Arguments
Global warming continues, but volcanoes are slowing down the warming of the atmosphere
Posted on 25 February 2014 by John Abraham
It is exciting to watch our understanding of climate merge in the scientific literature. Right now, many studies are coming out that investigate the slowdown of global temperatures; of problems accounting for all the energy in the Earth's climate system; and the role of natural and human factors in these questions.
First, let's establish a few facts. Increases or decreases in temperatures, particularly atmospheric temperatures, are not equivalent to increases or decreases in Earth energy – that is, the Earth can continue to warm whether atmospheric temperatures increase. Part of the reason for this is that most of the Earth's extra energy is stored in the oceans which have continued to heat over the past few decades with no cessation or pause.
With respect to the so-called slowdown, we've seen studies that show part of the "slowdown" in global atmospheric temperatures is associated with measurement problems. That is, are we measuring the entire globe, in particular the polar regions. Other studies point to internal movements of energy between various parts of the climate as an explanation for recent slowdown in atmospheric temperatures. In fact, this topic was discussed recently by my colleague Dana Nuccitelli.
When you think about it, how would you measure the entire globe temperature? You need to be certain you have enough measurements taken for long enough periods of time to be sure you can identify temperature trends. You have to be mindful of putting sensors in regions where there are artificial impacts to the temperature (such as in cities). You have to measure not only at the Earth surface but throughout the ocean depth and atmosphere height. How do you handle changes in instrumentation that occur over the many decades? How do you handle biases in temperature sensors? How do you position sufficient sensors across the globe and maintain them over time? These questions reflect the Herculean task facing climate scientists.
But perhaps the so called slowdown isn't just due to measurement problems? Perhaps something is blocking some of the sunlight from reaching Earth in the first place? We call such energy blocking a "negative forcing". If negative forcings are happening, we would expect to see an impact on global temperatures. I recently discussed a study which looks at combinations of measurement and negative forcings. Now I want to shift to a very new study that focused extensively on volcanoes.
In the study, Dr. Ben Santer and colleagues asked whether small volcanoes could be causing a slight reduction in the amount of sunlight that reaches the Earth. We've known for years that large eruptions can cause a temporary decrease in the Earth temperature but what about small eruptions? The authors found that in the past decade or so, the impacts of volcanoes are found in the optical depth (clarity) of the atmosphere and in temperatures of the lower part of the atmosphere (the troposphere). The authors input the results into computer models and compared the calculations to models that ignored volcanic effects. They discovered that when volcanoes are included, the models were more able to match the observed temperatures.
So, what does this all mean? First, it confirms an emerging picture amongst scientists. Is there a slowdown in warming or not? If there is, what is the cause? Volcanoes? Solar activity? Internal variability? The emerging consensus is the so-called slowdown primarily exists in the atmosphere (but not in the oceans) and it is being caused by all three of these factors. In a nutshell, global warming is continuing, despite what people want you to believe, and natural factors influence short term temperatures measurements.
It also means that the models are doing things correctly. When inputs to the model are improved, the fit to actual observations improve. Consequently, people who have incorrectly stated that climate models are too sensitive to the increased greenhouse effect (for example, John Christy in Senate testimony accessed here) need to rethink their positions. The models work, period.
The significance of the recent article is best captured by co-author Carl Mears who said,
I could only access the new paper's abstract but if I have understood it correctly, the volcanic influences over the past decade or so is not very large.
[RH] Shortened link to preserve page formatting.
I wonder if the models also take into account the massive pollution form primarily coal fired plants that exists in places like China. if it has increased significantly, was this increase accounted for?
Yes, it is the total energy reaching the earth that is important, but doesn't an increase in aerosols reduce the total energy reaching the earth?
Are the emissions from volcanoes greater during the last 15 years than we were in previous period when we have a greater degree of surface temperatures?
If we are having measurement problems now, were we having measurement problems before?
Another thing. I infer from this article that the amount of heat transferred to the earth has slowed down during the so called slowdown or pause. They imply that an increase in the amount of energy going into the oceans is not the issue. I wonder if these authors know what they are talking about.
Climate scientists have stated that there is no slowdown in the energy reaching the earth. This, I presume is measurable and is measured on a continuing basis. This article seems to contradict what I thought was a fairly straight forward measurement of energy transfer and blockage by greenhouse gases.
I may be misunderstanding this article because I find it hard to believe that climate scientists are not measuring the heat gain properly.
Can someone please explain this to me?
[JH] Unnecessary white space inserted at end of post deleted.
On the one hand it is argued that material erupted from volcano’s can reduce solar luminosity producing a decrease in the rate of global surface warming. Sounds plausible. Is there evidence of this reduction? If so, how does it result in decline of atmospheric temperature but increase in ocean temperature?
John,
I believe the merge in the opening statement was meant to be emerge as is presented towards the end of the article. It is a little thing, and I know this is a reprint of your article in the Guardian, but I wondered about the wording when I read the opening statement.
Agnostic @ 5.
My understanding, from reading the WMO publication "Climate into the 21st Century", printed in 2003, and many other sources since then including SkS, is that the mechanism leading to warming of the oceans is a separate influence on the measured global average surface temperature.
The volcanic emissions are reducing the amount of solar energy that reaches the surface, but a lot still gets through. The reduced energy penetrating into the lower atmosphere slightly reduces the global average surface temperature compared to what it would have been without the volcanic emissions. When there is very little volcanic activity the 'clearer' global atmosphere leads to a temporarily warmer global average surface temperature. There was very little volcanic activity affecting 1998.
The ENSO trade wind circulation being more on the La Nina side of neutral is resulting in cooler surface water over a large area of the Pacific. It also produces currents in the ocean that take surface waters that have drawn heat from the atmosphere down into deeper waters, warming those deep waters. During a La Nina the warm waters in the Pacific are compressed into the western region, with cooler deeper layers of water appearing to reach the surface in the east, near South America.
When the trade winds shift to the El Nino side of neutral the warm surface waters spread eastward over more of the Pacific. The result is less heat energy being taken from the atmosphere down into the ocean depths. When a very strong El Nino forms, a much larger surface of the equatorial Pacific is warm, including the waters near South America. This type of event temporarily bumps the global average surface temperature because the trade winds spreading away from the warmer surface are warmer, leading to other areas of the surface of the globe also being warmer.
So 1998 was an extreme aberration from the norm produced by a very strong El Nino, stronger than any that have occurred since then, combined with very little volcanic dimming. That makes it a year that should not be the basis for starting an evaluation of a trend, or for any meaningful comparison to other years that do not have similar temporary forcing.
That rather obvious point seems to have been 'curiously' missed by some well-informed people. They claim to be 'just questioning the validity of the science' when they point out a lack of significant warming in the recent global average surface temperature values compared to 1998. And they get rather testy when evaluations like the one performed and published by Cowtan and Way show they have even less of a basis for their preferred claim about the rate of warming in the global average surface temperature data since that 1998 time period.
Perhaps someone knows the answer to this one. It came about because of the headline in this morning's Press. China chokes on smog: crops die. How does the quantity of particulate air pollution from China compare with the amount put out by volcanoes. There was a theory that the lack of warming when America was putting out mega amounts of pollution was due to this pollution. She cleaned up her act and atmospheric warming continued. What would the effect be of China cleaning up her act.
Someone else can probably be more quantitative, but I would think that the amount of heat reflecting emssions put out by China would be at least what the U.S. and others were emitting during the period when we had a significant cooling effect. I do remember that pollution used to be a lot worse in places I have lived like Denver, but it doesn't seem close to comparing with what is going on in China.
However, I would be interested also in the actual quantitative impact on the results of the models and if the models try to take into account the cooling effect of ongoing heat refleting emissions.
If/when China cuts its emissions to that approaching western standards, it seems like this is going to cause an ugly spike in warming.
You can get the historical radiative forcing from aerosols from the IPCC reports
Aerosols have improved since 1990 but way worse than 1950. What matters from climate point of view is the net forcings. Aerosols have got worse but dont cool because overwhelmed by increased CO2.
tstreet@9,
Human aerosol emissions can be acounted for quite reasonably in the past 100y or so, as seen on this graph from tamino:
The emissions clearly peaked in 70s, after they started cleaning what you've experienced in Denver, and what other experienced throughout the whole NAmerica & Europe.
I don't see any jump on this graph as the result of recent boom in China. The graph ends at 2000 however, and would love to see latest update on this account. But so far, I don't see anything what you describe as "what's going on in China" on this graph.
So my conclusion: "if China cuts its emissions", there will be no "ugly spike in [global] warming", because the drop in aerosol emissions should not be very signifficant. Perhaps the local temps would be affected. But the global effect might well be diluted. Often, what looks grandiose & very scary (especially when seen through sensationalism of the media) may not be actually a big deal when seen through the actual data analysis.
chriskoz @11.
Klimont et al (2013) shows sulphate emissions to 2011. There is a balance between rising emissions in the developing world and falling emissions in the developed world. This also results in emissions increasing at lower latitudes.
Its silly to imply climate models are getting it wrong when they are not designed to factor in certain aspects of the climate. Climate models should be adjusted each year to factor in increased ocean heat, volcano eruptions and what ever else is not accounted for.
Chris #2 Hansen, Sato & Ruedy paper you linked came right out and said "Thus it is puzzling that no reflight has been scheduled for the mission". Puzzling indeed. By way of contrast, I found the many comments out there about billions wasted, wealthy scientists, glad funding's being cut and whatnot to be comically transparent.