This graph is from NOAA. (click to enlarge) The top graph is of temps since 1720, the middle is of all the studies since 900 BP (=AD) and the bottom shows the probability of temperatures - the central dark areas being the most certain, and the lighter extremities showing the outside possibilities.
This is the result of many scientific observations, and it shows clearly that recent temperatures, since 1970, are way out of line with previous averages.
The Medieval Warm Period (apologies about the spelling, but proper spelling may get missed on North American searches) does show, but modern trends exceed that warming.
Clearly, the pre 1800 temperatures could only be down to natural variation with a tiny input from wood burning.
On this next graph I have combined solar variations with the temperature record.
(all other graphs are sourced from Robert Rhodes' excellent Global Warming Art). The brownis fuzzy line is the global temperature, and the grey dotted line is solar activity, increasing if the line is going up.
(Sorry about the appalling graphic quality: I had to stretch, invert &c to match the date lines up.)
Interestingly, it suggests a correlation between drops in solar output, but not much of a correlation with increases of solar output, except in the 20th century.
The next graph below shows what has been happening in recent years.
Solar activity has been falling since 1978, but temperatures continue to climb, although the last decade has been flat.
Skeptics make much of the flattening or fall in temperatures since the peak of 1998, concluding, as is their wont, that "This disproves AGW".
My view, which is of an interested bystander, not of a climate scientist, is that this recent flattening of the temperature line reflects the 11-year solar cycle, which is in decline at the moment, and is due to pick up in 2012, although more recent observations show that this upswing is delayed.
This is the short term cycle, which is only weakly related to temperature, as we can see from the combined to the left here.
Below I have combined sunspot activity since 1960 with smoothed temperature since 1960, and we can see a persuasive fit between them. The sunspots (red and blue, at bottom) are in phase with the sinuous fluctuation of the rising temperature red line.
This match is not of course conclusive. There is a small hump on the temperature at the same time as a trough in the solar cycle, and in order to convince that two series are in phase, there has to be a far longer match than the four we have here. But it does give an indication.
Now, what about the longer term solar cycle?
Below I have pasted a version of the long term solar activity graph with a speculative continuation of the longer term solar cycle, shown as a red line.
If there is a long term fall in solar output due, it may reduce the warming drive in the 21st century. Global temperatures could possibly even fall, since the first graph shows that falls in solar output are associated more strongly with falling temperatures than rises in solar output are associated with rising temperatures.
I stress that this line of argument is not science, just impressionistic speculation. I put it up here to show that models do include all factors. It is not either greenhouse gases or solar, but both greenhouse and solar, together with all the other factors, known and unknown.
The danger is that the statement "Global temperatures could even fall", coming from a Green AGW apologist and advocate of rapid decarbonisation, will be seized on by the skeptic lobby, as a victory for their business as usual, keep burning carbon scenario.
It is nothing of the kind. I have definitely not gone over to the other side. At the end of 5 weeks' intensive study of the arguments, I am more deeply convinced than before that AGW theory is correct, and that the only reasonable policy response to the global situation is to decarbonise the economy as a matter of urgency. I am also more firmly of the opinion that the driving force behind AGW skepticism is the psychological defence mechanism of denial, covered with a thin veneer, in some cases, of selective and partial deployment of scientific facts and reasoning.
The line of argument presented here, that the long-term solar variation may take the pressure off the rising global temperature, is just a possibility. I have drawn a falling line, reflecting the peaks 200, 400 and 600 years ago. If the next peak is more like the plateau in the Mediaeval Warm Period, global warming will increase in line with IPCC projections. Policy responses must be matched to this worst case scenario.
We can and must decarbonise the global economy for four reasons:
- reducing the greenhouse effect,
- because of Peak Oil,
- because of ocean acidification,
- because it will re-balance the divergent international economy by giving hot developing countries an income from solar power.
PS I could be totally wrong on this. Even a Grand Solar minimum might not have a significan effect.
Solar change and climate: an update in the light of the current exceptional solar minimum, Mike Lockwood
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