Anthropogenic Climate Change
Last night, a reader’s comment caused to me provide an explanation of the greenhouse effect and how this shows us that human activity is primarily driving climate change. I was asked to repost that comment here.
The scientific process is simple: state a hypothesis, test it, and analyze the results. There are many hypotheses involved in climate change, but let’s start with the one most fundamental to human causation. We know that so-called greenhouse gases trap heat in the Earth’s atmosphere; if they didn’t, the Earth would resemble Mars and life would probably never have evolved (or at least, never gotten beyond single-celled extremophiles living in volcanic vents). The greenhouse effect is the only reason I’m sitting here typing this response; it’s supposed to occur.
But let’s prove that this is true. The Vostok ice core (perhaps the most famous of the ice cores drilled so far) gives us measures of temperature and carbon dioxide concentration for the past 420,000 years, a period twice as long as the age of our species and involving multiple major fluctuations in both metrics (natural climate change). In that period, the highest concentration of carbon dioxide occurred about 320,000 years ago, when it reached 300 parts per million (ppm). This was also one of the hottest period in the record. Every fluctuation in carbon dioxide levels is matched by a fluctuation in temperature; both go up at the same time, and both go down at the same time.
So here is our testable hypothesis: an increase in the concentration of greenhouse gases will lead to an increase in the heat trapped by the atmosphere. The current concentration of carbon dioxide is 390 ppm, the highest in 800,000 years (known from other ice cores). In 1832, around the start of the Industrial Revolution, the concentration was 284 ppm.
We have accurate temperature records based on meteorology, rather than ice cores, from 1880 onward. The 10 warmest years on record for global temperature in that period (averaging out land and ocean temperatures) were: 2005, 1998, 2003, 2002, 2006, 2009, 2007, 2004, 2001 and 2008. We have a correlation for this time period: increasing carbon dioxide levels matched with increasing temperature levels.
Now, most carbon dioxide emissions come from natural sources, which are offset by natural “sinks,” processes which remove carbon dioxide from the atmosphere, such as photosynthesis or absorption into the ocean. However, this is a very fragile balance; a shift in carbon dioxide levels leads to a warming period or an ice age. These are natural occurrences. But humans are producing massive amounts of carbon dioxide; in 2008, it was 31.8 gigatons. That’s 31,800,000,000 tons. Human production of carbon dioxide has overwhelmed these natural processes, leading to the observed and measured increase in carbon dioxide concentration in the atmosphere.
According to the Vostok ice core data, a concentration of 300 ppm accounted for a temperature increase of about 3 degrees Celsius. This of course is not immediate; even a century is less than the blink of an eye compared to a 4.5 billion year old Earth. But the scientists are clear: 2 degrees Celsius means the ice caps are done for. It’s pretty simple really: water is in a solid state when 0 degrees Celsius, but is liquid at 1 degree.
One effect of the absorption of carbon dioxide in the ocean is that the ocean’s acidity will increase (which can also be phrased as having its pH decrease). This is another hypothesis we can make and test. Bear in mind that a pH scale goes from 0 to 14. Between 1751 and 1994, the pH of the ocean has decreased by 0.075. The projection for 2050 is a total decrease of 0.230.
All of the available data supports the hypothesis that human emission of greenhouse gases has led to climate change.
This is really only the proverbial tip of the iceberg; I haven’t even mentioned receding glaciers and ice caps, rising water levels, rapidly shifting weather patterns, increased incidence of severe storms, increased incidence of disease, the spread of disease-carrying insects, the thinning of the atmosphere, the increasing level of radiation making it through our thinning atmosphere, the appalling extinction rate, the rapidly decreasing fresh water supply, the increased incidence of both flooding and drought and the ensuing crop failures, and, most frightening of all, the thawing of the tundra and the release of the immense quantities of carbon dioxide and methane that had been previously been locked underground. I’m sure I’ve left items off that list.
If you want more information, I’d direct to you a paper published in Nature in 2008, which examined data from 80 studies that involved at least 20 years of data collection. As a refresher in Greek, “anthropogenic” means “derived from human activities.”
Rosenzweig C et al. 2008. Attributing physical and biological impacts to anthropogenic climate change. Nature 453(15): 353-358.
6 Responses to Anthropogenic Climate Change
Climate Change and Anthropogenic Climate Change (not “anthropocentric”) are not necessarily the same thing. Inexplicably, skeptics seem to want to first debate Climate Change itself, so that’s where ice cores and receding iceberg data are needed and relevant. Your points here are all well made. Keep making them.
However, as to whether this Climate Change is Anthropogenic, this is not so easily determined. Take a simple question regarding the environmental impact of heating ones home via wood stove. Is the CO2 released by the burning a cause of environmental increases of CO2? Or are the stands of trees grown to supply that firewood (and their CO2 consumption) a net decrease? Do we charge humans with the burning increase, and credit nature with the photosynthetic decrease? Or does the whole thing net to zero, and is the increasing CO2 coming from elsewhere? And, even so, can we conclude that it’s the CO2, and not a solar cycle, or volcanic ash, or some other cause, that’s responsible for the temperature increase or portions thereof?
The danger, as demonstrated by researchers fudging trivia among the UN climate change studies, is that logical shortcuts discredit larger points–that, and people making logical fallacies (e.g. temperatures and CO2 are rising, so therefore the latter caused the former and it’s all people’s fault), are part of the problem, not the solution.
My opinion? Temperatures are rising, and between violent weather, rising oceans, and a soon-to-be sudden decrease in fresh water (as glaciers disappear and no longer feed our rivers) we’re going to be up that proverbial creek without a paddle. It doesn’t matter what or who is causing it, only what the economic impact will be, and what economic responses are justified. (I.e. cost-beneficial). Skeptics hate the idea (and I do too) of wasting everybody’s money on something that they aren’t convinced is necessary. Step 1: show them why it’s expensive not to mitigate global temperatures–and don’t try to argue with them about whose fault it may be.
Thanks for pointing out the typo; not sure how I managed that one.
Unfortunately, you’re talking about a negligible amount of carbon dioxide. We’re burning fossil fuels: primary oil and coal. There’s no offset to these fuels; the fraction that were plants lived millions of years ago. The point is that there is a massive, non-natural increase in the amount of carbon dioxide entering our atmosphere.
Yes, the solar cycle does affect temperatures, as do various other things. But we’ve known for about a century that carbon dioxide traps heat. I’m not sure what standard of proof is going to be good enough for you. We know carbon dioxide traps heat. We know there are unnaturally high levels of carbon dioxide in the atmosphere. We know that temperatures are rising. What more proof are you demanding? No one is implying correlation means causation; we know what carbon dioxide does. We knew temperatures were rising and, from that, you could make a retrodiction that carbon dioxide levels had risen. That was a correct inference.
Yes, the IPCC report has a few errors. The most egregious of which is that glaciers in the Himalayas aren’t melting as fast as they claimed.
I could not agree more forcefully. Your statement assumes the process is over. But, if climate change is not over, then what is causing it matters very much. All evidence points to it continuing to worsen, not end or get better. What standard of proof are you demanding? Do you even think we’d be having this debate if the oil and coal companies weren’t funding so much of the research in this area and the media had not such a horrendous job of accurately presenting the findings of independent scientists?
Why would it be expensive? The list is in the original post. Crop failures. Lack of water supply. Increased medical costs and lowered production capacity due to disease. Rising water levels. The list goes on.
There is also the fact that, when the Earth runs out of oil within 50 years, our economy collapses. Not just transportation, but also agriculture (fertilizers are made with oil). I could also make the argument that the rest of the world is investing aggressively in alternative energy and we’re falling behind.
But I’m not going to make excuses. The national security arguments are beside the point. At question is the veracity of the science. Read Science. Read Nature. You tell me if there is any reason to think that scientists have not proven beyond reasonable doubt that humans are causing climate change. I have yet to see any evidence of that claim.
I can tell you that I’m not convinced something else isn’t contributing beyond and besides the human impact of burning all these “fossil fuels”. The most recent trend in rising temperatures began around 1850, and we can tell by ice cores and other means that global temperatures have gone up (and down) many times in earth’s history. Clearly there are other factors. Where is the explanation for this???
My concern is that we are failing to understand the complete science behind what is going on–folks are rabidly pointing to ACC, and other folks are rabidly refusing to believe it, and all that time and energy is being wasted while our proverbial Rome burns.
It is pretty clear that temperatures are rising, the clarity not because of the current heat wave, but because of longer term evidence such as rising sea temperature, glacier melting and Artic ice retraction.
There may be some question of heat and carbon dioxide in a chicken-or-egg issue, but we certainly lean toward the carbon dioxide increase as the culprit.
And we can probably all agree with the troublesome results of continual increase in temperature.
And there may be other reasons besides our man-made bias in the release of carbon dioxide as the cause of the rising temperatures.
But we can’t do much to control those other unknown causes right now, whereas we can limit the problem if it is indeed caused by the burning of fossil fuels.
So we should do at least that, if only to mitigate the problems that we might better control in the future, once we more fully understand the causes.
Oil is cheap, but that is partly due to the fact that all its costs are not captured in its production. Recognizing these added costs may level the playing field for alternative sources of energy that would temper the imbalance in carbon release.
I think that Joe hit the nail on the head with his comment.
Absolute certainty in science is very hard to come by. Most climate scientists think that climate change is being driven primarily by human activity, but no one is arguing that natural factors aren’t involved. Climate change is a natural process. (It actually almost drove our species to extinction shortly before our ancestors left Africa.)
Cutting carbon emissions does two things. One, it removes a source of warming, regardless of how significant that source is. And second, it tells us if warming is actually being primarily driven by natural causes.
If we were to assume that climate change was occurring, but not being caused by human activity, then the only thing we could do would be geoengineering. I think most people agree that that’s not something we want to do. We have no idea of what the consequences could be. There are alternatives; we now have the technology (just not the capacity) to literally scrub carbon dioxide out of the atmosphere. But that’s admitting that human carbon emissions are the problem.
About four years ago I stumbled across what I thought was an effective argument. Either climate change is caused by human activity or it isn’t and either we will do something about it or we won’t.
If climate change is not driven by human activity and we do nothing, then nothing really changes. We couldn’t have solved the problem by going off oil. If climate change is driven by human activity and we do nothing then we are exacerbating the problem
If climate change is driven primarily by human activity and we do something, then we are making a large payment now to avoid much larger costs in the future. And, this is the key in my opinion, if climate change is not driven primarily by human activity and we do act, we end our dependence on foreign oil and create an entirely new industrial base in the United States.
Kad barma, you’re right, there is far too much hysteria. But I find myself sympathetic to climate scientists. The theory of evolution is 150 years old and was fully accepted in the scientific community by the 1870s, but anywhere from 30-40% of the country completely rejects evolution. No matter what evidence we produce, we are ignored. I think that climate scientists feel the same way. The deniers are much louder than the skeptics and that’s why the advocates of action are so prone to being overly emotional about their topic.
And it IS a very scary topic. I listed most of the consequences of climate change, regardless of what is causing it, in the original post. It’s far more frightening than any other issue in my opinion.
re ‘fear’ and consequences’, climate change pales in comparison to fukushima contamination of the pacific. it’s ironic and deeply tragic that so few climatologists discuss it. re deniers v skeptics v advocates, who is doing the best science? i disagree there is ‘rarely’ perfect truth in science. i find that statement indicative of the climate change criticisms for being ‘junk science’. i was never taught in any science class that science was about anything less than clear and certain proof. this is the main reason i will not believe in climate change. its scientists do not appear to respect science fundamentals at all. ie ipcc lying in its reports should be considered ‘trivial’. that is not science at all. it is fraud.