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Scientific theories must make predictions that not only bolster the theory if the predictions come true, but also falsify the theory if the predictions turn out to be wrong. Some climate skeptics believe that the AGW hypothesis is impervious to falsification, short of waiting several decades to directly it, and pending that test, climate scientists and in particular climate modelers have boundless latitude to massage their theories and models to match what has become their pet hypothesis.
Over the last million years, temperature and CO2 have been highly correlated, but with CO2 lagging behind temperature by several hundred years. The mainstream explanation amongst climate scientists is that Earth's orbital changes initiated warmings and coolings, and a positive feedback between temperature and CO2 amplified those changes. However, many climate skeptics interpret the lag during this period as evidence that CO2 can only be the effect rather than the cause of temperature change.
Many skeptics of Anthropogenic Global Warming argue that our difficulty in predicting weather even a week ahead, demonstrates that it's foolish to try to predict long term climatic changes. Climatologists respond by pointing out that predicting specific short term events is unlike predicting general long term trends.
The strongest empirical evidence of anthropogenic global warming has occurred since the 1970s, where temperatures have been steadily rising. However, some skeptics have suggested that temperature records over the last decade have been steady, falsifying the hypothesis that humans are to blame.
Since the late 1970s, CFCs and other human generated gases have contributed to ozone depletion, most notably the holes over the polar regions. In 1987, the Montreal Protocol was signed by 43 countries, with the goal of replacing the use of CFCs with environmentally friendly alternatives, which has been largely successful. The issue has many parallels today with Anthropogenic Global Warming.
The equilibrium of Earth's climate is a balancing act between the heating effect of the sun countered by the cooling effect of radiation from earth sent back into space. Earth's rich atmosphere and diverse surface complicates this equation with effects such as the greenhouse effect (the trapping of heat), and it's this complexity that climatologists study. The IPCC believe they understand this system well enough to predict it, at least in terms of global averages over decadal time periods.
The IPCC (Intergovernmental Panel on Climate Change) is a scientific body formed by the United Nations in 1988 to summarize research on climate change for the purpose of informing policy makers. Those who are skeptical of anthropogenic global warming have questioned the objectivity of the organization.
Geoengineering (also Climate Engineering, Terraforming) is the act of deliberately modifying earth's climate. Advocates claim it's cheaper, faster and more feasible than controlling emissions. Some suggest it's the only solution to fighting global warming given the amount of greenhouse gasses already in the atmosphere and negative political-economic realities. Skeptics worry that tinkering with the atmosphere may lead to unforeseen consequences and fighting over how much Geoengineering to do.
The earth's climate is described with GCMs (General Circulation Models or Global Climate Models). GCMs are complex, containing many input variables and positive and negative feedback loops. These models are simulated on supercomputers to create predictions. The IPCC's predictions are based on an aggregate assessment of several GCMs. Global Warming skeptics have suggested that climates are in fact so complicated that such predictions cannot be trusted.
David Keith
… And so I guess my view on this is not that I want to do it, I do not, but that we should move this out of the shadows and talk about it seriously, because sooner or later we’ll be confronted with decisions about this, and it’s better if we think hard about it, even if we want to think hard about reasons why we should never do it.
Mitt Romney
My view is that we don’t know what’s causing climate change on this planet. And the idea of spending trillions and trillions of dollars to try to reduce CO2 emissions is not the right course for us.
Mitt Romney
I believe that climate change is occurring — the reduction in the size of global ice caps is hard to ignore. I also believe that human activity is a contributing factor. I am uncertain how much of the warming, however, is attributable to factors out of our control.
Robin Hanson
CO2 is clearly way up (~30%) over 150 years, and rising fast, mainly due to human emissions. CO2 is denser than its been for a half million years. ... The match between recent warming and CO2 rise details is surprisingly close, substantially raising confidence that CO2 is the main cause of recent warming. ... This adds support for mitigation. ... It was mostly skeptics bending my ear, and skeptical arguments are easier to find on the web. But for now, the other side has convinced me.
Tony Abbott
I've never been in favour of a carbon tax or an emissions trading scheme. A 5 per cent carbon emissions cut is “crazy”
Tony Abbott
We don't want to play games with the planet. So we are taking this issue seriously and we would like to see an ETS. I also think that if you want to put a price on carbon, why not just do it with a simple tax?"
David Evans
There are now several independent pieces of evidence showing that the earth responds to the warming due to extra carbon dioxide by dampening the warming. Every long-lived natural system behaves this way, counteracting any disturbance. Otherwise the system would be unstable. The climate system is no exception, and now we can prove it.
David Evans
I am a scientist who was on the carbon gravy train, understands the evidence, was once an alarmist, but am now a skeptic. The whole idea that carbon dioxide is the main cause of the recent global warming is based on a guess that was proved false by empirical evidence during the 1990s... In science, empirical evidence always trumps theory, no matter how much you are in love with the theory.
Donald Trump
With the coldest winter ever recorded, with snow setting record levels up and down the coast, the Nobel committee should take the Nobel Prize back from Al Gore. Gore wants us to clean up our factories and plants in order to protect us from global warming, when China and other countries couldn't care less. It would make us totally noncompetitive in the manufacturing world, and China, Japan and India are laughing at America's stupidity.

New Comments

0 Points       524yuanyuan       24 May 2016     Will IPCC climate models make accurate predictions? Neutral
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0 Points       MTC       23 Feb 2013     Is substantially reducing CO2 emissions worthwhile? Agree
Whether or not it is possible to reverse global warming by reducing CO₂ emissions, there is good reason to believe we should be trying regardless. At the very least, I haven’t seen any good arguments for not reducing CO₂ emissions.

0 Points       MTC       23 Feb 2013     Is global warming caused primarily by humans? Agree
The scientific consensus is clear: global warming is happening and is primarily human‐caused.

1 Point       Nashhinton       19 Nov 2011     Is global warming caused primarily by humans? Mostly Agree
It is a known scientific fact that global warming occurs because the earth occasionally goes through warming and cooling periods. But the thing that bothers me is that the earth's temperature has been substantially rising ever since the beginning of the industrial revolution, which makes me speculate if the burning of fossils fuels or the emission of certain chemicals are causing the dramatic increase in the earth's temperature. However, I am unsure if human activity is a major component for causing global warming, but I'm going to believe that it is on the basis of my current understanding of the evidence. I believe that more scientific evidence needs to be evaluated and tested to see if the majority of global warming is caused by human activity. The right wing's hatred for science and their constant conspiracy theories should be avoided if we are to fully comprehend the dire consequences and nature of global warming. We should continue to promote scientific exploration and not believe that global warming is a conspiracy created by Al Gore. Scientific progress is based on empirical research and continual testing. It's not based on a total rejection of the scientific evidence. We should ignore the Republican Party's hatred for science if we are going to fully save humanity from destroying itself. In the mean time, we should start by using alternative and renewable energy.

My beliefs on what I've read so far about global warming is that global warming is mostly caused by human activity.

0 Points       Benja       20 Jul 2011     Is substantially reducing CO2 emissions worthwhile? General Comment
In defense of Tony Abbott, half of Australia is too drunk to remember what he previously said.

0 Points       Benja       13 Apr 2011     Are recent climatic changes consistent with the AGW hypothesis? General Comment
Regional or short term weather patterns can defy global or long term climatic patterns. You get regions further from the equator that are warmer than regions closer to the equator. You get warm days in winter and cool days in summer. Similarly, Global Warming will not make every region warmer than it used to be, and every year warmer than the last.

Unfortunately, politicians on both sides of this debate have no patience for communicating this. Instead they justify their position with anecdotes about how warm or cool a region has been recently. While it may be good politics, it's quite literally mad science. Even if you look globally over the long term, the warming has been very modest so far. Climatologists' worries are primarily based on their theories and models which suggest that the trend we're seeing will continue.

0 Points       Benja       05 Apr 2011     Is the Anthropogenic Global Warming hypothesis falsifiable? General Comment
Gotcha climate scientist again!

Climate scientists make the elementary semantic error of confusing predictions with projections!

I'd reply with a counter-gotcha but I suspect you have a bottomless bag of gotchas.

0 Points       blacktrance       10 Feb 2011     Is global warming caused primarily by humans? Agree
The consensus is quite clear.

0 Points       Benja       25 Jul 2010     Are recent climatic changes consistent with the AGW hypothesis? General Comment
Julia Gillard, the Prime Minister of Australia, is wrong when she says "Every decade since the 1940s has been warmer than the last". The proponents of AGW say here that "The cooling trend from the 40’s to the 70’s now looks more like a slight interruption of an upward trend".

Tony Abbott, the leader of the opposition in Australia, is simply ignoring the mainstream scientific opinion altogether. In terms of rhetoric, aside from using The Ignored Evidence Pitch, he's using the "fact vs. faith" association reversal tactic used by creationists, to associate climate skepticism with fact and climate scientists with faith, just as creationists associate creationism with fact, and evolutionists with faith.

0 Points       Benja       15 Jul 2010     Will IPCC climate models make accurate predictions? General Comment
Thanks for bringing up the issue of falsifiability - you prompted me to add a new question on that specific issue here.

"The IPCC does not claim that its models make predictions. What it claims is that they make 'projections'"
Whether it's a crystal ball or a climate model, if the output tells us something about the future, we have a prediction. Let's not fail to address the issue of falsifiability by getting bogged down in semantics. The climatologist Gavin Schmidt is very representative of the IPCC, and he says in the opening sentence in this article that "There is a simple way to produce a perfect model of our climate that will predict the weather with 100% accuracy.", so if he's using the term "predict", I think that's an acceptable use of the term.

0 Points       Benja       15 Jul 2010     Is the Anthropogenic Global Warming hypothesis falsifiable? General Comment
Valuable insight from Ray Ladbury found on Real Climate here:


There seems to be a lot of misunderstanding about falsification/verification of theories and rejection/replacement of models. If you have a theory that gives a definitive prediction of an event, and that event does not occur, then that model is falsified. However, most models give statistical predictions, and statistical tools for model verification are mostly comparative–it’s a question of which model is more likely to have produced the result. In classical frequentist statistics this manifests in terms of comparison between a hypothesis and a null hypothesis. The likelihood ratio is another tool, as are comparisons between the Bayesian prior and posterior distribution.

In the case of climate models, you really don’t have a credible rival to models that feature a significant CO2 sensitivity. This sensitivity is constrained by multiple, independent lines of evidence, so if the sensitivity in the models were to be wrong, ALL of these other data would cease to make sense and have to be reinterpreted. Much more likely would be a hard look at other forcers–especially aerosols, clouds, etc. So if the predictions of models started to be drastically different from reality over an extended period of time, the models would likely be modified slightly, with little change in CO2 forcing. In this sense the situation is very close to that of evolution.


Climatology Question Index

Is global warming caused primarily by humans?
Is Geoengineering a good strategy to combat global warming?
Are the causes of climate change well understood?
Are recent climatic changes consistent with the AGW hypothesis?
Is substantially reducing CO2 emissions worthwhile?
Do negative feedback loops mostly cushion the effect of atmospheric CO2 increases?
Does cosmic radiation significantly affect earth's climate?
Does atmospheric CO2 cause significant global warming?
Are humans responsible for ozone depletion?
Is the Anthropogenic Global Warming hypothesis falsifiable?
Are climate records (of temperature, CO2, etc.) reliable?
Have climate models made good predictions so far?
Will IPCC climate models make accurate predictions?
Has CO2 passively lagged temperature in past climates?
Does unpredictable weather imply unpredictable climate?
Is it possible to accurately predict climate?
Is the IPCC objective?
Have solar cycles significantly affected earth's recent climate?
Can life adapt to a warmer earth?
Would a rise in global temperature catastrophically increase sea levels?
Has earth's orbit significantly affected its recent climate?