA: Pacific North America pattern
14 PSA: Pacific South America pattern
15 QBO: Quasi-Biennial Oscillation
16 SAM: Southern Annular Mode
17 TBO: Tropospheric Biennial Oscillation
Multi-temporal scale oscillations are typical of short term weather patterns and this makes weather prediction such a complicated science. The existence of these oscillations is well known but this is only because it's relatively easy to discern their recurring pattern over weekly and monthly periods.
Global climate patterns may be very similar - which is why the IPCC bases its computer climate modeling predictions (Atmospheric/Oceanic Global Climate Models, or AOGCMs) on weather forecasting models - yet any patterns on time scales larger than decadal will be very difficult to pick out of the background noise of paleoclimate proxy data and this goes along with the inherent problem of there simply not being enough time elapsed for us to observe them as they occur.
While any possible oscillations that may occur at these larger time scales will also "center around a neutral state" the fact that we've not been able to detect them (if they exist) means that deciding what the "neutral state" temperature should be is dependent on knowing the magnitude of the variation and our current position (2013) relative to it.
Volcanic aerosols have a cooling effect on the planet by having a significant but short term effect on temps. Their effects are impressively well understood - even in the 90's Hansen correctly modelled and projected golbal temps in response to the Mt pinatubo eruption.... but it's impossible for a climate model to predict things like eruptions and oceanic oscillations. Once again - volcanic eruptions do NOT have long term effects on temp trends.
Understood. And I didn't dispute this. The IPPCC reports also include extensive documentation on radiative forcing due to orbital variations (Milankovich cycles) but I didn't mention them either because they had no significant effect on temperature variation in the past century.
Of course there are other natural forcings which have effected climate over millenia - variations in TSI (solar), orbital oscillations, and GHG levels INCLUDING naturally occurring CO2. To say that it can't possibly be CO2 because of Al Gore and some derpy conspiracy theory is just daft. Climate scientists are trying to quantify exacly how much of an effect each of these different components have on the bigger picture. Obviously when you have a MASSIVE uptick in one of these components you're quite likely to see some kind of physical effect.... and we are.
I didn't mention Al Gore - or any derpy conspiracy theories. I also did not dispute the fact that the increased CO2 due to the burning of fossil fuels is a driver of global warming. I concede that it may even be the dominant driver. The only thing I've addressed are statements contained in the IPCC reports that seem to exaggerate the effects of CO2, and their premature assumption that anthropogenic effects are the ONLY significant natural factors.
Correct but this is not ignored by the IPCC. Climate science is based on analasys of prehistoric proxy data. These things are not dismissed as irrelevant or ignored. They are quantified and put into context.
There is a limit to the reliability of proxy data and the uses that it can be put to. One of my criticisms of the IPCC reports is that it makes assumptions that exceed those limits. For example: Diverse sources of proxy data of very different types are merged together and processed in such a way as to smooth out and obscure any significant variations on global temperature except on very large time scales. This is then compared to much more accurate data from the 20th century that includes the appearance of actual variation so that it seems to show that there has been relatively little temperature change occurring in the past two millennia and very large change occurring during the last century. The fact that the way the data was processed ensures such a result, whether it actually exists in nature or not, means that the conclusion is inherently fallacious. The further fact that the same conclusion is used as a quantitative basis for calibrating the GCMs would seem to call into doubt the usefulness of those models.
There are many charts in the AR4 and 5 quantifying different climatic influences.
This chart is the single most important piece of information contained in the report. It correctly shows the relative importance of all known influences on atmospheric warming (or cooling) in a concise and quantifiable form complete with appropriate error bars. In fact, one of my criticisms of the IPCC is that it spends so much time getting to the point of creating this useful chart only to virtually ignore the information it contains in favor of climate models that rely on dubious calibration techniques to make predictions of future warming trends. [detailed citations to be added when I finish compiling them]
They have come to a conclusion that you don't like so you assume they are wrong and are looking hard for a reason. That is bad science.
You are the one assuming things about something that you cannot know or guess - my motivation for criticizing the IPCC reports.
Perhaps it didn't occur to you that I might possibly be a committed environmentalist who decided to take the time to thoroughly study the scientific background material found in the IPCC reports (the accepted authority on Global Climate Change)
with the intent of being able to counter the arguments of those who wish to ignore the seriousness of the issue and who found out that the good science contained within the report was being compromised by the introduction of a certain amount of flawed methodology for the seeming purpose of exaggerating the severity of the problem.
I consider dishonesty in the name of a higher purpose to be eventually self destructive. I believe the reputation of the entire scientific community is in danger of being severely undermined by the measured amount of virtual pseudoscience that's being injected into the IPCC reports just because the lead authors believe that the end justifies that means, and a certain amount of exaggeration and dishonesty is okay as long as it gets people scared enough to join the cause of combating anthropogenic global warming.
I greatly fear that the time will soon come when the true global warming deniers (those who refuse to believe that human activity could possibly alter the climate) will be able to say, "See, we we're right all along. The global warming crisis mongers abused their science and now we've proved their warnings were based on false information and lies."
The scientific "community" needs to collectively go through these reports themselves rather than just blindly endorsing it - as many have done, assuming that because the information making up the reports is valid, then it must be true that the conclusions of the report are equally valid - and
these diverse scientists must critically judge for themselves, after careful and meticulous study of the material, how much of it to endorse.
