UQx DENIAL101x 3.4.3.1 Daily and yearly cycle

Scientists predict that human-caused global warming should result in certain specific patterns of warming. Because these patterns are consistent with what we expect to happen as a result of the increased greenhouse effect, they’re considered “fingerprints” of the human influence on the Earth’s climate. As far back as 1865, physicist John Tyndall predicted that warming caused by the increased greenhouse effect should cause nights to warm faster than days, and winters to warm faster than summers. He was able to make this prediction by knowing that at night and during the winter, the Earth’s surface cools by radiating heat out to space. Greenhouse gases trap some of this heat, slowing that nighttime and winter cooling. The sun doesn’t shine all the time, the greenhouse effect is at work 24/7. Additionally the moon gives us a good counter-example because it doesn’t have an atmosphere. During the day, there’s nothing between the Sun and the Moon’s surface to block incoming sunlight.

At night, there are no greenhouse gases to trap the outgoing heat from the Moon. As a result, the difference between day and night temperatures is extreme. Daytime temperatures on the moon reach 120˚ Celsius, or 250˚ Fahrenheit. Nighttime temperatures fall below minus 200˚ Celsius, or minus 330˚ Fahrenheit. At the other extreme, Venus has a runaway greenhouse effect, much bigger than the greenhouse effect on Earth. Its temperature is an intense 460˚ Celsius, or 730˚ Fahrenheit. It’s like this day and night, all year long. Venus doesn’t even have seasons because its greenhouse effect is so strong. As these two examples illustrate, the bigger the greenhouse effect, the smaller the difference between daytime and nighttime temperatures. We know humans are increasing the greenhouse effect on Earth by burning more and more fossil fuels. If the greenhouse effect is increasing, then the difference between nighttime and daytime temperatures, and between winter and summer temperatures, should be shrinking. There’s a common myth that global warming is caused by the Sun rather than humans.

That myth fails to account for the available evidence. If the Sun were responsible, we would see an entirely different pattern of global warming. In that scenario, we would expect to see the Earth warming most when sunlight is bombarding the surface the most – during the daytime, and during the summer season. That means that if the Sun were responsible, we would see days warming faster than nights, and summers warming faster than winters. These expected patterns of global warming give scientists a clear test to determine whether the evidence matches the fingerprints of human or solar-caused warming. It took over 130 years before John Tyndall’s prediction was confirmed, but over the last few decades, surface measurements have found nights warming faster than days, and winters warming faster than summers. The difference between nighttime and daytime temperatures, and winter and summer temperatures, is shrinking, just as Tyndall anticipated would happen due to the increased greenhouse effect.

Fingerprints in the Earth’s climate change, like these changes in global warming patterns, clearly point to humans, and not the Sun, as the culprit responsible for global warming over the past century..

It’s so Cold, there can’t be Global Warming

“The test of a first-rate intelligence is the ability to hold tow opposed ideas in the mind at the same time, and still retain the ability to function.” – F. Scott Fitzgerald Meanwhile we’ve got this updated Fox news global warming alert, it is still cold, in fact it is getting colder, much colder, environmentalists telling me DUHHH “because it’s winter”…IT IS FREEZING! We’ve heard a lot of talk lately from deniers that cold temperatures are proof that there is no such thing as global waming. It looks like it will be an annual event for me to remind people that winter still follows summer. So, before we get started, a little review. It was a cool summer, right? Chicago, New York, places like that, so, how can it be global warming? This is how. Look at the context. These blue dots over North America represent below average temperatures for the summer, June, July, August, what we call climatological summer.

But look at the context, they’re lost in a sea of red dots, across much of the rest of the globe, just a couple other blue dots here and there, those red dots are above average temperatures. What that translates to in terms of a ranking, for this summer and for august, globally, second warmest on record, period of record going back a little more than a century. June through august globally, the third warmest on record, the oceans, which had cooled for a couple years, now recovered with a vengeance, August the warmest on record, June through August, also the warmest on record, and in the southern hemisphere, August was the warmest on record. The warm summer was followed up by a very warm november, globally, including abnormally warm temperatures in north america. Ironically, unseasonal warmth set the stage for dramatic winter weather, when temperatures did drop in december.

Let’s talk about why we’re seeing such a huge and significant lake effect event. The Great Lakes themselves, the water temperature there is still some 3 or 4 degrees warmer than it should normally be this time of year, because of a very mild November. Now again, its very cold air right now, its about 17 degrees, the cold air is coming over these warm lakes, picking up all this moisture, and dumping inch after inch of snow down wind, and, people, waking up on your friday, dealing with perhaps 2 to 4 feet of snow. People love to talk about the weather, and a series of strong storms and cold temperatures in December and early january sparked a lot of discussion. What scientists are telling us is that an important circulation pattern, the arctic oscillation, is in it’s negative phase. Normally, in the positive phase, the arctic oscillation produces strong winds around the arctic that keep cold air bottled up. When the oscillation is in its negative phase, cold air spills out of the arctic, and flows into north america and eurasia. Paradoxically, while temperate zones feel an arctic chill, the arctic itself becomes warmer than usual, exactly the effect that has been observed over the last several weeks.

The UK meteorological office produced this map, and described the observations. “Canada, North Africa, the mediterranean, and south-west Asia have all seen temperatures above normal, in many places by more than 5° C, and in parts of northern Canada, by more than 10° C.” When we look at the graph of the monthly arctic oscillation index, we can see that the current one is the strongest negative since the 1970s, which is why many people were surprised by the blasts of cold air, that are expected under these conditions. One effect was on air circulation over western europe, which normally flows from the west over the atlantic, delivering warmer air. Under the negative arctic oscillation, the warmer winds are blocked, and most of of the air flow is cold arctic winds, leading to snow and cold in many european countries. This diagram from NOAA shows the pattern of warmth in the arctic and unusual cold in mid latitudes around the northern hemisphere.

Dr Mark Serreze, director of the National Snow and Ice Data center, told reuter’s news agency: “It’s very warm over the Arctic, with air temperatures locally at 10 to 15 degrees F (5.6 to 8.4 degrees C) warmer than they should be in certain areas,” This map from NASA also shows the pattern, which was well illustrated in a BBC report with graphics from the UK Met office. This MET office maps show’s today’s temperatures around the northern hemisphere. There’s cold air over us, but warmer air elsewhere. Look further south and east, there’s an unusually warm band of air there. Then, further east, and over China, another very cold pocket. But just as the arctic was unseasonably warm, other areas of the globe also were not feeling the cold. While much of the Northern Hemisphere suffers from one of the hardest winters in years, the thermometer is shooting way up, down under. On Monday, Melbourne was melting with highs soaring to 110 degrees fahrenheit, monday night, Melbourne sweltered through its hottest night since 1902, the temperatures topping 34 degrees Celsius, or 93 degrees fahrenheit.

Most people think of global warming as a process where the planet sets new warming records year after year. A clearer picture comes in a new study from the National Center for Atmospheric research, described here by senior scientist Gerald Meehl. But what we noticed is in the last 10 or 20 years there’s been this ratio of about 2 to 1, for every 2 record high maximum temperatures, there’s only been about one record low minimum temperature set, on average over the US. We looked at a model simulation going off into the future, and in this model simulation we had a scenario where we are increasing carbon dioxide and other greenhouse gases going off into the twenty first century. And as the climate continued to warm, this ratio continued to grow. In other words, you kept having more and more record high maximum temperatures, fewer and fewer record low minimum temperatures. So by the mid twenty first century, this ratio, which is now about 2 to 1, was about 20 to one, by the end of the century, with this continued warming, this continued change in the distribution of records, the ratio is about 50 to 1.

One of the messages of this study is, you still get cold days. Even at the end of the twenty first century, in the model simulation, when the climate’s warmed up by 3° or 4° Centigrade on average across the US, you’re still setting record low minimum temperatures on a few days every year. So, people always get very alarmed if there’s a cold snap in the winter, and they say, “what’s happened to global warming? We’re freezing out here.” And you say, well, that’s just the weather. In the northeast we’re talking temperatures well above average, Boston heading up to 43, warm in New York at 44, DC, we’re in the 50s, that’s about 10 degrees above average. And no cold in the midwest either, we are well above average here, friday temperatures 20 degrees above average in Bismark, at 39 degrees, we’ll be warm in Kansas City, in Denver will be mild, and in Great Falls, Montana, about 20 degrees above average, the warmth hangs on on saturday, all across the midwest.

When I look out at the world from a limited perspective, my senses tell me that the earth is flat. For thousands of years, most human beings probably believed that this was so. But in a technological, scientific world, our perception is greatly expanded, and we have a much larger view of the world and our place in it. We need to understand the larger perspective about our changing climate as well. Sophisticated instruments and advanced science show us details that our senses could never see, and recent satellite measurements show, that in fact, on january 13th, global temperatures were the warmest for a january day in the satellite record. And this week, NASA released data showing that 2009, was the second hottest year in the instrumental record. We’ll be looking more at this new data in coming weeks and months. The science of global climate is vital for us to understand if we are to pass along to our children a planet that is liveable, diverse, and abundant.

It’s the most important task this generation will undertake, and you can keep track of our progress right here, on climate denial crock of the week..

Attack on science

Hayhoe: These days, to get attacked, all we have to do is step foot off campus and tell anybody, even a local Kiwanis club, or a local church, or even a group of elementary school kids, that climate change is real, and then the angry letters start to flood in. Mann: Typically the attacks are not really about the science. The attack on the science is a proxy for what is really an effort to discredit science that may prove inconvenient for certain special interests. Oreskes: That’s when I started getting attacked. And that was when life sort of changed, it was a bit going through the looking glass. I started getting hate e-mail. What happened then was I mentioned to a couple of colleagues what was going on, and one of my colleagues at Scripps, at the Scripps Institution of Oceanography, said to me, “You should talk to Ben Santer.

Something sort of similar happened to him.” Santer: I remember sitting in a bar in Madrid with Stephen Schneider, the late Stephen Schneider, immediately after the final sentence had been agreed on in the 1995 report, a sentence that’s forever engraved on my memory. The balance of evidence suggests a discernible human influence on global climate. Here we are at this bar, and Steve says to me, “This changes everything, you know. Your life is going to be changed forever.” I had no idea what he was talking about. I really didn’t. Hayhoe: There is definitely a pattern of what happens: nasty e-mails, complaints to your university, requests for your e-mails, and a lot of attacks online. Mann: Often it takes the form of an attack on individual scientists. It’s part of the strategy of ad hominem attack.

Santer: Go after the scientist. Go after their integrity. Go after their funding. Make life miserable for them. Mann: I have received letters in the mail that in one case contained a while powder that I had to actually report to the FBI. They had to come to my office and investigate this and send this off to a lab to make sure that it wasn’t anthrax or some very dangerous substance that my entire department would have been subject to because of this. Santer: Then there’s the power of the Internet, which really was not available back in 1995, to harness your supporters to go after individual scientists, send them threatening e-mails or worse, and let them know, “We’re watching you. We don’t like you. We don’t like what you do.

” Mann: One of the tactics that you see in climate change denialism is an effort to spin and misrepresent peer reviewed scientific studies. So often studies that say one thing, for example, show that some aspect of climate change is even worse than we thought, will somehow be spun by climate change deniers as if it doesn’t provide evidence for concern. Oreskes: Clearly misrepresenting scientific information, cherry picking scientific data, one egregious example that we talk about in the book is an early work by Jim Hansen that Bill Nierenberg, Bob Jastrow and Fred Seitz take out of context and use it to argue that climate change is caused by the sun when, in fact, if you go back to the original paper, Hansen is arguing exactly the opposite. Santer: I think an additional weapon in the arsenal is Freedom of Information Act requests, which are being used not really to advance understanding or, again, shed light on complex scientific issues but as a tactic to threaten, to intimidate, to throw a spanner in the works to take up your time.

Mann: They will bully editors to try to get them to retract articles that are a threat to their case, their case being that climate change isn’t real, it’s not something to worry Oreskes: The weirdest day of my whole life practically was the day I got a phone call from a reporter in Tulsa, Oklahoma ,who said to me, “Are you aware of the fact that Senator James Imhofe is attacking you?” [laughter] I was like, at that time, I honestly didn’t know who Senator Imhofe was. In fact, I think I had been to Oklahoma maybe once but, I mean, and so I said, “No, I have no idea.” At first I thought he was making a mistake, this was some other, well, I have a very unusual name, so it didn’t seem plausible it was some other Naomi Oreskes. And then he had, he read to me from this speech that Imhofe was making and it was part of what we all are very familiar with now that I was a part of the “global conspiracy,” the scientific conspiracy to bring down global capitalism. And I remember thinking, “Conspiracy?!? Scientists are not that organised.” Santer: hacking e-mails, releasing them, all of these things. The technology has moved on since 1995, but it’s the same playbook: don’t really focus on the science and advancing understanding, contributing, but tear down, destroy.

Hayhoe: I think the best we can do is shield ourselves from the attacks and try not to dwell on them, unless it’s a safety issue, in which case we should take appropriate steps, and try to move on, focusing on what we want to achieve rather than what’s trying to hold us back. Mann: So if you are a prominent scientist, if you participate in the public discourse, as I’ve often said, you better develop a thick skin because you will be attacked personally. Hayhoe: My number one rule of thumb is: do not Google myself. I don’t want to see. My number two rule of thumb is to not read the comments section. I don’t want to know. Oreskes: One of the things that I think is really important us that by writing about these things and by documenting about it in a scholarly way with high standards of documentation, we can explain to our colleagues, our institutions, editors at journal, and the public and the media what this is. Because this is not a scientific debate.

I mean if I have one message that’s what my message has been all along and it still is: this is not a scientific debate; it’s a political debate. But it’s a political debate being made to look like a scientific debate. We now know why people do that. Because it’s a very very effective strategy because if you can make people think it’s a scientific debate then people will think it’s too soon to act. But if people see the truth, if they realise that this is a political debate, that it’s related to people’s ideologies to their values, structures, that gives a whole different cast. So it’s very very important for people to understand the character of what this thing is. Santer: Some things are worth fighting for. That perhaps was the most profound lesson for me back then: that a clear public understanding of the science, doing the kind of thing that you’re doing here, that was truly worth fighting for..

Carbon cycle

House: The carbon cycle is, very simply, it’s about the cycling of carbon through natural systems – through plants, through soils, through the ocean – and back out into the atmosphere. Le Quéré: In the natural carbon cycle, there’s a lot of fluxes of carbon dioxide, so the carbon goes in and out of the ocean, in and out of the terrestrial biosphere every year. House: The carbon is constantly flowing between these different systems and large amounts of carbon moves all the time. Le Quéré: I mean in the terrestrial biosphere, in the trees and the forests, it’s very easy to see. If you live in a place that has a forest area with seasons, you see in the winter the trees they have no leaves, and the spring comes and the leaves build up. This is all good carbon dioxide that goes in the leaves. And in the fall and in the autumn when the leaves fall down then their carbon is emitted back in the atmosphere.

So you have a huge signal there of CO2 going in and out of the atmosphere. House: So the ocean will take up the CO2, it dissolves in the surface of the ocean and also when the ocean will release CO2 to the atmosphere and that depends on the concentration of CO2 in the atmosphere and the concentration of CO2 in the ocean. And they form a balance with each other. There’s a continuous massive exchange of carbon dioxide between the atmosphere on land and the atmosphere on the ocean. That is roughly in balance until we introduce human change. Osborn: The experiment that we’re inadvertently perhaps conducting with the climate system is to move huge volumes of carbon from these stores undergrounds in the form of fossil fuels and bringing them to the surface and burning them and adding this carbon to the atmosphere. Le Quéré: What we’re doing now is putting everything out of balance, so we’re adding carbon to the atmosphere. It’s new carbon. It’s not part of the natural cycle.

It’s one that we’ve dug out of the fossil reservoir where they were stored, and we’ve put them back in the atmosphere. This is new carbon, and it puts the system out of balance. House: Although the human emissions are much smaller than the natural fluxes, the natural fluxes approximately are in balance and so they’re not causing an increase of carbon dioxide in the atmosphere. The human emissions, however are very rapid, and the natural systems don’t have time to respond to them. And so you get a net imbalance of raised carbon dioxide concentrations in the atmosphere. Lunt: It’s unequivocal that the amount of carbon dioxide in the atmosphere is increasing and is increasing fast and is increasing faster than ever. House: Oh the rate of change now is incredibly rapid, and what’s more it’s pushed us outside the bounds of what we’ve seen in terms of atmospheric concentration throughout the Ice Ages. Thompson: We have not had levels of C02 at 400 parts per million by volume in 800,000 years of history. House: In the Earth’s past throughout in and out of the Ice Ages, the concentration of CO2 in the atmosphere ranged between about 180 parts per million to 280 parts per mission.

And it took thousands of year for it to change between those states. The difference is now it’s gone up to 350 and even topping 400 parts per million on a single day basis. And that’s happened over a period of a couple hundred years. Friedlingstein: Every single generation is emitting more than the previous generation because emission of CO2 increased exponentially. We emit it so far, if you start from the beginning, which is like the industrial revolution in 1750 or something, when we start to burn fossil fuel, from that time up until today we emitted something like 2000 gigaton of CO2. More than half of this has been emitted over the last 50 years. Thompson: And we know where that CO2 is coming from because we do the isotopes of the carbon. We know it’s coming from fossil fuels. Le Quéré: So carbon is increasing in the atmosphere, but it doesn’t entirely stay there, so about half of the emission and maybe a bit more than half of the emission that we put in the atmosphere ends up in the natural environment. It ends up in the ocean and in the forest. Friedlingstein: For the carbon cycle today absorbed about half of the emissions we put in the atmosphere, so we emit, as I said, 40 gigaton of CO2 per year, about half of it, 20 gigaton of CO2 are taken back from the atmosphere by the land and by the ocean.

House: There’s a multitude of different processes that remove carbon dioxide from the atmosphere. So for example, CO2 from the atmosphere dissolves in the surface of the ocean and then that’s turned over and taken into the deep ocean. Really for that amount of CO2 to be completely removed from the atmosphere it has to be completely dissolved and go down into the deep ocean. And then we’re talking about geological timescales – so hundreds and thousands of years. Le Quéré: So what happens when we put carbon emissions into the atmosphere, new carbon from burning fossil fuel or from different station, what happens is this takes a long time for this carbon to readjust in the land and ocean. Eventually if we’re prepared to wait long enough, so that’s thousands of years, a lot of this carbon, maybe 70 percent will end up in the ocean, and the reason this takes time is that you have different adjustment times, so the CO2 goes in the surface ocean, it takes about 1 year to dissolve. But how it is transported from the ocean’s surface to the intermediate and to the deep ocean depends on the ocean circulation.

The ocean circulation takes hundreds to a thousand years to mix the entire ocean. That’s the timescale that is really relevant here is taking a molecule of CO2, we’ve put it in the atmosphere, how long is it going to take before it ends in the deep ocean? House: So about 65 to 80 percent of the carbon dioxide pulse that’s put into the atmosphere will be removed within about 2 to 200 years. The rest of it, the remaining 35 percent, will take between 2 and 20 millennia to be completely removed from the atmosphere. So roughly you have to think whatever we’re doing today, whatever CO2 is being emitted, roughly a third of it is going to stick around essentially forever really when you consider it in our lifetime. Pelto: We can’t change the atmosphere, the chemistry, with one of the main constituents carbon dioxide by 25 percent and expect nothing to happen. You change your diet by 25 percent. You decide you’re going to start consuming 25 percent more calories, and you don’t change your exercise or anything else. You can’t realistically expect nothing to happen. And that’s what you have to understand.

If we change fundamentally our atmosphere chemistry, we can’t expect climate to stay the same..

Making sense of the slowdown

The Earth’s climate is controlled by the energy balance at the top of the atmosphere. If more heat enters the atmosphere than leaves, then the planet warms. Adding heat trapping gases changes the balance, which in turn causes warming. Ocean heat measurements show that the planet is indeed absorbing heat. Despite this fact, it is often claimed that the global warming has stopped. This claim is inspired by evidence that warming of the atmosphere has been slower over the past one and a half decades. This slowdown is sometimes called the hiatus. However, there are other factors which affect the atmosphere over shorter periods. These can cause faster or slower warming of the atmosphere. To understand the slowdown in warming, we need to understand some of these factors.

If we look at the global surface temperature over the past 3 decades, there are big changes in temperature from year to year. We know the cause of some of these variations. One of the biggest is the El Nino cycle. El Nino is a phenomena in which heat is stored up in the western Pacific Ocean, and then released to the atmosphere in the eastern Pacific. This happens over the course of a few years. El Nino is not predictable, but we can track it in retrospect through sea surface temperature measurements. If we compare past El Nino cycles with temperature changes over the past three decades, we can see that there is a strong relationship between the two. El Nino years tend to be hot years. Recent years have been dominated by the cool phase of the cycle. This is responsible for some of the slowdown in warming. However, El Nino doesn’t explain everything. There are cooler periods in the early eighties and nineties which don’t fit the El Nino cycle.

These were caused by two major volcanic eruptions, El Chichon and Pinatubo. Dust from the volcanoes spread in the upper atmosphere, cooling the surface. Smaller eruptions happen all the time, but can also affect temperatures. There has been an increase in the number of small eruptions over the past few years, offsetting a bit of the greenhouse warming. Another factor is the solar cycle. Satellites tell us that the sun varies in brightness with the sunspot cycle. The last cycle has been particularly weak. A dim sun also offsets a little bit of warming. Yet another factor is pollution. Rapid industrialisation in Asia has led to more particulate pollution in the atmosphere, which also has a cooling effect. The final factor is in the observations themselves. Two of the major temperature data providers, the UK Met Office and NOAA, don’t include the Arctic in their global temperature calculation, because there are no weather stations there.

But the Arctic has been warming faster than anywhere else on the planet. Missing it out leads to an underestimation of the rate of warming. To recap, greenhouse gases have continued to grow over the last one and a half decades. But over the same period, volcanoes, the weak sun and pollution have had a cooling effect, and the rate of warming has been underestimated as well. Two recent studies have put all of these together. If we ignore the short term influences, climate models predict faster warming than we have observed. However, if we use global temperature estimates, and add the influence of El Nino, volcanoes, the weak sun and pollution into the models, then the agreement is good. What can we conclude from this? When we put everything we know into the models, the answers match what we observe. So the slowdown in warming makes sense in retrospect, and doesn’t give us a reason to doubt the models.

However, we couldn’t have predicted it in advance, because we can’t predict volcanoes, pollution or the sun. The slowdown in warming has created a whole family of myths with different levels of sophistication. At one extreme, it is possible to argue that the hiatus should reduce our estimates of climate sensitivity. This is a genuine scientific argument, although the analysis we have just seen suggests that no reduction is required. At the other extreme, it is sometimes claimed that the hiatus disproves the role of CO2 in global warming. They claim that CO2 has increased, but the world hasn’t warmed. This is an example of a strawman, and a complex cause fallacy. Climate science doesn’t claim that CO2 is the only factor which affects temperature. This is why the hiatus is so hard to deal with. The myths may be wrong, but they are simple and convincing. The complex cause fallacy exists because people like things to be simple, but explaining the complex drivers of climate is hard. But in the end, all the hiatus myths revolve around drawing attention away from the big picture. When we look at the big picture, the hiatus does not change our understanding of human caused global warming.

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Human CO2 emissions trump volcanoes’

In the past 150 years, human emissions have put a lot of carbon dioxide in the air. We now measure a concentration of about 400 parts per million. This is about 40% higher than at any time in the past 400,000 years. Of all of the conclusions of modern climate science; this is one of the most reliable. But, despite all of the evidence, some people persist in claiming that the recent rise in carbon dioxide is all natural— for example, they say that instead of it being caused by humans, it all came out of volcanoes. Now, it is quite true that volcanoes emit some carbon dioxide. Over very long periods of geological time those small amounts can add up to make a really significant change to the atmosphere.

However, over a couple of hundred years, the emissions aren’t large enough to make a difference. There are two main classes of volcano: there are the ones that erupt under the ocean and the ones that erupt into the air. Both kinds are linked to the goings-on at the boundaries of the tectonic plates and to the upwelling of hot rock from the Earth’s mantle; the layer below the Earth’s crust. The undersea volcanoes are by far the more numerous, making up about 90% of the world’s volcanoes, although few of us have ever seen them. These volcanic chains are where new ocean crust is produced. But undersea volcanoes don’t produce very much carbon dioxide—only about 100 million tonnes per year—about the same amount as an average US state emits. Humans produce about 350 times as much carbon dioxide as the undersea volcanoes do. Carbon dioxide not only gets produced at the oceanic ridges, it also gets consumed there. What happens is that the newly formed basaltic rock undergoes chemical changes when it contacts seawater. This reaction absorbs carbon dioxide from the water at a rate of about 150 million tonnes per year.

The mid-ocean ridge volcanic processes as a whole, therefore, probably consume more carbon dioxide than they emit. We are much more familiar with the kind of volcanoes that erupt into the air. The biggest chain of these is the so-called “Pacific Ring of Fire”. This is a belt running all the way around the ocean from New Zealand to Japan, then to Alaska and down to the Andes. Old oceanic crust is consumed at these places and they form volcanoes that produce much more carbon dioxide than the ones under the sea. The magma in these volcanoes comes not just from the Earth’s mantle, but also from the melting of the more carbon and water-rich rocks in the crust. One reason these types of volcano tend to be more explosive is because of the larger amount of water vapour and carbon dioxide in their magma. Mount Etna in Sicily is one of the most prolific carbon-dioxide producing volcanoes in the world. It produces about 13 million tonnes per year, but this amount is still only about half as much as what Sicily’s five million people emit from burning fossil fuels.

In addition, dormant volcanoes and volcanic lakes together emit as much carbon dioxide as the actively erupting volcanoes do. Altogether, volcanoes that emit carbon dioxide into the air produce much more than undersea volcanoes: about five times as much. Volcanic rocks on the surface undergo weathering and this chemical process absorbs carbon dioxide out of the air, about 180 million tonnes per year, that’s approximately one-third of the amount put into the air by volcanoes. So if we add up all the sources of volcanic carbon dioxide, we get 640 million tonnes per year. Once we subtract the carbon dioxide that the reactions with volcanic rocks consume, we are left with a net 310 million tonnes per year. This last amount is roughly equal to the human emissions from the country of Turkey, that’s less than one percent of all human emissions. Human emissions for the planet as a whole in 2012 were 60 to 120 times bigger than volcanic emissions. Carbon dioxide emissions from cement-making alone are 3 to 6 times bigger than those from volcanoes.

Not only are volcanic emissions much too small to account for the rising carbon dioxide levels in the air, but, over the past few thousand years, natural emissions and natural sinks must have been in rough balance. The carbon dioxide composition of the air started to change really quickly after the 1950s. We can readily explain this as being due to the greatly increased rate of consumption of fossil fuels after the end of the Second World War. On the other hand, if volcanoes had suddenly started to erupt many times faster in the second half of the twentieth century, we surely would have noticed. After all, volcanoes don’t just silently produce carbon dioxide, they also throw out huge quantities of ash and magma and they often cause havoc for humans living nearby. Only about 40% of the carbon dioxide emitted from any source remains in the air, the rest goes into the oceans and is taken up by plants on land.

If we add up the carbon dioxide emissions and convert them into concentrations in the air, we see that emissions from humans over the past hundred years fit the observations like a glove, but the volcanoes don’t even come close. People who incorrectly blame volcanoes for the change in the air take the fact that volcanoes do indeed produce some carbon dioxide and then they jump to the false conclusion that this amount is enough to explain the increase we have measured. And they haven’t done the basic arithmetic that shows that it isn’t nearly enough to make any real difference at all in such a short time period. We know what caused the recent rise in carbon dioxide concentrations. We did..