Two recent posts (here and here) have dealt with a comment by sTeve on my blog on NOAA’s claim that the temperature had increased by .2° Celsius in the past decade. As I showed, this claim is based on one of the four climate monitoring agencies, the Goddard Institute of Space Studies, headed by arch-warming alarmist James Hansen and therefore so politicized as to be of little credibility. The other three agencies, as I’ve written, show little (“statistically insignificant”, to quote Climatic Research Unit head Phil Jones) warming since 1998.

This lack of warming for the decade was not predicted by the IPCC’s climate models, yet if the models were correct the past decade would have warmed by the suggested .2°C. This failure suggests that natural factors, particularly the oceans and sun are more powerful than human activities in causing warming, or in not causing warming. This should not be a surprise, given that the sun and oceans have always been the main causes of climate change-are at least, they were until alarmist climatology came into being.

But what about the cooing from 1945-1975? Was that human-caused? sTeve thinks so. He writes:

You mention “The planet also cooled from 1945-75″. Did you not also find that the Clean Air Act of 1975 had a major impact on global temps by removing particulates from the atmosphere, thus removing a masking effect on global heating? Our industrial processes during the period 1945 – 1975 were overwhelming the warming of the planet due to the air pollution we were producing. The particulate matter in the pollution acted to reflect the suns warming of the planet. Once the Nixon Administration passed the Clean Air Act, the next 5 – 10 years saw a demonstrable decrease of air pollution, and we now know that global temps began to rise significantly. This is what has our scientists so very worried!

You write: “And, speaking of short periods of time on which to be drawing conclusions: the anthropogenic global warming hypothesis, correlating carbon dioxide increases with temperature increases, is based on only about 23 years-1975-1998. This is hardly a long enough period of time to be drawing long-term conclusions that might well wreck industrial civilization with poorly thought-out carbon curbs. Correlation, as you well know, doesn’t equal causation.”

Sounds plausible…until we look at the facts. “The SCIENCE says that temperatures did not rise from the mid-30s to the mid-70s because of sulfate aerosols in fossil fuels. And what happened in the mid-70s? Clean-air legislation, and more importantly the phasing out of sulfur-rich fuels.”

In response to sTeve: It’s important for global warming alarmists that the climate changes of the past 70 years, both warming and cooling, be attributed as little as possible to natural causes, because that would imply that perhaps recent warming (1975-1998) was also natural. And we can’t have that. However, when we look at what the oceans and sun were doing during the cooling period 1945-1975, what do we find?

Sunspot activity is closely correlated with climate: the fewer sunspots, the colder the climate; with more sunspots, the planet warms. What’s the sunspot record for the past century or so?

Figure 1: Sunspots are strongly correlated to climate

Sure enough, from 1942 to about 1975, sunspot activity fell. And the planet got colder. As sunspot activity increased in the mid-1970s, the planet got warmer.

As an aside, it’s a curious thing that the IPCC does not consider the fluctuation of solar activity, about .1 per cent, to be a significant climate driver, but a .01% increase in carbon dioxide in the atmosphere (from 280 ppm to 380 ppm) is. And, very small changes in solar intensity are considered to be the drivers of the Milankovitch Cycles that, in turn, have triggered a million-year cycle of glaciations and interglacials.

What about the oceans? What were they doing in the cool 1945-1975 period?

The Pacific Decadal Oscillation (PDO, Figure 2) shows a remarkable correlation with the so-called human-caused cooling of 1945-75.

Figure 2: Pacific Decadal Oscillation and temperature cycles

Most recently, the PDO has gone into a cooling phase.

The North Atlantic Oscillation (NAO) follows a similar pattern, as Figure 3 shows. That is, once again, the North Atlantic current cooled during the 1945-75 period, then warmed up, but is now in a cooling phase.

Figure 3: North Atlantic Oscillation and temperature cycles

What these figures point to is natural cooling during the 1945-75 period, not human-caused cooling due to aerosols.

Another problem with sTeve’s theory is that, if the warming after 1975 was caused by cleaned up aerosols (the Clean Air Act of 1975), why hasn’t this cleaner air caused warming over the past 12 years? You can’t have it both ways: either cleaner air produces warming due to human activities or it doesn’t. The logical conclusion is that cleaner air, while very desirable, isn’t a key factor in producing warming.

In other words, factors other than human carbon emissions must be driving the climate, and the most likely factors are the changes in the sun and oceans, which were largely responsible for climate change before human emissions became an issue. At most, human activities are causing a slight additional warming, or cooling, to what is otherwise a natural trend.

Another look at this issue should make this logical conclusion a bit clearer. The IPCC says that the planet would be cooling right now due to natural factors, but is warming because of human factors. Here’s its chart from the 2007 report (Figure 4, which rather conveniently ends at 2000 and therefore doesn’t show the lack of warming since then):

Figure 4: Natural versus human cooling in IPCC 2007 report

The IPCC claims that, as of about 1950, the planet’s temperature diverged from what would have been its “natural” pattern of cooling (the blue line) and went into warming (the pink line). Leaving aside the question of why we would want the planet to cool, with all the damage this would cause to agricultural output, the IPCC’s graph supports the claim that the 1945-1975 cooling was, in fact, naturally caused, not human-caused. Natural cooling factors clearly overwhelmed whatever human warming factors were present during that time.

Then, in 1975, the planet started to warm again. Aha, said the IPCC, that proves that human activities are overwhelming natural drivers. Except that, again, the planet went into a non-warming phase in 1998, which, according to the IPCC models should not have happened.

What this diagram indicates is that the IPCC’s models for temperature sensitivity to CO2 have been set too high—at least 50 per cent too high. That is, human warming activities may well be holding cooling at bay to produce a decade of non-warming. However, it is also clear that human activities were not enough to produce the.2°C warming that the IPCC expected. This means that the warming power of carbon dioxide has been set too high in the IPCC’s models and/or that the power of natural drivers is stronger than human drivers.

Putting this all together: the cooling of 1945-75 seems to have been natural, caused by fluctuations in sunspot activity and ocean temperature oscillations—as the IPCC itself seems to acknowledge. The warming of 1975-1998 seems to have been caused by increases in sunspot activity and warmer ocean currents in both the Atlantic and Pacific. And the cooling of 1998-2010 seem to be due to a rather marked reduction of sunspot activity over the past few years plus cooling of the two oceans.

In other words, human activity is a minor player in the larger picture of climate fluctuation—fluctuation that is primarily caused by natural factors, with humans playing a small role.