Nov 7, 2008
Climate response to solar forcing less than reported

While recent studies have found that changes in the amount of sunlight reaching Earth have caused 65% of surface warming over the last 100 years, a new study puts that figure at just 10%. The researchers found that, if anything, in the past 25 years solar forcing has caused a very slight overall cooling, not 20-30% of the warming.

"The influence of the Sun, in particular, versus anthropogenic influences on global change is extremely controversial and these recent articles have provoked this controversy further, evoking major consternation and confusion amongst scientist and the policy-making community," Judith Lean of the Naval Research Laboratory, US, told environmentalresearchweb. "Our own recent work analyzes the entire historical surface temperature record, using the IPCC anthropogenic and solar forcings simultaneously with ENSO [El Niño-Southern Oscillation] and volcanic influences. In this way we attempted to account simultaneously for the major forcings known to impact climate, whereas the prior studies that concluded a dominant role for solar variability neglected one or more of the other known influences."

Lean, who worked with David Rind of NASA, reckons their results clearly show that natural changes cannot account for the significant long-term warming in the historical global surface temperature anomalies, and further strengthen the likelihood that the recent warming is anthropogenic in origin.

The pair says their findings suggest deficiencies in general circulation models used to simulate and forecast climate change. "We showed that climate appears to respond to solar variability more rapidly - within months versus years - and with larger amplitude, by a factor of four or five, than the models simulate," explained Lean. "Contrary to model-based expectations, the 11-year solar cycle is reliably detected in the historical surface temperature record. Surface temperature responds rather rapidly, in phase with and lagging only by a month or so, the solar irradiance changes."

The researchers believe that dynamical processes are involved rather than, or as well as, thermodynamic processes. "Existing circulation patterns - Hadley, Ferrel, and Walker cells - are likely engaged, along with atmosphere - ocean interactions (ENSO)," said Lean. "Furthermore, there are likely both direct (surface heating) and indirect (stratospheric influence) components. Current models are not able to represent these processes very well; many lack, for example, adequate stratospheres and ENSO representations." Lean hopes that future validation of models with the pair's empirical results may lead to improvements, which would then enable better estimates of responses to greenhouse gases.

Lean and Rind also carried out the first comparison from observations of the geographical distributions of responses to the individual forcings. This produced the first estimate of the geographical pattern of ENSO and volcanic aerosols over the entire globe. "IPCC [2007] did not report geographical patterns of climate responses to individual natural and anthropogenic influences because of model uncertainties at smaller than continental scales and over timescales less than 50 years," said Lean. "Our derived regional response patterns presage the next IPCC (AR5), which plans to focus more on regional responses compared with the 2007 focus on global attribution."

The researchers found that anthropogenic warming appears to have a much smaller signal at northern high latitudes than the IPCC reports, and than general circulation models simulate, at least in the annual averages. "However, our analysis is confined to latitudes less than about 65°N, where more reliable surface temperature observations exist, and captures only that variability at high latitudes which linearly tracks the four forcings (at appropriate lags)," said Lean.

Next Lean and Rind plan to determine the seasonal variation in regional responses to different climate influences; to extend the analysis to the atmosphere above the surface rather than just looking at surface temperatures; to compare empirical and modeled regional response patterns in detail; and to work on forecasting surface temperatures in the next decade by looking at the response to solar and greenhouse gas changes in the context of plausible scenarios for ENSO and volcanic activity, which are difficult to forecast.

"We have completed a large suite of model simulations using the GISS Middle Atmosphere GCM of climate range in the last 50 years (see Rind et al., JGR, in press)," said Lean. "Preliminary analyses indicate significant differences between the modeled and observed temperature responses to both solar and anthropogenic forcings, which we plan to elucidate and quantify, annually and seasonally, at the surface and in the atmosphere."

The researchers reported their work in Geophysical Research Letters.

he-he-he

The latter was for PPJ, I translated the paper into language he could understand.

By his own admission, he knows nothing of climatology.

David Appell showed David Evans the AGW signature from the IPCC report that Evans claimed was missing. Evans replied:

    Comparing a model to observations doesn't prove the model works. It's encouraging to the model builders, but it's not proof. For instance, the model could just be lucky.

So when Evans wrote:

    The greenhouse signature is missing. We have been looking and measuring for years, and cannot find it.

He meant that we had found the signature, but Evans didn't think it should count.

and here:

The Australian continues to display its contempt for science, scientists and the scientific method. They've published this piece of AGW denial by David Evans. Last time I looked at Evans he was saying that new evidence since 1999 had changed his mind about global warming, with this new evidence including the fact that the world had cooled from 1940 to 1975. Apparently this was too silly even for the Australian, so he now offers us four alleged facts.

    1 The greenhouse signature is missing. We have been looking and measuring for years, and cannot find it.

    Each possible cause of global warming has a different pattern of where in the planet the warming occurs first and the most. The signature of an increased greenhouse effect is a hot spot about 10km up in the atmosphere over the tropics.

This couldn't be more wrong. Study the graphs below (from RealClimate). The left one shows the pattern predicted for doubling CO2, while the right one shows the pattern for a 2% increase in solar output.

Graph  1

Graph 2

Both patterns include a hot spot. The difference between the two graphs is that the CO2 one shows cooling in the stratosphere, while the right one does not, so the "greenhouse signature" is stratospheric cooling. And guess what, that's what's been happening. Evans continues:

    We have been measuring the atmosphere for decades using radiosondes: weather balloons with thermometers that radio back the temperature as the balloon ascends through the atmosphere. They show no hot spot. Whatsoever.

    If there is no hot spot then an increased greenhouse effect is not the cause of global warming. So we know for sure that carbon emissions are not a significant cause of the global warming. If we had found the greenhouse signature then I would be an alarmist again.

Actually we have found the greenhouse signature, so Evans should change his mind. I'm not holding my breath.

If the hot spot really is missing it does not prove that CO2 is not causing warming, but it would indicate something wrong with the models. (Which might mean that things are worse than what the models predict.) However, the radiosonde measurements have been found to be wrong in the past, and it looks like they may well be wrong again.

Evans continues:

    2 There is no evidence to support the idea that carbon emissions cause significant global warming. None. There is plenty of evidence that global warming has occurred, and theory suggests that carbon emissions should raise temperatures (though by how much is hotly disputed) but there are no observations by anyone that implicate carbon emissions as a significant cause of the recent global warming.

This is pure denial. There is plenty of evidence and denying that it exists does not make it disappear. For instance, Figure 4 of the SPM. The blue bands show temperature changes modelled using only natural forcings, while the red bands include anthropogenic forcings as well. The black line shows observations. Clearly, we must include anthropogenic forcings if we want to match the observations.

    3 The satellites that measure the world's temperature all say that the warming trend ended in 2001, and that the temperature has dropped about 0.6C in the past year (to the temperature of 1980).

Let's look at the lower troposphere trends from RSS:

    Figure 7. Global, monthly time series of brightness temperature anomaly for channels TLT, TMT, TTS, and TLS. For Channel TLT (Lower Troposphere) and Channel TMT (Middle Troposphere), the anomaly time series is dominated by ENSO events and slow tropospheric warming.

The people who publish the data don't think that the warming trend ended in 2001, and if you look at the graph, it's only significantly deviated from the long term warming trend in 2008. Such short-term deviations have happened in the past without affecting the long term trend.

Evans continues:

    Land-based temperature readings are corrupted by the "urban heat island" effect: urban areas encroaching on thermometer stations warm the micro-climate around the thermometer, due to vegetation changes, concrete, cars, houses. Satellite data is the only temperature data we can trust, but it only goes back to 1979.

The land-based temperature readings are corrected for UHI, while the satellite readings have been found to be wrong in the past.

    NASA reports only land-based data, and reports a modest warming trend and recent cooling. The other three global temperature records use a mix of satellite and land measurements, or satellite only, and they all show no warming since 2001 and a recent cooling.

Study the title of the NASA temperature graph:

Global Temperature Land-Ocean Index

Does it report only land-based data, or does it include ocean temperatures as well?

    4 The new ice cores show that in the past six global warmings over the past half a million years, the temperature rises occurred on average 800 years before the accompanying rise in atmospheric carbon. Which says something important about which was cause and which was effect.

This is wrong. The temperature rises started on average 800 years before CO2 levels rose, but most of the warming occured after CO2 levels started rising. Jeff Severinghaus writes:

Does this prove that CO2 doesn't cause global warming? The answer is no.

The reason has to do with the fact that the warmings take about 5000 years to be complete. The lag is only 800 years. All that the lag shows is that CO2 did not cause the first 800 years of warming, out of the 5000 year trend. The other 4200 years of warming could in fact have been caused by CO2, as far as we can tell from this ice core data. ...

In other words, CO2 does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2 (along with other greenhouse gases CH4
and N2O) causes about half of the full
glacial-to-interglacial warming.

That's it for all of Evans' evidence. The rest of his article is more pure denial. For instance:

    If there really was any evidence that carbon emissions caused global warming, don't you think we would have heard all about it ad nauseam by now?

He has, but he just denies that it is evidence.