Sun-dimming volcanoes slow global warming - study

Tungurahua volcano spews gas and ash south of Quito in Ecuador earlier thid month. REUTERS/Carlos Campana
Tungurahua volcano spews gas and ash south of Quito in Ecuador earlier thid month. REUTERS/Carlos Campana
Small volcanic eruptions help explain a hiatus in global warming this century by dimming sunlight and offsetting a rise in emissions of heat-trapping gases to record highs, according to a new study.

Eruptions of at least 17 volcanoes since 2000, including Nabro in Eritrea, Kasatochi in Alaska and Merapi in Indonesia, ejected sulphur whose sun-blocking effect had been largely ignored until now by climate scientists, it said.

The pace of rising world surface temperatures has slowed since an exceptionally warm 1998, heartening those who doubt that an urgent, trillion-dollar shift to renewable energies from fossil fuels is needed to counter global warming.

Explaining the hiatus could bolster support for a U.N. climate deal, due to be agreed by almost 200 governments at a summit in Paris in late 2015 to avert ever more floods, droughts, heatwaves and rising sea levels.

"This is a complex detective story," said Benjamin Santer of the Lawrence Livermore National Laboratory in California, lead author of the study in the journal Nature Geoscience that gives the most detailed account yet of the cooling impact of volcanoes.

"Volcanoes are part of the answer but there's no factor that is solely responsible for the hiatus," he told Reuters of the study by a team of U.S. and Canadian experts.

Volcanoes are a wild card for climate change - they cannot be predicted and big eruptions, most recently of Mount Pinatubo in the Philippines in 1991, can dim global sunshine for years.

Santer said other factors such as a decline in the sun's output, linked to a natural cycle of sunspots, or rising Chinese emissions of sun-blocking pollution could also help explain the recent slowdown in warming.

The study suggested that volcanoes accounted for up to 15 percent of the difference between predicted and observed warming this century. All things being equal, temperatures should rise because greenhouse gas emissions have hit repeated highs.

"Volcanoes give us only a temporary respite from the relentless warming pressure of continued increases in carbon dioxide," said Piers Forster, Professor of Climate Change at the University of Leeds.

A study by the UN Intergovernmental Panel on Climate Change last year suggested that natural variations in the climate, such as an extra uptake of heat by the oceans, could help explain the warming slowdown at the planet's surface.

The IPCC projected a resumption of warming in coming years and said that "substantial and sustained" cuts in greenhouse gas emissions were needed to counter climate change.

It also raised the probability that human activities were the main cause of warming since 1950 to at least 95 percent from 90 in 2007. Despite the hiatus, temperatures have continued to rise - 13 of the 14 warmest years on record have been this century, according to the World Meteorological Organisation.



Clare: the answer to your question is: it's because 'chemtrails' and the like are nothing more than pseudo-scientific claptrap only believed in by people like the Conservative Party

No cherry-picks

I fully agree that cherry-picking goes against the search for scientific knowledge and that it should be detected and eliminated during the peer-review process of any scientific paper. However, I do not think the present study we have been discussing is an example of it.

The authors want to test the hypothesis that volcanoes had an effect on the 'hiatus', which is a valid question to ask. They then perform simulations and compare with observations to test this hypothesis. Although they found a reduction of the error between simulations and observations when accounting for post-2000 eruptions, they certainly do not make statements that try to justify the whole cooling as a results of these eruptions.

Moreover, the authors do not use their results as a justification for man made GW. In fact, the whole last paragraph explains that natural variability and errors in orther forcings do play an important, justifying the need for future work. They even conclude: "It is not scientifically justifiable to claim that model climate sensitivity errors are the only explanation for differences between
model and observed temperature trends. Understanding the causes of these differences will require more reliable quantification of the relative contributions from model forcing and sensitivity errors, internal variability, and remaining errors in the observations."

It seems to me that you are the one cherry-picking this study without reading it properly to support your skepticism of man made GW. 

20% Global dimming has already been achieved

Why does this article leave out mention of the elephant in the living room?  Mega-tons of aerosol material have already been sprayed into the atmosphere under the guise of saving us from man-made global warming by the so-called "geoengineers" or "Earthmasters."  The BBC has reported under the heading "Global Dimming," that the amount of sunlight reaching earth has been reduced by a massive 20% in the last decade or so. Coincidence? No.

Look skywards, get educated, get rainwater samples tested for the heavy metals they use in their aerosols, (Al, Ba & Sr) and visit for further information, plus watch 'Aerosol Crimes' and 'Why In The World Are They Spraying?' free online.


The simple act of cutting down a large percentage of the earth's natural carbon sinks and oxygen makers (trees)  has the effect of leaving more carbon un-absorbed and decreasing the quality of our air.

The answer is for the world to start using more trees for things like buildings as this locks the carbon away and replace the trees at a faster rate than we use them, each successive tree is a carbon sink. We can even use them for fuel as there is always scrap and left overs that aren't burnt and may even be used for making paper for example. The tree that replaces it then absorbs more than the one it replaced etc.

This can also help reduce natural disasters like flash floods and help reverse the desertification of areas, can help alleviate the intensification of farming by helping break down the cattle wastes and the polutants that are a result.

This simple act that no one wants to do will solve more problems than any carbon tax which only makes some bankers somewhere richer. We can start by planting non productive areas.

It won't solve the whole problem though as long as the earth is in its warming cycle. Look around next time you are driving the very terrain shows you there used to be a lot more free flowing water around and that the earth was warmer before.

It's been proven Antarctica used to be ice free, a natural cycle would mean it is going to be again no matter how we try to stop it. We are just lucky to be living during a relatively benign part of the cycle for the last few thousand years. The sheer size of the forests before we cut them down shows how much carbon was around. We can still use oil etc but we have to re-create the natural enviroment to absorb it.

No grudge

No, I don't have a grudge against climate scientists, I have a grudge againt anyone who cherry-picks data to suit. In this case they want volcanoes to explain the cooling to justify the lack of warming to prove man made GW, but neglect to mention this very cooling may be part of a natural trend of volcanic activity resulting in an overall warming trend since the last ice age.

Just because it helps explain why theres cooling during a warming period it does not prove their theory that it's mans fault. All it proves is there is a natural cycle.

I myself don't doubt that man has contributed to this cycle - in fact, I believe it's impossible for us not to have. However, I do object to the GW scientists blaming it all on us. Compared to the natural cycle I believe we are bit players, however I do not see that as a reason to carry on as we are.

GW is a fact, mans relative contribution is debateable. But as long as people cherry-pick their data to fit their arguments while ignoring the rest of the picture we will get nowhere.  


So cooling makes sense

Thanks Lynden for the good read, although it seems to me that it supports fully the study reported in the article.

Cooling effects dominate for the first few months/years, while warming effects can be significant only after many eruptions on time scales of thousands or millions of years. While looking at the so-called warming 'hiatus'  on a time scale of a decade, it therefore makes sense to only consider cooling effects.

I really don't see the cherry-picking you are referring to. The radiative forcing due to aerosols (sorry, not clouds) is known to have a cooling effect. You obviously have a grudge against climate scientists, which is difficult to understand in this context.


Capri: Thanks for the assist but this time I'm not debating the science; in fact I'm quoting it.

"Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. 

"For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole-to-equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere con-tinents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades"

And it goes on to basically say volcanoes can cause both heating and warming. Full document here




It does both

Daf: That's exactly my point. It does both and depending on the particulars of an eruption could affect cooling or warming.I can remember over the last few years scientists putting forth proof of both, but unfortunately climate scientists will cherry-pick one or the other depending on which suits their argument - you never get a balanced answer on climate science.

Also ash permits less heat to escape so it comes down to how much ash, how long it lasts, how much heat penetrates and how much escapes compared to the greenhouse effect of any given eruption. Also clouds are very different than ash. 

In fact, your answer in admitting it can effect both is the most balanced I have ever seen. Therefore I wasn't very much wrong I was in fact right. 

There's a very good basic summary here While cooling tends to dominate over long periods it can have a signifacant warming effects.

Clouds and the greenhouse effect

That is very much wrong Lynden! Ash clouds reflect incoming sunlight directly back to space, therefore lowering the warming input due to the sun. Then it has a cooling effect. It also increases the concentration of greenhouse gases, so also has a warming effect! The question is: which is more important than the other? Overall the effect of clouds in the atmosphere is to cool the planet, which is well established in all textbooks on climate science.

'Plateau' would be better

'Plateau' would be better word to use than 'hiatus' since it makes no presumption about the future global temperature change, whether up, down or static. It is unlikely that volcanoes are the full answer to the plateau, now 17 years and counting. None of them match Pinatubo, which did indeed depress global temperature by a few tenths of a degree, but only for a couple of years. Incidentally, the Toba eruption on the island of West Nusa near Bali, some 70,000 years ago, was so huge it plunged the world so deeply into the ice age that mitochondrial DNA studies suggest it reduced human breeding population to a few score of couples. When Mother Earth throws a real wobbly all we can do is hang on and hope!


Come on Lyndon don't spoil their game, you're not supposed to question the science.

What about

Can't have it both ways. What about the greenhouse gases released in an eruption?

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